THE MOISTURE PROBLEM 81 



such soils the lessening of seepage can only be brought 

 about by increasing the organic matter content a 

 practice which is seldom profitable except on the better 

 grades of these types of soil. The dry farmer should 

 avoid soils that are so light and loose that loss by seep- 

 age is probable. 



The loss of moisture by evaporation from the soil 

 into the atmosphere is very great. No data giving the 

 actual amount of loss from a soil surface in this climate 

 are available, but when it is realized that from 60 to 100 

 inches of water evaporates from a water surface in a 

 year in the southern portion of the Great Plains, the 

 extent of the evaporation from a soil surface may be 

 imagined. The very great loss by evaporation may be 

 lessened ( 1 ) by the use of a mulch on the surface of the 

 land, and (2) by increasing the moisture-holding power 

 of the soil by maintaining or increasing its supply of 

 humus or partially decomposed organic matter. While 

 it is a fact that a soil mulch lessens the amount of water 

 that leaves the soil by evaporation in humid climates, 

 there is some question as to its effectiveness in dry clim- 

 ates and also as to how much expense a farmer is justified 

 in assuming in order to make a relatively small 

 saving. (See "The Application of the Capillary Theory 

 to Dry Farming Practices" in Chapter XVI.) 



The loss of moisture through its use by growing plants 

 is very great. As little as 250 pounds of water and as 

 much as 1,000 pounds have been found to be taken into 

 the roots of plants and transpired into the atmosphere 

 through the leaves in the process of taking in food ma- 

 terials sufficient to make one pound of dry matter. So 

 long as the plants using it are useful to man this largfc 

 amount of water is not a loss, even though it may hav» 



