THE; sou, AND WATER 



133 



of the larger amount of stubble left by the crop produced with a 

 complete mineral fertilizer, this soil also holds more water than 

 the one with no manure. 



Method of Expressing Water in Soils. The amount of water 

 contained in a soil may be expressed in three ways 1 ; first, in 

 terms of the volume of water which occupies a given volume of 

 soil ; second, in percentage of water contained in the wet soil ; 

 third, in percentage of the dry soil. The following table (after 

 Warington) gives the water in some soils fully saturated: 



It is better to compare volumes of water in given volumes of 

 soil in considering the water content of different soils. The roots 

 of the plant are distributed through a given space, which varies 

 according to the kind of plant, depth of soil, etc., and it is the 

 quantity of water and plant food in the space occupied by the 

 roots which is important. This method of expression is, how- 

 ever, cumbersome; for, in addition to the weight of soil and weight 

 of water, there must enter into the calculation the real and appar- 

 ent specific gravity of the soil. 



The expression of the water absorbed in terms of the weight of 

 the dry soil has decided advantages, especially in laboratory work. 

 Only two quantities are involved, the weight of the soil and the 

 weight of the water. It is thus easy to calculate the amount of 

 water which should be present in a given weight of soil to produce 

 a definite degree of saturation. 



1 Warington, Physical Properties of Soils, p. 69. 



