SOIL FORMATION, COMPOSITION, ETC. 87 



heavily on a particular element, followed by another crop 

 that feeds heavily on the same element; nor is a crop 

 that requires a large amount of any particular element 

 adapted to a soil that does not contain a fair amount of 

 that element. Shallow-rooted crops should be followed 

 by deep-rooted crops; clean-cultured crops as much as 

 possible by crops that will leave much organic matter to 

 be incorporated in the soil. Leguminous crops should be 

 used frequently in rotations, in order that the largest 

 amount of the expensive element, nitrogen, may be obtained 

 from the supply that exists in the atmosphere. It is only 

 when a high-priced crop is being grown that a farmer 

 can afford not to rotate his crops. 



67. Use of Manures. When manure is intelligently 

 conserved, a profit can be made by feeding leguminous 

 crops ta stock and, while obtaining profit on the increase 

 in flesh, recovering most of the fertilizing elements in the 

 manure, in a better state of mechanical division than it 

 was as plant tissue. It does not follow necessarily, however, 

 that the plant food will be more available in manure than 

 in the plant tissues. The question for the farmer to de- 

 cide is, whether or not it is more economical for him to 

 feed the crops to animals, conserve the manure and apply 

 it to his soil, or to incorporate the organic matter from 

 the crops directly in the soil. Hopkins, in his " Soil Fer- 

 tility and Permanent Agriculture," gives the table on 

 page 88, showing that a large part of the organic matter 

 during the processes of digestion and assimilation is decom- 

 posed into carbon dioxide and water, and that little 

 over 25 per cent of the dry matter is recovered in the 

 manure. 



Doubtless, the best practice for the farmer to follow 

 will depend upon the money value of the crop that he 

 grows. If, for example, a valuable crop is to be grown for 

 market, it will pay to grow a previous crop and incor- 

 porate it in the soil, provided the increased yields of sue- 



