Planting 137 



potato and are very often too hard. The plank float, 

 or clod crusher, is a better tool to crush lumps, and does 

 not settle the soil below the surface as does the roller. 

 Such lumps crush easiest a few hours after a rain. 



The depth of plowing for the potato should be as great 

 as the fertility of the soil will permit. The weak potato 

 roots need all the space they can get. Outside of the 

 arid regions of the United States, care must be taken 

 not to expose much of the cold and infertile subsoil at 

 any one plowing. Where it is necessary to plow land 

 deeper than formerly, not over one inch of subsoil should 

 be turned up at a time. Organic matter must be added 

 to lighten the subsoil turned up, as it is very deficient in 

 this. Sandy soils, in which potato roots penetrate easily, 

 need deep plowing less than heavy soils. Only three to 

 five inches is used in some sandy sections. Heavier 

 soils, if well provided with humus, are frequently plowed 

 to the depth .of ten inches or more, usually about 6 or 

 7 inches. 



RESULTS OF TILLAGE 



The results of soil tillage are : 



(1) The organic matter in stubble, manure, and the 

 like is buried in the soil, to decay there. 



(2) The mineral particles are made finer, and fresh 

 surface exposed to the action of solvents, such as soil 

 water and carbonic acid. . 



(3) The soil organic matter is broken up and easily 

 changed into more useful forms. The rapidity with 

 which soil organic matter is destroyed by tillage is 

 little appreciated. The common saying, that "tillage 

 is manure," is practically true. Tillage is expensive in 



