INFLUENCE OF CULTIVATION 39 



crop production on heavy clays. Sandy and loamy 

 soils have a high degree of permeability, and it is not 

 necessary that it should be increased. 



35. Fertilizers. — When water contains dissolved 

 salts, it is more susceptible to the influence of surface- 

 tension, and is more readily brought to the surface of 

 the soil. In commercial fertilizers soluble salts are 

 present. The beneficial effects of commercial fertili- 



Fig. 15. Sandy soil without manure. 



zers upon the moisture content of soils are liable to 

 be overestimated, because the fertilizer undergoes fix- 

 ation when applied, and does not remain in a soluble 

 condition. Fertilizers containing soluble salts exercise 

 a favorable influence upon the moisture content of 

 soils, but the extent of this influence has never been 

 determined under field conditions. 



36. Farm Manures. — Well-prepared farm manures 

 exercise a beneficial effect upon the moisture content of 

 soils. When well-rotted manure is worked into a soil, 

 the coarse soil particles and masses are bound together, 



