SOIL FERTILITY 



159 



than doubled. Oats, unfertilized and turned under while green, increased 

 the yields some 250 pounds. The addition of nitrogen to the oats resulted 

 in a further increase in yield of 275 pounds, suggesting that part of the re- 

 sponse to the vetch was due to the nitrogen supplied by the legume. 

 Vetch appeared to have little influence on peanut yields when grown prior 

 to cotton in a peanut, vetch, cotton rotation. 



Table 11. — The Effect of Green Manure Crops on the Yield of Spanish 

 Peanuts. Experiments Conducted at Auburn, Alabama, on a Norfolk Sandy 



Loam Soil (1). 



• N = 36 pounds nitrogen from nitrate of soda. 

 P-K = 300 pounds 0-14-10 per acre. 



Workers (15) in North Carolina have studied recently the efifect of 

 several different cover crops upon the yields of peanuts in a cotton-peanut 

 rotation. The results are shown in figure 11. The legumes were found to 

 increase the yields of peanuts an average of 40 percent. It was concluded 

 that the increase was not due to the nitrogen supplied by these crops since 

 the yields of the "no-cover" plots were not affected by the addition of 

 60 pounds of nitrogen. Yet, as seen in figure 11, ryegrass was not as efifec- 

 tive as were the legumes. These investigators indicated that turning under 

 large amounts of winter cover crops prevented packing and left the soil 

 in better physical condition. Penetrometer measurements indicated that 

 the soil in the vetch plots was more easily penetrated than in the "no- 



