Methods
All varieties evaluated were from Takii & Co., Ltd., Kyoto, Japan. The plots were seeded on August 30, 1979, with a plant population of about 15/foot. Plot size was two rows x 12.5 feet with 1.5 feet between rows. The plot area was fertilized with 500 pounds/acre of 13-39-0 before planting and four pounds/acre of propachlor (Ramrod) herbicide was applied immediately after seeding. An early (1) and a late (2) spring nitrogen application was made as follows: (1) 300 pounds/acre of 34-0-0 on January 2, 1980, and again on February 15, 1980; (2) 300 pounds/acre of 34-0-0 on February 20, 1980, and March 20, 1980. The fertilizer treatments were applied in a randomized block design with four replications and with cultivars as subplots. All plots were harvested on June 10, 1980, after most tops had died back. Plant population at harvest was 10-13/foot.
Results
The timing of the spring N application did not significantly affect the yield of any onion cultivar (Table 3) but the later application slightly delayed maturity. The highest yielder, Keep Well, had elongated bulbs. Express Yellow and Dragon Eye had the most desirable characteristics of the higher yielding cultivars (Table 4).
Table 3. Effect of Timing of N Application on Yield of Onion Cultivars Yield, tons/acre Cultivar Early N application Late N application Mean, cultivar Amber Express 13.7 13.6 13.7 bcZ Dragon Eye 14.3 14.7 14.5 bc Express Yellow 14.5 15.0 14.8 c Imai Early Yellow 11.8 11.7 11.8 ab Kaizuka Extra Early 11.9 11.1 11.5 ab Keep Well 16.2 15.6 15.9 c Senshyu Yellow 10.8 10.6 10.7 a Mean, N application 13.3 13.2 ZMeans followed by same letter not significantly different at 95% confidence level. Table 4. Notes on Onion Quality Characteristics Two Weeks before Harvest Cultivar Maturity rank Mildew susceptibility Uniformity Percent bolted Amber Express 1Z 2Y 3X 0 Dragon Eye 5 4 3 2 Express Yellow 2 4 5 0 Imai Early Yellow 7 4 3 4 Kaizuka Extra Early 4 3 3 4 Keep Well 6 4 4 4 Senshyu Yellow 3 4 4 2 Z1 = most mature, 100% of tops down and dry; 7 = least mature, 25% of tops down Yl = most susceptible, 5 = least susceptible Xl = least uniform bulb size and shape, 5 = most uniform