4O SOILS AND FERTILIZERS 



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

 ing the soil is beneficial in a dry season on a soil con- 

 taining large proportions of sand and silt. Rolling 

 compacts the land and improves the capillary condi- 

 tion, enabling more of the subsoil water to be brought 

 to the surface. Experiments show that when land is 

 rolled the amount of water in the surface soil is in- 

 creased. This increase is, however, at the expense of 

 the subsoil water. 15 Unless rolled land receives surface 

 cultivation, excessive losses by evaporation, due to im- 

 proved capillarity, may result. The use of the roller on 

 heavy clay during a wet season results unfavorably. 

 Occasionally, light rolling of clay land is beneficial in 

 pulverizing the clods. 



In some localities rolling and subsequent surface cul- 

 tivation are not admissible on account of drifting of the 

 soil, caused by heavy winds. 



31. Subsoiling. By subsoiling is meant pulverizing 

 the soil below the furrow slice. This is accomplished 

 with the subsoil plow, which simply loosens without 

 bringing the subsoil to the surface. The object of sub- 

 soiling 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 resorted to, but is not bene- 

 ficial on soils containing large amounts of sand and silt. 

 Rolling and subsoiling are directly opposite in effect. 



