A factor in water conservation and efficiency of use

A supply of available water in the soil for the use of growing crops as they need it is one of the most important factors in agriculture. Often it is the one factor that determines whether there will be any crop. 

Organic matter on or in the soil cannot of course act as a substitute for water, but under many conditions it can go a long way toward assuring that the best use will be made of the water that reaches the soil, either in the form of rain or through irrigation. 

The amount of water required to produce a crop of corn under normal conditions is only about 6—8.5 inches (Bertrand, 1965), although the annual rainfall may be 30-50 inches. This emphasizes the inefficiency with which this water is utilized in agriculture. The water not used by the crop is lost through runoff, deep percolation and evaporation. The lower the annual rainfall the more important is the loss by evaporation from the soil surface. 

For a more complete discussion than can be given here of the factors that influence infiltration rates and permeability of soils, reference should be made to the publication by Parr and Bertrand (1960). They also describe methods used for measuring infUtration and discuss the theoretical considerations involved. 

In the Southern Piedmont area of the United States, where the annual rainfall averages about SO inches, it has been estimated that about 11 inches of this is lost as runoff. Fortunately, a considerable portion of this loss occurs during the season when crop growth, if any, is at a minimum, and when the soil is already at field capacity. Under these conditions, if runoff could be prevented, most of the water so captured would merely percolate through the soil to the groundwater. 

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