266 



CROP ROTATION 



Proper Rotation Improves Tilth. The rapid depletion of the 

 soil organic matter resulting from the growing of crops without 

 clover and without the use of manure and green-manuring crops 

 has a destructive effect on good tilth. Sandy soils become much 

 looser; and the heavier soils lose their crummy structure, becoming 

 more compact, and easily puddled when worked in a wet condition, 

 A rotation which maintains and builds up the supply of organic 





FIG. 169. The development of good sod increases the soil organic matter. A , root develop- 

 ment on land properly fertilized; B, root growth on same land but unfertilized. 



matter in the soil also improves the workability of soils and 

 maintains good tilth. The growing of grass, pasture and deep- 

 rooted legumes on heavy soils greatly aids in improving their tilth. 

 On a portion of a field (silt loam) at the University of Illinois, 

 corn was grown continuously for forty years; while on another 

 portion, during the same period, a three-year rotation was prac- 

 ticed, consisting of corn, oats and clover. The soil on the first 

 portion has become compact, it "runs together" badly, and heavy 



