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Soil Moisture Tension as a Measure of Water Removal Rate from Soil and Its Relation to Weather Factors¹

ABSTRACT

The moisture tension in the soil at any specified time can be expressed as a function of depth. When it is possible to express the moisture content as a function of tension, it is then possible to express moisture content as a function of depth in the soil. The equation relating moisture content and depth is integrated over the depth of the root zone to give the total quantity of water in the soil. The quantity of water in the soil at any time is then subtracted from the amount which can be held without excessive deep percolation occurring. The difference represents the amount of water that can be retained by the soil from an irrigation. This amount should be increased by the runoff, evaporation, and other expected losses, in order to determine the quantity of water that should be applied at an irrigation.

Moisture tension has been measured as a function of depth by using both resistance blocks calibrated in terms of tension and tensiometers. The relationship between moisture tension and moisture content has been expressed mathematically and the quantity of irrigation water required has been applied. Good results have been obtained.

Indications have been found that the amount of water required at an irrigation may possibly be calculated from climate as indicated by weather records during the irrigation interval. It does not seem likely, however, that the irrigation interval can be established for all crops on all soils in any one area from weather data alone.

¹ Report of work done under Regional Research project W-9 with eleven Western States, Hawaii, Alaska, BPISAE, S.C.S. Research, Amalgamated Sugar Company, and Utah-Idaho Sugar Company are cooperating. Presented before Division VI, Soil Science Society of America, Cincinnati, Ohio, November 18, 1952.

² Research Assistant and Associate Professor of Agronomy, Utah State Agricultural College, Logan, Utah.

Received for publication November 28, 1952.