Farm scale trials of variable rate irrigation to assess the benefits of modifying existing sprinkler systems for precision application

Farm-scale trials are being conducted to assess the benefits of variable rate irrigation (VRI). Three farms have been selected where existing sprinkler irrigation systems have recently been modified to provide variable rate control of each individual sprinkler. Irrigation is being varied according to soil and crop differences, and is also being shut off over exclusion zones, such as drains and raceways, and for farm operations such as pasture renovation. Under each VRI irrigator, soil variability has been quantitatively assessed using a mobile soil mapping system, which consists of an electromagnetic (EM) sensor pulled behind an all-terrain vehicle, with an on-board accurate RTK-GPS, datalogger and field computer. The EM sensor measures soil apparent electrical conductivity (EC), and the resulting soil EC maps were ground-truthed and used to define irrigation management zones. Soil moisture sensors have been installed into each zone to monitor real-time soil moisture status. This information is then used for variable rate irrigation scheduling. Trial plots have been established in each zone at each site to compare a blanket uniform rate of irrigation to all zones with variable rates of irrigation fine-tuned to zone differences. A goal of this research is to assess irrigation water use efficiency of a VRI system, as well as to develop a precision irrigation system with capability for full automation.