TILLAGE 345 



crop. Experience indicates that eight or nine inches is about 

 the limit. For rich, deep soils six to seven inches is sufficient. This 

 gives a deep reservoir for water storage and an abundance of soil 

 for root development. 



Deep Tilling. Deep tilling plows have been put on the market, 

 by which plowing may be done to a depth of twelve to eighteen 

 inches. As a result of nine tests for corn, the yield was 2.7 bushels 

 higher for ordinary plowing than where plowed twelve to fourteen 

 inches deep. This may have some advantages for alfalfa and other 

 deep-rooting crops. The Kentucky Station found an increase of 

 416 pounds of alfalfa hay in two cuttings in favor of deep tilling. 



Subsoiling. Subsoil plows have been used for loosening the 

 soil to a greater depth than is possible with the ordinary plow. This 

 practice was more common a few years ago than at present. The 

 results do not indicate that the operation in humid soils is of very 

 much value. As a result of 40 tests in southern Illinois the sub- 

 soiled land gave an average of 2.7 bushels less than the land not sub- 

 soiled. 1 This practice may have some value in semi-arid regions and 

 for certain crops, but it is certain that it has very little value for 

 the principal cereal crops in humid regions. 



Dynamiting. The use of dynamite for breaking up the im- 

 pervious or hardpan subsoils has been resorted to in some cases. 

 This is a good practice where trees are to be planted. A charge of 

 dynamite is exploded and the tree is planted in the loose soil thus 

 produced. The expense involved in breaking up the subsoil in this 

 way makes the practice almost prohibitive for ordinary crops, unless 

 the increase in yield is much greater than the experiments up to 

 the present would indicate. 



Effect of Deep-Rooting Crops. Without much doubt nature 

 has provided the best method of deep tillage. This is by means of 

 deep-rooting plants, and more especially legumes. A crop of red, 

 mammoth, sweet clover or alfalfa fills the soil with roots and leaves 

 it open and readily permeable to water and air. These roots extend 

 to a depth of several feet and render heavy clays pervious, bring 

 plant food from the subsoil to the surface, and benefit such soils in 

 .various other ways. The crop should be seeded much thicker than is 

 done ordinarily. There should be from six to twelve or more plants 

 to the square foot, as one plant to the square foot is of comparatively 

 little benefit. 



Preparation of the Seed Bed. The ordinary farm crops re- 

 quire better conditions for their growth than the wild plant* with 



