Water Capacity of Soils. 



131 



It is not probable, however, that the hygroscopic mois- 

 ture of a soil can in any direct way aid plant growth. 



155. Ways of Expressing the Water Content of Soils. The 

 amount of water a soil will or may contain has been ex- 

 pressed in different ways: (1) As a per cent, of the wet 

 weight of the soil, (2) as a per cent, of the dry weight of 

 the soil, (3) as a per cent, of the volume of the soil, (4) 

 in pounds per cubic foot, (5) in inches per cubic foot. The 

 amount of moisture a soil does contain may be most readily 

 and precisely stated as per cents, of the wet or dry weight, 

 but for agricultural purposes it is best to state the amount 

 in per cent, of the volume or in inches per cubic foot. 



156. The Maximum Water Capacity of Soils. The largest 

 amount of water a soil may contain is expressed by its per 

 cent, of pore space and if reference is made to the table in 

 ( 145) it will be seen that this ranges from about 32 to more 

 than 52 per cent., that is from 4 to 6 acre-inches per acre- 

 foot of soil, and from 20 to 32 Ibs. per cubic foot. These 

 amounts of water, however, are never found in soils under 

 field conditions. 



157. Water Capacity of Soils Under Field Conditions 



The amount of water which may be retained by soils under 

 field conditions is extremely variable and depends upon a 

 number of factors. In the table below are given the 

 amounts of water which were found in three types of soil 

 with the undisturbed field texture, when they contained aa 

 much as they would retain after a few days of drainage fol- 

 lowing heavy rains. 



Capacity of field soils for moisture. 



