The Adaptation of the Neutron Scattering Technique of Soil Moisture Determination to Field Application

At the present time there is a recognized need for a better means of measuring soil moisture in situ. Soil moisture measurements are required in fundamental studies of soil moisture flow and soil-plant-water relationships as well as in practical studies in irrigation practices. Various phases of engineering also utilize soil moisture data, for example, soil moisture determinations are made during the construction of earth dams, road cuts and fills, and under airfield runways. The desired method should be quick, reliable, and adaptable over the moisture range from oven dryness to saturation. Research in nuclear physics has revealed the neutron scattering phenomena which may be utilized as a means of determining soil moisture. It is known that hydrogen nuclei have a large influence on the scattering of neutrons and that most of the hydrogen nuclei in soils occur primarily in water. Using this information it should be possible to correlate the scattering of neutrons in the soil with moisture content. Measurement of soil water in this would be independent of its physical or chemical state in the soil. This would eliminate variables that are inherent in the present methods, such as temperature, soil texture, and salt concentrations. The object of this study is to adapt the neutron scattering phenomena to a method of soil moisture determination in situ. The problem is one of instrumentation and calibration. The emphasis will be toward developing an instrument to be used for soil moisture determination in experimental plots. Other diverse applications will also be considered. The prerequisites of the method require that it be more accurate and precise than the present methods without increasing the time and costs involved