38 SOILS AND FERTILIZERS 



depth for several seasons, the pressure of the imple- 

 ment and the trampling of the horses in time solidify 

 the bottom of the furrow, but if the plowing is shallow 

 in the spring and deep in summer and fall, the objee- 

 tional hard pan will be largely prevented." 



In regions of scant rainfall deep plowing of silt soils i 

 should be done only at intervals of three or five years., 

 With an average rainfall, deep plowing should be the 

 rule on soils of close texture. The depth of plowing 

 should be varied to meet the requirements of the crop, 

 of the soil and the amount of rainfall. 



34. Permeability of Soils. — The rapidity with 

 which water sinks into the soil after a rain depends 

 upon the nature of the soil, and upon the cultivation 

 which it has received. Shallow surface cultivation 

 leaves the soil in good condition to absorb water. 

 When the surface is hard and dry a large per cent, of 

 the water which falls on rolling- land is lost bv sur- 

 face drainage. Soils of close texture which contain 

 but few non-capillary spaces, offer the greatest resist- 

 ance to the downward movement of water. 



The term permeable is applied to a soil when it is 

 of such a texture that it does not allow the water to 

 accumulate and clog the non-capillary spaces. Culti- 

 vation may change the texture of even a clay soil to 

 such an extent as to render it permeable. Deep 

 plowing increases permeability. In regions of heavy 

 rains increased permeability is very desirable for good 



