Variable Rate Irrigation and Water Use Efficiency.

Water is perhaps the most valuable resource to crop productivity of agriculture. In arid regions dependent upon irrigation, water scarcity threatens population growth and sustainable food production. With growing populations consuming water, it is expected that in these regions farmers will be required to sustain and increase crop productivity to meet the demand with less available water. Farmers more commonly implement variable rate seeding and fertilization to increase crop productivity based on soil spatial and temporal variability, but irrigation generally remains constant regardless of variability. Variable rate irrigation (VRI) is a promising technology capable of increasing water productivity by adjusting the irrigation rate according to soil types, topography, crop growth potential, or other factors. A variable rate center-pivot irrigation system was installed near Grace, Idaho over a 45 ha field in 2015. Approximately half of the field is grown with a wheat (Triticum spp.) and potato (Solanum tuberosum L.) cropping system and the other half is a short mowed Kentucky bluegrass (Poa pratensis L.) permanent sod. The field has high variability with some areas requiring full water and others (rock outcrops) requiring zero. The first year of the utilizing the system resulted in reduced water consumption of 44% without any measured loss of plant growth. An analysis of water use efficiency was conducted for the 2016 season to evaluate crop water use efficiency within a system that incorporated variable rate irrigation, fertilization, and seeding.  Eighty, three foot core samples were taken in the spring of 2016 and just after harvest and gravimetric water content was calculated to represent the beginning and end of season soil moisture. Crop water use efficiency was used to evaluate the VRI’s influence on water productivity in a precision agriculture system and will be presented.