THE ESSENTIALS OF AGRICULTURE 



LOSS IN CROPS 1 



RETURNED TO SOIL 



Under such a system, therefore, the supply of nitrogen and 

 organic matter of the soil can be maintained or even increased. 

 The losses are in phosphorus and potassium, which must be 

 secured from outside sources, such as fertilizers or purchased 

 feeds. Under such a system of stock farming, particularly on 

 soils naturally well supplied with lime, phosphorus, and potas- 

 sium, it would require many years to show a decrease in soil 

 fertility. 



145. Grain farming and soil fertility. It is possible through 

 the use of green manure and commercial fertilizers to maintain 

 soil fertility under a system of grain farming, where all the grain 

 is sold off the land except what little is used to feed working 

 stock. This plan necessitates, first, the growing of certain legume 



1 The figures on this page are based on a return of 70 per cent of the nitro- 

 gen, 75 per cent of the phosphorus, and 85 per cent of the potassium contained 

 in the crop fed, such as is possible under the best systems of handling manure. 



