Cooperative Wokk with Columbia University -129 



the fundamental requisites of fertility in tlie soil — proper drain- 

 age and tillage. 



The addition of manurial substances to the land may result in 

 large crops indirectly, as with lime, through the effects upon the 

 soil structure, the life within the soil, or the changes in soil con- 

 stituents that render plant food available. Or, the increase may 

 be due to the addition of available plant food. Lime is a* sub- 

 stance that we add primarily for its indirect effects. Green man- 

 ures are added for the same reason, or, in the case of legumes, for 

 the sake of increasing the plant-food supply by taking nitrogen 

 from the air. The use of maaiure and the wastes of the fann. in 

 the form of compost constitutes an addition that hasr in view 

 both the promotion of better physical, biological, and chemical 

 relations in the soil, and the addition* of plant foods. The use of 

 commercial food carriers is primarily for the sake of supplying 

 plant food, though the indirect effects should never be lost sight of. 



Since favorable physical and biological conditions are prerequi- 

 site to any successful use of added plant food, it behooves us to 

 look carefully to the substances that we add with respect to the 

 nature and the effects, both direct and indirect, that science and 

 experience have taught us to expect from them. But it is not 

 enough to study them merely from the point of view, of productive 

 increases. We may purchase that increase too dearly. Thus the 

 factor of economy must balance with the factor of utility in the 

 ,use of manure. 



There is no magic in green manures. When we plow rye under, 

 we do not in any way mysteriously increase the supply of food 

 for succeeding crops. By borrowing most cheaply from the air 

 .that bulk which tends to the physical betterment of the soil, and 

 by furnishing fodder for the organisms whose activity accelerates 

 the change to more soluble form of the plant food already in the 

 soil, concentrated in the upper layers by turning in the crop, we 

 increase crop yields. By turning under clover, or soy beans, or 

 vetch, or an alfalfa sod, we bring about the same effect and add 

 economically to the supply of nitrogen. 



There is no magic, either, by which passing food through the 

 body of an animal gives it value as a manure. From the point of 

 view of fertility, the virtue of feeding live stock lies largely in the 



