132 Fertilizers 



Green-manure crops that consume the nitrogen in the soil. 



In addition to the legumes, other crops are used as green- 

 manures. Chief of these are rye, wheat, buckwheat, 

 mustard, oats, barley and rape, not because they are 

 capable of gathering nitrogen directly, but because their 

 period and time of growth are such as frequently to 

 enable them to serve a very useful purpose in preventing 

 losses in fertility. In the growth of these crops, however, 

 the only real addition to the soil is the amount of non- 

 nitrogenous organic matter contained in them. The 

 nitrogen gathered is in direct proportion to the amount 

 contained in the soil and the relative feeding capacity of 

 the plant. The nitrogen is not obtained from the atmos- 

 phere, and the soil has not accumulated nitrogen by 

 virtue of their growth, and is not richer in this element, 

 except in so far as by their growth they prevent the 

 escape of readily available nitrogen into the drainage 

 waters. The nitrogen gathered is "soil nitrogen," and its 

 conversion into a crop simply results in changing its form 

 and place. The specific use of these crops, therefore, so 

 far as directly contributing to the fertility of the soil is 

 concerned, is to prevent the possible loss of nitrogen and 

 other constituents by leaching, which is more liable to 

 occur on uncropped soils, though they further contribute 

 toward soil improvement by accumulating stores of non- 

 nitrogenous vegetable matter. 



These crops, also, in order that they may produce largely, 

 must be freely supplied with the mineral elements, as well 

 as with nitrogen in some form, and cannot be regarded as 

 a substitute for the leguminous crops, or as a substitute 

 for commercial fertilizers in the permanent improvement 

 of the soil, in the sense that they actually contribute to 



