Crops. 



205 



This effect was obtained without a sacrifice of the crop and 

 must have been chiefly due to the nitrogen supplied by the stub- 

 ble and second growth of the clover. 



The distribution of nitrogen in the legume crop bears an im- 

 portant relation to its proper use in rotations. Shutt gives the 

 distribution of nitrogen between the roots and stubble and the 

 tops of legumes as follows: 



The proportion of the total nitrogen of the crop contained in 

 the roots of common red and mammoth clovers and alfalfa in- 

 dicate the effectiveness of the residues of these crops as sources 

 of nitrogen, when they are grown in rotations and the crop 

 harvested. The figures for alfalfa are probably much below the 

 average and fail to do justice to the crop. The condition is dif- 

 ferent with shallow rooted legumes. Thus, with the vetch and 

 pea, a large supply of nitrogen in the tops is correlated with a 

 comparatively small amount in the roots. Marked benefit from 

 these crops in rotations can be secured only where the whole 

 growth is turned in. Snyder states that the nitrogen content 

 of the soil can be maintained and even slightly increased when 

 clover is grown two years in a five course rotation with grains 

 and timothy to which farm manures are applied. 



