Comparison of Variable Rate Irrigation Based on Soil Sensor Irrigation Scheduling and Farmer Uniform Irrigation.

During the last decades, crop yields in the Southeast USA have shown an increasing trend coinciding with the adoption of irrigation. Net profit increase is one of the main reasons to adopt irrigation along with adapting to environmental and climate changes. Advanced irrigation systems and tools such as variable rate irrigation (VRI) and soil sensors can help reducing water use and improving water use efficiency. The objectives of this study are: (1) develop a procedure to create site specific prescriptions from real-time soil sensor data (2) quantify the benefits of soil sensor-based variable rate irrigation compared to farmer’s uniform irrigation strategy. The study was conducted in Samson, Alabama in 2018. Management zones (MZ) were delineated using soil electrical conductivity, terrain elevation, and data of soil physical and chemical properties. Undisturbed soil cores were collected within each MZ to determine soil water retention curves (SWRC) properties. Strips 230 feet wide spanning the length of the field representing the two irrigation treatments, VRI and farmer, were laid out so they traversed all management zones. A UGA smart soil array system composed of 18 Watermark® sensors was installed on each treatment-zone combination to track real-time changes of soil matric potential at 6, 12 and 24 inches soil depth. Irrigation prescriptions were calculated independently for each MZ within each VRI treatment combining the data of soil sensors and the SWRC values. Yield, water use efficiency, and irrigation amounts were measured to test the differences between the two irrigation treatments. Preliminary results suggest the ability of the soil-sensor approach to define better irrigation rate and timing prescriptions. Data showed there was a crop water use efficiency increase and reduction of total water applied (-32%, -410 m³/ha) where soil sensors were used. Further research will be necessary to refine the irrigation prescriptions.