Determining Local Crop Coefficients for Efficient Irrigation Scheduling in Montana.

There are over two million acres of irrigated land in the state of Montana. Approximately 64% of these acres are gravity fed with water diverted from rivers such as the Sun, Yellowstone, Milk, Missouri, Jefferson, and Flathead, all of which are tributaries to either the Missouri or Columbia drainage systems. Conservation and protection of these water networks are of regional, state, and national concern. The science of irrigation scheduling using estimates of evapo-transpiration (ET) is well established and methodology published by many including the Food and Agriculture Organization of the United Nations. But local calibration of crop coefficients (Kc) is still required to provide accurate estimation of crop water use. The eddy covariance method provides a measure of actual crop ET. Coupling measured ET with model estimates from proximal electronic weather stations provides a means to calculate Kc for irrigated crops. In 2015 instrumented towers using eddy covariance systems, which included CSAT-3 triaxial sonic anemometers and LI-7200 closed path infrared gas analyzers, were placed in spring barley (near Huntley, MT) and spring wheat (near Kalispell, MT) fields at crop establishment to measure crop ET. Ancillary data such as planting date, growing degree days, crop canopy development and closure dates were measured directly and remotely using Landsat images. The goal of the study was to predict regional Kc values using these ancillary data to extend our effective use of ET estimates for more efficient irrigation scheduling. Results from this first year of research will be presented.