44 



SOILS AND FERTILIZERS 



36. Permeability of Soils. The rapidity with which 

 water sinks into the soil after a rain depends upon 

 the nature of the soil, and 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 roll- 

 ing land is lost by surface drainage. Soils of close tex- 

 ture, which contain but few non-capillary spaces, offer the 

 greatest resistance to the downward movement of water. 

 A soil is permeable when it is of such a texture that 



it does not allow the 

 water to accumulate 

 and clog the non-capil- 

 lary spaces. Cultiva- 

 tion may change the 

 tilth 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 crop production 

 on heavy clays. Sandy and loamy soils have naturally 

 a high degree of permeability, and it is not necessary 

 that it should be increased. 



FIG. 17. Sandy Soil without Manure. 



37. Fertilizers. When water contains dissolved 

 salts, it is more susceptible t,o the influence of surface 

 tension, and is more readily brought to the surface of the 

 soil. In commercial fertilizers soluble salts are present. 



