Effect of Five Planting Dates on Yield of Six Sweet Onions

Transcription

1 Effect of Five Planting Dates on Yield of Six Sweet Onions Dr. Ron Goldy Southwest Michigan Research and Extension Center Benton Harbor, Michigan Objective: The main objective of this trial was to determine if direct seeding of sweet onions would produce adequate bulb size. A secondary objective was to determine how planting date influences bulb size and yield. Summary: Direct seeding six sweet onions did not result in adequate commercial yield for any of the six. However, transplants did have adequate size and yield. Growers wanting to reliably produce sweet onions of adequate size in Michigan should rely on transplants. Of the five planting dates (April 2, 9, 20, May 3 and 13) only April 9 was among the best dates for all entries. April 9 stood alone as the best date for Ovation. May 13 was the worst planting date for all entries. More research on other factors contributing to yield (fertilizer, irrigation and others) is needed before direct seeding of sweet onions can be recommended. Methods: Fertilizer: Prior to planting, nitrogen, sulfur and Cal-fortified (10Ca-6Mg-5S-2Fe-3Zn) were broadcast at 60, 25 and 100 pounds per acre, respectively. After planting, nutrients were applied weekly through the drip irrigation system with Nitro Plus 18 (18N- 5Ca-1.5Mg and a proprietary growth regulator) starting the week of May 28 and ending the week of August 2, providing 148 pounds per acre total nitrogen. Weed control: Due to multiple planting dates, weeds were difficult to control using chemicals. Therefore, weed control was primarily by hand hoeing but Select was applied once to help control grass weeds. Planting: Six onion cultivars were direct seeded April 2, April 9, April 20, May 3 and May 13, 2010 into four-row beds with 6-feet from bed center to bed center. Rows were one-foot apart with four-inches between seed (approximately 87,000 plants per acre). Plots consisted of two rows 10-feet long and were planted as a completely randomized design with four replications. For comparison, transplants of the cultivars were also started in the greenhouse February 26 and planted to the field May 4. Transplants were for observational comparison only. Plant care: Plots were irrigated daily through a drip line placed between the rows (two rows/line) and pests controlled using standard commercial practices.

2 Harvest and data collection: Plots were harvested and tops removed in the field when bulbs were mature. Bulbs were allowed to continue to dry and dirt and outer, loose skin removed before grading and weighing. Transplants were harvested August 12 and seeded plots harvested as bulbs matured from late August through early September. Results: The six cultivars evaluated were chosen due to their past good performance in transplant trials. The six continued to perform well in the 2010 observation trial (Table 1). There was a range of 52 to 81 pounds for the weight of the 100 random bulbs evaluated (Table 1). Ovation, Aruba and Desperado each had colossal bulbs ( ) while Western Giant, Red Defender and Solid Gold did not. Red Defender matured later than the other five. For comparison, 100 random bulbs from direct seeded Ovation and Desperado were also evaluated. Most bulbs from the direct seeded entries were graded into the medium category ( ), neither had any colossal bulbs. Statistical comparisons were not made within the transplanted trial or between the transplanted and direct seeded trials. Table 1. Evaluation of 100 bulbs from six sweet onion cultivars grown as transplants (T) or directly seeded (S) at the Southwest Michigan Research and Extension Center in Benton Harbor, Michigan in Weights are in pounds. Plant population was approximately 87,000 plants per acre. Variety Total Weight Avg. Bulb Weight Colossal Jumbo Medium Small <2.0 Ct. Wt. Ct. Wt. Ct. Wt. Ct. Wt. Ovation (T) Ovation (S) Aruba (T) Desperado (T) Desperado (S) Western Giant (T) Red Defender (T) Solid Gold (T) Statistical comparison between cultivar performances has not been made at this time. Those comparisons have been made in previous trials and the six cultivars were chosen due to previous transplant performance. The primary objective of this trial was to determine which planting date (if any) had the highest potential for producing adequate commercial yields for each cultivar, and attempt to connect performance to any event (rain and/or temperature, plant growth prior to bulbing, etc.) that might influence performance. The earliest possible planting time is generally thought best for Michigan onions. However, weather conditions often make it difficult to get fields ready much

3 before early April. This gives a short window for germination and growth to occur prior to long-day onions receiving the bulbing signal in May. Differences between planting dates within cultivars was observed (Table 2, Figure 1). The second planting date of April 9 was among the best dates and the last planting date of May 13 was the worst across all cultivars. Ovation was the only entry to have a single planting date (April 9) statistically better in total yield than the other four dates. Table 2. Best planting date/s for total hundredweight of six sweet onion cultivars planted at the Southwest Michigan Research and Extension Center, Benton Harbor Michigan in Variety Best Planting Date For Total Yield Western Giant April 9, April 20, May 3 Ovation April 9 Red Defender April 2, April 9, April 20 Solid Gold April 9, April 20 Aruba April 2, April 9, April 20, May 3 Desperado April 2, April 9, April 20, May 3 Those entries having low yield and bulb size generally had less separation between planting dates, indicating these cultivars may be poor candidates for direct seeding. Low total yield is a function of small bulb size and low bulb counts. Each plot had the capability of producing at least 60 bulbs. No effort was made to adjust for low bulb counts. Since seed of each cultivar had an equal opportunity to germinate and grow, it was determined lack of plants was a function of adaptability similar in importance to growth and therefore should be an equal factor in determining economic potential. Correlating weather or other events with why some planting dates were better than others is difficult. Low yield at the final planting date was likely due to late planting. Why April 9 was among the best across all cultivars is unclear. Average soil temperatures during germination and emergence ranged from 56.6 o F for April 2 to 65.7 o F for May 13. The common best date of April 9 had an average soil temperature of 57.3 o F. Shortly after planting, the April 2 planting received of rain while the April 9 planting date did not receive rain until toward the end of seedling emergence. The May 3 planting had during the same phonological time period. The April 20 planting had close to one-inch with half occurring shortly after planting and half at emergence. Of the cultivars evaluated Ovation, Solid Gold and Aruba probably have the best chance at producing the size and yield needed to be economical for direct seeding. Further research is needed since yield and size is still not adequate at this time. Research will continue on nutrient application and timing and irrigation management.

4 Planting date and yield (hwt) for six onion cultivars Total Hundred Weight Apr 9-Apr 20-Apr 3-May 13-May Planting Date Western Giant Ovation Red Defender Solid Gold Aruba Desperado Figure 1. Yield in hundred weight per acre for total yield in relation to planting date of six sweet onions grown at the Southwest Michigan Research and Extension Center in Benton Harbor, Michigan in Plant population is approximately 87,000 plants per acre.

5 Direct seeded Ovation sweet onion planted April 2, 9, 20 and May 3 and 13, left to right, respectively. Transplanted onions: left to right; top row: Solid Gold, Red Defender and Desperado ; Bottom row: Aruba, Western Giant and Ovation.