126 NATURE AND PROPERTIES OF SOILS 



67. Resume. — An understanding of the complex organic 

 relationships within the soil is of great practical value, as 

 it determines to a large degree the yield of crops, their rota- 

 tion order and their fertilization. Moreover, tillage operations 

 must be varied according to the organic nature of the soil. 

 Unless a system of soil management is adopted which will at 

 least partially keep up the organic matter of the soil, crop 

 yields may be expected to decrease materially in a few years. 



Good soil management seeks to adjust the addition of or- 

 ganic matter, the physical and chemical condition of the soil, 

 and the losses through cropping and leaching, in such a way 

 that paying crops may be harvested while impairing the or- 

 ganic supply of the soil as little as possible. Any system of 

 agriculture that tends permanently to lower the organic mat- 

 ter of the land is impractical and improvident, as well as un- 

 scientific. 



