84 HOW CROPS FEED. 



wliich would be taken from the field twice or thrice the 

 above amount of nitrogen, although the period of growth 

 of the two crops is about the s.ime. Ulbricht found in 

 his investigation of the clover plant ( Vs. St., IV., p. 27) 

 that the soil appears to have but little influence on the 

 content of nitrogen of clover, or of its individual organs. 

 These facts admit of another expression, viz. : Clover, 

 though containing two or three times more nitrogen, and 

 requiring correspondingly larger supplies of nitrates and 

 ammonia than Avheat, is able to supply itself much more 

 easily than the latter crop. In parts of the Genesee wheat 

 region, it is the custom to alternate clover with wheat, be- 

 cause the decay of the clover stubble and roots admirably 

 prepares the ground for the ]a<t-nanied crop. The same 

 preparation might be had by the more expensive process 

 of dressing with a higlily nitrogenous manure, and it is 

 scarcely to be doubted that it is the nitrogen gathered by 

 the clover which insures tlie wheat crop that follows. It 

 thus appears that the plant itself causes the formation in 

 its neigliborhood of assimilable compounds of nitrogen, 

 and that some plants excel others in their power of accom- 

 l)lishing this important result. 



On the supposition that ozone is emitted by plants, it is 

 plain that those crops which produce the largest mass of 

 foliage develop it most abundantly. By the action of 

 this ozone, the nitrogen that bathes the leaves is convert- 

 ed into nitric acid, which, in its turn, is absorbed by the 

 plant. The foliage of clover, cut green, and of root crops, 

 maintains its activity until the time the crop is gathered; 

 the supply of nitrates thus keeps pace with the wants of 

 the plant. In case of grain crops, the functions of the fo- 

 liage decline as the seed begins to develop, and the plant's 

 means of providing itself with assimilable nitrogen fail, 

 although the need for it still exists. Furthermore, the 

 clover cut for hay, leaves behind much more roots and 

 sLubble per acre than grain crops, and the clover stubblu 



