Vegetable Research 1987, Commercial Vegetable Production Guides, North Willamette Research and Extension Center

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Vegetable Research at the North Willamette Research and Extension Center, 1985-1986 On-line version of Oregon Agricultural Experiment Station Special Report 788, May, 1987
CONTENTS Introduction Overwinter Leek Variety Trial Early Cabbage Variety Trial Early Autumn Cauliflower Variety Trial Lime and Fertilizer Effects on Overwintered Cauliflower Nitrogen Rate, Form, and Timing on Yield of Sweet Corn Nitrogen Rates and Phosphorus on Carrots Nitrogen Rates and Phosphorus on Onions Lime and Fertilizer Effects on Overwintered Onions Lime and Gypsum Effects on Spring-planted Onions Weed Control in Overwintered Onions Response of Cucumber to Floating Row Covers and Herbicides Floating Row Covers Reduce Virus Transmission to Potato Seed Stock Response of Tomato, Broccoli, and Muskmelon to a Polypropylene Row Tunnel Response of Tomato and Lettuce on Straw Bales to a Plastic Cover Cultural Practices on Yield and Head Rot of Broccoli Anticrustants on Seedling Emergence of Carrot and Lettuce Return to: AUTHOR: Dr. Delbert D. Hemphill, Jr., Assoc. 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. Garvin Crabtree (emeritus) was Professor of Weed Science, Department of Horticulture, Oregon State University Dr. T.L. Jackson (deceased) was Professor of Soil Science, Department of Crop and Soil Science, Oregon State University Dr. Harry Mack (emeritus) was Professor of Horticulture (emeritus), Department of Horticulture, Oregon State University Dr. N.S. Mansour (emeritus) was Extension Vegetable Specialist and Professor, Department of Horticulture, Oregon State University, Corvallis, OR 97331 Mr. Robert McReynolds is District Vegetable Extension Agent, North Willamette Research and Extension Center, Oregon State University Dr. Mary Powelson is Professor of Plant Pathology, Oregon State University, Corvallis Dr. Gary Reed is Professor of Entomology, Hermiston Agricultural Research and Extension Center, Oregon State University. Introduction to the Report A full-time program of vegetable crop research has been conducted at the North Willamette Experiment Station since 1976. The Station, a branch of the Oregon State University Agricultural Experiment Station, is just north of Aurora, a historic farming community 20 miles south of Portland, Oregon. The land is provided by Clackamas County, with facilities maintained by the university. Major vegetable research emphasis is on the needs of fresh market growers in the Willamette River Valley, but research is also conducted on home garden and small farm intensive vegetable culture, and processed vegetable crops. Many research projects reported here involved cooperation with research and Extension Service colleagues in the Oregon State University system and with area vegetable growers. Their contributions are gratefully acknowledged. The financial support of E.I. DuPont de Nemours & Co., Ethyl Visqueen Corp., Kimberly-Clark, CDK International, the Northern Willamette Valley Horticultural Society, the Oregon Processed Vegetable Commission, the Oregon Danvers Onion Commission, the Northwest Plant Food Association, Velsicol Chemical Co., Botanical Resources, Inc., and the Oregon Department of Environmental Quality was essential to completing these projects and is greatly appreciated. The first two sections of this report concern trials which may help growers choose plant varieties most suitable for the Willamette Valley. The next 13 sections report research on cultural practices to improve yield and quality of several crops. Soil and plant tissue analysis associated with several of these experiments was performed by the Department of Soil Science or the Plant Analysis Laboratory of Oregon State University. Twelve crops from cabbage to tomato were involved in these experiments. This report is the fifth 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. Overwinter Leek Variety Trial Extremely high quality leeks are being produced on a small scale in the Willamette Valley with good yields. The crop is usually seeded in early spring, matures in autumn, and can be held through the winter for harvest the following spring. Very few varieties are grown commercially and the highest quality plants have been transplanted and grown in trench culture. The most lucrative market is the restaurant trade, which demands long, thick, blanched stems. Healthy foliage can also be used decoratively in presentation of restaurant dishes. This trial had two purposes, to evaluate a number of varieties in a late spring planting for overwinter harvest, and to evaluate several winter hardy varieties in a late planting for overwinter harvest. Growers would benefit if planting of the overwinter crop could be delayed, allowing the possibility of double cropping with a short season crop and reduced weed control problems. This report includes data from two harvests each of spring and summer plantings made in 1984 and harvested in the spring of 1985. Methods Nine leek varieties were seeded in flats on a greenhouse bench on March 23, 1984, and seven were seeded on June 6. The plot area received a broadcast application of 1,000 pounds/acre of 10-20-10, followed by formation of raised beds with 18-inch tops, 40 inches furrow to furrow, and about 7-inch height. Seedlings were transplanted on May 31 and July 31, respectively, into holes dibbled approximately 4 inches deep on 6-inch spacing, with two rows/bed. A single plot consisted of 20 feet of bed (80 plants). Treatments (varieties) were replicated 3 times in randomized complete block design. Propachlor herbicide was applied at 4 pounds/acre after planting and was reapplied on June 29, July 31, and October 8. The plots were also hand-hoed twice during the summer. An additional 25 pounds N/acre as nitroform was applied on July 6 and again on August 31. Twenty plants were harvested from each plot of the early planting on August 24 and on October 8. Harvested plants were topped 2 inches above the growing point (base of leaves). An additional 50 pounds N/acre as nitroform was applied on February 13, 1985, along with propachlor, chlorpropham and fluazifop-butyl herbicides. Both plantings were harvested on March 8, 1985. The late planting was harvested a second time on May 7. Results At the first harvest in August 1984, all plants were somewhat immature and did not differ significantly in weight/plant, blanched stem length, or stem width (Table 1). Often there appeared to be more variation between blocks than between varieties. Stem length did vary significantly with variety, with Conqueror and Acadia the shortest and Tivi the longest. All stems were slightly bulbed at the root end; color was light blue-green for all varieties. At the second harvest of the early planting, all varieties had produced mature, marketable plants. Mean leek weight did not vary greatly with variety, except that Conqueror was lighter and Argenta heavier than most other varieties (Table 2). Stem length varied considerably among varieties, with Tivi, Bluvetia, and Kilima producing longer stems and Conqueror and Electra shorter stems. Blanch length did not vary significantly and appeared to be mostly controlled by transplanting depth. Stem width also varied little with variety, with great variability within a variety. Differences in growth habit and foliage color were very evident by the second harvest. Acadia and Conqueror had the darkest blue foliage; Argenta, Bluvetia, Kilima, and Tivi had pale, green foliage, with the other three varieties intermediate in color. Tivi plants were tall and upright; Electra and Kilima plants were taller than average but with less upright foliage. Alaska and Conqueror had the shortest leaves. All varieties were judged of acceptable quality, with the blue-foliage plants more attractive. Table 1. Leek size on August 24, 1984,85 days after transplanting, early planting Variety Stem wt. Stem length^Z Blanched length^Y Stem width^X ounces ----------------------inches----------------- Acadia 4.3 3.3 2.2 1.2 Alaska 3.6 3.5 2.3 1.0 Alberta 4.4 4.0 2.8 1.2 Argenta 4.7 3.8 2.8 1.2 Bluvetia 4.6 4.0 2.2 1.2 Conqueror 4.0 3.2 2.0 1.0 Electra 4.9 3.5 2.0 1.3 Kilima 4.8 3.7 2.1 1.3 Tivi 5.1 4.3 2.5 1.3 LSD(0.05) NS 0.7 NS NS ^ZMeasured from base of bulb to point of leaf branching. ^YMeasured from base of bulb to mean extent of white area. ^XMeasured just above the bulb. Table 2. Leek size on October 8, 1984, 130 days after transplanting, early planting. Variety Stem wt. Stem length Blanched length Stem width ounces ----------------------inches----------------------- Acadia 7.9 4.7 2.5 1.5 Alaska 7.4 3.9 2.4 1.4 Alberta 8.4 3.9 2.6 1.4 Argenta 9.9 4.5 2.9 1.6 Bluvetia 8.2 5.2 2.1 1.4 Conqueror 6.4 3.3 2.5 1.4 Electra 7.6 3.5 2.5 1.5 Kilima 9.0 5.1 2.1 1.6 Tivi 8.4 5.2 2.6 1.4 LSD (0.05) 2.5 0.6 NS NS Table 3. Leek size on March 28, 1985 Early planting Late planting Variety Stem wt. Stem length Stem width Stem wt. Stem length Stem width ounces ---------inches--------- ounces ---------inches--------- Acadia 12.2 4.2 2.0 3.2 3.7 1.0 Alaska 11.7 4.3 1.8 3.2 3.3 1.0 Alberta 12.5 4.6 1.9 2.7 3.7 0.9 Argenta 14.0 5.0 1.9 4.2 4.0 1.1 Bluvetia 13.0 5.3 1.9 - - - Conqueror 11.9 4.0 1.8 3.5 3.0 1.1 Electra 14.7 5.2 1.9 3.8 2.8 1.1 Kilima 15.0 7.3 1.9 - - - Tivi 14.2 7.2 1.8 - - - LSD(0.05) NS 1.2 NS NS 0.8 NS Table 4. Leek size on May 7, 1985, late planting Variety Stem wt. Stem length Stem width Comments ounces ---------inches--------- Acadia 5.1 4.2 1.3 bulbed, bolting Alaska 4.7 3.8 1.3 pronounced bulb, bolting Alberta 4.8 3.7 1.2 bulbed, bolting Argenta 5.3 4.7 1.3 slightly bulbed, bolting Conqueror 4.8 3.7 1.2 bulbed, bolting Electra 5.4 3.7 1.3 slightly bulbed, bolting LSD(0.05) NS 0.3 NS The early planting overwintered nicely. All varieties had excellent size when evaluated on March 28, had not yet bolted, and the stems were not woody. Mean stem weight increased by 50 percent or more, because of increased diameter and length (Table 3). Kilima and Tivi had the longest stems, but were not significantly heavier than the other varieties. These two varieties also had a less desirable light blue-green color. Only varieties suggested by the seed companies to be very winter hardy and bolting-resistant were included in the late planting. At first harvest on March 28, 1985, most varieties had longer stems than the industry standard, Electra, but were not heavier or thicker. All varieties were somewhat immature at this harvest. At the May harvest of the late planting, all varieties had bolted, even though the stems were still somewhat small. This indicates that the July 31 transplanting date was too late. To successfully overwinter, plants must be set out early enough that mature stems are formed in the fall. This trial indicates that of the several varieties available, none significantly outperforms the popular variety Electra. Transplanting should probably occur no later than June for either fall or overwintered harvest. The dibble planting method was acceptable, but did not produce blanch length equal to that of trench culture. Early Cabbage Variety Trial The purpose of this trial was to evaluate lines of cabbage for late spring or early summer harvest. This requires planting out in early spring and many varieties will bolt under these conditions. Direct seeding is often impossible in early spring and emergence would be slow and erratic. Thus, the lines were seeded in an unheated glasshouse for later transplant. This is the second in a series of early cabbage trials. Methods Twelve lines were seeded into 2-inch pots of peat-vermiculite mix on January 11, 1985 and were transplanted to a Willamette silt loam on February 25. Land preparation included a broadcast, incorporated application of 800 pounds/acre of 10-20-10, 0.75 pounds/acre trifluralin and 1.3 pounds/acre chlorpyrifos. Plants were spaced 3 feet between rows and 1.5 feet in the row, with five plants/plot and three replications of each variety or line in randomized complete block design. An additional 50 pounds N/acre as urea was sidedressed on March 27. A diazinon drench at 1 pound/acre and metalaxyl at 8 ounces/acre were applied on April 2. Harvest began on June 3 and continued at weekly intervals until July 8. Results and Discussion Head size was generally smaller than in 1984, with more tendency to bolt in 1985 for varieties included in both trials. The planting was more than a month earlier in 1985 than in 1984. A freeze in early May, after heads had started to form, may have contributed to a tendency to bolt prematurely. Most varieties produced elongated or pointed heads. Highest gross and marketable yields were obtained with Bravo. Earliest varieties were Earliana, Conquest, Express, Head Start, and Sunup. Head Start did not perform as well in this trial as in 1984, but was still above average in head size and percent marketable yield. Bravo performed well in 1984 as well as 1985, but was later maturing in 1984. Table 1. Harvest range and yield of cabbage lines, 1985 Variety Source^Z Harvest range Mean head Yield Bolting Usable Comments First Peak Last wt.(lb) (tons/A) (%) heads(%) Bravo 2 6/10 6/10 7/01 2.4 12.2 0 100 green, slightly pointed. Conquest 5 6/03 6/03 6/10 1.1 3.6 13 0 soft, elongated, purple. Earliana 3 6/03 6/03 6/03 1.6 8.3 19 40 light green, pointed. Express 5 6/03 6/03 6/24 1.3 4.9 33 13 slightly elongated, purple. Head Start 5 6/03 6/03 7/01 1.8 8.5 0 53 slightly elongated, green-purple. Market Prize 2 6/03 6/24 7/01 1.5 5.9 0 40 soft, elongated, green. Market Topper 2 6/03 6/10 7/08 1.6 8.1 0 40 elongated to pointy, some edema. Ocala 1 6/10 7/08 7/08 2.3 9.4 13 80 round to slightly pointed. Sunup 2 6/03 6/03 7/01 1.3 5.9 7 7 green, slightly pointed. XPH 1104 5 6/03 6/03 7/08 1.7 8.6 13 67 purple, very pointed. 55-629 4 6/03 6/03 7/08 1.4 6.4 7 20 green, elongated. 55-707 4 6/03 7/08 7/08 2.1 7.9 20 40 purple, pointed. LSD(0.05) 0.6 3.4 11 27 ^ZSources: 1. Sun Seeds 2. Harris-Moran 3. Burpee 4. Takii 5. Asgrow Early Autumn Cauliflower Variety Trial Trials to evaluate the heat tolerance of cauliflower have been conducted at the North Willamette Station for several years. These trials were transplanted in late May for July harvest. The 1985 trial differed in that the varieties were transplanted in early July for late summer to early autumn harvest. As with the earlier trials, the major desired quality is the ability to withstand high temperatures without ricing or discoloration while producing a high density, moderately sized head. Methods Ten varieties or lines of cauliflower were seeded on May 31, 1985, in 2-inch pots of peat-vermiculite mix and placed in a glasshouse. Seedlings were transplanted to a Willamette silt loam, pH 5.9, on July 5. Land preparation included broadcast and incorporation of 500 pounds/acre of 14-14-14 fertilizer, 7.5 pounds B, 0.75 pounds trifluralin/acre, and 1.3 pounds chlorpyrifos/acre. Diazinon was applied as a drench at 1 pound/acre on July 26. An additional 300 pounds/acre of calcium nitrate was sidedressed on August 7 and again on August 21. Plant spacing was 3 feet between rows and 1.5 feet in the row. Varieties were replicated three times in randomized block design. Heads were harvested at 3- or 4-day intervals and were not tied to determine which cultivars were adequately self-blanching. Results Seed sources, yields, and harvest spans are presented in Table 1. Table 2 contains comments on curd quality. Weather from transplanting until the end of August was unusually warm and sunny. Plant growth was less than in most previous trials and some of the earlier varieties, particularly Andes, had reduced head weight. Weather during the harvest period of September 3 to October 7 was cooler than normal with higher than normal rainfall in early September. As a result some of the varieties, particularly Cervina, had greatly improved curd quality compared to previous trials. Highest gross yields and head size were with Silverstar. The highest percentage of Grade No. 1 (white curd, no defects) was with Silverstar, Cervina, and Andes. The performance of Silverstar in this trial was similar to that previously obtained for July and August harvest. Cervina and Vernon also appear promising, with good curd color, density, and head weight. Andes had good curd quality, but head size was less than 1 pound, compared to 1.5 pounds or better in some years. Dok did not perform up to expectations. These results are too preliminary to serve as a guide for planting. Several years of trials are necessary to insure that performance of a variety will be consistent. Table 1. Source, yield, and grade of cauliflower varieties, 1985 Mean Yield of^Y Gross % Harvest period head No. 1 yield No. 1 Variety SourceZ First Peak Last wt. (g) heads (T/A) (T/A) heads Andes 4 9/03 9/09 9/27 439 3.3 3.7 84 Cervina 4 9/16 9/27 10/01 701 5.9 6.2 90 Dok 1 9/16 9/20 9/27 578 2.9 4.8 58 Hormade 6 9/03 9/13 9/23 538 2.8 5.7 46 Matra 4 9/20 10/01 10/07 760 2.7 4.7 57 Silverstar 5 9/23 9/27 10/07 974 7.3 7.7 94 Snowball 42 3 9/16 9/20 10/04 581 2.0 5.1 40 Snowball 123 2 9/13 9/20 10/04 587 1.2 4.9 21 Suprimax 4 9/09 9/16 9/27 668 3.3 6.5 45 Vernon 4 9/20 9/23 9/27 737 3.4 4.9 73 LSD(0.05) 141 1.5 1.6 19 ^Z1. Elsoms 2.Harris-Moran 3.Ferry Morse 4.Royal Sluis 5. Rijk Zwaan 6. A.R. Zwaan. Some varieties available from more than one source. Source listed above provided the seedlot used in this trial. ^YGrade No. 1: Curd white; free of defects such as riciness, fuzz; no leaves or bracts in curd; dense and tight. Table 2. Comments on cauliflower curd quality, 1985 Andes: Small, fairly dense heads. Small plants had less cover than usual. A few (16%) yellow heads. Cervina: Many ricey heads in July and August (previous trials) but only 10% ricey or discolored heads in this trial. Appears to be well adapted to early autumn cropping. Dok: Major problem was bracts or leaves in curd. Hormade: Rather small heads, many discolored. Matra: Good size but many heads with fuzzy curd. Silverstar: Good size and color. Curd a little rougher than usual, but still graded No. 1. Snowball 42: Ricey curd. Snowball 123: Ricey and yellow curd, some pink curd. Suprimax: Major defect was riciness; some yellowing and leaves in curd. Vernon: Fairly good. size, some heads discolored but majority were snow white. Lime and Fertilizer Effects on Overwintered Cauliflower Overwintered cauliflower trials at the North Willamette Station and by growers have usually given acceptable yields and quality. However, yields of early varieties, and particularly in cold springs, have occasionally been disappointing. Since plant nutrient uptake is limited on cold soils, these low yields may have been caused by inadequate availability of P or other elements. Past recommendations for overwintered cauliflower have called only for application of N in the spring. The effects of spring-applied P and the type of spring-applied N on cauliflower yield and quality had not been investigated. Likewise, the response of overwintered cauliflower to lime, which increases P availability, had not been studied. The purpose of this trial, the third in a series, was to investigate the effects of lime, banded P at planting, gypsum, and source and rate of N on the yield and grade of overwinter cauliflower. Methods 'Inca' cauliflower was seeded on August 2, 1984. The lime main plots were split by a banded application of 0 or 90 pounds P205/acre, placed two inches to the side and two inches beneath the seed row at planting. On February 6, 1985, the plots were again split by a sidedressed application of gypsum at 0 or 150 pounds/acre. Resulting sub/subplot size was three rows x 24 feet. Treatments, harvest rows, and plants sampled for tissue analysis came from the center row of each plot. Additional N as ammonium nitrate was applied to all plots at 75 pounds N/acre on February 6, and again on March 6. Leaf samples were collected for tissue analysis on March 25. Plots were harvested on April 15 and on April 22. In a separate experiment, 'Inca' was seeded on August 2, 1984, in three-foot rows on a uniformly limed area, pH 6.1. The seedling stand was thinned to 18-inch in-row spacing in late September. Napropamide was applied at 2.0 pounds/acre in October, following hand-hoeing. On February 6, 1985, the following N sources were applied at 75 pounds N/acre in a randomized block design with four replications: ammonium nitrate, ammonium sulfate, calcium nitrate, and urea. The N sources were reapplied at the same rate on March 6. Leaf samples were collected for tissue analysis on March 25. Plots were harvested on April 15 and 22. Results and Discussion Lime tended to increase total yield slightly at the first harvest but had no effect on head quality (Table 1). Gypsum had no effect on head weight or quality but fewer heads were harvested on gypsum-treated plots. This appeared to be from chance, a non-random decrease in number of plants present on gypsum-treated plots. Banded P at planting also tended to reduce the number of heads harvested/plot, with no effect on head weights when averaged over lime and gypsum treatments. There were no significant interactions affecting the first harvest. Lime tended to increase total yield slightly at the first harvest but had no effect on head quality (Table 1). Gypsum had no effect on head weight or quality but fewer heads were harvested on gypsum-treated plots. This appeared to be from chance, a non-random decrease in number of plants present on gypsum-treated plots. Banded P at planting also tended to reduce the number of heads harvested/plot, with no effect on head weights when averaged over lime and gypsum treatments. There were no significant interactions affecting the first harvest. Neither lime, gypsum, nor banded P affected yield or quality for the sum of two harvests (Table 2), when averaged over the other treatments. However, lime and banded P significantly interacted in their effects on total weight harvested for the two harvests. Banded P tended to increase yield at low soil pH but not at high soil pH (Table 3). Treatments had no effect on leaf tissue concentrations of N, P, Ca, Mg, Zn, and Cu (data not shown). Gypsum increased leaf K level from 2.86% to 3.13%, and S level from 1.07% to 1.16%, when averaged over all treatments. In contrast to previous effects of lime application on leaf Mn levels, leaf Mn was increased from the range of 35 to 37 ppm for the lower rates of lime, to 49 ppm at the highest rate. However, only one replicate showed high leaf Mn levels at the high rate of lime. Three years of experiments on the effects of lime and P on overwinter cauliflower yield and quality indicate that the effect of lime is small but significant when averaged over the three years. Neither a subsurface-banded application of P at planting nor a sidedressed spring P application appreciably affected yield on this soil of high P content. A single year's work indicates no response to a spring application of gypsum. Table 1. Main effects of lime, banded P, and gypsum on yield of overwintered cauliflower at the first harvest, 1985 Treatment Yield Mean head wt. Heads/plot % No. 1 No. 1 heads All heads No. 1 All No. 1 Total heads -------tons/acre------ ---pounds--- Lime (T/A) 0 1.1 3.6 1.25 1.34 2.9 8.9 33 2 1.1 3.6 1.22 1.32 2.9 9.5 29 4 1.5 4.2 1.40 1.33 3.5 10.5 34 6 1.3 3.8 1.24 1.33 3.1 9.5 33 LSD(0.05) NS^Z 0.5 NS NS NS NS NS + Gypsum 1.1 3.6 1.27 1.30 2.8 9.1 31 - Gypsum 1.3 4.1 1.29 1.35 3.3 10.1 33 NS NS NS NS NS * NS + P 1.2 3.8 1.24 1.34 3.1 9.1 34 - P 1.2 3.9 1.31 1.31 3.1 10.1 30 NS NS NS NS NS * NS ^ZNS;: no significant differences; significant differences among means at 5% level. Table 2. Main effects of lime, banded P, and gypsum on yield of overwintered cauliflower, total of two harvests, 1985 Yield Mean head wt. Heads/plot % No. 1 Treatment No. 1 heads All heads No. 1 All No. 1 Total heads -------tons/acre------ ---pounds--- Lime (T/A) 0 1.5 4.9 1.28 1.31 3.6 12.5 29 2 1.2 5.0 1.17 1.25 3.3 13.4 25 4 1.6 5.1 1.43 1.30 3.7 13.1 28 6 1.4 4.8 1.26 1.19 3.5 13.4 26 NS^Z NS NS NS NS NS NS + Gypsum 1.4 4.8 1.30 1.26 3.4 12.8 27 - Gypsum 1.4 5.1 1.26 1.27 3.6 13.4 28 NS NS NS NS NS NS NS + P 1.5 4.9 1.31 1.27 3.7 13.1 30 - P 1.3 4.9 1.26 1.25 3.3 13.2 26 NS NS NS NS NS NS NS ^ZNo significant differences Table 3. Interaction of lime and banded P on total yield of overwinter cauliflower, 1985 Lime Rate P rate (pounds/acre) (tons/acre) 0 90 ---- tons/acre ---- 0 4.6 5.3 2 4.9 5.0 4 5.4 4.7 6 4.8 4.8 LSD(0.05) = 0.5 In the N source experiment, yield of grade No. 1 heads at the first harvest (Table 3) and for the season (Table 4) was higher with the strictly ammonium-N sources than with the strictly nitrate source, calcium nitrate. The mean weight of No. 1 heads was increased by ammonium-N at the first harvest but not for the sum of two harvests. Mean weight of all heads was not affected by N source. For the sum of both harvests (Table 5), highest total yield but the lowest percentage of grade No. 1 heads was obtained with calcium nitrate. More foliar growth on ammonium N-fertilized plants may have provided more cover for the curd and improved curd color and quality. Source of N had no effect on leaf tissue concentrations of N, P, K, Ca, Mg, S, Zn, and Mn (data not shown). Leaf Cu level was significantly higher with urea as N source (11.9 ppm) than with the other N sources (6.9-7.1 ppm). While indicating a significant advantage to providing an ammonium-N source, these results do not agree entirely with results obtained in 1983 and 1984. Larger scale experiments will be needed to determine if there are significant advantages to use of a certain N source or if choice of N source should be determined only by price. Table 4. Effect of N source on yield of overwinter cauliflower at first harvest, 1985 No. of heads Yield of Mean head wt. % No. 1 N source harvested/plot No. 1 heads All heads No. 1 All heads -------tons/acre------- ---pounds--- Amm. nitrate 8.8 1.3 3.3 1.38 1.27 37 Amm. sulfate 10.3 2.2 4.4 1.31 1.42 54 Calcium nitrate 9.5 0.7 4.4 1.01 1.49 24 Urea 10.0 2.5 4.2 1.50 1.37 53 LSD(0.05) NS 1.3 NS 0.35 NS 18 NS: no significant differences. Table 5. Effect of N source on yield of overwinter cauliflower, total of two harvests, 1985 No. of heads Yield of Mean head wt. % No. 1 N source harvested/plot No. 1 heads All heads No. 1 All heads ----- tons/acre ------ ---pounds--- Amm. nitrate 14.8 2.0 5.5 1.50 1.23 31 Amm. nitrate 13.5 2.3 5.1 1.28 1.33 44 Calcium nitrate 17.0 1.2 7.3 1.46 1.42 16 Urea 13.5 2.5 5.5 1.50 1.31 39 LSD(0.05) NS 0.9 1.0 NS NS 11 NS: no significant differences. Nitrogen Rate, Form, and Timing on Yield of Sweet Corn Experiments at the North Willamette Experiment Station in 1979 and 1980 indicated that, for N applied as ammonium nitrate at 160 pounds N/acre, sweet corn yields were increased by delaying application of most of the N until the corn was 10 to 12 inches tall. These experiments were at fairly high levels of early season irrigation, and the lower yields when all N was applied at planting may have been caused by leaching of nitrate-N out of the root zone. In a trial in 1984, however, splitting the N application did not increase yield with ammonium nitrate as N source. In addition, application of N as urea or urea plus ammonium chloride did not increase yields over those with ammonium nitrate, indicating no leaching of nitrate. The objective of the 1985 trial was to compare the yield response of sweet corn to three rates of N, applied as either ammonium nitrate or urea, with all N applied at planting. In addition, three rates of split application of ammonium nitrate, with three methods of application (surface banded, subsurface banded, irrigation water) were compared. In 1986, yield of sweet corn was studied as a function of N rate and form, a nitrification inhibitor, and timing of N application. Methods* 1985 'Jubilee' sweet corn was seeded in a Willamette silt loam, pH 5.8, on May 14, 1985, following a broadcast application of potassium sulfate at 85 pounds K/acre. Plot size was 4 rows x 40 feet, between row spacing 30 inches, and plant population about 28,000/acre. Forty pounds N and 120 pounds P205/acre (13-39-0) was banded 2 inches below and two inches to the side of the seed row at planting on all plots. In addition, treatments 1, 2, and 3 received an additional 60, 120, or 180 pounds N/acre, respectively, as ammonium nitrate broadcast at planting. Treatments 4, 5, and 6 received an additional 60, 120, or 180 pounds N/acre, respectively, as urea, also broadcast at planting. Treatments 7, 8, and 9 received a surface banded application of ammonium nitrate on June 26, when the corn was about 12 inches tall. The N rates were 60, 120, and 180 pounds/acre, respectively. Treatments 10, 11, 12 received a subsurface banded application of ammonium nitrate on June 26 at the above rates. For treatments 13, 14, and 15, the three rates of N were applied on June 26, after the appropriate amounts of ammonium nitrate were dissolved in 5 gallons of water. Application was from sprinkler cans to simulate the effect of applying N through the irrigation system. Treatments were replicated four times in randomized complete block design. Although it was a dry spring and soil moisture was low, the stand was not irrigated up, in order to maintain normal grower irrigation practices. Leaf samples were taken for tissue analysis on July 22, at first tasseling. All ears were harvested from 20-foot sections of the center two rows of each plot on August 22 and were graded as mature, immature, or culls. Culls were not included in yield measurements. 1986 Methods were as in 1985 except that treatments 1,2,and 3 received an additional 60 pounds N/acre as ammonium nitrate, urea, or urea plus DCD-treated urea (2:1 ratio), broadcast at planting (May 29). The DCD-treated urea contained 7.2 percent dicyandiamide. Treatments 4, 5 and 6 received an additional 60 pounds N/acre ammonium nitrate, urea, or urea plus DCD-treated urea (2:1 ratio) sidedressed on July 8. Treatments 7-12 received the above forms of N and timing of N application, but the additional N applied was 160 pounds/A (200 pounds total N/acre). Treatments were replicated four times in randomized complete block design. The stand was irrigated up to assure even emergence. Harvest was on September 3. Results 1985 Total ear yield (sum of mature and immature ears), mean ear weights, and ear lengths varied significantly with treatment (Table 1). However, the main effects of N rate, method of placement and timing, and N source were not statistically significant except that total yield was reduced with urea as compared to ammonium nitrate, and mean weight of mature ears increased with increasing N rate (Table 2). Both leaf tissue N and Ca concentrations increased significantly with increasing rate of N (Table 3). Nitrogen source and application method had no effect on leaf N and Ca concentrations and there were no significant interactions. Only the main effects of N rates are given in Table 3. Leaf tissue P, K, and Mg concentrations were not affected by treatment (data not shown). This experiment provided no evidence for any yield differences attributable to timing or method of placement of N. A combined ammonium and nitrate source of N gave yields equal or superior to those with a source containing no nitrate. Since 1985 was a very dry year, with only 4.3 inches precipitation between planting and harvest, leaching of nitrate-N was probably negligible. Table 1. Effects of rate, source, timing, and placement of N on sweet corn yield, 1985 Treatment Total N Source^Z Application Ear yield Mean ear weight Ear number applied of N method Mature Total Mature Total length lb/A --tons/acre-- ----pounds----- inches 1 100 Am. nitr. surface^Y 6.4 8.6 0.76 0.72 8.8 2 160 Am. nitr. surface^Y 6.9 8.6 0.74 0.72 9.1 3 220 Am. nitr. surface^Y 7.5 9.3 0.77 0.72 9.4 4 100 Urea surface^Y 6.3 8.1 0.78 0.74 9.0 5 160 Urea surface^Y 5.9 7.4 0.78 0.72 8.9 6 220 Urea surface^Y 6.1 7.9 0.79 0.72 8.7 7 100 Am. nitr. surface^X 5.9 8.0 0.78 0.70 8.8 8 160 Am. nitr. surface^X 8.1 9.5 0.77 0.73 8.8 9 220 Am. nitr. surface^X 6.9 8.7 0.80 0.74 9.0 10 100 Am. nitr. subsurface^X 7.5 9.5 0.78 0.70 8.9 11 160 Am. nitr. subsurface^X 7.4 9.5 0.77 0.70 8.8 12 220 Am. nitr. subsurface^X 7.5 9.9 0.79 0.72 9.3 13 100 Am. nitr. sprinkler^X 5.6 7.5 0.76 0.70 9.2 14 160 Am. nitr. sprinkler^X 7.0 8.7 0.78 0.72 9.0 15 220 Am. nitr. sprinkler^X 7.2 9.3 0.83 0.77 9.1 LSD(0.05) NS 0.7 0.06 0.06 0.6 ^ZAll plots received 40 pounds N/acre as 13-39-0 at planting. ^YAll N applied at planting. ^XBulk of N applied on June 26. NS: no significant differences. Table 2. Main effects of N source on total ear yield and main effect of N rate on mean ear weight of mature ears, 1985 N source Total yield N rate Mean ear weight (tons/acre) (pounds/acre) of mature ears (pounds) Amm. nitrate 8.9 100 0.77 Urea 7.8 160 0.77 ^Z 220 0.80 ^Z: significant differences among means at 5% level. Table 3. Main effects of N rate on leaf tissue N and Ca concentrations, 1985 N rate (pounds/acre) Leaf N (%) Leaf Ca (%) 100 3.13 0.68 160 3.30 0.71 220 3.35 0.74 ^Z ______________________________________________ ^Z*,: significant differences at 1% and 5% levels, respectively. 1986 Total ear yield, mean ear weights, and ear lengths varied significantly with treatment (Table 4). However, the main effects of timing of application and N source were not statistically significant. Increasing the N rate from 100 to 200 pound/acre increased total yield and ear length and tended to increase ear weight and yield of mature ears (Table 5). This experiment provided no evidence for any yield differences attributable to timing of application or source of N. A combined ammonium and nitrate source of N gave yields essentially equal to those with a source containing no nitrate. The presence of a nitrification inhibitor also did not affect yield. 1986 was, again, a very dry year, with only 1.7 inches precipitation between planting and harvest. Leaching of nitrate-N was probably negligible. Nitrate-N may be lost more readily in early plantings in wet springs and if irrigation is not kept to the minimum required for adequate plant growth. Table 4. Effects of N rate, source, and timing of N application on sweet corn yield, 1986 Treatment Total N Source Timing of N Ear yield Mean ear wt. Ear number applied of N application Mature Total Mature Total length lb/A --tons/acre-- ---pounds---- inches 1 100 Am. nitrate planting 8.8 9.3 0.63 0.61 8.2 2 100 Urea planting 9.7 10.0 0.70 0.69 8.1 3 100 Urea-DCD planting 9.4 10.0 0.66 0.63 8.1 4 100 Am. nitrate split 8.7 9.2 0.68 0.67 8.2 5 100 Urea split 8.9 9.3 0.64 0.63 8.3 6 100 Urea-DCD split 10.1 10.2 0.66 0.66 8.0 7 200 Am. nitrate planting 9.9 10.5 0.67 0.67 8.5 8 200 Urea planting 9.8 10.2 0.69 0.68 8.6 9 200 Urea-DCD planting 10.8 11.0 0.70 0.69 8.4 10 200 Am. nitrate split 9.6 10.1 0.67 0.67 8.4 11 200 Urea split 9.8 10.3 0.65 0.64 8.3 12 200 Urea-DCD split 8.7 9.2 0.65 0.65 8.4 LSD(0.05) NS 1.3 0.05 0.05 0.5 Table 5. Main effects of N rate, source, and timing of application on sweet corn yield, 1986 Ear yield Mean ear weight Ear Treatment Mature Total Mature Total length --tons/acre-- -----pounds---- inches Amm. nitrate 9.3 9.8 0.66 0.65 8.3 Urea 9.5 9.9 0.67 0.66 8.3 Urea + DCD 9.8 10.1 0.67 0.66 8.2 NS^Z NS NS NS NS 100 lb N 9.3 9.7 0.66 0.65 8.2 200 lb N 9.8 10.2 0.67 0.66 8.4 NS * NS NS * planting 9.7 10.1 0.67 0.66 8.3 split 9.3 9.7 0.66 0.65 8.3 NS NS NS NS NS ^ZNS, : means do not differ significantly, and significant differences between means at the 5% level, respectively. Nitrogen Rates and Phosphorus on Carrots Cooperator: H.J. Mack Higher yields and improved root quality are essential for processing carrot growers to remain competitive. Nitrogen fertilizer applications range from 50 to 150 pounds N/acre with most between 50 and 80 pounds. More research is needed to clarify yield response to nitrogen, especially at higher rates, and the influence of N on such root characteristics as diameter, length, splitting, and rots. The response to N should be investigated at plant densities typically used for slicing and dicing. The objectives of this trial were to evaluate the effects of five N rates and 2 plant populations on yield and root characteristics and to evaluate the effects of banded P fertilizer at two rates of N. Methods* A base fertilizer of 300 pounds/acre of 10-20-10 was disked into a Willamette silt loam on April 30, 1986, and 5-foot wide beds were formed by rotary tillage. 'Chantenay' carrot was seeded at 50 or 80 seeds/foot, three rows per bed, with a belt planter. Concentrated superphosphate was banded at 50 pounds P/acre beneath the seed row of appropriate plots. Plot length was 15 feet. Linuron was applied at 1.0 pounds/acre immediately after planting. The nitrogen variable was established on May 30 when half the remaining N was sidedressed as ammonium nitrate. The final N application was on July 3 when the largest roots were 0.5 to 0.8-inch diameter. The two seeding rates and five N rates were in factorial combination. Plots were in randomized block design with 4 replications. Nitrogen rates were 50, 85, 120, 155, and 190 pounds/acre. The P variable was added at N rates of 85 and 155 pounds/acre and the higher seeding density. Leaves were sampled for tissue analysis on July 30 and plots were harvested on October 16 and 17. Good roots were graded into two size categories (greater than 1.5 inch diameter and 5-inch length and all others). Each root was visually inspected for cracking and rots and defective roots were weighed and counted separately. Results The yield of roots in the large size category did not vary significantly with N rate but decreased from 1.71 tons/acre to 0.24 tons/acre with the increase in plant population from 46/foot to 77/foot. Yield of large roots increased significantly with banded P but this may have been caused by a reduction in stand on the banded P plots. Total yield did not vary significantly with either N rate or plant population but the yield tended to be highest with 85 pounds N/acre. Phosphorus tended to reduce total yield because of the reduced stand. Mean root weight did not vary significantly with N rate, when averaged over plant populations, but at the high plant population, root weight increased to a maximum at 155 pounds N/acre. Root weight decreased with increasing population and increased with banded P. Root length did not vary significantly with any treatment (data not shown). The percentage of rotten or pitted roots increased with plant population and increased linearly with N rate (r2 = 0.225, p = 0.002) but decreased with banded P. Increasing plant population decreased the percentage of cracked or split roots but banded P had no effect on cracking. Cracking increased linearly with increasing N rate at high plant population (r2 = 0.0978, p = 0.049) but not at the low population. The leaf tissue analysis confirmed that the higher rates of N were available to the plants as reflected in the increased N concentration of leaves from heavily fertilized plots. These results indicate that the commonly applied rates of N are adequate for good carrot yields. The plant populations used in this experiment were higher than normal, however, and at lower plant densities the response to N rate may be different. Incidence of rot and other disorders also may be lower at reduced plant density. Table 1. Effect of N rate, plant population, and banded P on yield and root characteristics of carrot, 1986 Roots/ Root yield (T/A) Mean root Cracked Rot Leaf N Treatment foot Large All wt. (g) % % % 50 lb N, low density 38.3 2.3 41.8 48.0 2.6 2.8 2.47 85 56.3 1.4 58.4 43.1 1.8 4.8 2.75 120 43.9 1.7 44.2 41.8 2.1 4.0 2.97 155 49.5 1.0 51.7 43.5 2.4 13.8 3.39 190 44.1 2.2 48.5 45.7 2.9 5.5 3.56 50 lb N, high density 85.7 0.6 44.5 22.4 0.8 1.7 2.37 85 82.2 0.0 47.5 23.9 0.8 6.5 2.65 120 78.1 0.0 48.6 27.0 1.2 9.4 2.84 155 68.9 0.4 47.0 28.8 2.4 12.6 3.20 190 68.4 0.1 44.6 27.6 2.3 24.7 3.11 85 lb N, high densityZ 55.3 2.4 38.2 31.8 1.4 2.8 2.73 155 lb N, high densityZ 40.9 1.6 38.7 40.4 1.0 8.0 3.21 LSD(0.05) 21.1 1.1 9.8 10.2 1.3 4.4 0.38 Significance: N rate NS^Y NS NS NS NS Plant density NS ** * * ** N x density NS NS NS * * * NS P rate * * * * NS * NS ^ZPhosphorus banded at planting. ^YNS,, : no significant differences among means; significant differences at 5% and 1% levels, respectively. Nitrogen Rates and Phosphorus on Onions Cooperators: Robert B. McReynolds and T.L. Jackson Storage onions in western Oregon have been grown almost exclusively on lake bottom soils which are high in organic matter (more than 10%). Recently, production of onions on mineral or "upland" soils with low organic content and N availability has increased rapidly and now equals production on the organic soils. Response of onions to nitrogen rate and to applications of phosphorus and potassium on the mineral soils is not well understood. The 1985 trial evaluated onion yield, size grade, and keeping quality as a function of nitrogen rate, broadcast and banded application of P, and a K application. The 1986 trial evaluated onion yield and keeping quality as a function of nitrogen rate and phosphorus application. Methods* 1985 After disking and harrowing, 75 pounds N/acre as ammonium sulfate was applied to a Willamette silt loam, pH 6.0 on April 10, 1985. The field was then divided into plots of 5 x 30 feet and potassium chloride at 150 pounds K/acre and treble superphosphate at 60 pounds P/acre were applied to the appropriate plots and worked into the surface two inches of soil. Plots were then seeded with three rows of onion with 20 inches between rows. On April 11, two of the four replicates were seeded with 'Sure Crop'; the remaining replicates were seeded with 'Benny's Red', because of a shortage of 'Sure Crop' seed. Propachlor herbicide was applied at 4 pounds/acre immediately after planting and was reapplied on June 6 and July 12. Plots were also hand-weeded once. The eight fertilizer treatments were as follows: 1) 75 pounds N/acre as ammonium sulfate (N1, no sidedressed N); 2) 75 pounds/acre additional N as ammonium nitrate (N2); 3) 150 pounds additional N/acre as ammonium nitrate (N3); 4) N2 plus 60 pounds P/acre banded 2 inches to the side and 2 inches beneath the seed row; 5) N2 plus banded P at 60 pounds P/acre plus broadcast P at 60 pounds/acre; 6) N3 plus banded P; 7) N3 plus banded P plus broadcast P; 8) N plus banded P plus 150 pounds K/acre, broadcast as potassium chloride. In addition, 225 pounds N as ammonium nitrate was applied to border plots (N4). All ammonium nitrate was sidedressed on June 4. Treatments were applied in randomized complete block design except for N4. Leaf samples were collected from all treatments on July 23. Plots were harvested after topping on September 24. Bulbs were separated into three size grades: No. 1, over 3.5-inch diameter; No. 2, over 2.3-inch diameter; No. 3, others. 1986, Experiments 1 and 2 Methods were as in 1985 except that 50 pounds N/acre as ammonium sulfate was applied to a Willamette silt loam on April 21, 1986. Five-fool wide, 30-foot long plots were seeded with three rows of 'Granada' onion ith 20 inches between rows on April 22. Concentrated superphosphate was banded two inches to the side and two inches beneath the seed row of appropriate plots. Propachlor herbicide was applied at 4 pounds/acre immediately after seeding and was reapplied on June 12, July 1, and July 29. Plots were also hand-weeded twice. Diazinon was applied at 20 pounds/acre on July 1, and azinphosmethyl and oxydemetonmethyl were applied at 0.75 pounds/acre on July 15 for thrips control. Azinphosmethyl was reapplied on July 29. The eight fertilizer treatments included 100, 150, 200, and 250 pounds N/acre in factorial combination with banded P at 0 or 60 pounds P/acre. The additional N was sidedressed as ammonium nitrate on June 13. Treatments were in randomized block design with four replications. Plots were harvested after topping on October 7. Bulbs were separated into two size grades with the No. 1 grade at least 3.0 inches diameter, and the No. 2 grade consisting of all others. The No. 1 bulbs were collected for a storage trial. Bulbs were removed from storage and evaluated for rots and sprouting on January 21, 1987. The methods for Experiment 2 were the same, except that the variety was 'Simcoe,' the seeding date was May 19, and onions were not kept for storage. 1986, Experiment 3 The trial was planted by grower Jim Schlecter on his field of Woodburn clay loam. Methods were Schlecter's standard practice except that N rates were established following seeding. The base fertilizer program included 103 pounds N/acre as ammonium sulfate, 205 pounds K20/acre as potassium chloride, 2.0 tons lime/acre, and 41 pounds N and 61 pounds P/acre injected beneath the seed row as 10-34-0 solution. The trial was seeded with 'Granada' onion, 4 rows/bed, on April 10. Additional N was sidedressed as urea on May 15. The eight treatments included N rates of 144, 184, 224, and 264 pounds N/acre in factorial combination with broadcast P at 0 or 107 pounds P/acre. Treatments were replicated four times in randomized complete block design. Results 1985 Yield of No. 1 (jumbo) bulbs tended to increase up to 225 pounds N/acre (N3) and dropped off sharply at 300 pounds N (Table 1). At 150 pounds N/acre, banded P tended to increase No. 1 yield. Addition of P also tended to increase No. 1 yield at the 225-pound rate of N. At both rates of N, the combination of banded P plus broadcast P tended to yield more jumbo onions than did banded P alone. Addition of K did not increase yield of jumbos beyond that obtained with banded P alone. Yield of No. 2 onions did not vary significantly with treatment, but there was a trend towards increasing yield of No. 2's with increasing N up to 225 pounds/acre. At 150 pounds N/acre, banded P tended to increase No. 2 yield. Trends for yield of No. 1 plus No. 2 bulbs and total yield were similar. Yields were highest at 225 pounds N/acre and banded P increased yield at 150 pounds N/acre but not at 225 pounds/acre. Application of K did not increase yield. Within size categories, N, P, and K had very little effect on mean bulb weights (Table 2). Mean bulb weight for all bulbs did increase with 150 rather than 75 pounds N/acre but P and K did not affect mean bulb weight of all bulbs. The major effect of increasing N rate up to 225 pounds/acre was to shift bulbs from the No. 3 category into the No. 2 category (Table 3). The percentage of No. 1 bulbs and No. 1 plus No. 2 bulbs was highest at 150 pounds N/acre. The slight reduction in percentage of large bulbs at 225 pounds N/acre may be caused by the higher average stand on these plots (Table 3). Stand differences were not significant, but there was a trend toward an inverse relationship between stands and the percentage of large bulbs, Phosphorus and K did not have a consistent effect on the percentage of No. 1 or No. 1 plus No. 2 bulbs. The fertilizer applications had little effect on leaf tissue elemental concentrations (Table 4). Potassium application increased leaf K content. Leaf P concentration tended to increase with P application and leaf N concentration tended to increase up to the 225 lb/acre rate of N application, but these differences were not significant. The high rate of N reduced leaf P content. Both leaf Zn and Mn concentrations tended to increase with K application. Table 1. Effects of N, P, and K on yield of onions, 1985 Treatment No. 1 No. 2 No. 3 No. 1 + No. 2 Total ------------hundred weight/acre-------------- N1 56.5 343.1 157.9 399.6 557.5 N2 89.0 356.2 118.8 445.2 563.0 N3Z 92.1 496.0 151.9 588.1 740.0 N4 15.3 247.3 239.6 262.6 502.2 N2 P band 96.4 455.8 127.5 552.2 679.7 N2 P+P band 117.1 453.1 117.6 570.2 687.8 N3 P band 124.4 383.9 100.2 508.3 608.5 N3 P+P band 140.8 465.4 135.4 606.2 741.6 N3 K+P band 104.1 452.6 160.8 556.7 717.5 LSD(0.05) 61.8 NS NS 134.7 165.4 ^ZNot randomized with other treatments NS: no significant differences Table 2. Effects of N, P, and K on mean bulb weight of onions, 1985 Treatment No. 1 No. 2 No. 3 No. 1 + No. 2 Total --------------------g/bulb------------------- N1 318 204 96 214 159 N2 347 213 117 240 207 N3^Z 321 203 99 215 175 N4 295 172 87 177 117 N2 P band 335 205 107 219 185 N2 P+P band 347 208 106 230 192 N3 P band 350 208 107 233 196 N3 P+P band 340 207 100 227 185 N3 K+P band 356 212 101 229 178 LSD(0.05) NS NS NS NS 40 ^ZNot ramdomized with other treatments NS: no significant differences Table 3. Effects of N, P, and K on number of bulbs harvested and grade distribution by number, 1985 Treatment No. bulbs/30 row feet No.1 No. 1 + No. 2 No.2 No. 3 -----------------%----------------- N1 189 5.5 53.6 48.1 46.4 N2 160 14.8 69.5 54.7 30.5 N3^Z 222 6.9 64.6 57.7 35.4 N4 217 1.3 32.4 31.1 67.6 N2 P band 196 8.1 68.2 60.1 31.8 N2 P+P band 191 11.0 69.4 58.4 30.6 N3 P band 169 13.2 70.9 57.7 29.1 N3 P+P band 209 10.2 66.3 56.1 33.7 N3 K+P band 210 7.5 60.7 53.2 39.3 LSD (0.05) NS NS 12.1 8.6 8.6 ^ZNot randomized with other treatments NS: no significant differences Table 4. Effects of N, P, and K on onion leaf mineral content, 1985 Treatment N P K Ca Mg S Zn Mn Cu --------------%---------------- -----ppm------ N1 3.5 0.38 3.4 1.3 0.20 0.78 21 58 9 N2 3.7 0.38 3.6 1.4 0.22 0.78 22 57 9 N3^Z 3.8 0.39 3.5 1.3 0.20 0.77 23 61 9 N4 3.8 0.30 3.7 1.4 0.22 0.64 23 109 8 N2 P band 3.8 0.39 3.5 1.3 0.20 0.83 20 51 9 N2 P+P band 3.7 0.43 3.2 1.1 0.18 0.87 21 46 9 N3 P band 3.8 0.40 3.4 1.3 0.20 0.78 21 49 9 N3 P+P band 3.8 0.41 3.9 1.3 0.19 0.78 21 54 9 N3 K+P band 3.9 0.41 6.2 1.3 0.20 0.79 24 73 9 LSD(0.05) NS NS 1.9 NS NS NS 3 16 NS ^ZNot randomized with other treatments NS: no significant differences 1986, Experiment 1 Banding P beneath and to the side of the seed reduced stands by nearly 12% (Table 5). The N rate had no effect on stands, as expected, since the N variable was not applied until the stand was established. Total yield decreased 7% with banded P, attributable to the decreased stand. Yield of No. I bulbs tended to increase with banded P but the increase was not statistically significant. Mean bulb weights were increased with banded P and the percentage of large bulbs tended to increase. Banding P slightly increased basal plate rots of onions in storage. Soil available P content averaged 134 ppm, a high level. The response of onions to banded P in the presence of high levels of available soil P is in agreement with results obtained for several other crops on Willamette soil, including sweet corn, bush beans, and overwintered onions. Nitrogen rate did not significantly affect yield of large onions or total yield, but in each case the trend was for the highest yields to occur at 150 pounds N/acre. Mean bulb weight and percent large bulbs were also greatest at this N rate but mean weight of large bulbs was greatest at 200 pounds N/acre. In each case, the differences were not statistically significant. Nitrogen rate did not significantly affect rotting or sprouting of bulbs in storage. 1986, Experiment 2 Banded P again tended to reduce stands but the difference was not significant. Mean bulb weight again tended to increase with banded P (Table 6). The percentage of large onions was very small in this trial, partly because of the late planting date, the slightly greater stands of 'Simcoe,' and the tendency of 'Simcoe' to form smaller bulbs than 'Granada.' Heavy incidence of mildew and blast also may have contributed to the small 'Simcoe' bulb size, only slightly greater than half the mean bulb size for 'Granada.' Yield and bulb size tended to increase with increasing N rate, but the differences were not significant. 1986, Experiment 3 Broadcast P increased yield of No. 1 bulbs and tended to increase mean bulb weight and percent of No. 1 bulbs (Table 7). Total number of bulbs harvested/plot was not affected by the broadcast P. Nitrogen rate had no effect on any component of yield. In the absence of broadcast P, the percentage of large bulbs increased linearly with increasing N rate. In the presence of P, the percentage of large bulbs was greatest at the lowest N rate. Neither N rate nor P significantly affected rots of onions in storage. No sprouting was observed. The lack of a response to N in 1986 differs from the strong yield increase up to 150 to 225 pounds N/acre seen in 1985. In the case of Experiment 3, the high base rate of N may have been optimal. In all experiments, the below normal rainfall during the growing season, particularly in June, may have prevented leaching of N from the root zone. Table 5. Main effects of N rates and banded P on yield and size of 'Granada' onion, Experiment 1, 1986 Treatment Seedling Yield Mean bulb wt. No. 1 Rot after Sprouting stand/ No. 1 bulbs All bulbs No. 1 All bulbs storage in storage foot Basal Neck ---50-lb bags/acre---- -----(g)----- ---------------%-------------- N rate (lb/acre) 100 3.2 320 762 306 230 32.8 10.1 13.3 4.3 150 3.1 362 774 309 240 38.9 10.2 15.5 2.2 200 3.2 324 762 313 233 33.7 7.1 23.4 1.0 250 3.1 348 770 312 231 33.4 8.4 13.9 8.2 NSZ NS NS NS NS NS NS NS NS P rate (lb/acre) 0 3.3 310 796 303 220 29.7 5.1 16.0 3.5 60 2.9 368 740 317 247 39.7 12.8 17.1 4.4 * NS NS * * NS ** NS NS ^ZNS, , : no significant differences, significant at the 5% level and 1% level, respectively. Table 6. Main effects of N rates and banded P on yield of 'Simcoe' onion, Experiment 2, 1986 Treatment Seedling Yield Mean bulb No. 1 stand/foot (bags/acre) wt.(g) bulbs (%) N rate (pounds/acre) 100 4.0 612 125 0.1 150 3.9 612 133 0.7 200 3.5 644 134 0.3 250 3.6 658 141 0.6 NS NS NS NS P rate (pounds/acre) 0 3.9 632 130 0.2 60 3.7 630 137 0.8 NS NS NS NS Table 7. Effects of N rates and broadcast P on yield and size of 'Granada' onion. Experiment 3, 1986 N rate P rate Yield (50 lb bags/acre) Mean bulb wt. (g) Percent % rot after (lb/A) (lb/A) Total No. 1 bulbs No. 1 bulbs All bulbs No. 1 bulbs storage Basal Neck 144 0 1047 506 336 205 28.8 4.0 1.5 184 0 859 517 338 197 29.9 8.0 5.0 224 0 898 444 310 200 32.2 4.0 7.8 264 0 1037 563 336 208 34.0 4.0 2.0 144 107 1001 545 326 212 35.4 4.0 8.0 184 107 998 515 346 212 31.5 7.8 5.3 224 107 1058 563 334 211 33.5 0.0 5.3 264 107 934 506 324 198 32.8 0.0 2.0 LSD (0.05) NS 35 NS NS 5.1 NS NS Main effects, N rate 144 lb/A 1024 525 331 208 32.1 4.0 4.8 183 929 516 342 204 30.7 7.4 5.1 223 978 504 322 206 32.9 4.0 6.0 263 986 535 330 203 33.4 4.0 2.0 NS NS NS NS NS NS NS Main effects, P rate 0 lb/A 960 507 329 202 31.2 5.0 3.8 107 998 532 333 208 33.3 2.8 5.1 NS NS NS NS NS NS Interaction NS NS NS NS * NS NS Lime and Fertilizer Effects on Overwintered Onions Cooperator: T.L. Jackson, Department of Soil Science, OSU Overwintered onions in the Willamette Valley are seeded in early September for harvest the following spring. Strong growth in the spring is essential for producing high value jumbo bulbs. However, air and soil temperatures in the spring are less than optimal, possibly limiting response to fertilizers. Phosphorus availability is limited on cold soils; thus overwintered onions might respond to applications of P fertilizers or lime, which increased P availability. Onions also have a high S requirement, but overwinter onion response to a fertilizer S source had not been previously studied in the Willamette Valley. This trial was the third in a series commencing in 1982/83. Onion yields increased markedly with liming in 1982/83 and 1983/84, both because of increased stands and to increased bulb size. Onion yield did not vary significantly with a broadcast application of superphosphate in the spring in either year, except for a very small increase in mean bulb size. Yields increased slightly with spring-applied gypsum (CaSO4) in 1982/83, indicating a possible S response. Another earlier trial resulted in slightly higher yields with ammonium sulfate (21-0-0-24) rather than ammonium nitrate (34-0-0) as N source. It was not determined whether this was a response to sulfur in the ammonium sulfate or indicated an advantage to a 100 percent ammonium-N source. The purpose of the 1984/85 trial was to further evaluate the response of overwintered onions to lime, gypsum, an at-planting banded application of superphosphate, and various sources of N. Methods Agricultural limestone (95% CaCO3 equivalent) at 0, 2, 4, and 6 tons/acre was applied in 1979 to 2,300-square-foot plots of Willamette silt loam with four replications of each lime rate in randomized block design. Soil pH in 1982, at the start of this series of experiments, averaged 5.5, 6.0, 6.2, and 6.6, respectively. Raised beds (8 inches high, 5 feet wide) were formed in early September 1984, following a broadcast application of 700 pounds/acre of 10-20-10 fertilizer, and were seeded with three rows/bed of Sweet Winter (ARCO Seed Co.) onion on September 12. The lime plots were split by application of concentrated superphosphate at 0 or 90 pounds/acre in a band 2 inches to the side and 2 inches beneath the seed row. Propachlor herbicide was applied at 4 pounds/acre at planting, and again on October 17, December 6, February 22, and May 7. Metalaxyl fungicide was applied at 8 ounces/acre on October 17 and April 4. Chloroxuron herbicide was applied on February 22. Plots were also hand-hoed twice to control grasses, vetch, and late-germinating groundsel. On February 18, gypsum was broadcast on the appropriate plots at 150 pounds/acre. Ammonium nitrate was applied at 50 pounds N/acre to all plots on February 18, March 25, and May 7. Leaf samples were collected for tissue analysis on May 1. Plants were topped and harvested on July 16. Soil samples were collected for pH determination following harvest. For the N source experiment, methods were similar to the above. Seeding was on September 11. On February 18, the appropriate plots were treated with a broadcast application of 50 pounds N/acre as calcium nitrate (15.5-0-0), ammonium nitrate, ammonium sulfate, urea (46-0-0), ammonium chloride (38-0-0), or ammonium nitrate plus 150 pounds gypsum/acre. The N treatments were re-applied on March 25 and May 7. Leaf samples were collected for tissue analysis on May 1. Plants were topped and harvested on July 16. Results As in the preceding years, onion stands increased with increasing soil pH (lime application), and this is reflected in the greater number of bulbs harvested at the higher rates of lime (Table 1). In the previous trials, most of the stand increase with lime occurred with application of only 2 tons/acre. In 1984/85, however, the stand was significantly higher at the 4 tons/acre than at the 2 tons/acre rate. This may have been because of the general decline in soil pH of the lime-treated soil over the intervening years (Table 2). The sharp decline in soil pH between 1982 and 1985 may be partially explained by the heavy applications of acid-forming N fertilizers during this time. Another contributing factor is that the sampling in 1982 occurred in the spring with saturated, well-leached soil. The 1985 sampling was on dry soil with high residual fertilizer content, which would tend to produce lower readings. Overall stands and yields were lower in 1984/85 than in 1982/83, primarily because of reduced seeding rather than reduced emergence. Liming also greatly increased the mean bulb size and percentage of large (grade No. 1) bulbs (Table 1). The combination of increased stands and greater bulb size contributed to a nearly 8-fold increase in total yield between the lowest and highest rates of lime. This confirms the 4-to 9-fold yield increases with lime in the previous years. Lime had no effect on leaf tissue concentration of K, Ca, and Cu, but reduced concentrations of N, Mg, Zn, and Mn and increased leaf S concentration (Table 3). The reduced Mg content may be a dilution effect of increased leaf growth or may reflect competition for uptake between Mg and Ca. The large reduction in Mn concentration on limed soil and the high level in tissue grown on unlimed soil indicate that Mn toxicity may play a role in poor onion growth at low pH. Banding P at planting had no effect on plant stands (Table 1), but increased the mean bulb weight, reflected in an increase in yield of grade No. 1 bulbs and the percentage of No. 1 bulbs. Total yield also tended to be increased with banded P, but the difference was not significant. This was in contrast to the previous trials, in which the response to broadcast P was very small and usually not statistically significant. Banded P reduced leaf tissue concentrations of N, S, Mn and Cu, but the differences were small (Table 3). Gypsum application slightly increased the percentage of No. 1 bulbs and mean bulb weight, but the increases were not significant. The number of bulbs harvested and total yield tended to decrease with gypsum. These results are in contrast to 1982/83, when all components of No. 1 and total yield were increased with gypsum application and the gypsum response was greatest at higher soil pH. Gypsum application increased leaf tissue N and S concentrations. There were no significant 2- or 3-way interactions of lime, gypsum, and P affecting any yield component or leaf tissue elemental concentration, thus only main effects are reported in the tables. Table 1. Main effects of lime, banded P, and gypusm on yield components of overwintered onions, 1984-1985 Stand Total bulbs No. 1 bulbs Total No. 1 Mean wt. Mean wt. Percent seedlings/ harvested/ harvested/ yield yield All bulbs No. 1 bulbs No. 1s plot plot plot Lime (tons/acre) --------------No./24 ft----------- --tons/acre- --------ounces-------- % 0 22 18 0.5 1.6 0.1 1.9 10.0 2 2 41 35 3.8 5.6 1.4 4.3 9.8 11 4 62 55 10.0 11.1 3.8 5.9 10.7 19 6 63 57 13.2 12.3 5.2 6.3 10.7 26 LSD (0.05) 9 15 5.1 2.9 0.8 0.6 0.5 9 + P 46 42 8.4 8.4 3.2 5.0 10.7 18 - P 48 41 5.3 6.9 1.9 4.2 10.1 11 NS^Z NS ** * ** * NS ** + Gypsum 47^Y 40 6.9 7.5 2.8 4.8 10.5 15 - Gypsum 47 43 6.8 7.9 2.5 4.5 10.3 14 NS NS NS NS NS NS NS NS ^Z, , NS: significant differences among means at 1% and 5% levels, and non-significant, respectively. ^YStand recorded before gypsum was applied. Table 2. Effect of liming on soil pH for samples taken in 1982 and 1985 Lime rate (tons/acre) Soil pH, 1982 Soil pH, 1985 0 5.5 4.5 2 6.0 4.7 4 6.2 5.0 6 6.6 5.2 Table 3. Effects of lime, banded P, and gypsum on onion leaf tissue elemental concentrations Treatment N P K Ca Mg S Zn Mn Cu Lime (tons/acre) ----------------%------------------- ------ppm----- 0 3.8 0.16 2.04 0.90 0.169 0.22 24 323 4.0 2 3.6 0.17 2.06 0.81 0.138 0.26 20 126 4.0 4 3.6 0.18 2.27 0.85 0.134 0.28 18 79 4.2 6 3.3 0.15 2.16 0.81 0.127 0.27 17 61 3.9 LSD(0.05) 0.4 NS NS NS 0.017 0.03 5 87 NS + P 3.4 0.16 2.09 0.83 0.141 0.24 20 140 3.7 - P 3.6 0.16 2.17 0.85 0.143 0.27 20 154 4.4 ^Z NS NS NS NS NS * * + Gypsum 3.6 0.16 2.15 0.85 0.142 0.30 20 145 4.1 - Gypsum 3.4 0.17 2.12 0.83 0.142 0.22 20 149 3.9 * NS NS NS NS NS NS NS ^Z, , NS: significant differences at 1% and 5% levels, and no significant differences, respectively. In the N source trial, the number of bulbs harvested per plot varied significantly with treatment, but the stands may have varied before the treatments were applied (Table 4). Total yield varied with N source, but the differences were not directly proportional to stand differences. Mean bulb weight and percent No. 1 bulbs were greatest with ammonium sulfate, in spite of a greater than average stand. They were lowest with ammonium chloride, in spite of a low stand. The high percentage of No. 1 bulbs and high mean bulb weight with ammonium sulfate confirms the efficacy of this fertilizer observed in 1982/83. Among the other fertilizers, there was no clear advantage for ammonium-N over nitrate-N sources. Adding the sulfur source, gypsum, to ammonium nitrate did not improve yields. Although the amount of S provided by the gypsum (36 pounds/acre) was much lower than that provided by the three ammonium sulfate applications (171 pounds/acre), it should have been sufficient to cause a yield response if S were deficient in the soil. Gypsum at this rate also did not increase yields in a parallel study of the effects of lime, P, and gypsum on overwintered onions in 1984/85. However, in a study of the effects of lime and gypsum on spring-seeded onions in 1985, this rate of gypsum increased yields significantly. Source of N had no effect on leaf tissue concentrations of N, P, K, Ca, Mg, Zn, and Cu (Table 5). Leaf Mn concentration was highest with the acid-forming ammonium chloride and ammonium sulfate. These levels of Mn are all in the normal range and should not have affected yield. Leaf S concentration was highest with ammonium sulfate or with ammonium nitrate plus gypsum, indicating plant availability and uptake of the fertilizer sulfate. Although leaf S levels were low with the other N sources, there was no correlations between leaf S levels and yield, because of the low yields with ammonium nitrate plus gypsum. While confirming that ammonium sulfate is a good spring N source for overwintered onions, this trial provided no new information on the relative importance of the ammonium or sulfate ions in providing the yield response. The increase in leaf Mn with ammonium sulfate, and tendency toward increased leaf Zn content with this fertilizer, may indicate that ammonium sulfate, through its acidifying effect on the soil, is increasing availability of micronutrients which were limited in availability on this well-limed soil. Table 4. Effect of N source on yield of overwintered onions, 1985 Total bulbs No. 1 bulbs Total No. 1 Mean wt. Mean wt. Percent harvested/plot harvested/plot yield yield All bulbs No. 2 bulbs No. 1s --------No./24 feet----------- ---tons/acre-- -------ounces---------- Amm. nit. 54 12 10.9 4.6 5.9 10.4 23 Amm. sul. 68 19 15.0 6.7 6.5 10.0 28 Cal. nit. 59 15 12.2 5.3 6.2 10.4 26 Amm. chl. 55 3 7.4 1.1 3.9 9.7 6 Urea 74 15 12.8 4.8 5.1 9.5 19 Amm. nit.+gypsum 56 11 11.1 3.8 5.8 10.0 20 LDS (0.05) 10 3 4.0 2.8 1.4 NS 14 Table 5. Effect of N source on onion leaf tissue elemental concentrations, 1985 N Source N P K Ca Mg S Zn Mn Cu ----------------%---------------- -----ppm------ Amm. nitrate 3.9 0.20 2.34 0.82 0.13 0.22 21 47 4.6 Amm. sulfate 3.5 0.19 2.25 0.80 0.12 0.37 21 61 4.3 Cal. nitrate 4.0 0.22 2.39 0.82 0.13 0.21 19 47 4.1 Amm. chloride 3.3 0.20 2.23 0.82 0.12 0.18 20 86 4.1 Urea 3.4 0.19 2.17 0.88 0.12 0.22 18 51 3.9 Amm. nit.+gypsum 3.7 0.19 2.15 0.76 0.12 0.34 18 41 4.3 LSD(0.05) NS NS NS NS NS 0.05 NS 8 NS Lime and Gypsum Effects on Spring-Planted Onions Cooperators: Robert B. McReynolds and T.L. Jackson Fertilizer trials with overwintered onions at the North Willamette Station indicated a strong yield increase with application of lime, an increase with gypsum (calcium sulfate), and higher yields with ammonium sulfate rather than other N sources. The yield response to gypsum and ammonium sulfate indicated that when soil pH, N, P, and K are optimal, S may be the limiting element in onion production. A trial on spring-planted onions in 1984 indicated increased bulb size with liming, but no yield increase, because of reduced stands at higher pH. This stand reduction was in contrast to previous results with overwintered onions which indicated improved stands at higher pH, over the pH range of 5.0 to 6.2. The mean bulb weight of the spring-planted onions increased with gypsum when calcium nitrate was the N source, but not when ammonium sulfate was the N source, indicating a response to the sulfate in the gypsum. The following trial was undertaken to further evaluate the effects of lime and gypsum on onion stands and yield, independent of N source. Methods* Lime was broadcast and disked into a Willamette silt loam at 0 or 3 tons/acre in March, 1982, with four replications of each treatment in randomized block design. Soil pH in spring of 1984 averaged 5.5 and 6.0, respectively. On April 10, 1985, 120 pounds N/acre as urea was broadcast and incorporated into the surface 2 inches of soil. On April 11, the field was seeded with 'Sure Crop' onion with 3 rows/bed on 20-inch spacing between rows. Propachlor herbicide was applied at 4 pounds/acre immediately after planting and again on June 6 and July 12. Plots were also hand-weeded twice. Stand counts were made on May 6 and again on May 13. Methomyl and diazinon (0.5 pounds/acre of each) were applied on August 16 for thrip control. The lime variable main plots were randomly split by application of gypsum at 0 or 150 pounds/acre on May 10. Each gypsum treatment was replicated twice per lime main plot. Another 60 pounds N/acre was applied to all. plots on June 4. Leaf samples were taken for tissue analysis on July 23 and soil samples for pH determination on August 6. Plants were topped and bulbs harvested on September 26 after separating into the size grades: No. 1, over 3.5-inch diameter; No. 2, over 2.3-inch diameter; No. 3, others. Results Soil pH was not measured just before planting, but soil samples taken in August indicated a drop in soil pH of about 0.5 units since the previous measurement in 1984. The difference between treatments was maintained, however (Table 1). The reduced pH probably reflects application of heavy rates of acid-forming N fertilizers following a dry winter in which normal leaching may not have occurred. In contrast to the previous year, onion stands were not affected by liming (Table 1). There were no significant lime x gypsum interaction affecting any component of yield or leaf tissue mineral content. Only main effects are reported in Tables 2, 3, and 4. Yield of jumbo (No. 1) onions was low, possibly limited by suboptimal N or by a heavy infestation of thrips. Thrip damage appeared to be less severe on gypsum-treated plots, but no damage ratings were made. Liming increased yield of No. 1 and No. 2 onions markedly, without reducing the yield of No. 3 onions (Table 2). This is because of the smaller number but greater size of No. 3 onions produced on limed soil (Table 3). Liming increased total yield by 28 percent and more than doubled the percentage of No. 1 plus No. 2 bulbs. Gypsum application also increased yield, primarily by increasing the yield of No. 2 bulbs (Table 2). Mean bulb weight of No. 1 and No. 2 bulbs tended to be increased by gypsum, even though stands at harvest were slightly increased with gypsum. Mean weight of No. 3 bulbs and all bulbs was increased by gypsum application, and the percentage of No. 1 + No. 2 bulbs was increased 35 percent with gypsum. The highest percentage of No. 1 + No. 2 bulbs (44.9 percent) was obtained with the combination of lime plus gypsum. Lime application decreased leaf N, Zn, Mn, and Mg concentrations and tended to increase leaf P and Ca concentrations (Table 4). Gypsum slightly increased leaf P concentration and increased leaf S concentration. This trial confirms the positive effect of lime on mean bulb weight found in 1984. The desirability of providing an S source is indicated by the yield increase with gypsum. This response to an S source has not been found in all experiments, however. Table 1. Effect of lime on soil pH and stand of spring-planted onions, 1985 Lime rate Soil pH Seedling stand (No./foot) (tons/acre) Spring 1984 Summer 1985 May 6 May 13 0 5.5 5.0 4.8 5.6 3 6.0 5.5 4.6 5.2 NS NS NS: no significant differences Table 2. Main effects of lime and gypsum on yield of spring-planted onions, 1985 Lime rate Yield (hundredweight/acre) Total bulbs (tons/acre) No. 1 No. 2 No.1+No. 2 No. 3 Total harvested/foot 0 0.0 63.3 63.3 127.8 191.1 3.8 3 6.2 135.2 141.4 125.1 266.5 3.8 ^Z * NS NS +Gypsum 3.7 119.2 122.9 136.6 259.5 4.0 -Gypsum 2.5 79.3 81.8 116.3 198.1 3.7 NS * * NS * NS ^Z, , NS: significant differences between means at 5% level, and 1% level, and no significant differences, respectively Table 3. Main effects of lime and gypsum on mean bulb weight and grade distribution by number, 1985 Lime rate Mean bulb weight(g) Percent by number No. 1 No. 2 No. 1+ No. 2 No. 3 All No.1 No. 1+No. 2 0 -- 158 158 72 86 0.0 17.5 3 306 170 172 92 126 1.4 38.7 NS^Z * * +Gypsum 309 167 169 90 117 0.8 33.1 -Gypsum 303 161 162 74 95 0.6 23.0 NS NS NS ** NS * ^Z, , NS: significant differences between means at 5% level and 1% level, and no significant differences, respectively. Table 4. Main effects of lime and gypsum on leaf tissue mineral concentrations, 1985 Lime rate % ppm (tons/acre) N P K Ca Mg S Zn Mn Cu 0 4.23 0.314 4.6 1.77 0.37 0.30 28 232 9 3 4.04 0.326 4.1 1.84 0.32 0.35 23 101 9 ^Z NS NS NS ** NS * ** NS +Gypsum 4.12 0.313 4.3 1.82 0.34 0.39 24 160 9 -Gypsum 4.15 0.326 4.4 1.79 0.35 0.27 26 173 9 NS * NS NS NS ** NS NS NS ^Z, , NS: significant differences between means at 5% level and 1% level, and no significant differences, respectively. Weed Control in Overwintered Onions Cooperator: Robert B. McReynolds The major cultural problem in overwintered onion production is weed control. Onions are a slow-growing crop which competes poorly with weeds. Since the crop is in the ground for eight or nine months, and cultivation is nearly impossible during the winter rainy season, both good weed control at planting and good postemergence control are necessary. The weed control task has been made more difficult by the loss of registration of effective preemergence herbicides such as propachlor. The purpose of this trial was to compare the effectiveness of two preemergence herbicides in combination with several alternatives for fall and spring postemergence herbicides. In addition to weed control rating, observations were made on onion injury and stand reduction by the herbicides and onion yield data were obtained. Methods* 'Sweet Winter' onions (ARCO Seed Co.) were seeded in 3 rows on 5-foot beds at about 20/foot on August 28, 1985. The seedbed was prepared by rotary tillage following a broadcast application of 10-20-10 fertilizer at 800 pounds/acre, and gypsum at 100 pounds/acre. Either Dacthal at 10 pounds active/acre or Ramrod at 4 pounds active/acre was applied on August 29 and irrigated in. These main plots consisted of 3 beds x 80 feet and were replicated four times in randomized block design. On October 11 the plots were split by four postemergence ("fall application") treatments. These were oxyfluorfen (Goal) at 0.125 pounds/acre, oxyfluorfen plus cultivation between rows on October 2, pendimethalin (Prowl) at 0.5 pounds/acre, or pendimethalin plus cultivation. The resulting subplots consisted of 3 beds x 20 feet. All plots received an application of oxyfluorfen at 0.125 pounds/acre on January 6, 1986. The "fall application" subplots were split by "spring" application of oxyfluorfen at 0.125 pounds/acre, chloroxuron (Tenoran) at 3.0 pounds/acre, or ureasulfuric acid (N-Tac) at 15 gallons/acre (30 gallons/acre total volume) on February 21, 1986. The resulting sub/subplots consisted of a 20-foot section of a single bed. On April 8, 1986, all plots received an application of metolachlor (Dual) at 2.25 pounds/acre. All herbicide applications were followed by rainfall or at least 0.5-inch irrigation. An additional 100 pounds N/acre was applied as ammonium nitrate in February and March. Weed control and crop injury ratings were made after each treatment. Bulbs were topped and harvested on July 16, 1986. Results and Discussion The preemergence herbicides had no effect on seedling stand (Table 1). Weed control ratings were first made on October 1, 1985. Each bed was scored separately within each main plot. Weed control was clearly far superior with Ramrod as compared to Dacthal (Table 1). Dacthal provided good control of chickweed but little control of Poa annua, groundsel, dog fennel, shepherdspurse, and mustards. Ramrod also provided inadequate control of knotweed and the larger grasses, but these were not a problem in most of the plot area. Ramrod provided very little chickweed control. Weed control ratings were made again two weeks after the "fall application" of herbicides and cultivation of appropriate plots. For the main effect of the preemergence application, Ramrod was again clearly superior (Table 2). Goal provided superior burn down of escaped weeds, especially shepherdspurse and groundsel, but had no effect on grasses or chickweed. Cultivation had no effect on weed control ratings as the soil moisture was too high to get good weedkill from the cultivation alone. Some plots receiving Ramrod and Goal were essentially weed-free at this point. There were no significant interactions affecting weed control between preemergence and fall herbicide treatments or between the fall-applied herbicides and cultivation. Only main effects are given in Table 2. Dacthal and Ramrod had no significant effect on onion injury rating, but Goal injured the onions more than did Prowl. The Goal stunted and twisted the onion leaves. Cultivation tended to reduce Goal and Prowl injury slightly, probably by shielding the onion leaves from the herbicide spray or by providing more cover for the roots. There were no significant interactions and only main effects are given in Table 2. Table 1. Effects of Dacthal and Ramrod at planting on weed control rating on October 1, 1985, and on onion seedling stands Seedlings/foot Weed control rating^Z Dacthal 10.6 2.7 Ramrod 10.9 7.2 NS^Y * _______________________________________________________________ ^ZTen point scale, 9 = no weeds, 0 = no control. ^YNS = no significant difference, = difference significant at 1% level. Table 2. Main effects of preemergence and "fall" herbicide applications and cultivation on weed control and onion injury on October 25, 1985 Weed control Onion injury^Z Dacthal 3.0 2.1 Ramrod 5.4 1.8 Y NS Goal 5.6 2.8 Prowl 2.7 1.1 Cultivated 4.1 1.8 Non-cultivated 4.2 2.1 NS * ^ZFive point scale with 0 = no injury, 4 = seedling destroyed. ^Y*, , NS: differences significant at 1% and 5% levels, and no significant differences, respectively. The "spring" herbicide applications were made between February 21 and 26, 1986. There were no interactions between preemergence, fall and spring applications, so means given in Table 3 are main effects only. Weed control was rated on a 0-9 scale with 9 being weed free. Onion stands and vigor were rated on a 0-5 scale, with 5 the most desirable rating. Notes were also taken on weed species in each plot. Goal spotted grass leaves but did not kill the grasses. Tenoran was ineffective on grasses but controlled chickweed. N-Tac provided no control of established weeds. Ramrod controlled most grasses and Dacthal plots were still free of chickweed. No difference was expected at this time between the fall treatments (Goal vs. Prowl) since all plots had a Goal treatment in January. Looking at simple effects, the highest mean weed control ratings were obtained with Ramrod + Goal (no cultivation) + Tenoran (8.25), followed by Ramrod + Goal + cultivation + Tenoran (7.6), followed by Ramrod + Prowl + cultivation + Tenoran (7.25), followed by Ramrod + Prowl (no cultivation) + N-Tac (7.0). The lowest mean rating was for Dacthal + Goal (no cultivation) + N-Tac (1.5), followed by Dacthal + Prowl + cultivation + Tenoran (2.5). The best combinations using Dacthal at planting were Dacthal + Goal (no cultivation) + Tenoran (5.5), and two with a score of 5.0: Dacthal + Goal + cultivation + Goal and Dacthal + Prowl + cultivation + Tenoran. Ramrod and Goal both reduced the stand rating and reduced onion vigor. Lowest vigor was on plots receiving Ramrod and two or three applications of Goal. There was a strong negative correlation between weed control rating and onion vigor rating (Rxy = -0.638, p=0.001). However, the very best vigor ratings did not coincide with the worst weed control. Vigor was usually highest on plots with high populations of low growing Poa annua or chickweed, but few large weeds. Table 3. Weed control, stand, and vigor ratings on March 17, 1986 Herbicide Weed Onions/ Onion Major weeds control foot vigor present Dacthal 3.8 3.1 3.0 Poa, grasses, groundsel Ramrod 6.6 2.6 2.4 chickweed, groundsel, Poa Goal 5.2 2.0 2.1 Poa,grasses, chickweed Goal+Cultivation 5.6 2.3 2.5 Poa, grasses, chickweed Prowl 4.7 3.4 2.9 Poa, grasses, groundsel, chickweed Prowl+Cultivation 5.3 3.7 3.3 Poa, grasses, groundsel, chickweed NS ** Goal 5.2 2.6 2.4 Poa, grasses, chickweed Tenoran 5.6 2.9 2.7 Poa, grasses, groundsel N-Tac 4.9 3.0 3.0 Poa, chickweed, grasses, groundsel NS NS * The reduced stand ratings with Ramrod at planting (Table 3) or Goal applied in the fall were reflected in lower numbers of bulbs present at harvest (Table 4). The main effect of Ramrod at planting, when averaged over the other herbicide treatments, was to slightly reduce the total number of bulbs, increase the number of large bulbs, and increase mean bulb weight, grade 1 yield and total yield as compared to Dacthal (Table 4). Since the stand reduction with Ramrod was very small, the yield increase can be attributed to improved weed control. Goal, when compared to Prowl, reduced stands by more than 50 percent, and decreased both total and grade 1 yield. Mean bulb weights were greater with Goal. This increased bulb weight could be caused either by reduced competition among onion plants or by superior weed control. Cultivation in the fall prevented stand reduction and tended to increase bulb weight, resulting in highly significant increases in total and grade 1 yield. Cultivation may have shielded the onion plants from spray damage. Prowl produced a higher number of grade 1 bulbs/plot than did Goal when following Ramrod, but not when following Dacthal (Table 5). This can be attributed to the relatively greater impact on weed control of Goal following Dacthal than Goal following Ramrod. Main effects of the spring-applied herbicides on yield were not significant (Table 4), but the trend was toward greatest yields with Tenoran. There were interactions of herbicides at planting with spring-applied herbicide affecting several components of yield (Table 6). Total yield and number of grade 1 bulbs/plot were highest with Tenoran following Ramrod but not following Dacthal. Since the major effect of Tenoran was to burn down chickweed and Ramrod-treated plots contained more chickweed than did Dacthal-treated plots, the greater effect of Tenoran following Ramrod was to be expected. The highest yielding treatments were Ramrod + Prowl + cultivation + Tenoran, Ramrod + Prowl + cultivation + Goal, Ramrod + Prowl + Tenoran, and Dacthal + Prowl + cultivation + Goal (Table 7). Each of these except the last produced much better than, average weed control. The correlation of total yield and weed control rating made in March was not strong, however (Rxy =0.291, p=0.085). This is to be expected since stands were often reduced with those treatments producing excellent weed control. The yield of grade 1 bulbs (Rxy =0.35, p=0.005) and mean bulb weight (Rxy =0.63, p=0.001) both correfXted strongly with weed control rating. xYhe major weeds present at harvest were grasses, dog fennel, and chickweed (except on Tenoran-treated plots). In summary, these results confirm that loss of use of Ramrod and Tenoran as onion herbicides greatly increases the difficulty of growing a successful crop of overwintered onions. Goal is promising as a postemergence burn down treatment but may injure the crop. N-Tac provided little weed control in this trial, but its contribution to the N needs of the crop must be considered. The Prowl used in this trial was old, with crystals precipitating out. This material deserves further investigation. Table 4. Main effects of weed control programs on yield and bulb size of overwintered onions, July 16, 1986 Yield Mean bulb wt. No. of bulbs/plot Timing Herbicide Grade 1 bulbs^Z All bulbs Grade 1 All Grade 1 All __________________________________________________________________________________ --------tons/acre-------- ----ounces--- Planting: Dachthal 1.5 9.6 19.5 2.9 3.4 89.4 Ramrod 4.5 14.9 10.0 4.7 11.2 81.2 ^Y NS NS Fall: Goal 2.4 8.4 10.6 4.1 5.7 55.5 Prowl 3.5 16.1 9.6 3.5 8.9 115.1 * ** * * * Cultivated 3.9 15.0 10.2 3.9 9.7 96.8 Non-cultivated 2.0 9.6 10.0 3.6 4.9 73.9 NS NS * Spring: Goal 3.0 12.1 10.4 3.9 7.2 82.5 Tenoran 3.6 13.6 9.9 3.8 8.8 89.2 N-Tac 2.4 11.7 9.9 3.6 5.8 88.2 NS NS NS NS NS NS ^ZOver 3-inch diameter. ^Y*, , NS: Means differ significantly at 1% and 5% levels, and no significant differences, respectively. Table 5. Interaction of herbicides at planting and fall herbicide applications on number of grade 1 bulbs/plot, July 16, 1986 Herbicide No. of grade Planting Fall 1 bulbs/plot Dacthal Goal 2.0 Goal + cultivation 5.1 Prowl 2.6 Prowl + cultivation 4.0 Ramrod Goal 4.6 Goal + cultivation 11.0 Prowl 10.4 Prowl + cultivation 18.8 LSD (0.05) 5.6 Table 6. Interaction of herbicides at planting and spring herbicide applications on total onion yield, mean weight of grade 1 bulbs, and number of grade 1 bulbs/plot, July 16, 1986 Herbicide Total yield Mean wt. of No. of grade 1 Planting Spring (tons/acre) grade 1 bulbs (ounces) bulbs/plot Dacthal Goal 11.0 10.6 4.8 Tenoran 8.1 10.4 2.5 N-Tac 10.4 9.3 3.0 Ramrod Goal 13.1 10.1 9.6 Tenoran 19.1 9.4 16.0 N-Tac 13.0 10.5 8.4 LSD (0.05) 4.0 1.0 4.9 Table 7. Simple effects of all treatment combinations on yield of grade 1 bulbs, total yield, and mean bulb weight, July 16, 1986 Herbicide Total yield Grade #1 yield Mean bulb Planting Fall Spring wt. ----------tons/acre--------- ounces Dacthal Goal Goal 4.7 1.3 2.6 Tenoran 1.5 0.3 2.3 N-Tac 4.7 0.5 2.0 Goal+Cult. Goal 2.8 1.4 6.5 Tenoran 6.7 1.2 2.2 N-Tac 9.1 2.7 3.1 Prowl Goal 12.6 1.6 2.6 Tenoran 6.7 0.7 3.4 N-Tac 11.7 0.3 2.0 Prowl+Cult. Goal 16.6 2.6 3.2 Tenoran 12.0 1.2 2.3 N-Tac 9.0 0.5 2.6 Ramrod Goal Goal 6.6 2.9 5.1 Tenoran 4.3 2.8 5.6 N-Tac 6.7 3.1 4.0 Goal+Cult. Goal 9.0 4.7 4.4 Tenoran 15.3 5.8 5.8 N-Tac 14.5 3.8 4.8 Prowl Goal 9.9 1.5 3.3 Tenoran 17.2 5.0 3.9 N-Tac 13.9 4.1 4.5 Prowl+Cult. Goal 24.5 8.3 4.6 Tenoran 25.8 6.6 4.6 N-Tac 9.4 2.1 3.8 LSD (0.05) 8.0 4.0 2.7 Response of Cucumber to Floating Row Covers and Herbicides Cooperators: Garvin Crabtree and N. S. Mansour Crop protection with floating row covers interferes with tillage or other means of weed control. Therefore, herbicides or ground mulch are the likely means of weed control under covers. A successful weed control program depends on understanding the environmental and physiological interactions between the herbicide and other components of the cropping system. Results in 1983 with bunching onions (N. S. Mansour) indicated that paraquat residues on row covers might injure the subsequently emerging crop. It is also possible that row covers could alter the effectiveness of an herbicide program because of changes in soil moisture and temperature, more rapid weed seed germination, and decreased crop resistance to the herbicide in the warm, moist row cover environment. The primary objective of this research was to broaden the information base available on the use of the currently accepted cucumber herbicide combination in conjunction with row covers and to evaluate the possibility of applying the contact herbicide paraquat through the covers. A second objective was to generate new information on the yield response of cucumbers to floating row covers and black plastic ground mulch. Methods Five weed control treatments [non-weeded, hand-weeded, bensulide plus naptalam (BN), bensulide plus naptalam plus paraquat (BNP), and black plastic ground mulch (GM)] were factorially combined with three row cover treatments (no cover, Reemay, Vispore) in randomized complete block design with four replications. The sequence of events is outlined below. On April 24, 1985, and April 23, 1986, beds were formed by rotary tillage of a Willamette silt loam following application of a 14N-6.1P-11.7K fertilizer at 1,000 pounds/acre. On April 25, bensulide (Prefar) and naptalam (Alanap) were applied to the appropriate plots (1 bed x 4 m) at 5.0 and 3.0 pounds active ingredient/acre, respectively, in 100 gallons water/acre. The entire plot area was then rototilled to a depth of 2 inches to incorporate the herbicides. Biwall drip irrigation tubing with emitters at 12-inch intervals was laid the length of each bed, followed by application of 1.5 mil x 4 foot GM to the appropriate plots. In 1985, plots were seeded with 'Sweet Success' parthenocarpic cucumbers at 5 hills/plot, 2 seeds/hill, on April 26. Reemay and Vispore row covers were applied to the appropriate plots on April 29. On May 6, paraquat was applied to the BNP plots at 1 pound/acre and also to the hand-weeded plots as a substitute for weeding. First emergence of cucumber seedlings was on May 8, but frosts on May 11 and 12 (29°F) reduced stands considerably. The decision was made to replant with transplants. Paraquat was re-applied to BNP and hand-weeded plots on May 17. On May 20, the entire plot area was replanted with greenhouse-grown transplants, 5/plot, which had been seeded on April 30. Row covers were removed on June 11 and harvesting commenced on June 21. An additional 30 pounds N/acre as ammonium nitrate was sidedressed around the plants on June 24. A 30N-4.3P-8.3K soluble fertilizer was applied through the drip system at 100 pounds/acre on July 22. Air and soil temperatures were recorded from April 30 until June 11, 1985, for all combinations of row covers with GM or bare ground. Thermocouples were installed at 1.0-inch depth in soil and 1.0 inch above the soil surface. Temperatures were recorded every half hour with a Leeds and Northrup Speedomax 250 recorder. Soil mechanical resistance or crusting was measured with a Technicon Products Co. penetrometer one day before cover removal. Cucumbers were harvested two or three times a week from June 21 until September 23, when yields and quality declined markedly. Each fruit was weighed separately to determine variability in fruit weight. Yields reported here include only marketable fruit (more than 200 grams, straight). Cull fruit were not recorded, but the number appeared to be less than 20 percent for all treatments until late in the season. Weed control ratings were made at cover removal on June 11. Weeds were counted by species on June 13. In 1986, row covers were applied on May 8 and paraquat was applied to the appropriate plots on May 14. The cucumbers were transplanted on May 16 after lifting one edge of the covers. Covers were removed on June 6 and harvest started on June 13. Fruit was harvested weekly until August 20. Weed control ratings were made on June 9. Results Air and Soil Temperatures. Plastic ground mulch alone increased daily mean air and soil temperatures by nearly 2°F in 1985 and by over 4°F in 1986 (Tables 1 and 2), but the effect of the GM on average maxima and minima differed for air and soil temperatures. GM increased the average daily maximum air temperature but daily minima were not affected. In contrast, daily maximum soil temperatures were not greatly affected by GM, but minimum temperatures increased by an average of nearly 4°F in 1985 and 6° in 1986. Reemay and Vispore alone increased both air and soil temperatures and the combination of row covers with GM produced the highest temperatures. Heat unit accumulation more than doubled with either Reemay or Vispore plus GM. While the effects of row covers on mean temperatures were substantial, seedling loss to freezes on May 11 and 12, 1985 was severe. Weed Control. The bensulide plus naptalam herbicide combination provided adequate weed control on most plots for up to four weeks after planting. The herbicides were much less effective on row-covered plots (Tables 3 and 4), but this may have been due primarily to row cover stimulation of weed growth rather than earlier breakdown of the chemicals. The reduction in weed control rating with row covers was similar for both weedy and BN plots, indicating no significant row cover x BN interaction. Thus, there was no evidence that row covers caused premature breakdown of BN activity. No sign of BN damage to cucumbers was noted, either with or without row covers. Row covers tended to bring on early germination and growth of pigweed and other weeds which are normally not a problem until summer. BN provided partial control of most species, without a major shift in weed species present. The BNP combination provided significantly improved weed control compared to BN alone when row covers were present. The BNP x row cover interaction was significant in 1985: weed control was poorer with row covers for weedy or BN plots, but weed control ratings were as good or better with row covers compared to bare ground when paraquat was added to the control program. It is possible that additional weed control was provided by paraquat adhering to the row covers. This explanation is unlikely, however, since no crop damage from paraquat residues was noted. The more likely explanation is that the paraquat was particularly effective with row covers because weeds emerged earlier under row covers and these flushes of weed growth were damaged or eliminated by the paraquat. Weeds may also have been more sensitive to paraquat under the row covers. Emerged weed seedlings and cucumber seedlings surviving the May 11 and 12 frosts were severely damaged or killed by the paraquat application of May 17, indicating that this form of "stale seedbed" technique is possible with Reemay and Vispore. In most situations crop emergence would occur simultaneously with or closely follow weed emergence, so that a post-plant paraquat application would not be practical. An alternative for certain crops would be to spray milder contact herbicides such as chloroxuron, linuron, oxyfluorfen, and fluazifop through the row covers after crop emergence. Soil Mechanical Resistance. Visual observations in past experiments indicated that row covers might act as an anticrustant and maintain the aggregate structure of soil particles at the soil surface, perhaps by breaking the impact of rainfall or irrigation water or by maintaining soil surface moisture. These observations have now been confirmed (Table 5). Both GM and row covers reduced soil crusting as measured by penetrometer, with Reemay providing slightly more reduction in crusting than did Vispore. Plant Development. Seedling emergence, recorded on May 8, 1985, did not vary significantly with weed control treatment, but increased with row covers (Table 5). Following the freezes of May 11 and 12, the reduction in stand under row covers was similar to that on bare ground, indicating that the row covers did not provide adequate frost protection in this situation. Stand reduction with Reemay tended to be slightly greater than with Vispore, so that there was a significantly higher stand on Vispore-covered plots than on Reemay-covered plots when stands were re-evaluated on May 16. This result is in accord with the slightly higher mean soil and air temperatures recorded under the Vispore (Table 1). However, the minimum air temperature recorded during the freeze was 31°F for both row cover materials. After setting transplants on May 20, only insignificant plant losses occurred and stands did not vary with treatment. Weather conditions were nearly ideal in late May and early June for obtaining a response to row covers. Temperatures were mild and solar radiation was higher than normal. The effect of GM and row covers on development of the transplants can be seen in the number of flowers/plant on June 14 and the days to first fruit harvest (Table 5). GM alone did not affect early flower production but did reduce time to first harvest by 4 days compared to the hand-weeded plots. Reemay and Vispore significantly increased the number of flowers/plant and reduced time to first harvest by 7 to 8 days, respectively, in 1985 and 9 days in 1986 (Table 7). The earliest harvests occurred with the combination of GM and Reemay. Early Yield. Both weed control program and row covers affected the very early yield (by July 1). Numbers of fruit from GM plots were greater than for any other weed control treatment, presumably because the GM affected temperatures and soil moisture as well as providing perfect weed control. Reemay and Vispore, when averaged over weed control treatments, increased very early yield by five to seven-fold in 1985 and more than two-fold in 1986, with the plants with a combination of Reemay or Vispore with GM significantly outyielding all other treatments (Tables 6 and 7). Similar yield responses were obtained for cumulative yields through July 15. In both years, the highest yields were with GM and Vispore, followed by GM plus Reemay, and GM alone. Averaged across all weed control treatments, the yields from Reemay and Vispore-covered plots did not differ significantly. Among weed control treatments, GM plots had by far the greatest yield, again indicating the additional benefits of GM. Herbicide-treated and hand-weeded plots significantly outyielded the non-weeded plots, indicating significant weed competition with the crop on non-weeded plots. BNP plots tended to outyield BN plots, in agreement with the superior weed control of the BNP combination. Row covers did not affect mean fruit weight. Among weed control treatments, mean fruit weight was highest with GM, intermediate with hand weeding or herbicide, and lowest on non-weeded plots. Total Yield. There were no significant interactions of weed control program and row covers in 1985. Only main effects are shown (Table 8). However, although not quite statistically significant, there was a tendency (P=0.06) in 1985 for yields to decrease with row covers on non-weeded plots, presumably because of increased weed competition. For the other four weed control treatments, yields consistently increased with either row cover. In 1986, this interaction was highly significant (Table 9). Row covers reduced yields on non-weeded, BN, and BNP plots but increased yield on hand-weeded GM plots. The highest cumulative yields in 1985 were with GM plus Vispore (32.7 fruit/plant), GM plus Reemay (27.7), hand-weeded Reemay (26.5), and hand-weeded Vispore (25.3). In 1986, the two highest yielding treatments were the same as in 1985, but the non-covered GM treatment produced the third highest yield. When averaged over all weed control treatments, row covers increased the number of fruit harvested by about 20 percent in 1985 and 10 percent in 1986, without significantly reducing mean fruit weight. The percentage of large fruit (over 400 g) was reduced slightly by row covers, probably because of increased competition among the greater number of fruit present. Row covers had no effect on variability in fruit weight. Among weed control treatments, GM produced the highest yields, with BNP again intermediate between hand-weeded and BN plots. Fruit size as well as number was reduced on non-weeded plots. Variability in fruit size, expressed as the coefficient of variation, tended to be highest with GM and lowest for non-weeded and hand-weeded plots. The lower level of variability on non-weeded plots was expected since the absence of significant numbers of large fruit tends to cluster fruit weights nearer the mean. The higher degree of variability for cucumbers on GM than on hand-weeded plots was not expected. The higher proportion of very large fruit and the very rapid development of fruit size on the GM plots may have contributed to a tendency to harvest at a more advanced stage of maturity. Economic Return. As early as July 15, the additional materials costs of row covers (estimated at $600/acre) as well as any of the weed control practices ($200/acre for GM, less than $50/acre for herbicides) were easily recovered through increased yield (Tables 10 and 11). This analysis is very conservative since it assumes no price premium for early production and a low plant population of only 3,630/acre. The economic advantage of row covers was maintained throughout the 1985 season since previously row-covered plants continued to outyield the plants which had not been covered. In 1986, gross returns were not increased by row covers for BN, BNP, and non-weeded plots. Highest projected gross returns/acre i