TILLAGE. 77 



in rare cases, where there is a thin layer of compact 

 soil above a porous soil. In heavy clay soils the 

 effects are not permanent. In deep, loose soils the 

 practice may do some good but not always enough to 

 repay the extra cost. 



Subsoiling may be done either by a separate plow 

 or an attachment to the ordinary plow. 



A double plow with a small share and mold board 

 in front which cuts and turns over a shallow furrow, 

 followed by a larger plow which covers this furrow 

 with a deeper furrow, gives good satisfaction to many 

 farmers, especially in plowing sod land. 



Time for Plowing. — There are some obvious 

 advantages in fall plowing lands designed for spring 

 sown crops. The pressure of work in the spring is 

 lessened. The crops can often be put in more 

 promptly. Exposing the upturned surface to the 

 fi'eezing and thawing, to the snow and rain of winter, 

 often helps much. Some insects may be destroyed by 

 the process. With some soils replowing in spring 

 may be advisable, but this is not the rule. For fall 

 sown grains, as wheat and rye, it is generally thought 

 best to plow as long before time for seeding as is con- 

 veniently practicable; these crops often doing better 

 when the seed bed, while well pulverized, is well com- 

 pacted. On the other hand there are advantages, in 

 many cases, when plowing ground in the spring, from 

 planting or sowing the crop very promptly after the 

 plowing is done. This is especially true if there is 

 little moisture in the soil. If a crop of clover or other 

 green manuring crop is to be turned under, the plow- 

 ing will naturally be delayed as long as possible to 

 allow greater growth to the manure crop. 



