58 FARM DEVELOPMENT 



plant food and its supply is provided in the manner best 

 suited to the plants. It was on this kind of soil that 

 the greatest variety of natural crops first learned to grow. 

 Here plants flourished and sent many roots into the 

 soil. The decaying of both tops and roots furnished 

 humus which, mixed with the rock substances, rapidly 

 formed a great abundance of fertile soil. This made a 

 congenial soil for many of the clovers and other wild 

 leguminosae: the class of plants which have the power 

 to extract from the 'air quantities of nitrogen, which, 

 stored in the roots, stems and leaves, further enriches 

 the soil. 



Sustaining soil fertility. The soils that are built up 

 of a mixture of clay, sand, gravel and stones usually 

 afford superior conditions for the permanent growth of 

 large crops. It is on these soils that it is possible 

 from generation to generation to increase rather than 

 to decrease the productivity of the land by scientific 

 field management. It is our duty, not only to keep lands 

 up to their virgin fertility, but to increase their crop- 

 producing powers, so> that future generations may have 

 a richer heritage than we had. To do- this, we can raise 

 large crops and either leave a part of them on the fields, 

 or, having taken them to the barn as feed for our 

 animals, return the greater part of their substance in the 

 form of manure, to the soil, so as to keep up a supply of 

 vegetable matter. We can also use more artificial means 

 of keeping up the productivity of the soil, as by com- 

 mercial fertilizers. By allowing animals to take 

 toll from the annual crop produced, and yet return the 

 larger percentage of the organic matter, we can gradu- 

 ally increase the crop-producing power of most soils, 

 but often we may use commercial fertilizers also to 

 greatly increase the yields. 



The soil a complex bank. In a new bank, the money 

 deposited in excess of that withdrawn, is a simple form of 



