1762 



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work more easily than those that have net. An English farmer is reported 

 to have said that liming clay land enabled him to plow with two horses 

 where three had been required before. This is perhaps an extreme result, 

 but such a general effect of lime is well recognized. Some commercial 

 fertilizers affect soil in the same way. 



5. Freezing breaks up heavy soil. As water in the soil freezes it is 

 formed into long, needle-like crystals that cut through the soil in many 

 directions. If a soil is carefully dried from its frozen condition a check 

 will be seen to form wherever a crystal occurred. The network of crystals 

 is so complete and their cleaving action is so tremendous that the hardest 

 clod falls to many pieces after two or three such freezes. (Fig. 93.) The 



Fig. 93.- — ■ These figures represent two pans of clay soil which had been puddled and 

 molded with a smooth surface. While still wet, pan No. 2 was permitted to freeze. 

 Both pans were permitted to dry out. The cracks formed where the structure of the 

 soil was most open. The pattern in No. 2 shows the influence of the ice crystals, and 

 this soil was much more friable and crumbly than the soil that was dried without freezing 



lack of frost action is considered to be responsible for the denser nature 

 of soils in warm countries. 



Nothing is more effective in breaking up subsoils than deep fall plow- 

 ing, by means of which they are exposed to frost action during the winter. 

 In order to obtain its full effect, such fall plowing must be coupled with 

 good drainage. This will prevent the soil from running together during 

 the spring thaws. 



6. Penetration of the roots of plants, and the burrowing of earthworms, 

 ants, and other forms of animal life, are important agencies for soil improve- 

 ment. (Fig. 87.) Tons of material per acre are handled by earth worms 

 and ants in the course of a year. The roots of plants press through the soil, 



