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The soil had a cation exchange capacity of 20 meq/100 g and received fall fertilization of 80 lb N/acre and 100 lb/acre of phosphate as 16-20-00. Spring N fertilization consisted of 170 lb N/acre as ammonium nitrate.
Onions were lifted September 8, and the onions were harvested from September 18 through 20, 1997.
Treatments were as follows all out of the same field of Vega onions, 6 bins stored per treatment:
All onions were stored in the same storage at the Malheur Experiment Station. Onions were graded out of storage on January 7, 8, and 9, 1998. Onions were separated by mechanical injury, Botrytis infection including neck rot, black mold, plate rot, sprouted onions, and healthy onions. The healthy onions were graded into split double onions, and by diameter into small, medium, jumbo (3-4 inches) and colossal sized onions. Onions were rated subjectively for color, top retention, and skin retention out of storage.
Untopped onions had 1.07 percent tops out of storage and less total pack out in terms of weight per bin because there were 13 percent fewer onions in each bin. Untopped onions held their skins well, had the lowest percent of mechanical injury and a low amount of black mold. Untopped, hand topped, and topper/loader treatments were among the best in percentage of pack out (Table 2).
The topper/loader treatment had only 5.2 percent defective onions (Figure 1) and was among the lowest total shrink losses and was among the best in percentage pack out, 90.2 percent (Table 2). It would be desirable for growers to be able to reduce harvest cost while retaining onion quality in storage and pack out. One-time-over mechanical harvest with the topper/loader reduced onion damage without affecting storability as compared to onions that were windrowed then further cured before loading. This trial could be repeated over several years for a higher level of confidence in application of the experimental results to commercial production.
Over all bins, independent of topping and loading, the percent of loss to black mold tended to occur in the same bins with the highest percent of mechanical injuries recorded on different onions. This may be a factor of wider importance to the industry: rough handling and the loss of skins through handling could predispose onions to greater risks of losses from decomposition in storage.
At pack out, onions from each topping and handling treatment were set aside for subjective evaluations of color and skin retention (Table 2). Topper/windrower onions that were windrowed then loaded appeared lighter in color because less skin was retained. These onions suffered more damage in the grading process than the other treatments and were not as attractive a commercial product as the onions in the other four treatments.
||Botrytis mold||Plate rot||Black mold||No. 2||Sprouted||Mechanical injury||Defective|
|Topper/loader in one pass||4.4||0.11||0.39||0.01||0.01||0.3||5.2|
|Topper windrower then loader||6.63||0.09||0.86||0.05||0||1.3||8.9|
|Flail then loader||6.94||0.01||0.19||0||0||0.2||7.3|
|Hand topped then hand load||4.49||0.03||0.2||0.02||0||0.5||5.2|
|Untopped then hand load||5.12||0.04||0.01||0||0||0.1||5.3|
|Percent by weight||Subjective evaluations|
|Treatment||Leaves||Total shrink||Small onions||Pack out||Color||Skin retention|
|Topper/loader in one pass||0||9||0.8||90.2||3.5||4|
|Topper windrower then loader||0||12.8||0.4||86.8||2||3|
|Flail then loader||0||11.2||0.9||87.9||3.5||4|
|Hand topped then hand load||0||9||0.9||90.1||4||4.5|
|Untopped then hand load||1.07||10.2||0.7||89.1||4||5|