APPLIED ECOLOGY 341 



"stubble mulching" in which subsurface tillage keeps old organic 

 debris on the surface. Windbreaks of various kinds are known to 

 be effective also. 



All these are examples of modern practices that are proving 

 effective under special conditions. They are not by any means 

 new, since they have been reported in various forms far back in 

 history. It is their application in the light of modern knowledge 

 that marks advance. The more complete the knowledge of all fac- 

 tors involved— crop, soil, climate— the greater the success of their 

 application in the future. The research programs continue, and the 

 kinds of investigations in progress are invariably ecological in 

 nature. Here is a list of a few of the projects being studied for a 

 single district : 172 



1. The effect of contouring corn, soybeans, and oats on 

 soil and water conservation 



2. The effect of divergence of rows from the contour on 

 losses of soil and water 



3. Cultural practices and methods of handling crop resi- 

 dues in relation to soil and water conservation and crop 

 yield 



4. The effect of cover crops on the conservation of soil 

 and water and on crop yield 



5. Investigations of soil moisture content under different 

 crops, cropping systems, and mechanical conservation 

 practices 



6. Effect of crops and organic matter treatment on the 

 movement of water through the soil profile 



Other studies include effects of cropping systems, crop rota- 

 tions, handling of crop residues, and management in terms of run- 

 off, yield, and soil properties. 



Some special problems of soil conservation still requiring a 

 great deal of study are related to drainage of water-logged land 

 and swamps, irrigation of lands with insufficient water, clearing 

 of toxic salts from irrigated land and other lands not previously 

 cultivated. 



Water Supply-— The conditions necessitating soil erosion con- 

 trol and the prevention of runoff of surface water are commonly 



