248 THE SMALL GRAINS 



degree of sandiness as to allow " soil blowing." As a 

 matter of fact, practical crop growing shows that both 

 soils possess advantageous qualities, and either kind may 

 be the better under certain conditions. A much better 

 understanding of this subject is now possible through 

 very interesting results of recent investigations of Briggs, 

 Shantz, and McLane, on the moisture equivalent and 

 wilting coefficient of different soils. 



263. The moisture equivalent of different soils is the 

 percentage of water they can hold in opposition to a cen- 

 trifugal force 1000 times that of gravity. To determine 

 it, samples of soils of different texture " are placed in per- 

 forated cups and moistened with an amount of water in 

 excess of the quantity they can hold in opposition to the 

 centrifugal force mentioned. After standing 24 hours, 

 the cups are placed in a centrifugal machine which is 

 operated at a constant speed so chosen as to exert a force 

 1000 times that of gravity upon the soil moisture. Each 

 soil then rapidly loses water until the capillary forces 

 are increased sufficiently to establish equilibrium with the 

 centrifugal force employed. The moisture content of 

 each soil is now not only in equilibrium with a force 1000 

 times that of gravity, but is also in capillary equilibrium 

 with every other soil which has been similarly treated, 

 so that if the soils are placed in capillary contact in any 

 combination whatever, no movement of water from one 

 soil to another will occur. The moisture content of each 

 soil under these conditions is the moisture equivalent of 

 that soil" (Briggs and McLane, 1912). 



264. Application of the principle to different s.oils. 

 The soils of finer texture, of course, retain more water. 

 As between a coarse sand and a clay loam, the latter will 

 sometimes retain 30 times as much water as the former in 



