Abstract
Many agricultural fields across the country have a high degree of variability in soil type and water holding capacity that affects irrigation management. One way to overcome problems associated with the field variability for improving irrigation management is to utilize a site-specific irrigation system. This system applies water to match the needs of individual management zones within a field. A real-time continuous soil moisture measurement is essential for the success of site-specific irrigation systems. Recently the National Aeronautics and Space Administration (NASA) developed sensor technology that records the global positioning system (GPS) signal reflected from the surface of Earth, which estimates the dielectric properties of soil and can be used to estimate soil moisture contents. The overall objective of this study was to determine the feasibility of utilizing GPS-based technology developed by NASA for soil moisture measurements and to determine the influence of soil type, soil compaction, and ground cover on the measurements. The results showed strong positive correlations between soil moisture and reflected signals. Other factors (soil compaction and soil type), were not significantly related to reflectivity and did not significantly change the relationship between reflectivity and soil moisture contents. In addition, ground cover (rye crop) did not significantly reduce reflectivity. Therefore, this system could be used as a real-time and continuous nonintrusive soil moisture sensor for site-specific irrigation scheduling and watershed management.
Highlights
Site-specific or variable-rate irrigation (VRI) technology is a relatively new concept in agriculture that applies irrigation water to match the needs of individual management zones within a field, significantly reducing water consumption, runoff, and nutrient leaching to ground water
There is a need to develop advanced sensing technologies that can be installed on top of overhead irrigation systems to continuously map soil moisture as the system moves over the field
Soil moisture contents of the field changed between 1% and 12% only, due to high sand contents of test field
Summary
Site-specific or variable-rate irrigation (VRI) technology is a relatively new concept in agriculture that applies irrigation water to match the needs of individual management zones within a field, significantly reducing water consumption, runoff, and nutrient leaching to ground water. Real-time and continuous soil moisture measurements are essential for success of site-specific irrigation systems. Several different types of sensors, such as tensiometers [1], TDR [2], and multi-sensor capacitance probes [3][5], are currently commercially available for measuring soil water content. Since these sensors measure soil moisture in discrete locations in a production field, a significant number of sensors would be needed to provide a reasonable characterization of the spatial variability normally encountered in irrigated fields in the Southeast USA. There is a need to develop advanced sensing technologies that can be installed on top of overhead irrigation systems to continuously map soil moisture as the system moves over the field
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