Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Biological and Irrigation Engineering


Sterling A. Taylor


Soil moisture measurement embraces two basic concepts, namely, water content and relative activity. The measurement of moisture content, either on a weight or volume basis, yields the amount or quantity of water in the soil. The measurement of relative activity or the energy required to remove unit of water is related to the availability of the soil moisture to the plant. The measurement of soil bulk density, irrigation efficiency, and the amount of water to apply in an irrigation are a few examples that require the use of the moisture content concept. Whereas the first concept determines the amount of water to apply; the second cencept, since it is related to the tenacity with which water is held in the soil or the availability of soil water to the plant, determines the correct time to irrigate. Other examples of phenomena that relate closely to the relative activity concept are found in the study of seepage loss from canals and in the design of drainage systems to lower the water table (water movement).