ULLAGE 



353 



plant food it contained than for the moisture it conserved. The 

 experiment was conducted on the brown silt loam, the common 

 corn-belt soil of Illinois. The same experiment was tried on 

 the gray silt loam on tight clay with somewhat similar results, as 

 shown in this table : 



Results of Cultivation of Corn on Gray Silt Loam on Tight Clay at Fairfield, 

 Wayne County, 4 Illinois (Yields in Bushels Per Acre) 



* Computed from 5-yenr average. 



The Department of Agriculture" reports a number of experi- 

 ments somewhat similar to this, and the average yield of corn on 

 the uncultivated plots was 52.0 bushels, while that of the cultivated 

 was 52.5 bushels per acre. These were conducted on various kinds 

 of soils in 2S different states. The necessity for cultivation is 

 greater on heavy soils than on light ones. -This is shown bv the 

 fact that uncultivated sandy loams and sill loams produced 1 ().">. 7 

 per cent and 102.1 per cent of the cultivated, while the day loams 

 and clays produced, respectively, !H.. r > per cent and !>2.! per cent 

 as much as the cultivated. \Yhcn the crop becomes large enough to 

 partly shade the soil, and the roots become thoroughly distributed 

 through the soil, there is very little necessity for cultivating to 

 conserve moisture. The water that moves upward is captured by 

 the roots before it reaches the surface and evaporates. 



Root Injury. Most of the crops grown in humid regions that 

 require cultivation are shallow rooting. A large supply of moisture 

 and plant food is in the surface soil. The roots naturallv develop 

 23 



