4 MASS. EXPERIMENT STATION BULLETIN 424 



The rye grasses developed a heavy sod which was clearly distinguishable up 

 until the time the land was disced the following spring. It was evident that this 

 sod, even though plowed, had been effective in reducing water erosion and prob- 

 ably wind erosion also. The field brome grass formed a heavy, resistant sod 

 but was in no way superior to either of the rye grasses. Oats developed a rather 

 loose sod which disintegrated rapidly; and buckwheat, of course, formed no sod 

 at all. It would seem that in rye grass a cover crop is available which exerts a 

 protective influence throughout the winter and spring even though it is plowed 

 late the preceding fall. It is a crop which is already being used extensively' as a 

 winter cover following many other crops. 



The use of nitrogen fertilizer to stimulate growth of cover crops is questionable 

 in the average season on most onion land. There is usually enough residual 

 fertility in the soil to support near optimum growth, but there may be situations, 

 particularly following wet growing seasons when most of the nitrates have been 

 lost through leaching, where the application of additional nitrogen on the cover 

 crop may be justified. 



Fertilization and Liming 



Liberal use of complete fertilizers, broadcast in the spring, has long character- 

 ized Connecticut Valley onion culture. The application rate of 2000 to 3000 

 pounds per acre and the grades commonh- used have not changed greatly for 

 some time. There has been a trend toward higher concentration of some elements, 

 particularly nitrogen and to some extent potash. For example, the minimum 

 nitrogen content is now 5 percent instead of 4 percent. The fertilizer grades most 

 commonly used include 5-8-7, 5-10-5, and 5-10-10. As yet, the use of double 

 strength fertilizer has been limited, although some 8-16-16 and 8-16-8 have been 

 used. 



An abundant supply of available calcium in the soil is necessary for the vigorous 

 healthy growth of onions. Since practically all onion soils tend to become de- 

 pleted in available calcium from \ear to year, and therefore more acid in reaction, 

 it is necessary to replenish the calcium supply by occasional liming. Frequent 

 light applications of limestone are more desirable than infrequent heavy ones. 

 Most growers recognize this fact by applying a ton or more of limestone to their 

 onion land regularly every three to four years. The optimum soil reaction for 

 onions is about pH 6.0 to pH 6.5. 



The common practice in fertilizer application is to broadcast all of it prior to 

 planting. In 1941 an experiment was carried out in which the fertilizer applica- 

 tion was split, part being plowed under in the early spring and part being broad- 

 cast just before planting. Of a total application of 2250 pounds of a 5-8-7 ferti- 

 lizer, 1800 pounds were plowed under and 450 pounds were broadcast after plow- 

 ing. This method of fertilization was compared with another application of 

 2250 pounds of the same formula applied in the usual manner. There were no 

 significant differences in top growth, quality, and yield of onions between the 

 plots where the fertilizer was all broadcast on the surface and where part of it 

 was plowed under. 



Accumulated evidence indicates that the maximum rate of 3000 pounds per 

 acre should be reduced to 2500 pounds or less when a 5-10-10, 5-10-5, or 5-8-7 

 fertilizer is used. Heavy applications of fertilizer may cause serious injury, not 

 only immediately after planting but also later in the season, particularly during 

 dry seasons. Quite frequently in the middle of the growing season growth is 

 retarded and the tips of the leaves in some fields die back for two or three inches. 

 That the trouble is due to fertilizer injury is shown by the following facts: 



