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 



A 



B 



Fia. 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 continuotisly 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 



