PREPARATION OF SOILS FOR CROPS 251 



would be buried and be less available to the crop if 

 the land were plowed too deeply. On heavy clay 

 lands this method of preparing the seed bed without 

 plowing is not advisable but on the silt soils of the 

 northwest it is a practice which has given excellent 

 results and is beneficial as a means of conserving the 

 soil moisture. 



336. Mixing of Sub-Soil With Seed Bed. Some 

 soils are improved by deep plowing and by mixing 

 the surface soil and sub-soil to form the seed bed. Such 

 soils are usually acid in character and contain a large 

 amount of organic matter, in which case the mixing 

 of the surface soil and subsoil improves both the physi- 

 cal and chemical properties of the seed bed. In the 

 case of sandy soils, the mixing of the surface soil with 

 the sub-soil is not advantageous as it dilutes the stores 

 of plant food which are greater in the surface soil ; 

 then too the physical properties of the soil are not im- 

 proved. The combining of the surface soil and sub- 

 soil in the case of heavy clay should be done gradu- 

 ally and at each period in the rotation after an appli- 

 cation of farm manure. In the cultivation of clay 

 soils, it should be the aim to secure a deep layer of 

 thoroughly pulverized, aerated and fertilized soil. In 

 the preparation of the seed bed the character and con- 

 dition of the subsoil is equally as important as of the 

 surface soil. 



337. Cultivation to Destroy Weeds. One of the 



chief objects of cultivation is to destroy weeds. Cul- 

 tivation for this purpose should be given early in the 



