140 THE PRINCIPLES OF SOIL MANAGEMENT 



foot of soil, is a cumbersome method of saying the soil 

 contains 10 per cent of water by volume. 



The fifth method is most generally used in field prac- 

 tice in stating quantities of water. In irrigation practice, 

 water is often measured in inches in depth per acre of 

 area. In stating the quantity of water held within root 

 range by different soils, this method is also direct and 

 convenient. For example, a sand soil of a certain tex- 



Fig. 42. A common type of spike-tooth, iron-framed harrow. It operates 

 as a shallow cultivator, and may often be very effective in mulching the soil 

 and conserving moisture. 



ture will hold in the four feet surface 9 acre-inches 

 of water; clay soil, 16; and a muck soil, 40 inches; which 

 figures are directly comparable for purposes of crop- 

 production. 



The method used in stating the moisture content 

 of a soil will therefore depend upon the line of investiga- 

 tion and the application of the results to be made. Both 

 the percentage of dry weight and the percentage of 

 volume will be used in this book, according to the 

 point of view of the discussion. 



