12 MASS. EXPERIMENT STATION BULLETIN 424 



yields were the result of the bulbs growing to larger sizes. Larger bulb size may 

 in itself be a factor contributing to disease. Large bulbs tend to be soft and 

 succulent and they usually have a heavy, lush top growth. One might expect 

 that they would be more subject to disease infection as they mature than would 

 smaller bulbs. Valley growers have often observed that the large bulbs carry 

 more disease than smaller ones. 



It should be emphasized again that set quality is also important, for set lot 

 10 (Table 7) performed poorly on both dry and moist soils. This would indicate 

 that sets of inferior quality produce bulbs with poor keeping qualities irrespective 

 of soil conditions. 



Crop Rotation 



Another factor which may have an important bearing on loss by disease in 

 storage is the building up of soil-borne diseases as a result of the continuous 

 culture of onions for manj' years on the same land. There is some evidence to 

 suggest that this occurs and that rotating onions with other crops would reduce 

 diseases of onions in the field and in storage. 



In Canada(3), by following a crop rotation of one year in corn, three years in 

 alfalfa, and two >'ears in onions, Fusarium rots were reduced from 40 percent to 

 1 percent and the yield was increased from 6 tons per acre before rotation to 15 

 tons the first year, and 16J^ tons the second year, after rotation. 



A small crop rotation experiment was started in the Connecticut Valley in 

 1939. On a section of field which had been in continuous onions for 40 years 

 and from which onions usually rotted badly in storage, a plot was seeded down 

 with mixed grass and clovers in the spring of 1939. The surrounding field was 

 planted to onions by the owner. In the fall, after the onions had been harvested, 

 a strip adjoining the hay sod was seeded to a cover crop of r^e grass. In the late 

 fall the rye grass and part of the hay sod, together with the adjoining field, were 

 plowed. In the spring the whole area was planted to onions. 



Yields at harvest time were similar for the experimental plots and the adjoin- 

 ing field but losses in storage differed considerably. Loss from rots in onions 

 following onions was 17.3 percent; in onions following the rye grass cover crop, 

 22.4 percent; but in onions following one-year sod, only 13.5 percent. The results 

 are indicative rather than conclusive because the experiment was not adequately 

 replicated and could not be repeated. 



Fertilizers 



When large acreages of seed onions were grown in the Connecticut Valley, it 

 was a common practice to topdress onions with a nitrogen fertilizer sometime 

 during the growing season. Although this practice is much less common with 

 set onions because of the shorter growing season, supplemental nitrogen is occa- 

 sionally applied, particularly if the early part of the season is wet. The use of 

 topdressed nitrogen fertilizers during the growing season frequently impairs the 

 keeping quality of the crop. Losses from both rotting and sprouting may be heavy. 

 Additional nitrogen often produces a larger, more succulent growth of both tops 

 and bulbs and tends to delay maturity. Such conditions are favorable for the 

 infection of many bulbs by storage rot organisms, and their subsequent develop- 

 ment in storage may result in the destruction of many bulbs. 



