76 THE SOILS AND CEOPS OF THE FARM. 



Much of the fertile prairie soils of the central west 

 and some alluvial soils in other parts of the country 

 often show no increase of yield from deep plowing. 

 Deep plowing is less common on the black prairie soil 

 of Central Illinois, for instance^ than it formerly was. 

 These soils are so open in texture that neither roots, 

 air nor water find difficulty in descending to a consider- 

 able depth. Repeated experiments have shown that 

 good crops may be grown on such soils without plow- 

 ing; in fact without other preparation than co\^ring 

 the seed, it being understood that the surface mu^t be 

 freed from rubbish in some way. This practice is not 

 advised, but it illustrates the fact that the physical 

 condition of some soils may be as good without tillage 

 as that of others after much work has been done by 

 the farmer. The latter may produce as large crops 

 as the former, but it is at the cost of more labor. 



There is a disposition to over-estimate the depth of 

 plowing. For many soils six inches may be called 

 deep; comparatively few soils need frequent plowing 

 deeper than eight inches. Fall plowing may usually 

 be deeper than is advisable when the work is done 

 in the spring. 



ISabsoil and Trench Plowing, — Subsoil plow- 

 ing is loosening the subsoil without bringing it to the 

 surface. In trench plowing the loosened subsoil is 

 laid on the surface. Neither of these operations is 

 commonly practiced by American farmers. Many 

 thousands of acres are annually so treated, but the to- 

 tal is but a small percentage of the cultivated area. 

 Subsoiling is probably advisable on a larger variety 

 of soils in this country than is trench plowing. On 

 undrained soils it often is worse than useless, unless 



