SOIL RELATIONS 249 



opposition to the same force. In crop growing, it is the 

 transpiration force of the individual plants which corre- 

 sponds to the centrifugal force of the machine, and pulls 

 upon the water in opposition to soil capillarity. In 

 response to the force, the moisture content of the sandy 

 soil will be reduced to a lower point than that of the 

 heavy soil. It will depend upon several varying condi- 

 tions whether a sandy or heavy soil is better in any 

 particular locality or season. A clay loam will obtain 

 and hold more water in a season of summer tillage for 

 the next crop. However, owing to 'the greater ease of 

 absorption of torrential rains by sandy soils, these soils of 

 the Great Plains often have more available moisture an 

 acre than the heavier soils. 



265. The wilting coefficient. In 1912, Briggs and 

 Shantz reported the results of their investigations of the 

 wilting coefficient for different plants in different soils. 

 This is the moisture content (in percentage of the dry 

 weight) remaining in the soil at the time when permanent 

 wilting of the plant begins, as a result of deficiency in the 

 soil moisture supply. A very important result of the in- 

 vestigations is the proof that the wilting coefficient in 

 any soil is practically the same for all plants. Drought- 

 resistance, therefore, does not mean any special ability 

 on the part of the crop to obtain water, but varies in- 

 versely as the water requirement. No fact is of greater 

 agricultural importance in attempts to improve cereal 

 crops. As in the case of the moisture equivalent, the wilt- 

 ing coefficient is less in the coarser or sandy soils, showing 

 that these soils will support life in the plant with a much 

 lower moisture content than will heavy or clay soils. 



266. Alkalinity of the soil. The large percentages of 

 mineral bases in naturally adapted grain soils have been 



