CONTENTS
Introduction
Beet Western Yellows Virus Survey
Mechanical Harvest of Pickling Cucumbers
Cover Crops and Nitrogen on Sweet Corn Yield
Effect of Nitrogen Sources and Rates and Supplemental Calcium
on Broccoli Yield and Head Rot
Plug Transplanting Broccoli
Plug Transplanting Storage and Bunching Onions
Seedling Growth Comparison Among Several Greenhouses
Muskmelon and Tomato Production on Photodegradable and
Wavelength-Selective Mulches
The Effect of Floating Row Covers on Virus Transmission and
Yield of Potato Seed Stock
Return to:     
AUTHOR
Dr. Delbert D. Hemphill, Jr., Professor of Horticulture, has conducted
research on vegetable crops culture and management
since 1976 at Oregon State University's North Willamette Research and
Extension Center, 15210 NE Miley Rd., Aurora,
OR 97002-9543.
COOPERATORS
Dr. John Hart is Extension Soil Scientist and Associate Professor, Department of
Crop and Soil Science, Oregon State University, Corvallis, OR 97331
Dr. Richard Dick is Associate Professor of Soil Science, Department of Crop and
Soil Science, Oregon State University, Corvallis, OR 97331
Dr. N.S. Mansour is Extension Vegetable Specialist and Professor, Department of Horticulture, Oregon State University, Corvallis, OR 97331
Dr. John Selker is Assistant Professor, Department of Bioresources
Engineering, Oregon State University, Corvallis, OR 97331
Dr. Richard O. Hampton is Research Virologist, USDA-ARS and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
Dr. James R. Baggett is Professor of Horticulture, Department of Horticulture, Oregon State University, Corvallis, OR 97331
Mr. Robert B. McReynolds is District Extension Agent for vegetable crops and Assistant Professor, North Willamette Research and Extension Center, 15210 NE Miley Rd., Aurora, OR 97002-9543
Mr. Daniel McGrath is Extension Agent and Associate Professor, vegetable crops, Salem, Oregon 97301
Dr. Gary Reed is Professor of Entomology and Superintendent, Hermiston AREC, Hermiston, Oregon 97838
Dr. Jeffrey Steiner is Research Agronomist, USDA-ARS, National Forage Seed Production Center, Corvallis, OR 97331
Dr. Mary L. Powelson is Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331
Introduction to the Report
We have conducted a full-time program of vegetable crop research at the North
Willamette Research and Extension Center (formerly the North Willamette Experiment Station)
since 1976. The Center, a branch of both Oregon State University's Agricultural Experiment
Station and its Extension Service, is just north of Aurora, a historic farming community 20 miles
south of Portland, Oregon. The land is provided by Clackamas County, with facilities owned
and maintained by OSU. The Center serves the vegetable, small fruit, and nursery
crops industries and is located in an area noted for the diversity of its agriculture. Our vegetable
research emphasizes the needs of both the processed vegetable and the fresh market vegetable
growers in the Willamette Valley. We also conduct research on home garden and small-farm
intensive vegetable culture.
Many of the research projects reported here involved cooperation with Experiment Station
and Extension Service colleagues at OSU and at Washington State University. Their
contributions are gratefully acknowledged. The financial support of the Oregon Processed
Vegetable Commission, Nalley Fine Foods, UNOCAL, the Chilean Nitrate Corporation, the Oregon Potato Commission, and the
Agricultural Research Foundation was essential to completing these projects and is greatly appreciated.
Ten crops from broccoli to tomato were involved in these experiments. This report is the seventh in a series of biennial reports initiated in 1979.
DISCLAIMER: The use of trade names does not constitute an endorsement by the Oregon State University
Agricultural Experiment Station. Always check pesticide labels for currently registered uses.
Beet Western Yellows Virus Survey
Cooperators: N. S. Mansour, Dept. of Horticulture, and Richard O. Hampton,
Dept. of Botany and Plant Pathology
Introduction
Willamette Valley spinach and lettuce growers have complained of a yellows disorder, or chlorosis, affecting these crops. The bright marginal yellowing is particularly severe in spinach and in some lettuce cultivars, most notably, the Oregon State University crisphead release, 'Summertime.' Symptoms are usually less pronouced in other crisphead cultivars such as 'Ithaca' and 'Salinas,' but can be quite pronouced in romaine types. Red leaf lettuces do not usually show strong symptoms. Similar symptoms have been observed in Chinese cabbage cultivars.
Research carried at NWREC in 1987 eliminated soil pH, nutrition, and Fusarium wilt as causes of the symptoms. Cucumber mosaic virus and beet western yellows virus (BWYV) were isolated from plant tissue samples by the OSU Plant Disease Clinic. After severe outbreaks of the disorder in 1988, we decided to sample grower fields during the 1989 season to confirm the identity of the virus associated with the symptoms and to determine the severity of the problem.
Methods
Samples were collected from three grower cooperators in the Aurora, Milwaukie, and Parkrose areas of the Willamette Valley. At the first sampling date, on July 18, samples of romaine lettuce were collected from the Aurora site and from the Milwaukie site, and samples of 'Salinas' crisphead lettuce were collected at the Aurora site. Symptoms were not observed on spinach at Aurora, or on lettuce at the Parkrose site on this date. For each crop and site, a single leaf was taken from each of two plants judged asymptomatic and from four plants showing the typical marginal chlorosis, but thought to be free of other diseases or disorders.
For the second sampling, on August 29, spinach was collected at Aurora, and romaine and crisphead lettuces at Aurora, Milwaukie, and Parkrose. Samples were subjected to enzyme-linked immunosorbent assay (ELISA) with an extremely sensitive beet western yellows virus monoclonal antiserum, capable of detecting extremely low (less than 5 ng/ml) BWYV concentrations.
Results
At the first sampling date, all plants thought to be free of symptoms were found to be free of the virus, at least at the detection limit of the ELISA. Of the 12 samples identified as symptomatic, seven contained high levels of the virus and five were virus-free. Symptoms were apparently more clear-cut in 'Salinas,' as all six samples were judged correctly. ELISA results agreed with visual observations of syptoms in only seven of 12 instances for romaine. Field observations of symptoms indicated a higher degree of disease incidence at the Aurora site than at the Milwaukie site. Virus incidence was visually estimated at 4 percent for romaine at Aurora, 25 percent for 'Salinas' at Aurora, and less than 1 percent for romaine at Milwaukie.
At the second planting date, only two of 14 spinach samples did not contain BWYV, according to ELISA, even though six of the 14 samples were judged free of symptoms. The BWYV concentration in spinach was consistently 10- to 50-fold higher in spinach than in lettuce, indicating a higher tolerance to the disease in spinach. All 10 lettuce plants collected as disease-free controls were free of detectable BWYV. Plants judged to have the yellows disorder contained very low concentrations of BWYV. It is not known whether these lettuce cultivars resist the synthesis of BWYV or had only recently been infected. Disease incidence was judged to be high (over 50 percent) at all three locations, for both crisphead and romaine lettuce.
The ELISA data were of very high quality, with replications of the same sample always in close agreement. ELISA should be a dependable tool in identifying outbreaks of this virus.
Cooperator: N. S. Mansour, Dept. of Horticulture, OSU-Corvallis
Introduction
Predicting the harvest of cucumbers and controlling the flow of fruit to the processing plant requires a planting sequence based on known response of the crop to environmental conditions at different parts of the growing season. An accumulated heat unit system developed in North Carolina and modified in western Washington appears to predict harvest with a reasonable degree of accuracy under the environmental conditions in those two areas. However, the number of heat units required to achieve crop maturity differs greatly between the two regions. This lack of agreement may be explained by differences in daylength, light intensity, cultivar, and the daily duration of favorable temperature. Thus, it appears that heat unit models will have to be developed for each growing area.
New determinate, semi-determinate, and "little leaf" types of cucumber are becoming available to the industry. These need to be evaluated under Willamette Valley cultural conditions. These lines might respond differently to nitrogen rates and plant populations than do indeterminate lines; the restricted vine growth of determinate lines may favor both higher plant populations and higher rates of nitrogen. In addition, data on yield and size grade response to fertility and plant populations would be very valuable in the development of a multifactor harvest prediction model. Such a model must include the factors of population, cultivar, fertility, irrigation amount and method, and pollination practices, as well as days from planting or heat unit accumulation.
The objectives of this project were: 1) to obtain the accumulated heat units from planting to harvest for selected commercial plantings in the Willamette Valley and develop a harvest prediction model for cucumbers, based on size grade and dollar value; 2) to compare yields and size grades for three to four harvest dates for selected semi-determinate and determinate lines of machine-harvested cucumbers; and 3) to investigate the effect of nitrogen fertilizer rates and plant populations on representative determinate and semi-determinate types of pickling cucumbers.
Methods
Seed companies were contacted to obtain pickling cucumber lines with a fruit length-to-diameter (L:D) ratio of 2.9 to 3.2 and with disease resistance and other characteristics suitable for production in western Oregon. In 1989, ten lines received were selected for trial based on their L:D ratio. Plots were seeded with a V-belt push planter on June 2. Seeds were counted for each plot to give a target population of 80,000 plants per acre for all lines except 'H-19 Little Leaf.' On the suggestion of the breeder, Dr. T. Morelock, of the University of Arkansas, this line was seeded at 50,000 per acre and half of the plots were thinned to 27,000 per acre.
Plots were four-row beds on 78-inch centers and 50 feet long. Between-row spacing was 16 inches. Six plots of each line were seeded in completely random design, with two replications of three harvest dates. Preparation of the sandy loam soil, fertilization, irrigation, weed control, and pollinators were provided by the grower cooperator according to standard Oregon State University production recommendations. However, the grower inadvertently applied a total of 150 pounds N per acre, rather than the normal 50 to 70 pounds. All plots were machine-harvested with a Wilde mechanical harvester at two to three-day intervals. Harvest of most cultivars began when oversize fruit reached 6 percent of the total. Fruit was mechanically graded at a processor receiving station.
Seed of 10 different cultivars or lines was provided by seed companies for evaluation in 1990. Plot size was established to provide approximately one bin of pickling cucumbers for yield and grade measurement and for fruit quality evaluation by a processor.
Planting dates were June 22 and July 3, 1990. Research plots were four rows, spaced 16 inches apart, with beds on 7-foot centers. Plot lengths were 700 and 875 feet long for the first and second planting, respectively, with sufficient area planted to each variety to allow for up to four harvests. All plots were planted using commercial Stanhay planters set to seed at a rate of 80,000 to 85,000 per acre. Nitrogen rate was 100 pounds per acre.
All plots were machine-harvested at two to four-day intervals using the Wilde harvester, except for 'H-19 Little Leaf,' which was harvested only once. Harvest of the first planting began when most of the varieties reached a mean grade of 2.8 to 2.9, with a range throughout the harvest period running from 2.3 to 3.7 (Table 1). Harvest of the second planting commenced earlier with most of the varieties having a mean grade of 2.5 to 2.6, with a range throughout the harvest period from 2.5 to 3.5. All fruit harvested was graded at the receiving station. Dollar values per acre and per ton were calculated using the machine-harvest cucumber pay scale provided by the processor, with no correction for hauling or grower-owned harvester.
A third trial in 1990 was conducted at the North Willamette Research and Extension Center. The plot area was prepared in the last week of May. Initial seeding was on June 1, following broadcast and incorporation of 700 pounds per acre of a 10N-8.7P-16.7K fertilizer. Following seeding, chloramben and naptalam herbicides were applied at 2.0 and 3.0 pounds per acre, respectively, and incorporated with 0.5 inches of overhead sprinkler-applied water. The lines Peto 10588, 'Castlepik', and 'H-19 Little Leaf,' were seeded with four rows per 80-inch wide bed. Plot length was 45 feet. Each line was seeded at a target population of 70,000 and 100,000 plants per acre (except 35,000 and 70,000 for 'Little Leaf').
Main plots of variety x population x harvest date were in randomized complete block design with four replications. On June 29, these main plots were randomly split into three 15-foot long subplots by the application of either 0, 40, or 80 pounds nitrogen per acre as ammonium nitrate. Resulting total N rates were 70, 110, and 150 pounds per acre. Four hives were placed about 50 feet from the plot border for pollination.
Emergence of the Peto line was extremely poor and that of 'Little Leaf' was acceptable only on about half the plots. As a result, the Peto line and 'Little Leaf' were reseeded on July 12. Treatments and cultural methods were as above, with the additional nitrogen applied on August 10. Emergence of the Peto line was excellent on these plots. Emergence of 'Little Leaf' was acceptable, but much of the stand was lost to a root disease. Consequently, harvest data were taken for 'Castlepik' and 'Little Leaf' from the first planting and for the Peto line from the second planting. In addition, there were four harvests of the Peto line, but only a single harvest of 'Little Leaf,' due to the limited number of plots with acceptable plant stand.
'Castlepik' was harvested on August 1 and 6, 'Little Leaf' on August 9, and the Peto line on August 31 and September 4, 7, and 10. Each plot was harvested once and all fruit were removed to simulate a once-over machine harvest. Fruit was graded into size categories on a portable grader provided by Nalley's Fine Foods, Inc.
Results
1989 Variety Trials.
In 1989, the L:D ratio of most cultivars fell within the desired range of 2.9 to 3.0. Fruit lengths were shorter than normal this season, as evidenced by 'Calypso', which would normally have L:D of 3.0 to 3.1. 'Calypso,' 'Napoleon,' and 'HMX4490' showed greater stability in L:D ratio over the course of three harvests than did the other lines (Tables 1 and 2).
A 10:40:40:10 percent grade distribution of grade 1:grade 2:grade 3:grade 4 (0 to 1-inch:1 to 1.5-inch:1.5 to 2-inch:over 2-inch diameter, respectively) is considered a realistic average grade distribution for mechanical harvest. Fruit value for this distribution would be $137.00 per ton based on 1989 processor payment for the different size grades. The three Petoseed lines most nearly produced the desired size distribution commensurate with high yield and dollar return per acre (Table 2). 'H-19 Little Leaf' produced a high return per acre but an unfavorable size distribution. This cultivar does not usually produce a crown set, but rather a heavy secondary set. In these plots, however, crown set occurred on nearly half the plants, making determination of proper harvest period more difficult. This resulted in a high percentage of oversize fruit (grade 4, no value) at harvest.
Yield can be divided into two distinct groups (Table 2). One group of five cultivars produced less than 9,500 pounds paid fruit weight per acre. The other group of five, all determinate or semi-determinate types, yielded more than 9,500 pounds paid weight per acre. The highest yielding lines were 'H-19 Little Leaf,' 'Napoleon,' and PS10588. Dollar return continued to increase with each harvest, while value per ton decreased for most cultivars. Thus, a higher payment for small sizes may be necessary to encourage growers to harvest at a lower mean size grade. Plant population had no effect on yield, mean size grade, or quality of 'Little Leaf.' Data reported for this cultivar are the means of the two populations.
1989 Commercial Plantings.
Data for each commercial planting, harvest date, and delivery for Oregon was provided by a pickle producer. All data are for the cultivar 'Calypso.' Optimum commercial harvest was considered to have an average size grade of 2.5 to 2.6. According to results from Dr. W. C. Anderson for northwest Washington, this should represent an approximate 10:40:40:10 size grade distribution. Mean size grade was calculated for each lot delivered (Table
3). The high degree of correlation between mean size grade and value per ton indicates that mean size grade is a useful estimate of crop value.
The North Carolina accumulated heat unit model (AHU) was tested against days from planting as a predictor of mean size grade and crop value (Table 3). The correlation coefficients suggest that days from planting predicts maturity better than does the AHU model. Even when only harvests with a mean size grade between 2.45 and 2.80 are considered (Table 4), days from planting is the superior predictor of harvest maturity, reflected in the smaller Coefficient of Variation (C.V.) for days from seeding to harvest than for AHU. Other models are also tested, including the AHU plus cold penalty (CP) model developed by Dr. W. C. Anderson. The only model producing a smaller C.V. is Tmean-10-CP. This is in contrast to the results of the North Carolina studies, where models using Tmax were superior to those using Tmean.
Regression analysis was used, where possible, to calculate the probable heat unit accumulation at a mean size grade of 2.5 for several plantings (Table 5). As expected, this provides slightly better agreement in the number of heat units required to reach maturity at different planting dates. Again, only the Tmean-10-CP model is a better predictor than simple days from planting. The relationship between temperature and crop maturity in this study may have been altered by the excessive application of nitrogen and extreme vine growth seen in some of the plantings. These conditions are known to delay maturity. Cucumber growth is influenced by many other factors which may may affect maturity including plant stand, irrigation, pollination, and the environmental factors that affect pollinator performance.
1990 Variety Trials.
Due to unseasonable rains and soil crusting, plant stands were reduced in the 1990 variety trials. Stand counts taken in the second planting indicated estimated plant populations ranging from 43,200 per acre for 'Castlepik' to 89,600 per acre for 'Little Leaf.' Although nitrogen fertilization was reduced to 80 lbs per acre, about one-half the amount applied in 1989, excessive rains, reduced plant populations, and high temperatures combined to produce excessive vine growth again in 1990.
Table 6 provides a summary of yield, size distribution, mean grade, dollar value per acre, and dollar value per ton for four harvests of the eight varieties in the first planting. Mean grade and gross yield generally increased at succeeding harvests, but the greatest return to the grower usually occurred at the first or second harvest. The exception was 'Primepak,' a relatively late-maturing and low-yielding cultivar. For the three varieties with increased return at the second harvest, the mean grade at second harvest averaged 3.18, well in excess of the average grade desired by processors (2.5-2.6). For the four varieties with greatest return at the first harvest, it is not possible to judge from the data whether higher returns would have been generated from an earlier harvest. However, results from the second planting, with harvest starting at grades near 2.5, imply that higher returns would not have been generated by harvesting earlier (Table 8).
The main (average) effects of harvest date and variety for the first planting are given in Table 7. In the first planting, four varieties ('Castlepik,' Peto 50885, 'Calypso' and 'Cross Country') grossed over $600 per acre, when averaged over the four harvests.
Table 8 presents individual data for each cultivar and harvest for the second planting. Maximum gross dollar return per acre for the second planting occurred at a mean grade near 3.2 (when averaged over varieties). In this case, the highest dollar value per acre for all varieties except Peto 50885 occurred at the third harvest. A fourth harvest was not attempted because poor field conditions and rainfall prevented timely harvest, resulting in excessive fruit size.
The first harvest generally occurred at nearly the optimum mean grade from the processor's point of view, but with unacceptably low return to the grower. These results, along with those of the first planting, strongly suggest that the present pay scale actively discourages growers who own their own harvesters from harvesting at the mean grade desired by processors. In any case, it appears that it will be difficult for the Wilde harvester to recover sufficient small fruit to allow a grower to profit when harvesting at a mean grade of 2.5-2.6. Only Peto 50885 exceeded $600 per acre dollar return when averaged over the three harvests (Table 9).
The first harvest of the second planting provided the most realistic distribution for the various size grades at a mean grade desired by the processor (2.5 to 2.6). At this mean grade, yields were from 2.1 to 4.0 tons per acre, with dollars per acre ranging from $294 to $539. These relationships may be heavily influenced by harvester recovery efficiencies as well as crop condition, and environmental factors affecting crop growth and pollination. We can only guess whether greater fruit set per plant with reduced canopy growth might have produced an acceptable yield and dollar return at a mean grade more in line with the processor's product needs.
In contrast to 1989, when the proportion of grade 1 fruit was as high as 19 percent and the average for all varieties at first harvest was 12.6 percent, the proportion of grade 1 fruit in 1990 did not exceed 8 or 6 percent for the first and second plantings, respectively. The desired 10:40:40:10 ratio of size grades was not reached for any variety or harvest. The percentage loss in dollar value per ton over the harvest period is noted for each variety in Tables 7 and 9. This loss in value was least for 'Primepak' and 'Cross Country,' indicating a less rapid change in grade over the harvest period. High-yielding varieties which hold grade over a longer period of time would allow greater flexibility and margin for error in harvesting.
In comparing the commercial plantings harvested by the Byron machine with those harvested by the Wilde, for later planting dates, more accumulated heat units (AHU) are required to reach the same mean grade (Table 10). Inclusion of a cold penalty did not improve the predictive ability of the heat unit model for these plantings. Lowering the maximum cutoff temperature from 90 to around 85 oF might help correct the situation. Obviously, growth and development of 'Calypso' is not a linear function of AHU.
The three growers using the Byron harvester achieved higher gross yield (and dollars per acre) at a mean grade of 2.61 to 2.76 than the grower using the Wilde harvester was able to achieve at a grade of 2.86. Some possible reasons for higher recovered yields for the three growers include: a possible greater efficiency of the Byron harvester, particularly in recovering small fruit; differences in plant stand; or differences in canopy vegetative growth as affected by fertility, irrigation, soil type, and pollination efficiency.
Nitrogen Rate x Population, 1990.
The main effects of plant population, N rate, and harvest date on the yield and size distribution of 'Castlepik' are found in Table 11. Only main effects are shown in all tables since there were no significant interactions affecting any component of yield for any of the three lines.
Plant population per acre had no effect on the size distribution or mean grade of 'Castlepik,' but both gross yield and dollar value per acre were greater at 100,000 than at 70,000 plants per acre. Nitrogen rate had no effect on size distribution at either harvest and did not affect yield or dollar value. Canopy vigor, estimated on a three point scale at mid-season, also was not affected by N rate.
The first harvest of 'Castlepik' occurred at a mean grade of 2.74, with 20 percent oversize. Although at this point the size distribution was already skewed toward larger size grades than would be desired by processors, it is important to note that at the second harvest, with a mean grade of 3.19, dollar return was higher than at the first harvest. This result is consistent with that seen in the second planting of the commercial-scale variety trials (above).
It is also important to note that the size distribution obtained in this trial is probably weighted more heavily toward the smaller sizes than would be the case if the plots were harvested by machine. Our pickers harvested a greater percentage of small fruit than would be recovered by machine. However, a mechanical harvester also tends to drop a portion of oversized fruit that falls from the vine ahead of the pickup device. Also, with a ratio of four hives for only one-half acre of plot area, the high bee population may also have favored greater pollination. We did not make counts of the mean number of fruit recovered per vine, but up to three fruit were observed on many plants. Reduced plant canopy development compared to that observed in the commercial variety trials may also have favored greater visitation by pollinators and greater fruit set per plant.
As with 'Castlepik,' yield and dollar return of 'Little Leaf' were increased at the denser population (Table 12). The percentage of oversized fruit at the single harvest and the mean grade tended to be smaller with the higher plant population, indicating that doubling the plant population may have slightly delayed maturity. Our results, although tentative, indicate that 'Little Leaf' should not be grown at greatly lower populations than other cultivars.
Except for a slight effect on the percentage of nubs and crooks, nitrogen rate did not significantly affect size distribution or yield of 'Little Leaf.' Although not statistically significant, there was a consistent trend toward smaller yield and dollar value per acre with increasing rates of N, while mean grade remained the same.
Plant population per acre had no effect on size distribution of the Peto line 10588 (Table 13). In contrast to the results for 'Castlepik' and 'Little Leaf,' yield and gross value per acre were reduced at the higher population. Increased rates of nitrogen again tended to reduce yield, although the effect was not statistically significant. Harvest of the Peto line commenced when the mean grade was only 1.5 and was continued until the mean grade exceeded 2.8. It is important to note that at a mean grade of 2.8, gross dollar value exceeded that at the preferred mean grade of 2.6 by nearly $300 per acre. The Peto line was by far the greatest yielding line in the trial, with a calculated yield of about 13 tons per acre at a mean grade of 2.6, compared to eight tons for 'Little Leaf' and six tons for 'Castlepik.' However, this comparison is across two planting dates, with generally more favorable weather during growth and development of the Peto line.
In summary, the effect of N was consistent: there appears to be no reason to apply more than 70 pounds N per acre. However, it will be difficult to extrapolate these results to other fields as differences in soil type, organic matter content, tilth, amount of water applied, and other grower cultural practices (e.g. the practice of banding N and P at planting) will affect plant response to nitrogen. The effect of plant populations was not consistent across lines. More work will be needed to determine optimum plant populations for lines with promising yield and processing quality.
Table 1. Effect of planting date on yield and paid weight of ten pickling cucumber
varieties, 1989, Marion County, Oregon.
Harvest % in grade by weight Wt(lb)/ % Mean Wt. (lb/A)
Cultivar date AHU L/D 0-1" 1-1.5" 1.5-2" 2"+ plot ground grade Paid Total $/A $/T
August
Calypsoz 7 567 2.9 13.7 37.6 41.4 7.3 48 6.6 2.43 5963 6881 447 130
9 598 2.9 10.1 51.7 34.1 4.1 64 9.0 2.31 8241 9431 651 138
11 619 2.9 4.6 44.8 35.6 15.0 87 7.6 2.61 9916 12610 712 112
FancyPak 14 650 2.9 8.4 36.4 47.8 7.3 69 2.2 2.59 8375 9424 559 119
16 670 2.8 2.7 22.7 57.3 17.3 80 3.4 2.91 8710 10995 461 94
18 687 3.2 10.1 39.3 38.2 12.4 64 7.3 2.72 7102 10496 470 90
Flurry 5 543 - 10.1 26.7 53.0 10.3 63 1.5 2.63 7504 8502 485 114
7 567 3.3 5.9 32.6 49.0 12.5 70 3.9 2.69 8174 9942 517 104
9 598 2.8 7.3 34.3 45.0 13.4 109 7.2 2.64 12663 15765 851 108
H-19 LL 16 670 3.0 5.5 20.8 55.4 18.3 118 3.2 2.86 12864 16261 711 87
18 687 2.7 4.6 20.0 49.8 25.6 155 9.0 2.96 15477 22821 873 77
21 721 2.9 2.7 30.0 42.1 25.2 182 14.9 2.90 18224 28683 1128 79
HMX4490 7 567 2.9 13.9 55.5 27.0 3.7 48 2.7 2.22 6104 6620 520 157
9 598 2.8 14.2 47.1 31.4 7.3 40 12.8 2.33 4891 6044 401 133
11 619 2.9 3.5 43.3 40.8 12.3 100 3.5 2.63 11792 13876 795 115
Napoleon 7 567 2.9 9.0 42.7 41.9 6.3 78 4.9 2.45 9782 10931 709 130
9 598 3.0 4.5 32.2 47.3 16.0 122 4.2 2.75 13668 16992 858 101
11 619 3.0 4.1 47.8 41.5 6.6 126 3.4 2.49 15812 17460 1099 126
PS10488 1 567 3.0 15.0 45.0 36.2 3.9 40 9.5 2.29 5159 5927 413 139
2 598 3.0 12.1 40.9 40.5 6.5 83 4.8 2.44 10318 11591 765 132
3 619 3.2 3.7 52.8 37.5 6.0 137 6.0 2.46 17219 19457 1242 128
PS10588 5 567 - 19.2 38.7 39.5 2.6 69 5.0 2.28 8978 9719 718 148
7 598 2.9 10.9 44.6 40.4 4.2 98 5.8 2.38 12596 13953 939 135
9 619 2.8 6.8 37.0 48.4 7.8 132 3.7 2.58 16281 18368 1077 117
PS50885 7 567 3.0 17.8 44.8 36.6 0.8 42 4.8 2.21 5561 5953 455 153
9 598 3.1 11.0 67.8 19.4 1.9 83 4.5 2.12 10854 11581 963 166
11 619 2.9 6.0 54.8 34.9 4.3 119 5.6 2.38 15209 16831 1149 137
Sun 3519 9 598 3.0 13.6 48.5 29.4 8.6 52 5.1 2.34 6365 7350 527 143
11 619 3.0 4.0 54.7 33.6 7.7 87 9.5 2.45 10787 12851 804 125
14 650 2.7 1.8 24.4 60.9 12.8 155 3.9 2.88 17889 21567 914 85
LSD(0.05) NS 7.1 16.7 15.3 9.8 44 6.1 0.33 5021 5800 305 26
zSeed sources: PS lines and 'Little Leaf' from Petoseed; HMX4490 from Harris-Moran;
'Calypso,' 'Flurry,' and 'FancyPak' from Agrow; 'Napoleon' and Sun 3519 from Sun
Seeds. 'Little Leaf,' 'Napoleon,' and the three Petoseed lines were semi-
determinate to determinate in vine character.
Table 2. Main effects of cultivar and planting date on yield and paid weight of
pickling cucumbers, 1989, Marion County, Oregon
% in grade by wt. Wt(lb)/ % Mean Wt. (lb/A)
Treatment AHU L/D 0-1" 1-1.5" 1.5-2" 2"+ plot ground grade Paid Total $/A $/T
Cultivar
Calypso 595 2.9 9.5 44.7 37.0 9.1 66 7.7 2.45 8040 9641 603 127
FancyPak 673 3.0 7.1 32.8 47.8 12.4 71 4.3 2.65 8062 10304 497 100
Flurry 569 3.0 7.7 31.2 49.0 12.1 81 4.2 2.65 9447 11403 618 109
H-19 LL 693 2.8 4.3 23.6 49.1 23.0 151 9.0 2.91 15522 22588 904 81
HMX4490 595 2.9 10.5 48.6 33.1 7.8 62 6.3 2.38 7596 8846 572 136
Napoleon 595 3.0 5.9 40.9 43.6 9.6 108 4.1 2.57 13087 15128 889 118
PS10488 595 3.0 10.3 46.2 38.1 5.4 87 6.8 2.39 10899 12325 807 133
PS10588 595 2.8 12.3 40.1 42.7 4.9 100 4.8 2.40 12618 14013 911 134
PS50885 595 3.0 11.6 55.8 30.3 2.3 81 5.0 2.23 10541 11455 856 153
Sun 3519 622 2.9 6.5 42.6 41.3 9.7 98 6.2 2.54 11680 13923 748 119
LSD(0.05) NS 4.1 9.6 15.3 5.6 25 NS 0.19 2899 3349 176 15
Harvest
1 586 2.9 12.6 39.7 40.8 6.9 63 4.6 2.42 7665 8757 554 133
2 613 2.9 8.0 41.4 40.3 10.3 88 6.7 2.53 10372 12620 723 120
3 638 2.9 5.1 40.9 42.5 11.6 121 6.3 2.61 14211 17511 944 110
LSD(0.05) NS 2.3 NS NS 3.1 20 NS 0.10 1588 1834 97 8
Table 3. Grade distribution of 'Calypso' cucumber vs. heat unit accumulation (AHU) for
several planting and harvest dates, Willamette Valley machine-harvested fields, 1989
Planting Harvest % in grade by weight Mean
date date Days AHU 0-1" 1-1.5" 1.5-2" 2"+ grade $/ton
June 2 Aug. 10 69 610 7.6 34.8 41.1 16.5 2.67 115.63
June 2 Aug. 11 70 619 3.9 35.7 24.7 34.4 2.91 96.37
June 3 Aug. 12 70 616 3.7 54.4 30.3 9.9 2.47 135.07
June 3 Aug. 13 71 626 1.8 41.9 37.2 18.5 2.73 109.76
June 3 Aug. 14 72 637 1.6 27.5 55.3 15.7 2.85 92.88
June 3 Aug. 15 73 647 1.4 14.5 50.5 32.7 3.16 65.11
June 3 Aug. 16 74 657 1.3 11.7 49.3 36.4 3.22 58.68
June 6 Aug. 17 72 618 1.6 12.0 47.7 37.5 3.22 57.68
June 6 Aug. 18 73 626 1.6 12.1 46.2 40.1 3.25 57.78
June 7 Aug. 19 73 629 0.6 7.5 36.7 53.5 3.46 40.75
June 25 Aug. 28 64 567 5.0 39.6 43.0 7.7 2.56 120.66
June 25 Aug. 29 65 578 5.6 43.6 40.9 4.5 2.47 128.85
July 4 Sept. 12 70 657 7.7 54.6 30.7 4.7 2.33 147.84
July 4 Sept. 13 71 671 3.8 44.6 42.4 4.1 2.49 126.25
July 4 Sept. 14 72 687 3.1 38.1 44.1 3.8 2.55 115.67
July 11 Sept. 19 70 695 3.6 22.7 60.7 9.9 2.79 95.03
$/ton vs. mean grade: R2 = 0.9854, p<0.001
Mean grade vs. AHU: R2 = 0.0016, not significant
Mean grade vs. days: R2 = 0.4101, p<0.01
$/ton vs. days: R2 = 0.4109, p<0.01
$/ton vs. AHU: R2 = 0.0082, not significant
Mean grade vs. Tmean-10,CP: R2 = 0.0458, not significant
$/ton vs. Tmean-10, CP: R2 = 0.0222, not significant
Table 4. Cucumber accumulated heat unit models for selectedz machine harvests
of 'Calypso' cucumber in the Willamette Valley, Oregon, 1989
Planting Days, seed Tmax-15.5 Tmax-15.5 Tmean-10 Tmean-15.5
date to harvest Grade (AHU) -CP Tmean-10 -CP Tmean-15.5 -CP
June 2 68 2.61 619 546y 530x 471 181x 166
June 2 69 2.67 610 537 540 481 186 171
June 3 70 2.47 616 539 541 480 182 167
June 3 71 2.73 626 541 550 482 184 167
June 25 64 2.56 567 510 493 440 157 143
June 25 65 2.47 578 519 502 448 159 145
July 4 71 2.49 671 580 564 487 181 161
July 4 72 2.55 687 596 575 498 186 166
July 11 70 2.79 695 595 564 484 189 167
Mean 68.8 2.59 630 551 540 475 178 161
Std. Dev. 2.7 42.9 29.8 26.3 17.7 11.2 9.6
Coeff. Var.w 4.0% 6.8% 5.4% 4.9% 3.7% 6.3% 6.0%
___________________________________________________________________________________
zAll harvests for which the mean grade fell between 2.45 and 2.80.
yA cold penalty is subtracted from the next day's heat units when the minimum
temperature falls below 11oC. The penalty increases proportionally from 14% of the
next day's units at 10o to 100% at 4o or lower.
xIf the mean falls below this temperature (10o or 15.5oC, respectively), no heat
units are recorded for the date.
wCoefficient of variation = Standard Deviation of the Mean divided by the Mean and
multiplied by 100%.
Table 5. Cucumber accumulated heat unit models for machine-harvested 'Calypso',
Willamette Valley, Oregon, 1989, corrected to a mean grade of 2.5
Planting Days, seed Tmax-15.5 Tmean-10 Tmean-15.5
date to harvest Tmax-15.5 -CP Tmean-10 -CP Tmean-15.5 -CP
June 2 67 600 528 531 473 183 168
June 2 67 610 539 523 465 178 163
June 3 70 620 540 545 481 183 167
June 25 64 570 512 496 442 158 144
July 4 72 670 579 563 486 181 161
Mean 68 614 540 532 469 177 161
Std. dev. 3.1 32.6 22.1 22.4 15.4 9.5 8.7
Coeff. var. 4.1% 5.3% 4.1% 4.2% 3.3% 5.4% 5.4%
For explanation of heat unit models and coefficient of variation, see previous table.
Table 6. Effect of harvest on yield, size distribution and value per acre of eight
machine-harvested pickling cucumber varieties, first planting, 1990
Tot. Wt. % in grade by weight Mean Yield Value
Variety Harvest AHUz (lb) 1s 2s 3s 4s N&C grade (T/A) $/A $/T
_______________________________________________________________________________________________________________
Calypso 1 673 1409 2.7 31.4 42.9 2.0 0.0 2.86 6.3 666 106
2 699 1945 1.2 17.3 49.5 29.7 2.3 3.10 8.6 713 83
3 730 2523 0.5 6.2 40.7 50.5 2.1 3.44 11.2 579 52
4 738 2840 0.4 4.8 28.6 62.8 3.4 3.59 12.6 486 39
Castlepik 1 673 1884 2.3 22.0 52.9 22.8 0.0 2.96 8.4 810 97
2 699 1923 1.2 16.3 48.9 31.1 2.5 3.13 8.5 685 80
3 730 3106 0.7 7.2 41.5 49.1 1.6 3.41 13.8 753 55
4 738 3089 0.5 6.1 32.6 60.0 0.8 3.53 13.7 598 44
Cross Country 1 673 1475 2.2 24.6 52.3 21.0 0.0 2.92 6.6 659 101
2 699 2187 1.1 10.9 40.5 46.3 1.2 3.34 9.7 599 62
3 730 2773 0.6 6.5 32.3 59.9 0.8 3.53 12.3 546 44
Discover 1 673 1456 2.3 25.8 48.6 23.3 0.0 2.93 6.5 647 100
2 699 1604 1.1 10.3 40.3 47.5 0.7 3.35 7.1 429 60
3 730 2226 0.4 4.5 29.6 64.2 1.3 3.60 9.9 376 38
4 738 1352 0.3 3.4 28.0 64.7 3.6 3.63 6.0 210 35
Primepak 1 673 500 7.8 55.0 32.0 5.2 0.0 2.35 2.2 348 157
2 699 894 3.4 28.7 48.0 17.6 2.3 2.82 4.0 434 109
3 730 1657 1.3 13.5 52.0 32.0 1.3 3.16 7.4 570 77
4 738 1100 1.3 12.3 47.9 35.1 3.5 3.21 4.9 354 72
PS50885 1 673 1873 2.7 29.4 47.6 20.3 0.0 2.86 8.3 889 107
2 699 1917 1.5 17.8 48.5 30.9 1.4 3.10 8.5 706 83
3 730 2632 0.9 6.4 41.0 50.5 1.3 3.43 11.7 623 53
4 738 2632 0.4 4.9 26.4 67.6 0.7 3.62 11.7 414 35
Regal 1 673 1314 2.4 25.8 52.6 19.2 0.0 2.89 5.8 606 104
2 699 2314 0.9 11.2 46.2 40.3 1.4 3.28 10.3 687 67
3 730 2097 0.9 9.8 40.2 47.8 1.4 3.37 9.3 547 59
4 738 2887 0.3 3.3 22.6 69.5 4.3 3.69 12.8 389 30
Sun 3509 1 673 1111 3.2 27.2 41.5 28.1 0.0 2.94 4.9 489 99
2 699 1835 1.0 12.0 44.3 42.3 0.4 3.28 8.2 543 67
3 730 2395 0.5 6.2 31.9 61.0 0.4 3.54 10.6 458 43
4 738 2865 0.5 3.8 18.9 74.9 1.9 3.72 12.7 349 27
zAHU: accumulated Celsius heat units, Sum of Tmax-15.5, with a maximum temperature
cutoff of 32C (90F).
Table 7. Main effects of variety and harvest on yield, size distribution, and value
per acre of eight cucumber varieties, first planting, Marion County, Oregon, 1990
% in grade by weight Mean Yield Value Valuez
Treatment 1s 2s 3s 4s N&C grade (T/A) $/A $/T loss (%)
Variety
Calypso 1.3 14.9 40.4 41.5 2.0 3.18 9.7 611 70 64
Castlepik 1.2 12.9 44.0 40.8 1.2 3.22 11.1 712 69 55
Cross Country 1.3 14.0 41.7 42.4 0.7 3.26 9.5 601 69 56
Discover 1.0 11.0 36.6 49.9 1.4 3.33 7.4 416 58 65
Primepak 3.5 27.4 45.0 22.5 1.8 2.83 4.6 427 104 67
PS50885 1.4 14.6 40.9 42.3 0.9 3.23 10.1 658 70 54
Regal 1.1 12.5 40.4 44.2 1.8 3.24 9.6 557 65 71
Sun3509 1.3 12.3 34.2 51.6 0.7 3.35 9.1 459 59 72
Harvest
1 3.2 30.2 46.3 20.4 0.0 2.84 6.1 639 109 --y
2 1.4 15.6 45.8 35.7 1.5 3.21 8.1 668 76 30
3 0.7 7.5 38.7 51.9 1.3 3.44 10.8 557 53 51
4 0.5 5.5 29.3 62.1 2.6 3.57 10.6 400 40 63
zThe percentage loss in crop value (dollars per ton) between the first and last
harvest of the variety.
yThe average cumulative percentage loss in crop value between the first harvest and
successive harvests, averaged over all varieties.
Table 8. Effect of harvest on yield and size distribution of nine machine-harvested
pickling cucumber varieties, second planting, Marion County, Oregon, 1989
Tot. Wt. % in grade by weight Mean Yield Value
Variety Harvest AHU (lb) 1s 2s 3s 4s N&C grade (T/A) $/A $/T
Calypso 1 689 667 5.6 45.9 38.6 7.2 2.7 2.49 3.1 433 140
2 727 718 1.1 18.5 45.4 32.9 2.1 3.12 7.4 601 81
3 757 2678 0.5 13.1 41.7 43.1 1.6 3.29 9.5 621 65
Castlepik 1 689 1327 2.0 22.9 53.1 19.9 2.0 2.93 5.0 493 99
2 727 749 1.3 14.4 50.6 32.8 0.8 3.16 7.8 605 78
3 757 3597 0.6 10.0 34.2 53.9 1.3 3.43 12.8 675 53
Cross Country 1 689 877 3.3 33.3 46.6 13.2 3.5 2.72 3.3 386 117
2 727 338 3.6 28.1 49.4 18.9 0.0 2.84 3.5 382 109
3 757 1554 1.2 18.3 46.6 31.3 2.6 3.11 5.5 452 82
Discover 1 689 951 5.2 42.9 45.0 6.5 0.4 2.53 3.6 493 138
2 727 674 1.8 17.2 51.2 29.8 0.0 3.09 7.0 592 85
3 757 3006 0.6 9.9 38.1 48.6 2.7 3.38 10.7 609 57
Little Leaf 1 757 513 1.9 18.5 39.4 40.2 0.0 3.18 1.8 140 77
Pioneer 1 689 569 5.4 44.1 40.4 8.8 1.2 2.53 2.1 294 137
2 727 387 2.6 18.1 50.9 28.4 0.0 3.05 4.0 356 89
3 757 949 0.9 9.4 40.4 45.2 4.1 3.35 6.6 391 60
PrimePak 1 689 645 6.4 39.7 41.6 9.3 3.1 2.56 2.4 325 134
2 727 382 3.1 32.2 46.3 18.3 0.0 2.80 4.0 445 112
3 757 2081 1.1 15.9 48.7 33.2 1.2 3.15 7.4 579 78
PS50885 1 689 1068 5.7 37.9 49.0 7.0 0.4 2.58 4.0 539 134
2 727 956 1.6 15.8 39.7 42.2 0.7 3.23 11.9 849 71
3 757 2630 0.8 11.3 39.2 47.5 1.3 3.35 13.1 789 60
Regal 1 689 832 4.8 44.2 40.1 10.0 0.8 2.56 3.1 423 135
2 727 562 2.0 15.8 47.5 31.9 2.8 3.12 5.8 470 81
3 757 2954 0.7 10.1 35.6 50.7 2.8 3.40 10.5 583 55
Table 9. Main effects of variety and harvest on yield, size distribution, and value
per acre of eight cucumber varieties, second planting, Marion County, Oregon, 1990
% in grade by weight Mean Yield Value Value
Treatment 1s 2s 3s 4s N&C grade (T/A) $/A $/T loss (%)
Variety
Calypso 2.4 25.8 41.9 27.7 2.1 2.97 6.7 552 95 64
Castlepik 1.3 15.8 46.0 35.5 1.4 3.17 8.5 591 77 66
Cross Country 2.7 26.6 47.5 21.1 2.0 2.89 4.1 407 103 30
Discover 2.5 23.3 44.8 28.3 1.0 2.99 7.1 417 93 59
Pioneer 3.0 23.9 43.9 27.1 1.8 2.98 4.2 347 95 55
Primepak 3.5 29.3 45.5 20.3 1.4 2.84 4.6 450 108 41
PS50885 2.7 21.7 42.6 32.2 0.8 3.05 9.7 726 88 59
Regal 2.5 23.4 41.1 30.9 2.1 3.03 6.5 492 90 57
Harvest
1 4.8 38.9 44.3 10.2 1.8 2.61 3.3 423 129 --
2 2.1 20.0 47.6 29.4 0.8 3.05 6.4 538 88 32
3 0.8 12.3 40.6 44.2 2.2 3.31 9.5 587 64 50
Table 10. Summary of yield and mean grade for several fields of 'Calypso' cucumber
harvested by the Byron (B) and Wilde (W) harvesters, Willamette Valley, Oregon, 1990
Grower/ Planting Harvest Mean AHU to mean Tons/ Dollars/ Dollars/
Harvester date date AHU grade grade of 2.5 acre acre ton
1,B 5/29 7/31 591 2.76 560z 8.9 1037 117
1,B 5/31 8/03 621 2.74 580 5.8 695 121
2,B 6/15 8/05 592 2.68 580 6.7 761 114
3,B 6/14 8/04 591 2.61 585 6.7 841 126
4,W 6/22 8/14 673 2.86 633 6.3 666 106
6/22 8/16 699 3.10 " 8.6 713 83
6/22 8/19 730 3.44 " 11.2 579 52
6/22 8/20 738 3.59 " 12.6 486 39
7/03 8/27 689 2.49 690 3.1 433 140
7/03 8/31 727 3.12 " 7.4 601 81
7/03 9/03 757 3.29 " 9.5 621 65
zEstimated heat units required to obtain a mean grade of 2.5, based on the AHU
required to reach the mean grades listed in the table. For the plantings of grower
No. 4, a regression line was determined for the listed data and the AHU at grade
2.5 was estimated by extrapolation. For the other plantings, the estimate was made
on the basis of the rate of change in grade in the grower 4 plantings.
Table 11. Main effects of plant population, N rate, and harvest date on yield and
grade of 'Castlepik' cucumber, NWREC, Oregon, 1990
% in grade by weight Mean Yield Gross Value
0-1" 1-1.5' 1.5-2" >2" N&Cz Gradey tons/acre $/acre $/ton AHUx
_________________________________________________________________________________
Population
70,000/A 4.7 26.0 38.5 28.4 3.3 2.92 7.5 663 100 --
100,000/A 4.1 21.1 42.0 30.7 2.1 3.01 10.7 899 92 --
NSw NS NS NS NS NS ** * NS
N Rate
70 lb/A 3.6 21.2 42.4 29.3 3.6 3.01 9.4 798 92 --
110 4.8 24.6 35.3 32.6 2.6 2.98 9.0 745 95 --
150 4.7 25.0 43.1 25.3 1.9 2.91 9.0 801 102 --
NS NS NS NS NS NS NS NS NS
Harvest
Aug. 1 7.0 31.6 38.1 20.6 2.7 2.74 6.6 737 117 601
Aug. 6 1.8 15.6 42.4 38.6 2.7 3.19 11.6 826 75 667
** ** NS ** NS ** ** * **
zNubs and crooks.
yGrade 1 = 0-1", grade 2 = 1-1.5", grade 3 = 1.5-2", grade 4 = over 2" diameter.
xAccumulated celsius heat units: sum(Tmax.-15.5C) from day after planting to
harvest with maximum heat units per day set at 16.67.
wNS: nonsignificant; *,**: significant at 5% and 1% levels, respectively.
Table 12. Main effects of plant population and N rate on yield and grade of
'Little Leaf' cucumber, NWREC, Oregon, 1990
% in grade by weight Mean Yield Gross Value
0-1" 1-1.5" 1.5-2" >2" N&C grade tons/acre $/acre $/ton
Population
35,000/A 4.3 40.9 38.2 15.8 0.8 2.66 7.9 988 125
70,000/A 5.8 51.5 35.5 6.4 0.7 2.43 9.5 1364 147
NS NS NS * NS NS * * NS
N Rate
70 lb/A 3.0 48.0 38.3 9.5 1.2 2.55 10.3 1383 134
110 5.4 44.4 38.8 10.9 0.5 2.55 9.1 1249 141
150 6.5 46.8 33.3 12.9 0.5 2.55 7.8 1098 141
NS NS NS NS * NS NS NS NS
Table 13. Main effects of plant population, N rate, and harvest date on yield and
grade of 'PS 10588' cucumber, NWREC, Oregon, 1990
% in grade by weight Mean Yield Gross Value AHU
0-1" 1-1.5" 1.5-2" 2"+ N&C grade tons/acre $/acre $/ton
Population
70,000/A 15.1 47.2 28.6 5.5 3.6 2.25 11.0 1508 164 --
100,000/A 18.1 45.4 25.1 7.5 3.9 2.22 9.3 1215 167 --
NS NS NS NS NS NS * * NS
N rate
70 lb/A 15.0 43.7 29.9 7.7 3.7 2.31 11.0 1369 158 --
110 18.6 48.0 24.1 5.9 3.4 2.18 10.3 1436 172 --
150 16.3 47.2 26.6 5.8 4.1 2.22 9.2 1280 166 --
NS NS NS NS NS NS NS NS NS
Harvest
Aug. 31 48.1 40.8 4.3 0.0 6.8 1.53 2.1 485 238 614
Sept. 4 13.3 75.0 7.7 1.7 2.3 1.98 6.9 1314 189 643
Sept. 7 3.4 39.5 45.1 9.2 2.8 2.62 13.2 1676 127 686
Sept. 10 1.6 29.9 50.4 15.1 3.0 2.81 18.4 1971 108 718
** ** ** ** * ** ** ** **
Cover Crops and Nitrogen on Sweet Corn Yield
Cooperators: Richard Dick, Department of Crop and Soil Science, OSU, and Dr. Jeffrey Steiner, USDA-ARS, Corvallis, OR
Introduction
In the fall of 1989 a five-year study of the impact of various alternative crop rotations on crop yield and soil fertility was initiated at the North Willamette Research and Extension Center. The rotations involved ranged from five years of grass seed production on one extreme, to a vegetable-only rotation, unbroken by grain, grass seed, or legume crop, or by winter cover crops. The primary objective of the vegetable portion of this study is to investigate the effects of several rotations on the yield and quality of vegetable crops in the rotation and to determine the contribution of winter cover crops to the nutrient needs of the vegetable crop. Spring, 1990 saw the first introduction of vegetables into the rotation plots. Future years will involve different vegetable crops in the rotations.
Methods
The plot area is a Willamette silt loam, pH 5.5, which was planted to wheat in the fall of 1988. Four tons per acre of ground agricultural limestone was applied in September, 1989, to bring the soil pH to 6.0. Fescue, clover, and wheat plots of 30 x 60 feet were established in late September and early October of 1989, while other plots were plowed and left fallow. Another set of plots was seeded to cereal rye at 60 pounds per acre or to cereal rye at 40 pounds per acre plus Austrian pea at 80 pounds per acre.
On 2 March, 1990, all fallow, rye, and rye-pea plots were disked to turn under the cover crop and start preparations for planting. The plots were again disked on 30 March and were tilled with a Roterra on 2 April. Following cultimulching, the plots were seeded with 'Earliking' sweet corn on 26 April, with 12 rows per plot on 30-inch centers. No fertilizer was applied at planting. On 3 May, atrazine (1.2 pounds per acre) or atrazine (1.2 pounds) plus alachlor (2.0 pounds per acre) were applied to the appropriate plots. At the same time 50 pounds N per acre was applied as urea to eight rows of each 12-row plot, establishing a split between fertilized and unfertilized subplots.
Due to insufficient stands, the plots were disked, cultimulched, and replanted on 15 May, with no additional herbicide. On 18 June, additional urea was applied at 150 pounds N per acre to half (20 x 30 feet) of the previously fertilized area, resulting in a total N rate of 200 pounds per acre on these subplots. The experimental design was a factorial combination of cover crop-herbicide treatments applied to main plots, with N fertilizer rate as subplot. The plots were irrigated weekly at about one inch per week with a drip system set between every other row. Ears and stover were harvested from 70 square foot sections of each subplot on 16 August. Subsamples of ears and stover were transported to the OSU Department of Crop and Soil Science for determination of dry weight yields. The plots were disked, plowed, and prepared for cover crop seeding in September.
Results
Seedling stands were not sufficient for the first planting (Table 1). This was due to a combination of poor emergence and stand loss to birds. Emergence was significantly affected by the presence of a winter cover crop, with nearly double the stand on fallowed plots compared to the mean for plots with either the rye or rye plus pea cover crops. Type of cover crop and herbicide applied did not affect the stand. Soil condition at time of planting seemed ideal, with no surface cover crop residues to interfere with the seeding operation. Soil moisture was nearly ideal for planting. The poor emergence may have been due to an allelopathic effect of the cereal rye residues. An adequate stand was obtained on all plots after replanting and the replanted stand did not vary with treatment.
Fresh weight ear yield increased on cover crop plots as opposed to winter-fallowed plots, and yields were slightly higher on plots wintered with a rye-legume cover rather than rye alone (Table 2). Stover fresh weight and mean ear weight responded similarly. Number of ears harvested per plot and ear length did not vary with cover crop treatment. Herbicide had no effect on yield. Tipfill was rated on a three point scale, with higher means for ears from plots which had a winter cover crop. Yield of ears and stover, mean ear weight, and ear length all increased with increasing rate of nitrogen. The number of ears harvested per subplot also increased with increasing rate of N as there were more mature ears at time of harvest on highly fertilized plots. The tipfill rating did not vary with N rate. Stover moisture content increased with increasing rate of applied N and on cover crop plots as compared to fallowed plots. Kernel moisture content did not vary significantly with treatment but there was a tendency toward higher moisture content with increasing rate of applied N.
Crop response to added N was normal in this season, allowing a rough estimate of the fertilizer value of the cover crop. The first increment of applied urea resulted in increased fresh yield of 0.8 tons per acre. A rye cover crop resulted in an average yield increase of 0.4 tons per acre. If we assume that the response is due solely to cover crop nitrogen content, then the rye cover appeared to contribute about 25 pounds N per acre to the corn crop. Similarly, the rye-pea mix contributed about 50 pounds N per acre.
Table 1. Effects of winter cover crop and herbicide on the stand of sweet corn
seeded on April 26, 1990. Stands recorded on May 14, NWREC, Oregon
Winter cover crop Herbicide Seedlings per meter
Fallow atrazine and alachlor 3.5
Rye atrazine 1.4
Rye atrazine and alachlor 1.8
Rye and Austrian pea atrazine 1.6
Rye and Austrian pea atrazine and alachlor 2.1
LSD (0.05) 1.2
Single degree of freedom comparisons
Cover vs fallow: **
Rye vs. rye-pea NS
atrazine vs. combination NS
Cover x herbicide NS
Table 2. Main effects of cover crop and nitrogen fertilizer rate on yield and
quality of 'Earliking' sweet corn, crop rotation experiment, NWREC, Oregon, 1990
Fresh wt. (T/A) No. ears Mean ear Ear length Tipfill % moisture
Treatment Ears Stover per plot fr. wt. (g) (inches) rating Ear Stover
Cover crop
Fallow 4.1 5.7 34.8 169 8.6 0.8z 80 76.7
Rye-low inputy 4.4 6.6 34.8 183 8.7 1.1 78 80.5
Legume-low input 5.0 7.4 35.7 205 8.7 1.3 77 77.5
Rye 4.3 6.9 33.3 184 8.5 1.1 75 79.0
Legume 4.6 7.0 35.0 190 8.8 1.2 80 79.5
LSD (0.05) NS 0.9 NS 19 NS NS 2.5
N rate
0 lb/A 3.6 6.4 29.8 177 8.4 1.1 77 77.7
50 4.4 6.4 35.5 181 8.7 1.1 78 78.3
200 5.4 7.3 38.9 202 8.9 1.2 79 80.0
**lin **quad **lin **lin *lin NS *lin
Single degree of freedom comparisons
Cover crop:none * ** NS ** NS NS *
Rye:legume-rye * * NS * NS NS NS
Atraz:atraz-alach NS NS NS NS NS NS NS
zThree point scale with 0=more than 1 inch of tip unfilled, 1=0.25-1 inch unfilled,
2=less than 0.25 inch unfilled.
yLow input: atrazine only at planting rather than the standard combination of
atrazine plus alachlor.
Cooperators: M. L. Powelson, Dept. of Botany and Plant Pathology; N. S. Mansour, Dept. of Horticulture; D. McGrath, Marion County Cooperative Extension Office;
J. Hart, Department of Crop and Soil Science
Introduction
A soft rot of the broccoli head, caused by the bacterium Erwinia carotovora subsp. carotovora is one of the most devastating diseases of broccoli. The occurrence of this disease is influenced by the presence of the bacterium, free moisture on the florets, and temperatures ideal for bacterial growth. Past research at the Center has studied the effects of plant populations and irrigation practices on the incidence of the disease. Although much valuable information has been gained that may aid growers in avoiding the disease, no cure has been forthcoming. Recent research in Virginia indicated that nitrogen source might play a role in disease incidence. This might be due to differences in the companion ion accompanying the nitrogen, as various N sources also provide S, Ca, K, Na, or P to the crop. High tissue levels of Ca or the monovalent cations may help prevent the disease.
Broccoli growers in the Willamette Valley use high rates of N fertilizers, often exceeding 250 to 300 pounds of actual N per acre per season. While the common experience has been that these rates are necessary to achieve maximum yields and quality, our past research has indicated increased incidence of head rot at high rates of N. In addition, a considerable portion of this applied fertilizer is not actually taken up by the crop. This has raised concerns that the remaining nitrogen may be contributing to nitrate pollution of groundwater. Improved efficiency of nitrogen management in broccoli may be possible if the fertilizer could be applied at time of maximum crop need. The purpose of these trials was to study the response of broccoli yield and head rot incidence to a wide range of rates and sources of nitrogen fertilizer. Additional objectives were to evaluate the effect of applied calcium chloride on broccoli yield and quality and to evaluate the efficacy of copper compounds and selected bacterial antagonists for control of broccoli head rot.
Methods
In the first experiment of 1989, 'Gem' broccoli was seeded on 31 March in 31 cm3 plugs (Landmark Plastic Corp. 128-cell trays) in an unheated greenhouse and transplanted on 1 May to a Willamette silt loam, pH 5.4, to which had been applied 500 pounds per acre of a 10N-8.7P-16.7K fertilizer, 0.75 pounds trifluralin, 1.3 pounds chlorpyrifos and 2.0 pounds boron per acre. Carbaryl and diazinon were applied for looper control at 1.0 pound per acre, each, on 25 May. Treatments consisted of a factorial combination of six N sources (ammonium nitrate, calcium nitrate, urea, sodium nitrate, potassium nitrate, and sodium-potassium nitrate); two rates of total N (150 and 200 pounds per acre); and three rates of foliar-applied calcium chloride (0, 10, and 20 pounds Ca per acre). Each plot consisted of a four-row bed, 15 feet long, with plants on 16 x 9-inch spacing. Treatments were replicated four
times. The N sources were sidedressed on 29 May and again on 13 June, with half the total rate applied on each date. The calcium chloride was applied on 13 June. An aqueous suspension of Erwinia carotovora was sprayed onto the plants on 17 June and again on 29 June. The plots were harvested on 29 June and again on 7 July.
In the second experiment of 1989, 'Gem' was direct-seeded into Willamette silt loam on 21 June in 16-inch rows and thinned to an average within-row spacing of 9 inches. Treatments consisted of a factorial combination of the above N sources, with the addition of ammonium sulfate, and the same three rates of calcium chloride. Plot size was a four-row bed, 20 feet in length. Treatments were replicated four times. No preplant fertilizer was used; pesticide treatments were similar to those in the first experiment. The total N applied was split with 50 pounds N per acre applied on 7 July, and 75 pounds, each, on 26 July and 21 August. The calcium chloride treatments were applied on 21 August. Boron was applied at 2.0 pounds per acre on 27 July. Erwinia was applied on 21 August and again on 5 September. Plots were harvested on 5 and 12 September. Leaf samples were taken for plant tissue analysis on 5 September and samples of the surface centimeter of soil were taken for pH determination on 19 September.
In a third experiment in 1990, six potential head rot-control treatments were applied to 20-foot sections of two-row beds in a commercial field on 29 September. The same six treatments were reapplied on 6 October and were also applied in a second field on the same date. The treatments, replicated six times in each field, included three possible bacterial antagonists and Kocide at 4.0 pounds per acre. Each of these treatments also included inoculation with Erwinia at 106 cells. The fifth and sixth treatments consisted of Erwinia alone, and an untreated control, respectively.
The applications on 29 Sept. were made with 3XD4 hollow cone nozzles at 1.0 foot spacing and 40 psi, and 250 ml spray solution per plot. The applications on 6 October were made with 8003 T-jet nozzles at 28 psi and 333 ml spray solution per plot. Head rot ratings were made on 11, 16, 20, and 27 October.
In the first experiment of 1990, greenhouse-grown 'Gem' was seeded on 27 March and transplanted on 1 May. Plot preparation included a broadcast and incorporated application of triple superphosphate at 200 pounds per acre, trifluralin at 0.75 pounds per acre, and chlorpyrifos at 1.3 pounds per acre. Propachlor (4 pounds per acre) and boron (2 pounds per acre) were applied immediately after transplanting.
The N sources were ammonium nitrate, calcium nitrate, potassium nitrate, sodium nitrate, and urea. These were applied in factorial combination with three N rates (100, 175, and 250 pounds per acre) and two rates of calcium chloride (0 and 30 pounds Ca per acre) in randomized complete block design with four replications. The initial N application of 50 pounds per acre was made two days after planting. The remaining N was applied three weeks later. Plot size was 16 feet with four rows on an 80-inch bed. Within-row spacing was nine inches. Plots were sprinkler-irrigated as necessary. Harvests were 3 and 10 July.
In the second experiment of 1990, 'Gem' was direct-seeded on 18 July with target plant population equal to that in the first planting. Cultural practices were the same as for the first planting. Treatments consisted of a factorial combination of two N sources, sodium nitrate and urea, with four rates of total applied N (100, 175, 250, and 325 pounds/acre). The first 50 pounds N per acre was applied at planting, the remainder four weeks later. In addition to the above factorial combination, an additional set of plots received either 250 pounds urea per acre at planting or 50 pounds urea per acre at planting and 200 pounds per acre four weeks later. Plots were harvested on 18 and 25, October, and 1 November.
In the final experiment of 1990, 'Gem' was direct-seeded on 25 July, again with the same target populations and cultural practices. Treatments consisted of a factorial combination of three N sources (sodium nitrate, potassium nitrate, and urea) with three rates of applied N (100, 175, and 250 pounds per acre). The first N application was on 1 August, with the remainder applied four weeks later. Plots were harvested on 30 October and 6 November.
Results
In the first experiment of 1989, neither head weight, head width, percent good heads, percent head rot, nor percent downy mildew-affected heads was significantly affected by N source (Table 1). However, the incidence of head rot tended to be lower on plots receiving either potassium or sodium nitrate. This trend, though not statistically significant, was particularly strong at the first harvest. Bead size was affected by N source, with the smallest bead occurring with calcium nitrate as N source.
The higher rate of total N applied increased head size but also nearly doubled the incidence of head rot. At the first harvest there was a significant interaction of N rate and source on head rot incidence: head rot increased at the high N rate for five of six N sources, but decreased at the high N rate with sodium nitrate as fertilizer. With potassium nitrate, the tendency for higher rot incidence at the high N rate was reduced (Table 2).
Rate of calcium chloride had no effect on head weight or quality. Leaves of plants grown with potassium or sodium in the fertilizer were noticeably darker green in color.
In the second experiment of 1989, N source had no significant effect on mean head size, although there was a strong trend for heavier heads with urea as N source (Table 3). Yield on an area basis did vary with N source, with urea and potassium nitrate producing the highest yields. Head width varied slightly with N source. Head rot incidence in this trial was extremely low due to the unusually warm, dry conditions during the maturation and harvest period. Rot and downy mildew incidence did not vary with N source. Most favorable bead size occurred with sodium, potassium, and calcium nitrates. Rate of applied calcium had no effect on yield or rot incidence.
Soil pH was affected by N source, with the potassium and sodium fertilizers increasing pH of the surface centimeter of soil and ammonium nitrate and ammonium sulfate reducing pH compared to the control value of 5.4 (Table 4). Use of sodium and potassium nitrates should reduce the amount of lime necessary to maintain adequate pH on heavily fertilized soils.
Leaf tissue N levels were not significantly affected by N source. However, the leaf N levels were lowest with the combination of ammonium sulfate as N source and no applied Ca (data not shown). This may be related to the limitation of N uptake by the low surface soil pH in these plots. Leaf tissue levels of K, S, Ca, Mg, Mn, Fe, and Na were significantly affected by N source but not by rate of applied calcium (Table 4). Ammonium sulfate increased leaf K, S, and Mn concentrations, but reduced levels of Ca, Fe, and Mg. These effects may all be related to the acidifying effect of this fertilizer. The sodium-containing fertilizers dramatically increased leaf Na content.
In the bactericide trial, no rot was observed in either planting on 11 October. On 16 October, rot incidence of 1% was observed on the Erwinia-treated plots in the first field; no rot was observed in the second field. On 20 October, there was moderate to severe phytotoxicity on all Kocide-treated plots in the first field. Severe symptoms included large areas of necrotic floret tissue. Some head rot was also observed, primarily on Kocide-treated plots (Table 5). Severity of the rot was low except for two heads (out of approximately 180 heads total) which exhibited advanced rot of the entire head. Both of these heads were from Kocide-treated plots. No rot was observed in the second field, but mild phytotoxicity was observed on five of the six Kocide-treated plots. The symptom observed was a darkening and hardening of the florets.
On 26 October, a few heads had been cut for commercial harvest in the first field, including a few previously observed to have rot. Of the remaining heads, rot incidence was insignificant except for the Kocide- and WAR60-treated plots. As on 20 October, severe rot occurred only on heads injured by the Kocide treatment. No significant rot was observed in the second field. However, most heads of harvestable size had already been cut. Head rot incidence in these two fields was too low to adequately judge the effect of the antagonists. It is apparent, however, that 4.0 pounds per acre of Kocide is too high a rate to use in attempts to control head rot.
In all three 1990 experiments the source of N had no statistically significant effect on broccoli production, whether expressed on a yield per acre or mean head weight basis. In addition, there were no significant interactions of source and N rate on yield. Thus, only main effects are shown in the tables. No head rot developed in 1990.
Application of calcium nitrate had no effect on yield in the first experiment of 1990.
In the first experiment, N rate had a small but significant effect on broccoli yield (Table 6). Both mean head weight and yield on an area basis increased with increasing rate of nitrogen. However, there was very little increase beyond 175 pounds N per acre. There was a trend toward increased bead size of broccoli heads with increasing rate of nitrogen, but the effect was not significant (data not shown).
In the second experiment of 1990, yield and mean head weight increased with increasing rate of N to a maximum at 250 pounds N per acre (Table 7). Yields at 325 pounds N tended to be reduced slightly. High rates of N favored early maturity and larger heads at the first harvest (Table 8). At the second and third harvests of these plots, the largest head size was achieved at less than the maximum rate of N. The effect of applying all N at planting versus delaying the bulk of the application of N until the plants are well-established is seen in Table 9. Even though maximum N uptake does not occur until near head formation, it appears to be critical to provide ample N at time of planting. For a spring planting, this would increase the risk of leaching the N out of the root zone.
In the third experiment, yield on an area basis did not vary significantly with N rate because of variation in stand (Table 10).
However, mean head weight varied significantly with N rate, with a maximum at 250 pounds N per acre.
From these trials it appears that amounts of N in excess of 250 pounds per acre exceed crop needs and needlessly increase the chance of nitrate pollution of groundwater or runoff. Nitrogen source has little or no effect on broccoli yield at the rates of N needed for adequate yield and quality.
Table 1. Main effects of N source, N rate, and Ca rate on yield and quality
of broccoli, NWREC, Oregon, July, 1989
Mean head Head % good % head % Beadz
Treatment wt. (g) width (in.) heads rot mildew size
N source
NH4NO3 162 3.9 92.7 8.1 1.5 3.6
Ca(NO3)2 171 4.0 90.6 8.3 2.5 3.2
KNO3 164 4.0 90.6 4.5 2.5 3.7
NaNO3 168 4.0 92.6 5.4 1.5 3.6
K/NaNO3 167 3.9 91.1 7.1 1.5 3.5
Urea 169 4.1 93.0 6.8 1.0 3.9
LSD(0.05) NSy NS NS NS NS 0.3
N rate, lb/A
150 160 3.9 93.4 4.8 1.8 3.6
200 174 4.0 90.8 8.6 1.9 3.6
** ** NS ** NS NS
Ca rate, lb/A
0 173 4.1 91.1 7.8 2.1 3.6
10 161 3.9 93.2 5.9 1.7 3.5
20 166 4.0 91.9 6.5 1.7 3.6
LSD (0.05) 8 0.1 NS NS NS NS
Notes: No significant differences in stem color or hollow stem incidence.
zBead size rated on a five point scale, with 1=very fine bead, 5=very open
bead, some open flowers.
yNS,*,**: No significant differences, significant at the 5% and 1% levels,
respectively.
Table 2. Interaction of N source and N rate on broccoli head
rot incidence, first harvest, July, 1989, NWREC, Oregon
N source N rate (lb/A) % head rot
NH4NO3 150 1.9
200 13.9
Ca(NO3)2 150 6.3
200 9.0
KNO3 150 3.4
200 4.8
NaNO3 150 6.0
200 3.9
K/NaNO3 150 4.3
200 6.6
Urea 150 3.5
200 8.8
LSD (0.05) 5.9
Table 3. Main effects of N source and Ca rate on yield and quality of
broccoli, September, 1989, NWREC, Oregon
Yield Mean head Head % good % head % Bead
Treatment (T/A) wt. (g) width (in.) heads rot mildew size
N source
NH4NO3 4.8 166 3.6 96.1 1.3 2.6 3.3
(NH4)2SO4 4.6 161 3.6 88.7 0.0 11.3 3.3
Ca(NO3)2 4.9 167 3.5 90.4 1.7 7.9 3.1
KNO3 5.2 176 3.7 92.4 0.6 7.0 3.0
NaNO3 4.6 162 3.6 89.9 0.5 9.6 2.9
K/NaNO3 5.0 173 3.8 89.7 1.6 8.6 3.1
Urea 5.8 184 3.8 85.8 0.4 13.8 3.4
LSD(0.05) 0.5 NSz 0.2 NS NS NS 0.3
Ca rate, lb/A
0 5.0 174 3.7 88.4 1.2 10.4 3.3
10 5.0 166 3.6 90.8 1.1 8.1 3.0
20 4.9 170 3.7 92.1 0.4 7.6 3.2
LSD(0.05) NS NS NS NS NS NS 0.2
zNS: No significant differences among means within the column.
Table 4. Main effects of N source and Ca rate on soil pH and broccoli leaf
elemental concentrations, September, 1989, NWREC, Oregon
Percent dry weight Ppm dry weight Soilz
Treatment N K S Ca Mg Mn Fe Na pH
N source
NH4NO3 5.4 2.8 1.0 2.3 0.26 69 190 727 4.8
(NH4)2SO4 5.4 3.7 3.2 1.6 0.18 93 143 603 4.5
Ca(NO3)2 5.8 2.5 1.1 2.4 0.26 62 174 1289 5.4
KNO3 5.7 2.8 1.2 2.5 0.27 56 195 1301 6.0
NaNO3 6.2 2.7 1.1 2.2 0.24 62 175 5698 6.2
K/NaNO3 5.6 2.5 1.1 2.4 0.24 56 175 5330 6.1
Urea 5.9 2.9 0.9 2.0 0.24 62 181 1079 5.4
LSD (0.05) NSy 0.5 0.5 0.3 0.03 17 28 1473 0.3
Ca rate, lb/A
0 5.7 2.8 1.4 2.2 0.23 64 177 2312 5.5
20 5.7 2.9 1.3 2.3 0.24 67 175 2267 5.4
NS NS NS NS NS NS NS NS NS
zpH of the surface half-inch of soil at harvest. Unfertilized soil has a
pH of 5.4.
yNS: No significant differences among means within the column.
Table 5. Rot incidence (percent of heads affected) in the first
grower field experiment, October, 1989, Marion County, Oregon
Treatment Rate 20 October 26 October
Untreated control -- 1.0% 0.5%
Erwinia carotovora 106 cells/ml 2.0 0.0
Kocide 4.0 lb/A 4.5 14.3
3832 107 cells/ml 0.0 1.0
3871 107 cells/ml 0.0 1.0
WAR60 107 cells/ml 2.2 5.0
LSD (0.05) 2.4 4.7
Table 6. Main effects of N rate and source on yield and mean head
weight of 'Gem' broccoli, spring, 1990, NWREC, Oregon
Treatment Mean head wt. (g) Yield (tons/acre)
N rate (lb/acre)
100 169 5.3
175 175 5.6
250 176 5.7
*z *
N source
Ammonium nitrate 173 5.2
Calcium nitrate 179 5.6
Potassium nitrate 170 5.4
Sodium nitrate 174 5.6
Urea 172 5.5
NS NS
z*,NS: significant at the 5% level and nonsignificant, respectively.
Table 7. Main effects of nitrogen rate and source on yield of 'Gem'
broccoli for the sum of three harvests, early autumn, 1990, NWREC, Oregon
Treatment Yield (tons/acre) Mean head wt. (g)
N rate (lb/acre)
100 4.0 167
175 5.0 179
250 5.2 197
325 5.0 187
*z *
N source
Urea 5.1 184
Sodium nitrate 4.5 181
NS NS
z*,NS: significant at 5% level and nonsignificant, respectively.
Table 8. Main effects of nitrogen rate and source on mean head weight of
'Gem' broccoli over three harvests, early autumn, 1990, NWREC, Oregon
Treatment Mean head weight (g)
Harvest 1 Harvest 2 Harvest 3
N rate (lb/acre)
100 164 152 163
175 188 169 179
250 187 192 192
325 204 190 183
* * *
N source
Urea 179 175 182
Sodium nitrate 192 176 177
NS NS NS
Table 9. Effect of splitz versus single application of urea at 250 pounds
per acre on mean head weight of 'Gem' broccoli, 1990, NWREC, Oregon
50 pounds at planting 188 g
250 pounds at planting 207 g
*
zSplit application: 50 pounds/acre at planting and the remaining
200 pounds/acre applied four weeks later after final thinning.
Table 10. Main effects of N rate and source on yield, mean head weight and
quality of 'Gem' broccoli, late autumn, 1990, NWREC, Oregon
Treatment Mean head Yield Bead sizez Hollow
wt. (g) (tons/acre) stem (%)
N rate (lb/acre)
100 174 4.7 3.0 12
175 209 4.4 2.9 18
250 188 4.8 2.9 19
* NS NS NS
N source
Potassium nitrate 186 4.2 3.1 13
Sodium nitrate 199 4.8 2.9 16
Urea 184 5.1 2.8 20
NS NS NS NS
zFive point scale, with 1=fine and tight, 5=loose, near anthesis.
Introduction
Broccoli is not often transplanted in the Willamette Valley, but transplanting offers advantages in multiple cropping and establishing an early stand. The cost of using plug-grown transplants can be reduced by using the smallest plug capable of producing a quality transplant, thus reducing greenhouse bench space, number of trays, and amount of rooting medium needed to produce the crop. In addition, costs might be reduced further by growing multiple seedlings per plug and reducing the number of plugs needed to transplant a given area.
The purpose of these trials was to examine the feasibility of using very small plugs in combination with multiple seedlings per plug to produce broccoli transplants and to follow their performance in the field.
Methods
On 31 March, 1989, 'Gem' broccoli was seeded into either 5.1 or 31 cm3 plugs (Landmark Plastic Corp. 288- and 128-cell trays, respectively) containing a peat-vermiculite medium. Either 2, 3, or 5 seeds were placed in each cell and the seedlings were thinned to a final population of 1, 2, or 3 per cell two weeks later. The seedlings were watered daily as needed and fertilized weekly with a 10N-13P-16.7K soluble fertilizer at 100 ppm N.
The plugs were transplanted on 1 May to a Willamette silt loam, to which had been applied 500 pounds per acre of a 10N-8.7P-16.7K fertilizer, 2.0 pounds B, 0.75 pounds trifluralin, and 1.3 pounds chlorpyrifos per acre. Propachlor herbicide was applied at 4.0 pounds per acre immediately after planting. An additional 75 pounds of nitrogen per acre was applied as ammonium nitrate on 29 May and again on 13 June.
Treatments consisted of a factorial combination of the two cell sizes and three populations per cell. Spacing between plugs in the row was 18 inches for all plots. Plots consisted of 15 feet of a four-row bed with 16 inches between rows. Plots were harvested on 28 June, and again on 7 July. Only main shoots were harvested from the center two rows of each plot.
Methods in 1990 were similar except as follows. Seeding was on 27 March and the plugs were again transplanted on 1 May. Preplant fertilizer application included 200 pounds of triple superphosphate, 50 pounds of ammonium nitrate, and 2.0 pounds of B per acre. An additional 150 pounds of N per acre was applied as ammoniun nitrate on 17 May.
Spacing between plugs in the row was 9, 18, or 27 inches for one, two, and three seedlings per plug, respectively. Plots were harvested on 3 July, and again on 10 July.
Results
The interaction of plug size and number of seedlings per plug did not significantly affect any yield component in 1989 and only main effects are given in Table 1. The larger plug size increased mean head weight and bead size, indicating that the relative crowding in the smaller plugs either delayed maturity or resulted in smaller plants. The highest population of seedlings per cell (3) also delayed maturity, reflected in the smaller number of heads cut at the first harvest, the reduced head size, and the tendency toward smaller bead size.
For the total of two harvests, plug size did not significantly affect the number of heads harvested or total yield. However, the mean head weight and bead size were slightly smaller with the smaller plug size. With greater number of seedlings per plug, the total number of heads harvested increased, but the fraction of plants resulting in marketable heads (number of heads harvested divided by the target plant population) decreased markedly with increasing number of plants per plug. Mean head weight decreased dramatically with increasing number of seedlings per plug, indicating either severe competition among plants originating from the same plug or delayed maturity. Total yield did not vary significantly with seedlings per plug as the effect of increasing numbers of plants was almost exactly offset by the decline in mean head weight.
Target plant population per acre ranged from 21,780 for 1 seedling per plug to 65,340 for 3 seedlings per plug. At the higher populations, it is apparent that the competition among seedlings in a plug severely reduced head weight. Thus, no yield advantage was gained by using multiple seedlings and no cost benefits would have been realized. Some of this crowding effect could be offset by using a larger plug size, but only at the cost of increased bench space, trays, and medium needed to produce the plugs.
Table 1. Main effects of plug size and number of seedlings per plug on
broccoli yield, 1989, NWREC, Oregon
First harvest Total
No. of Yield Mean head Bead No. of % of Yield Mean head Bead
headsz T/A wt. (g) sizey heads maximumx T/A wt. (g) size
______________________________________________________________________________
Plug size
31 cm3 10.5 2.7 175 2.7 21.3 48.5 4.7 168 2.8
5.1 cm3 9.3 2.2 152 1.8 22.3 50.7 4.3 147 2.4
NSw NS ** ** NS NS NS * *
No./plug
1 11.1 3.7 233 2.5 12.9 58.5 4.1 223 2.7
2 12.3 2.6 147 2.4 23.2 52.8 4.7 140 2.8
3 6.4 1.1 111 1.9 29.4 44.5 4.6 110 2.4
** ** ** NS ** ** NS ** NS
zNumber per plot, 44 plugs/plot.
yFive point scale with 1 = very tight and fine, 5 = loose, open, near anthesis.
x100% x the total number of heads cut divided by the number of seedlings
originally planted.
wNS,*,**: no significant differences, differences significant at the 5% and
1% levels, respectively.
In 1990, the trial was repeated with single versus multiple seedlings per plug, but with spacing in the row varied to maintain the same target plant population per acre, assuming survival of all seedlings.
Again in 1990, the interaction of plug size and number of seedlings per plug did not usually significantly affect yield and only main effects are given for the first harvest in Table 2. The few significant interactions are found in Table 3. At the first harvest, the larger plug size increased the number of heads cut and the mean head weight and width, indicating that the relative crowding in the smaller plugs either delayed maturity or resulted in smaller plants.
Increasing the number of seedlings per cell also delayed maturity, reflected in the smaller number of heads cut at the first harvest, the reduced head weight, and the tendency toward smaller bead size and reduced head width. There was a significant interaction of cell size and number per cell affecting mean head weight and width (Table 3). The combination of small cell size and three seedlings per cell resulted in greatly reduced head weight and width.
For the total of two harvests (Table 4), the larger plug size significantly increased total yield, but not the number of heads harvested or mean head weight. However, both number of heads harvested and head weight tended to be greater with the larger cells. Head width was significantly greater with the larger cells. Mean bead size and incidence of hollow stem (data not shown) were unaffected by cell size. There were no significant interactions affecting any component of yield for the sum of the two harvests.
With greater number of seedlings per plug, the total number of heads harvested decreased. This is in contrast to 1989 when the number of heads harvested increased with greater number of seedlings per cell. Plugs were set at a uniform 18-inch spacing in 1989, resulting in a greater target plant population at greater number of seedlings per plug. In 1990 the yield per plot also decreased with increasing number of seedlings per cell, due in part to the decrease in number of heads harvested, but also due to decreased mean head weight. Mean head width and bead size were not significantly affected by number of seedlings per plug.
The reduction in number of heads harvested per plot at greater number of seedlings per plot indicates that fewer seedlings survived to produce a head or that fewer heads matured in time to be cut in two harvests. The approximate halving of yield in 1990, as the number of seedlings per cell went from one to three, indicates that multiple seedlings per cell causes too much crowding for rapid, uniform seedling growth and survival. These results argue against the practice of using multiple-seedling plugs for transplanting broccoli.
Table 2. Main effects of plug size and number of seedlings per plug
on broccoli yield, first harvest, 1990, NWREC, Oregon
No. of Yield Mean head Mean head Bead
headsz (T/A) wt. (g) width (cm) sizey
___________________________________________________________________
Plug size
31 cm3 8.6 1.5 151 8.5 2.6
5.1 cm3 4.9 0.8 126 7.0 2.5
**x ** * ** NS
No./plug
1 12.8 2.2 233 8.4 2.8
2 6.3 1.0 147 8.0 2.7
3 1.3 0.2 111 6.8 2.0
**lin **lin **quad NS NS
zNumber per plot.
yFive point scale with 1 = very tight and fine, 5 = loose, open, near
anthesis.
xNS,*,**: no significant differences, differences significant at the
5% and 1% levels, respectively. Lin, quad: linear and quadratic
regression, respectively.
Table 3. Interaction of plug size and number of seedlings per plug on
broccoli mean head weight and width, first harvest, 1990, NWREC, Oregon
Plug size No./plug Mean head wt. (g) Mean head width (cm)
31 cm3 1 162 8.7
2 144 8.2
3 145 8.6
5.1 cm3 1 154 8.0
2 149 7.9
3 75 5.1
LSD (0.05) 25 1.3
Table 4. Main effects of plug size and number of seedlings per plug on
broccoli yield, total of two harvests, 1990, NWREC, Oregon
No. of Yield Mean head Mean head Bead
heads (T/A) wt. (g) width (cm) size
Plug size
31 cm3 23 3.7 148 9.2 2.9
5.1 cm3 20 3.1 141 8.6 2.9
NS ** NS * NS
No./plug
1 25 4.5 159 9.1 3.1
2 22 3.5 144 8.8 2.9
3 17 2.4 130 8.8 2.8
**lin **lin **lin NS NS
Plug Transplanting of Storage and Bunching Onions
Introduction
Transplanting onions is not a common practice in the United States, but bare root transplants are used to establish stands of early maturing onions in a few growing regions. Use of plug-grown onion transplants is almost unknown. The primary reasons for transplanting bulb onions are to obtain earliness, to obtain a stand when soil or weather conditions are unfavorable for direct seeding, or to allow for multiple cropping. Transplants may provide a means for western Oregon growers to establish a stand on muck soils following spring fumigation for control of white rot and other pests. The season is usually too short to allow spring fumigation followed by direct seeding.
Growing and transplanting plugs is expensive compared to direct seeding. One means to reduce this cost is to grow multiple seedlings per cell, a practice used to some extent in the United Kingdom. This practice could lead to excessive crowding of plants and deformed bulbs at harvest, particularly at the high plant populations (80,000 to 120,000 per acre) common in production of bulb onions for storage. A preliminary trial in 1988 established the feasibility of using multiple seedlings per plug, since acceptable yields of well-formed, large bulbs could be obtained as long as plant population did not exceed four per foot, with two or three seedlings per cell. The purpose of the 1989 trial was to investigate the effects of plug size, number of seedlings per plug, and within-row spacing on the yield and quality of storage onions. Plug sizes were limited to commonly available sizes which would require minimal greenhouse bench space.
Reasons for transplanting green or bunching onions include to achieve earliness, to multiple crop, or to reduce the labor involved in bunching the onions in the field or packing shed. Seeding enough plants per plug to make a pre-formed bunch would save on labor if most plugs would produce a marketable bunch without having to separate and rebunch the stems. The major drawback is the large plant population per acre used in bunching onions and the consequent large number of plugs needed to establish a planting. The objective of this trials was to investigate the effects of three sizes of plugs, three populations per plug, and two within-row spacings on the number of marketable bunches per unit area.
Methods
For the storage (bulb) onion trial, 'Granada' was seeded in an unheated greenhouse on 28 March and 10 April, 1989, into two sizes of plugs. The smaller size was a 288-cell tray from Landmark Plastic Corp. with 5.1 cm3 per cell. The larger size was a 128-cell Landmark tray with 31 cm3 per cell. Both trays were filled with a peat-vermulite medium. Either 2, 4, or 5 seeds per cell were placed in each plug. Seedlings were thinned to 1, 2, or 3 per cell at the first true leaf stage. The seedlings were watered daily as needed and fertilized weekly with a 10N-13P-16.7K soluble fertilizer at 100 ppm N.
The plugs were transplanted to a Willamette silt loam on 8 May (first seeding) or 30 May (second seeding), to which had been applied 1000 pounds per acre of a 10N-8.7 P-16.7K fertilizer. The treatments consisted of a factorial combination of the two cell sizes, two populations per cell (2 and 3), and two within-row spacings (6 and 12-inch). In addition, a check treatment consisted of one seedling per 288 cell on six-inch spacing. For all treatments, plot size was a 10-foot section of a 4-row bed with 12 inches between rows. Target plant population per acre ranged from a low of 69,696 (1 per cell, 6-inch spacing or 2 per cell, 12-inch spacing) to a high of 209,088 (3 per cell, 6-inch spacing).
Propaclor herbicide was applied at 4 pounds/acre immediately after planting. Oxyfluorfen was applied at 0.25 pounds/acre on 13 June (first planting) or 21 July (second planting). An additional 100 pounds per acre of N was applied on 9 June to the first planting and on 22 June to the second planting. Methomyl was applied at 1.0 pound/acre on 21 July for thrips control. Plots were rated for degree of bolting on 31 August and harvested on 20 September (first planting) or 25 September (second planting), after all tops were down. Bulbs were separated into three size categories (less than 2-inch diam., 2 to 3-inch diam., and over 3-inch diam.), weighed, counted, and misshapen bulbs noted.
For the bunching onion trial, methods were similar except as noted below. 'Ishikura' onion was seeded into three sizes of plugs in an unheated greenhouse on 30 March, 1989. The smallest plug was a 5.1 cm3-cell in Landmark Plastic Corp. 288-cell trays, the medium plug was a 9.2 cm3-cell in Growers' Transplanting, Inc. 256-cell trays, and the largest plug was a 31 cm3-cell in Landmark 128-cell trays. Either 6, 8, or 10 seeds were counted into each cell.
The plugs were transplanted 3 May. The treatments consisted of a factorial combination of the three cell sizes, the three populations per cell, and either 6-inch or 12-inch spacing between bunches in the row. Target plant population per acre ranged from a low of 209,088 (6/cell, 12-inch spacing) to a high of 696,960 (10/cell, 6-inch spacing). An additional 90 pounds N per acre was applied as ammonium nitrate on 9 June. Plots were harvested on 11 July. Marketable (0.25 to 0.5-inch, no blemishes) stems were counted for each bunch.
Results
Storage Onions
Plant survival, expressed as the percentage of bulbs recovered at harvest compared to the number of seedlings planted, was decreased by greater number of seedlings per cell for both plantings (Tables 1 and 2). Larger cell size produced greater survival in the second planting but not in the first. Thus, crowding, whether due to cell size or number of seedlings per cell, appears to reduce seedling survival. The same trend was evident in 1988.
The percentage of bulbs forming seed stalks (bolting) was much smaller in 1989 than in 1988, perhaps because the seedlings were less developed at time of transplanting in 1989. Nevertheless, there was a significant effect of within-row spacing on bolting percentage for the first planting: bolting was nearly three times more likely when the spacing was six inches (Table 1). This is consistent with 1988 results. Bolting percentage did not vary significantly with treatment for the second planting, and unlike 1988, did not vary significantly with plug size or seedlings per cell in the first planting.
The percentage of small bulbs decreased with the larger cell size for the first planting but not for the second planting. Likewise, total yield and mean bulb weight tended to increase with the larger cell, but the differences were not statistically significant. In the second planting, cell size had no effect on bulb size distribution. In 1988, with a much larger difference in cell sizes, size distribution and mean bulb weight were affected to a much greater degree by cell size.
Three, rather than two, seedlings per cell increased the percentage of small bulbs and reduced mean bulb weight in both plantings, but tended to increase total yield, due to the larger number of bulbs harvested. Increasing the within-row spacing from 6 to 12 inches increased mean bulb weight and the percentage of large bulbs, but decreased yields since plant populations were halved. The percentage of misshapen bulbs was not greatly affected by treatment in 1989.
Compared to the check treatment of only one seedling per cell, all other treatments reduced mean bulb weight and the number of large bulbs produced, but only reduced total yield with 12-inch spacing in the first planting (Table 3). There were no significant two or three-way interactions among cell size, seedlings per cell, and spacing. However, the interaction means are given in Table 3 to permit comparison of each treatment combination with the control.
For the second planting, all combinations of treatments produced higher yields than did the check. Mean bulb weight was unusually low for the check, with both treatments having two seedlings per plug and 12-inch spacing tending to surpass the check in bulb weight.
This trial reaffirms the feasibility of using two seedlings per cell, halving the greenhouse bench space, trays, and media needed to establish a stand. Both cell sizes used in this trial produced acceptable seedlings and had little effect on subsequent growth.
Bunching Onions.
Plants in the 256 and 128-cell trays were not ready to pull easily on 3 May, but bunches in the 288 trays pulled readily. It may have been better to have trimmed the seedlings back and held them in the greenhouse a few more days.
Neither spacing between bunches in the row nor plug size affected the number of stems per bunch recovered at harvest (Table 4). Thus, the relative crowding imposed by the 6-inch spacing or the smaller cells did not affect seedling survival and development into a marketable stem. The actual number of marketable stems recovered increased from 5.1 when six seeds were planted to 7.8 when 10 seeds were planted. Since this reflects a decrease in the recovery from 85.7 percent when six seeds were planted to 77.8 percent when 10 seeds were planted, crowding and seedling competition increased with greater numbers of seedlings per plug.
The actual number of good bunches (those containing six or more marketable stems and not needing rebunching) recovered per unit area did not vary with plug size, but increased markedly as the number of seeds per plug increased or as the within-row spacing between bunches decreased (Table 4). The percentage of marketable bunches recovered increased somewhat at 12-inch as opposed to 6-inch spacing, but not nearly enough to offset the reduced plant population at 12-inch spacing. The percentage of marketable bunches increased dramatically at 10 seeds per plug compared to six or eight seeds per plug, indicating that plugs should be overseeded by 50 percent or more compared to the desired or minimum acceptable number of stems per bunch. However, the degree of overseeding necessary should vary with the percent germination of the seedlot and may vary with plug size for very small plugs.
The potential number of marketable bunches per unit area, assuming that all bunches having too many or too few stems are rebunched to six marketable stems per bunch, was also not affected by cell size. Potential bunches per unit area increased with 6-inch spacing and with the greatest number of seeds per plug. However, in percentage terms, the potential bunches was closest to the maximum possible for 12-inch spacing and 6 seeds per plug.
There were no significant two or three-way interactions affecting stems per bunch or bunches per acre. However, the three-way interactions are given in Table 5 so that all treatment combinations may be compared. The greatest number of stems per bunch occurred with the combination of 6-inch spacing, 10 seeds per plug, and the smallest plug size. The greatest number of marketable bunches per unit area and, if rebunching is assumed, the greatest potential yield also occurred with this combination. However, any other plug size also gave yields which were not signifantly different from those with 6-inch spacing, 10 seeds per plug, and the smallest plug.
These results affirm the possibility of growing good quality bunching onions from plugs. An economic analysis of the profitability of plug-started bunching onions is not possible from this data. The relative profitability would depend on the net effect of the increased cost of establishing a stand from plugs and the possibly reduced costs for bunching labor.
Table 1. Main effects of plug size, number of seedlings per plug, and within-row
spacing between plugs on seedling survival, bolting, bulb size, and yield of
transplanted 'Granada' onion, first planting, 1989, NWREC, Oregon
Seedling % % bulbs by no. Total yield Mean bulb Misshapen
Treatment survival (%) bolted 1-2" 2-3" 3-4" cwt/acre wt. (g) (% by no.)
Plug size
Small 85 0.6 16.0 79.9 4.0 331 143 5.1
Large 87 1.0 10.6 86.2 3.1 355 148 4.9
NSz NS * NS NS NS NS NS
No./plug
2 96 0.9 7.5 88.7 3.7 326 155 4.2
3 80 0.6 19.1 77.5 3.4 350 136 5.9
** NS ** * NS NS * NS
Spacing
6-inch 87 1.1 18.3 80.9 0.8 409 125 6.0
12-inch 85 0.4 8.3 85.3 6.4 268 166 4.0
NS ** ** NS * ** ** NS
Checky 98 0.3 1.3 85.2 13.5 306 203 0.0
____________________________________________________________________________________
zNS,*,**: Nonsignificant, significant at the 5 % level, and significant at the
1 % level, respectively.
ySmall plug, 1 seedling/plug, 6-inch spacing.
Table 2. Main effects of plug size, number of seedlings per plug, and within-row
spacing between plugs on seedling survival, bolting, bulb size, and yield of
transplanted 'Granada' onion, second planting, 1989, NWREC, Oregon
Seedling % % bulbs by no. Total yield Mean bulb Misshapen
Treatment survival (%) bolted 1-2" 2-3" 3-4" cwt/acre wt. (g) (% by no.)
Plug size
Small 83 0.3 17.2 75.0 7.7 350 158 4.6
Large 95 0.4 18.5 73.3 8.1 384 151 4.0
** NSz NS NS NS NS NS NS
No./plug
2 93 0.5 11.5 77.0 11.6 350 171 3.7
3 86 0.2 24.3 71.4 4.3 384 138 4.9
* NS ** NS ** NS ** *
Spacing
6-inch 90 0.3 24.3 72.8 2.9 445 132 4.7
12-inch 87 0.4 11.5 75.6 12.9 289 177 3.9
NS NS ** NS ** ** ** NS
Checky 93 0.0 13.5 83.0 3.5 235 165 0.2
____________________________________________________________________________________
zNS,*,**: Nonsignificant, significant at the 5 % level, and significant at the 1 %
level, respectively.
ySmall plug, 1 seedling/plug, 6-inch spacing.
Table 3. Interaction of plug size, number of seedlings/plug, and within-row spacing
between plugs on yield and mean bulb weight of transplanted 'Granada' onion, two
plantings, 1989, NWREC, Oregon
Plug No./ Spacing Plants/ First planting Second planting
size plug (inches) acrez Yield Mean bulb Yield Mean bulb
cwt/acre wt. (g) cwt/acre wt. (g)
Small 2 6 139392 396 131 378 145
Large 2 6 139392 381 137 439 152
Small 3 6 209088 428 108 457 118
Large 3 6 209088 430 123 508 115
Small 2 12 69696 264 179 297 208
Large 2 12 69696 265 171 288 179
Small 3 12 104544 235 154 269 162
Large 3 12 104544 306 161 302 157
Smally 1 6 69696 306 203 235 165
LSD (0.05) 57 36 105 32
zTarget population
yCheck
Table 4. Main effects of within-row spacing, number of seedlings per plug,
and plug size on plants per bunch, number of marketable bunches per acre, the
percentage of marketable bunches, and the number of bunches obtained after
rebunching of green onions, 1989, NWREC, Oregon
Stems/bunch Good bunches/acrez Potential bunches/acrey
_________________ ___________________ ________________________
Treatment No. % of nominal No. % of nominal No. % of nominalx
_____________________________________________________________________________
Spacing
6-inch 6.4 80.2 48500 69.6 76250 82.1
12-inch 6.4 79.5 27010 77.5 40460 87.1
NSw NS ** ** ** *
No./plug
6 5.1 85.7 22940 43.9 47430 90.6
8 6.2 78.1 40510 77.5 55900 80.2
10 7.8 77.8 49800 95.3 71830 82.4
** ** ** ** ** *
Plug size
Small 6.5 80.9 40370 77.2 61030 87.6
Medium 6.3 78.5 35860 68.6 56630 81.3
Large 6.4 80.1 37030 70.8 57410 82.4
NS NS NS NS NS NS
zActual number of good bunches of 6 to 8 onions recovered without rebunching.
yPotential 6-stem bunches after rebunching of over- or undersized bunches.
xPercentage of stems or bunches that would have been possible if all seedlings
survived and developed normally.
wNS,*,**: No significant differences; differences significant at the 5% and
1% levels, respectively.
Table 5. Interaction of within-row spacing, number of seedlings per plug, and plug
size on stems per bunch, number of marketable bunches per acre, and the number of
bunches obtained after rebunching of green onions, 1989, NWREC, Oregon
No./ Plug Stems/ Good bunches/ Potential bunches/
Spacing plug size bunch acre acre
6-inch 6 Small 5.3 33110 65340
Medium 5.0 21780 56630
Large 5.0 33110 61860
8 Small 6.7 63600 81890
Medium 6.1 54890 74920
Large 6.1 40950 65340
10 Small 8.2 66210 97840
Medium 7.5 59240 86250
Large 7.9 63600 96180
12-inch 6 Small 5.2 15680 33980
Medium 4.9 10450 29620
Large 5.5 23520 36590
8 Small 6.0 27010 36590
Medium 6.4 30490 39200
Large 6.1 26140 37460
10 Small 7.7 36590 50530
Medium 7.9 38330 53140
Large 7.6 34850 47040
LSD (0.05) 0.8 13370 13380
Introduction
Economic production of vegetable transplants (plugs) requires inexpensive greenhouses or other growing structures, small seedling cell size to maximize the number of plugs per unit area, and rapid production of a marketable plug. While less expensive than glasshouses, traditional double poly-covered
greenhouses reduce solar radiation reaching the seedlings and require power to run cooling fans during cloud-free periods. A possible solution to this
problem would be to raise the roof and sides of the greenhouse during periods of high solar radiation to allow full utilization of the sunlight and provide natural cooling. The SunpocketTM greenhouse or coldframe design features a roll-up plastic cover. This experiment was designed to compare the growth of seedlings of four vegetable species in the Sunpocket versus a glasshouse, two double-poly greenhouses, and a fiberglass-covered screenhouse.
Methods
'Tall Utah' celery and 'Granada' onion were seeded into 256-cell trays
(cell dimensions: 0.75 inch square x 1.2 inch deep) on 1 March, 1987, and
placed in a glasshouse to germinate. The glasshouse was set for a 60 F
minimum temperature. The rooting medium was a peat-vermiculite mix. Trays of each species were moved to the Sunpocket (50 F minimum); an unheated,
fiberglass-covered screenhouse; and two heated houses (50 F minimum) covered with a double layer of 6-mil clear polyethylene (longhouse and prophouse) on 22 March. 'Gem' broccoli and 'Ithaca' lettuce were similarly seeded on 24 March and moved to the final locations on 31 March. Maximum and minimum
temperatures were recorded for each house from 26 March to 24 April, when the experiment was terminated. Twenty plants from each tray were selected at
random and harvested at the soil line. Fresh weight, stem length, leaf
number, and stem diameter were determined and recorded individually.
Results
The highest mean temperature (71.3 F) was recorded in the glasshouse
(Table 1). However, the mean daily maximum temperature was greatest in the
Sunpocket, reflecting the lack of forced air cooling and rapid temperature
buildup when the Sunpocket cover was not raised early enough. Temperatures
often exceeded 90 F in the closed Sunpocket, even when the ambient temperature was in the 45 to 55 range. It was not possible to obtain an hourly mean
temperature for all the structures but the hourly mean in the Sunpocket was
nearly 10 F less than the average of the daily maximum and minimum
temperatures. This indicates that, except for brief periods, the daytime
temperatures in the Sunpocket were no higher than in the other structures.
Light transmission varied considerably among the structures.
Transmissivity was greatest for the glasshouse and only slightly reduced for the recently covered Sunpocket. The older covers on the longhouse and
prophouse further reduced transmisssion. The lowest transmissivity occurred with the fiberglass-covered screenhouse. Considering that the Sunpocket
covers were rolled up during the majority of the daylight hours, total solar radiation was probably as great for this structure as for the glasshouse.
Onion growth was slowest in the Sunpocket and greatest in the glasshouse (Table 2). For lettuce and celery, growth was also greatest in the glasshouse but slowest in the screenhouse. For broccoli, growth was greatest in the
longhouse, least in the screenhouse. Thus, no single environment stands out as promoting the most rapid growth of all species. The degree of variation in plant growth (expressed as the coefficient of variation or CV) differed
somewhat among structures, but no one environment was superior for all crops and components of plant growth.
A major problem with late winter and early spring transplant production is that the combination of low light intensity and relatively high daytime
temperature produces a spindly or leggy transplant. This problem can be quite severe in houses in which the cover greatly reduces light transmission. One measure of legginess is the height to weight ratio of the transplant: the
lower the ratio, the stockier or less leggy the transplant. For celery, the stockiest plants were produced in the Sunpocket. For onion and lettuce, the glasshouse produced the stockiest plants. Ths stockiest broccoli plants came from the longhouse.
That no one house stood out as superior is not surprising as the
temperature regimes were similar for all. Light intensity probably did not
play a large role either since the trial was carried out during a period of
non-limiting solar radiation. However, the energy required to maintain
moderate daytime temperatures was lowest in the Sunpocket since forced-air
cooling was not needed. If the watering and cover lifting mechanisms of the Sunpocket were automated (time clocks, solenoid valves, and
thermostat-regulated cover roll up), this structure would also be no more
labor intensive than the others.
Table 1. Effect of greenhouse structures on mean daily maximum and minimum
temperatures and transmission of solar radiation, NWREC, Oregon, March
26 - April 24, 1989
Structure Maximum (F) Minimum (F) Transmissivity (%)
Sunpocket 85.6 54.5 84
Glasshouse 84.4 58.2 92
Longhouse 85.3 53.6 61
Prophouse 83.8 54.3 60
Screenhouse 79.0 50.1 41
Table 2. Effect of greenhouse structures on growth parameters of four species
of vegetable transplants, NWREC, Oregon, April 24, 1989
Crop Location Weight CV Height CV No. of CV Stem diam. CV Ht./Wt.
(g) (%) (cm) (%) leaves (%) (cm) (%)
Onion Sunpocket 0.65 43 16.3 20 3.0 0 0.325 18 25.1
Glasshouse 1.56 39 30.2 15 3.1 9 0.353 13 19.4
Screenhouse 1.42 28 29.0 13 3.0 0 0.345 8 20.4
Prophouse 0.95 33 23.1 15 3.0 0 0.345 9 24.3
Longhouse 1.03 35 26.7 10 3.0 0 0.318 14 26.2
LSD (0.05) 0.32 2.8 NS NS
Broccoli Sunpocket 1.08 18 13.0 7 3.4 15 0.155 10 12.0
Glasshouse 1.35 17 19.3 6 3.3 14 0.155 5 14.2
Screenhouse 0.87 24 15.5 11 2.6 20 0.135 11 17.8
Prophouse 1.58 23 20.1 7 3.6 14 0.152 8 12.7
Longhouse 2.28 31 20.8 8 3.8 17 0.178 13 9.1
LSD (0.05) 0.32 1.3 0.4 0.013
Lettuce Sunpocket 1.36 51 9.7 16 4.1 16 7.1
Glasshouse 2.56 32 15.5 7 4.4 18 6.5
Screenhouse 1.19 25 11.9 12 3.7 13 10.0
Prophouse 2.40 34 15.0 12 4.3 15 6.3
Longhouse 1.98 41 13.2 22 4.5 23 6.7
LSD (0.05) 0.59 1.5 0.5
Celery Sunpocket 1.74 19 12.2 12 3.2 12 7.0
Glasshouse 2.23 26 18.0 12 3.3 14 8.1
Screenhouse 0.98 39 12.2 14 2.6 20 12.4
Prophouse 1.44 36 15.2 18 2.8 13 10.6
Longhouse 1.38 36 11.9 18 3.0 0 8.6
LSD (0.05) 0.38 1.5 0.3
Introduction
Tomato and muskmelon production in the Willamette Valley is limited by
cool springs, a short growing season, and relatively cool nights, even during mid-summer. Cultural techniques to increase the mean air and soil
temperatures around plants, such as plastic mulch and row covers, have hastened development and increased yield of both crops.
Removal of mulch residues following crop harvest is a large factor in total crop production costs and disposal of the plastic presents additional environmental problems and costs. Bio- or photodegradable films have been used as mulches for several years but have not been practical due to variability in degradation rate. Recently, new degradable mulch materials have shown promise in several production areas, but have not been evaluated under Willamette Valley environmental conditions.
Another new development in mulch technology is the advent of
wavelength-selective (WS) films. These films provide much of the weed
control benefits of black plastic mulch, but warm the soil more than do the
black films. Thermic films, such as the IR-303 thermofilm developed as a greenhouse cover, somewhat increase minimum temperatures compared to standard polyethylene films. These films may have a role as either floating or hoop-supported row covers.
The purposes of this trial were: 1) to compare several WS and photodegradable mulches with bare ground and standard black plastic ground mulch in promoting early and total yield of tomato and muskmelon; and 2) to compare combinations of standard black plastic mulch and row covers with standard black plastic mulch alone, for production of muskmelon.
Methods
In 1989, 'Pikred' tomato was seeded in 5-cm pots in an unheated greenhouse on 6 April; 'Superstar' muskmelon was seeded on 17 April. The plot area of Willamette silt loam was prepared by rotary tillage in mid-May following a broadcast application of 10N-8.7P-8.3K fertilizer at 1,000 pounds per acre. Mulches were applied to the appropriate plots after laying drip irrigation tubing and both crops were transplanted on 17 May. Plot size was 7.5 meters of bed with 10 plants per plot. Mulch treatments were replicated four times for each crop in randomized block design. Treatments consisted of a bare ground check, a standard 1-mil embossed black polyethylene, three formulations (2b, 19b, 131b) of Plastigone photodegradable polyethylene, and two formulations (IRT 64, IRT 70) of WS films from AEP industries.
Soil temperature was sensed by thermocouples placed 5 cm below the soil surface and was recorded for the period 8 June to 29 June on a Speedomax 250 multipoint recorder for two replications of selected treatments. Plots were harvested at least weekly from first fruit ripening until late September. Early yield was defined as that recorded during the first four weeks of the harvest season. Only USDA Grade No. 1 fruit were included in the yields.
In 1990, the same cultivars were seeded on 4 April (tomato) and 16 April (melon). Transplanting was on 16 May. Mulch treatments for tomato and muskmelon consisted of a bare ground check, an embossed 1.25-mil black polyethylene, three formulations of 1.25-mil WS films from AEP Industries (IRT 64, 70, and 76), a brown WS film (AL-OR, 0.8-mil) from Polyon-Barkai, and a 0.6-mil clear perforated polyethylene film (Polydak). Temperatures were monitored continuously at two inches soil depth from 1 June until 13 June in all mulch treatments.
Additional treatments for muskmelon only included the embossed black plastic combined with either a 2-mil perforated IR-303 Thermofilm (Polyon), Vispore micro-perforated polyethylene, Lutrasil 17 nonwoven polypropylene, or Lutrasil 30 polypropylene. The Thermofilm was hoop-supported while the other materials were allowed to float on the crop surface. Covers were removed on 19 June. Both soil and air (two inches above the soil surface) temperatures were measured from 15 June through 20 June in the cover treatments. The number of recorder channels was insufficient to take replicated readings from all mulch and cover treatments over the same time period.
Results
In 1989, all mulches tested increased both the mean maximum and the mean minimum soil temperatures (Table 1). Due to a limited number of temperature probes, soil temperatures were measured for only one of the photodegradable mulches. Both the mean maximum and mean minimum temperature under this mulch were about the same as under the standard mulch. Both IRT mulches increased soil temperatures above those under the standard mulch. The increase was particulary striking for the IRT 70 mulch which transmits approximately 70 percent of the infrared radiation but only 12 percent of the photosynthetically active radiation. Neither mulch transmitted enough light to permit weed growth.
As expected, the standard and the IRT films maintained their integrity
during the entire growing season, with little or no brittleness or holes and tears. The three photodegradable mulches degraded significantly during the season, with the 2b formulation nearing loss of any weed control effect by the end of the harvest period (Table 1). However, all three mulches maintained integrity long enough to prevent significant weed competition with the crop and hasten development of the melons.
Mulch treatment had no significant effect on the early yield of tomato; however, the total number of marketable fruit harvested per plant increased with all mulches compared to the bare ground control (Table 2). In contrast, the mean fruit weight was decreased by all mulches compared to the control, resulting in no significant diffences among treatments in total weight harvested per plant. Neither the number of fruit per plant, the mean fruit weight, nor the total weight per plant varied significantly among types of mulch.
All mulches increased early muskmelon yield, as no fruit were harvested from the bare ground check plots during the first four weeks of the harvest
season (Table 3). This is typical of the difference that mulch usually makes in the production of melons in the Willamette Valley. Among mulches, the IRT and the standard films tended to produce a greater early yield than did the degradable films. Total melon yield was very low for the control as compared to any of the mulches. Among the six mulches, total yield tended to be highest for the IRT films. Mean fruit weight did not vary significantly with treatment. Although not statistically significant, both early and total melon yield tended to be highest with the IRT 70 film.
Table 1. Effect of mulches on mean maximum and minimum soil temperatures (C),
8-29 June, 1989, and visual ratingsz of mulch degradation at selected days
after mulch installation, NWREC, Oregon
Days
Mulch Mean max. Mean min. 64 91 141
None 27.4 dy 14.6 c -- -- --
Standard 28.6 cd 17.6 b 1.0 c 1.0 c 1.4 c
Plastigone 2b 30.2 bc 17.6 b 2.6 a 3.4 a 3.9 a
Plastigone 19b -- -- 1.5 bc 2.0 b 2.9 b
Plastigone 131b -- -- 2.0 ab 2.0 b 2.8 b
IRT 64 30.9 b 17.8 b 1.0 c 1.0 c 1.1 c
IRT 70 34.3 c 18.3 a 1.0 c 1.0 c 1.5 c
zFive point scale with 1=no change; 2=slight brittleness; 3=brittle, small
holes or tears; 4=large longtitudinal or transverse tears; 5=complete loss
of mulching benefit.
yMean separation within columns by Duncan's MRT, 5% level.
Table 2. Effect of wavelength-selective and photodegradable mulches on yield
per plant of tomato, 1989, NWREC, Oregon
Early Total
Mulch No. Wt. (kg) No. Wt. (kg) Mean fruit wt. (g)
None 7.1 1.7 41 bz 10.5 259 a
Standard 6.8 1.8 68 a 14.5 214 b
Plastigone 2b 8.0 1.9 60 a 12.9 216 b
Plastigone 19b 5.6 1.3 59 a 12.8 216 b
Plastigone 131b 7.1 1.8 64 a 15.2 236 b
IRT 64 6.8 1.5 63 a 14.0 222 b
IRT 70 5.7 1.7 66 a 15.2 232 b
NSD NSD * NSD *
NSD;*: No significant differences; significant differences at the 5% level.
zMean separation within columns by Duncan's MRT, 5% level.
Table 3. Effect of wavelength-selective and photodegradable mulches on yield
per plant of muskmelon, 1989, NWREC, Oregon
Early Total
Mulch No. Wt. (kg) No. Wt. (kg) Mean fruit wt. (g)
None 0.0 bz 0.0 c 0.3 c 0.5 b 1365
Standard 1.0 a 2.0 ab 3.4 b 5.7 a 1686
Plastigone 2b 0.8 a 1.4 ab 3.7 ab 5.9 a 1571
Plastigone 19b 0.8 a 1.2 ab 3.3 b 5.2 a 1559
Plastigone 131b 0.6 ab 1.0 bc 3.6 ab 5.3 a 1501
IRT 64 0.9 a 1.9 a 4.0 ab 5.8 a 1487
IRT 70 1.4 a 2.2 a 4.2 a 6.2 a 1429
* * ** ** NSD
NSD;*;**: No significant differences; differences significant at the 5% and
1% levels, respectively.
zMean separation within columns by Duncan's MRT, 5% level.
Among the mulch treatments in 1990, the highest maximum soil temperature occurred on plots mulched with the IRT 76 and clear Polydak films (Table 4). Mean maximum soil temperature was increased significantly over bare ground for all mulches except the standard black plastic. The mean daily low temperatures were increased significantly by all mulches compared to bare ground, with very little difference among types of mulch.
Among the 1990 row cover treatments, the greatest mean maximum air temperature occurred with the Thermofilm tunnel and the two Lutrasil floating covers (Table 5). The Vispore cover also increased the mean maximum temperature compared to the plots with only a black ground mulch. All covers increased mean maximum soil temperature compared to mulch-only plots, with the greatest increase occurring with the lighter-weight Lutrasil cover. Apparently, this cover allowed more transmission of solar radiation and greater soil warming. Mean minimum temperatures were also increased by row covers. The highest mean minimum air temperature was recorded beneath the Vispore covers, while the highest minimum soil temperature was recorded beneath the Thermofilm tunnel. Since the temperatures were recorded for different time periods, one cannot directly compare soil temperature means for the mulch-only treatments with those for the mulch-cover treatments.
Early tomato yields were not significantly affected by mulch treatment in 1990 (Table 6). However, total yield for the growing season was usually slightly greater on mulched plots compared to bare ground. Differences among mulches were not significant. Mean fruit size was not affected by mulch and the increased yield on mulched plots was solely attributable to an increase in the number of fruit harvested. Although there was considerable weed growth under and through the clear mulch, the weeds apparently did not compete significantly with the rapidly developing and relatively upright-growing tomato plants. Some weed growth also occurred under the IRT 76 film but, again, yield was not reduced.
In comparing tomato yields between the two years, fruit size was about the same, but the number of fruit produced per plant was much greater in 1989 than in 1990. This can be attributed to a relatively late season in 1990 due to unusually cold, wet weather in May and June and to the very severe and early incidence of both early and late blight in 1990. In both years mulches failed to increase early fruit production but increased total fruit production, especially in 1989. In both years, plants grown on bare ground produced much less canopy growth and the plants appeared stunted throughout the growing season. While some of this is probably due to differences in soil and canopy air temperatures, the non-mulched plants may also have suffered from moisture stress, as there was no barrier to evaporation of applied water. The stressed bare ground plants, in both years, produced and ripened sufficient early fruit that mulch did not hasten fruit ripening. However, over the course of the season, the mulched plants, with greater vine growth, produced and ripened more fruit. Bare ground plants were probably under relatively more moisture stress compared to mulched plants in 1989 than in 1990 since 1989 had a drier growing season.
Tomato response to both mulch and row covers has been considerably less dramatic than melon response to the same treatments under Willamette Valley conditions. Some of our earlier work with tomatoes and mulches has shown significant increases in early tomato production for mulched plants, but this was not the case in 1989 and 1990. Among the plastic mulch films, the standard black plastic appears to be as effective as any of the wavelength-selective films for tomato production in this area.
Table 4. Effect of ground mulches on mean minimum and maximum soil
temperatures, NWREC, Oregon, 1-13 June, 1990
Treatment Mean minimum, oF Mean maximum, oF
____________________________________________________________________________________________
Bare ground check 54.8 71.3
Std. black mulch 57.9 74.2
IRT 64 57.2 78.3
IRT 70 58.0 83.3
IRT 76 57.2 85.3
AL-OR brown 57.1 77.5
Clear perforated 57.5 85.2
LSD (0.05) 0.7 5.3
Table 5. Effect of ground mulch-row cover combinations on mean minimum
and maximum air and soil temperatures, NWREC, Oregon, 14-19 June, 1990
Treatment Mean minimum, oF Mean maximum, oF
______________________ ______________________
Air Soil Air Soil
Std. black mulch 50.3 59.7 92.8 87.2
Mulch + Thermofilm 54.7 65.7 116.8 91.2
Mulch + Lutrasil 17 52.0 61.5 116.3 96.0
Mulch + Lutrasil 30 53.3 62.3 117.1 91.3
Mulch + Vispore 55.2 62.0 112.7 92.5
LSD (0.05) 2.3 0.9 4.1 1.1
Table 6. Effect of plastic ground mulches on yield and earliness of 'Pikred'
tomato, NWREC, Oregon, 1990
No. fruit/plant Mean fruit weight (g) Yield (T/A)
Treatment Early Total Early Total Early Total
Bare ground check 7 26 249 216 4.9 15.2
Std. black mulch 8 31 264 224 5.8 18.3
IRT 64 green mulch 7 33 231 214 4.0 18.4
IRT 70 green mulch 8 30 226 223 5.0 17.7
IRT 76 green mulch 8 31 216 216 5.1 17.7
AL-OR brown mulch 8 34 217 203 4.8 18.1
Perf. clear mulch 9 30 235 222 5.4 17.3
LSD (0.05) NSz 6 NS NS NS 2.9
__________________________________________________________________________________________________________
zNS: no significant differences among treatments.
Early melon yields in 1990 were generally highest for the mulch plus cover treatments (Table 7). However, early yield on plots with only the IRT 70 and 76 mulches were equal to those obtained with the combination of the black mulch and the Thermofilm tunnel. Mean fruit weight during the early part of the season was greater for any WS mulch or mulch-cover combination when compared to standard black plastic. But among the WS mulches and the mulch-cover combinations, mean fruit size was usually smaller for treatments producing greater numbers of early-ripening fruit. Thus, the IRT 64 and AL-OR films, which produced relatively few early fruit compared to several other treatments, produced the largest fruit during the early part of the season.
For the entire growing season, the greatest yields occurred with the combination of black mulch and the Thermofilm tunnel. Total yield with mulch plus Vispore and mulch plus Lutrasil 30 did not significantly exceed that for several of the better mulch-only treatments. Among the mulch-only treatments, total yield tended to be highest with the standard black plastic mulch. The greatest mean fruit size for the entire season was obtained with the AL-OR mulch. Differences among other treatments were relatively minor.
Although producing greater numbers of fruit, most mulch treatments also produced larger fruit. The one exception was the Polydak clear mulch. While weed control was acceptable under other mulches, the Polydak mulch promoted weed growth which probably competed significantly with crop growth. No fumigants or herbicides were used in this trial in order to compare the effectiveness of the mulches without confounding effects of herbicide treatments.
Growers in this area have successfully used standard clear polyethylene mulches under vine crops without use of fumigants or herbicides. Emerging weeds have generally been killed by the high temperatures under the mulch. However, with the unusually cold and damp weather in May and June, insufficient temperatures were generated to kill emerging seedlings. Also, the perforation of the Polydak mulch may have produced lower air temperatures under the mulch.
Some weed growth was also noted under the IRT 76 film, but it did not appear to interfere significantly with crop growth. However, it is interesting to note that neither early nor total yield on the 76 film exceeded that with the IRT 70 film. One season's data are hardly conclusive, but it interesting to speculate that the 70 formulation may be adequate for Willamette Valley conditions and that the 76 film may permit too much weed growth in some situations without the benefit of increased melon vine growth.
The relatively small melon size for the entire season for the tunnel and Lutrasil 17 treatments may be due to the greater number of fruit produced with these treatments.
For the mulch-cover treatments, early fruit production correlated strongly with mean maximum soil temperature, but not with minimum soil temperature or air temperature. For mulch only treatments, early fruit production also correlated strongly with mean maximum soil temperature except for the Polydak mulch where weed competetion probably played a role in the lower than expected yields. Total season yields did not correlate with the early-season temperature measurements. This is not surprising as canopy development strongly affects both air temperatures recorded just above the soil surface and soil temperature. Mulch effects should be negligible after the plant canopy has completely covered the bed surface and, of course, covers are effective only as long as they are in place, usually only the first four to six weeks after transplanting.
These results reaffirm the necessity of using a ground mulch for successful muskmelon production in the Willamette Valley. Some of the WS mulches appear to be more effective than black mulch and are nearly as effective as row covers for promoting early fruit ripening. The thermic films appear promising for promoting excellent vine development and high total yields.
Both the WS and the photodegradable mulches appear promising for
production of warm weather crops in the Willamette Valley and deserving of
further trial. The WS films increased soil temperatures more than did the
standard film, indicating the possibility of improved crop growth and
development in many growing seasons. The photodegradable films, particularly the early-degrading 2b formulation of Plastigone, appear to break down to very small particles which do not need to be removed from the field in preparation for the next crop.
Table 7. Effect of plastic ground mulches and row covers on the yield
and earliness of 'Superstar' muskmelon, NWREC, Oregon, 1990
No. fruit/plant Mean fruit weight (g)
Treatment Early Total Early Total
Bare ground check 0.0 1.2 -- 1483
Std. black mulch 0.1 2.3 1200 1659
IRT 64 green mulch 0.2 1.5 2169 1650
IRT 70 green mulch 1.1 2.2 1711 1652
IRT 76 green mulch 1.1 2.0 1578 1611
AL-OR brown mulch 0.4 1.6 2186 2098
Perf. clear mulch 0.3 1.0 1662 1418
black mulch + tunnel 1.1 4.6 1927 1408
black mulch + Lutrasil 17 2.4 3.1 1442 1391
black mulch + Lutrasil 30 1.7 2.3 1632 1679
black mulch + Vispore 1.8 2.5 1688 1770
LSD (0.05) 0.5 0.6 459 326
Cooperator: Gary L. Reed, Hermiston Research and Extension Center
Introduction
Control of virus-vectoring aphids is essential in potato seed production to exclude viruses such as potato virus Y (PVY) and leaf roll. Floating row covers might protect plants from insect attack, reducing the need for insecticides.
Previous trials at the North Willamette Center in 1986 through 1988 indicated that covers were far more effective than the standard insecticide treatment in reducing virus transmission. Gross yields were often reduced, however. This ususally involved both reduced numbers of tubers recovered and smaller mean tuber size. In general, the longer the covers were in place, the greater the yield reduction. The only exception was 1987 when a short-season cultivar was grown. The yield reduction with covers might be attributed to heat stress, restricted room for vine growth, abrasion of leaves or growing points by the cover fabric, or outbreaks of aphids or spider mites occassionally observed on covered vines. In contrast, there are several published report from eastern states and Canadian provinces indicating that row covers promote early harvest and increase the yield of new potatoes. Our results also have consistently indicated that covers promote early vine development in potatoes.
In 1988, covers were removed and then reapplied at various times during the growing season. Virus infection occurred mostly when the vines were exposed during early to mid-season. The objective of the 1989 trial was to confirm results obtained in 1988. The 1990 trial was intended to determine at what point in the growing season covers cease to promote potato development and begin to reduce tuber growth and development.
Methods
The trials were conducted on a Willamette silt loam, pH 5.5, to which was applied 1,000 pounds/acre of 10N-8.7P-16.7K fertilizer. On 15 May, 1989, nuclear virus-tested 'Russet Burbank' seed pieces were planted one foot apart in rows spaced four feet apart. Every third row was planted with virus-infected seed. The row cover plots consisted of a pair of virus-tested rows, 20 feet long. The rows were hilled on 19 May after additional N as ammonium nitrate was banded over the row at 100 pounds N per acre. Alachlor at 2.5 pounds and linuron at 1.0 pounds per acre were then applied to the plot area for weed control. Ten-foot wide covers of polypropylene-polyamide (Agronet M) were applied to the appropriate plots on 22 May. Aldicarb was applied to insecticide-treated checks at 2.0 pounds per acre on 23 May. Shoot emergence was first noted on 3 June. Yellow-pan aphid traps were distributed through the planting on 5 June, with approximately one trap for every 1500 square feet.
Of the 18 treatments, replicated four times, 15 were covered on 22 May. Of the remaining three treatments, one was aldicarb-treated and covered on 12 June. The other two treatments were uncovered checks, one with and one without aldicarb application at hilling. Other treatments were uncovered at weekly intervals during the growing season. Most were recovered one week later after an application of aldicarb. Dates of uncovering and recovering for all treatments are listed in Table 1. Aphids were collected from the traps weekly, just before cover removal and replacement took place. All covers were removed and the vines were sprayed with diquat at 0.25 pounds/acre on 5 September. Paraquat at 0.38 pounds per acre was applied to finish vine kill on 14 September. Plots were harvested on 18 September. Tuber samples from each plot were sent to the Hermiston Research and Extension Center for virus evaluation. The greenhouse-forced plants were rated on 6 Feb., 1990.
On 9 May, 1990, nuclear virus-tested 'Russet Burbank' seed pieces were planted nine inches apart in rows spaced three feet apart with 13 feet between the centers of each pair of rows. Plot length was six feet (18 seed pieces) with a four foot gap between plots. Aldicarb was applied to the seed furrow at 6 g per plot immediately after planting. The furrows were then closed and were rehilled one week later after applying 100 pounds per acre of nitrogen as ammonium nitrate in a band over the row. After rehilling, alachlor was applied at 2.5 pounds per acre and linuron at 1.0 pounds per acre. Ten foot-wide polypropylene-polyamide (Agronet M) row cover was applied to the appropriate plots on 24 May.
Plots were either left uncovered for the season, covered initially and then uncovered after four weeks, uncovered after nine weeks, or covered for the entire growing season of 16 weeks. Eight-plant samples were removed from the four replicates of each treatment at 2, 4, 6, 8, 11, and 16 weeks after shoot emergence. Shoot fresh and dry weights and tuber numbers and weight were measured at each harvest. Vines were killed with paraquat (0.4 pounds per acre) after 16 weeks. Air and soil temperatures were measured on two replicates of uncovered and covered plots for the entire growing season using a Speedomax 250 recorder and thermocouples set at six inches above the soil surface and at two inches depth in the soil.
Results
In 1989, as in most previous trials, row covers reduced the yield of potato tubers compared to vines which were never covered, primarily by reducing the number of tubers harvested (Table 1). The mean weight per tuber also was reduced for many of the cover treatments. Greatest mean weight per tuber occurred with the treatment that was uncovered early in the season and never recovered (treatment 5). Gross yield for this treatment also did not differ significantly from that of the never-covered treatment. Plots uncovered one month later (treatment 10) and not recovered did not significantly outyield plots covered for the entire season.
In Table 2, the treatments in which plots were uncovered for a week and then recovered are grouped into three four-week categories, consisting of plots uncovered during the first, second, and last third of the growing season, respectively. Yields tended to be slightly higher for plots uncovered earlier in the growing season. Also, plots which were not recovered tended to outyield recovered plots for each third of the growing season. Aldicarb treatment had no effect on yield, reflecting the absence of serious foliage-devouring insects in the plots.
In 1990, plants grown under row covers had significantly greater vine fresh weight at both 2 and 11 weeks after emergence (Table 3). Although not statistically significant, the same trend was observed at 4, 6, and 8 weeks after emergence. Vine dry weight, however, was not consistently affected by cover treatment. This was because of a consistent trend toward lower percent dry matter in covered than in noncovered vines. This may be due to greater moisture stress in plants grown in the open as row covers generally cause higher relative humidity and reduced air movement in the plant canopy.
Tuber development was first noted five weeks after emergence. As early as six weeks after emergence, tuber numbers tended to be reduced for covered plants. Although not statistically significant at each harvest, this trend continued for the remainder of the season. At the final harvest, there was a trend toward decreasing tuber number per hill with the exception that tuber number increased for plants covered the entire season. Mean tuber weight increased with length of the covered period. These results are consistent with those obtained in 1986, 1988, and 1989, except that in the previous years, both tuber number and tuber weight tended to decrease as the covering period lengthened.
It is not possible to determine from these results whether the reduced tuber yield with row covers is due to heat stress or to some other cause. Mean maximum air temperature under covers was 5oF (99.2 vs. 94.1) higher for the season, while the mean maximum soil temperature was increased by more than 11oF (89.1 vs. 77.9) under covers. Mean minimum soil and air temperature were not significantly altered by covers. The increase in mean maximum soil temperature could have caused tuber resorption or increased respiration may have limited tuber formation.
These results contrast strongly with those reported from several eastern states and provinces where row covers have promoted yield and earliness of new potatoes.
Effect of treatment on virus incidence was very consistent with the pattern seen in 1988. A one-week exposure to aphids early in the growing season led to greater PVY incidence than did exposure late in the season. Plants uncovered for a week in early August had infection levels that tended to be less than for those covered for the entire season. For plants left exposed the entire season, aldicarb treatment at planting had no effect on PVY incidence. Incidence of leaf roll virus did not vary significantly with time of exposure.
Table 1. Uncovering and recovering dates, yield, and percentage virus infection for
the treatments in the virus exclusion trial, NWREC, Oregon, 1989
Date Date Yield No. tubers Mean tuber % tubers with
Treatment uncovered recovered (T/A) harv./plot wt. (g) PVY Leaf roll
1 6/12 6/19 18.7 290 121 35.0 18.8
2 6/19 6/26 19.6 289 129 74.4 8.1
3 6/26 7/03 21.8 331 124 26.3 23.2
4 7/03 7/10 24.1 333 137 55.3 24.3
5 7/10 Never 30.5 353 162 50.4 11.8
6 7/10 7/17 20.3 293 132 52.7 18.6
7 7/17 7/24 19.2 289 127 41.8 11.3
8 7/24 7/31 18.9 285 126 55.7 14.3
9 7/31 8/07 16.0 282 108 15.6 22.5
10 8/07 Never 20.1 295 129 12.9 2.9
11 8/07 8/14 17.9 284 118 11.0 10.8
12 8/14 8/21 16.4 280 111 4.4 42.1
13 8/21 8/28 18.3 269 130 8.7 2.9
14 8/28 Never 18.3 280 124 13.5 23.4
15 9/05 Never 19.1 290 125 12.8 2.9
16z 6/03 6/12 21.0 323 124 16.3 0.0
17y Never covered 27.6 387 132 57.4 9.9
18x Never covered 31.5 427 138 52.2 6.9
LSD (0.05) 5.4 57 22 22.0 NS
zThis treatment was left uncovered at planting. Emerging shoots were exposed for
nine days before covers were applied.
yTreated with aldicarb at hilling.
xNo insecticide applied.
Table 2. Effect of early, midseason, and late season uncovering intervals
on yield and virus infection of potato, NWREC, Oregon, 1989
Mean yield No. tubers Mean tuber Mean % Mean %
Uncovering period (T/A) harv./plot wt. (g) PVY Leaf roll
Early season 21.0 311 128 47.8 18.1
Mid-season 18.6 287 123 41.4 14.7
Late season 17.5 278 121 9.4 17.3
Never uncovered 19.1 290 125 12.8 2.9
Never covered, +aldicarb 27.6 387 132 57.4 9.9
Never covered, no aldicarb 31.5 427 138 52.2 6.9
Early, not recovered 30.4 353 162 50.4 11.8
Mid-season, not recovered 20.1 295 129 12.9 2.9
Late, not recovered 18.3 290 125 13.5 23.4
Mean, all treatments 21.1 310 127 33.1 14.2
Table 3. Effect of row covers and cover removal date on potato vine and tuber
development over six harvests, NWREC, Oregon, 1990
Weeks after Treatment Vine wt. (g/plant) % dry Tubers/plant Mean tuber
emergence Fresh Dry matter No. Wt. (g) wt. (g)
2 No cover 15 1.8 12.4 -- -- --
Covered 2 weeks 25 2.3 9.4 -- -- --
*z NS **
4 No cover 164 -- -- -- -- --
Covered 4 weeks 230 -- -- -- -- --
NS
6 No cover 598 55 9.3 10.5 175 16.7
Covered 4 weeks 676 60 9.0 8.0 165 20.7
Covered 6 weeks 655 52 8.2 8.4 151 18.2
NS NS NS NS NS NS
8 No cover 818 139 17.3 10.9 445 41
Covered 4 weeks 879 137 15.6 9.6 411 43
Covered 8 weeks 939 121 13.3 10.3 428 42
NS NS * NS NS NS
11 No cover 698 85 12.3 12.0 795 67
Covered 4 weeks 1360 138 10.3 9.2 774 85
Covered 9 weeks 1051 103 9.8 9.3 675 72
Covered 11 weeks 1082 95 9.7 9.1 669 74
* NS NS * NS NS
16 No cover -- -- -- 16.8 1796 107
Covered 4 weeks -- -- -- 12.7 1553 123
Covered 9 weeks -- -- -- 9.7 1401 145
Covered 16 weeks -- -- -- 11.6 1714 148
** NS *
zNS,*,**: no significant differences, significant differences exist at the 5%
and 1% levels, respectively.
|