Overwintering Onion Variety Trial, 1980-1981

The purpose of this experiment was to evaluate the performance of several Japanese onion cultivars in overwinter trials. The Willamette Valley appears to have a suitable climate for production of spring-harvested onions if bolting, disease, and weed control problems can be overcome. Previous experiments at the North Willamette Station have indicated that late August planting dates are superior to September planting dates for maximum yields. With a June harvest, this would allow double-cropping the onion ground.


The cultivars evaluated were Amber Express, Dragon Eye, Express Yellow, Imai Early Yellow, Kaizuka Extra Early, Keep Well, and Senshyu Yellow Globe, all from Takii & Co., Ltd., Kyoto, Japan. The plots were seeded on August 30, 1979, with a plant population of about 15/foot. Subplot 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 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.


Table 1. 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.  

The timing of the spring N application did not significantly affect the yield of any onion cultivar 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 2. 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