SUBSOILING 33 



after a rain, because it hastens losses by evaporation, 

 while a soil mulch formed by surface cultivation has 

 the opposite effect. 



30. Rolling. The use of heavy rollers for com- 

 pacting the soil is beneficial in a dry season on a soil 

 containing large proportions of sand and silt. Rolling 

 the land compacts the soil and improves the capillary 

 condition, enabling more of the subsoil water to be 

 brought to the surface. Experiments have shown 

 that when land is rolled the amount of water in the 

 surface soil is increased. This increase is, however, 

 at the expense of the subsoil water. 13 Unless rolled 

 land receives surface cultivation, excessive losses by 

 evaporation, due to improved capillarity, may result. 

 The use of the roller on heavy clay land during a wet 

 season results unfavorably. In some localities rolling 

 and subsequent surface cultivation are not admissible 

 on account of the drifting of the soil, caused by heavy 

 winds. 



31. Subsoiling. By subsoiling is meant pulveri- 

 zing of the soil below the furrow slice. This is 

 accomplished with the subsoil plow, which simply 

 loosens the soil without bringing the subsoil to the 

 surface. The object of subsoiling is to enable the 

 land to retain, near the surface, more of the rainfall. 

 Heavy clay lands are sometimes improved by occasional 

 subsoiling, but its continued practice is not desirable. 

 For orcharding and fruit-growing, it is frequently re- 

 sorted to, but is not beneficial on soils containing 

 large amounts of sand and silt. Rolling and subsoil- 

 ing are directly opposite in effect. Soils which are 



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