Impact of Deficit Irrigation on the Productivity and Quality of Forage Corn and Sorghum.

Forages used to support western dairy systems have a very large water footprint. In California, for example, forages utilize over 20% of the state’s agricultural water.  Corn silage is a major component of this forage system, but the water use for corn silage is substantial.  Forage systems which can adjust to lower seasonal supplies are needed. One of such crops is sorghum. An experiment was implemented in 2014 and 2015 to examine water use efficiency of annual forage crop production under various water deficits. This experiment compared 4 cultivars of corn and sorghum each and their interactions with different irrigation regimes. Water was applied through a center-pivot irrigation system that was configured to deliver 100%, 70% and 40% of full Evapotranspiration demand.  Soils are a clay loam, located in western Fresno County, a region nearly entirely dependent upon irrigation during summer. The experimental design was a modified Randomized Complete Block Design with a split plot restriction with cultivar as a subplot, and unequal replications per block, 9 replications total. Regression analysis was used to determine response to irrigation treatments, and ANOVAs were used to determine differences between treatments. The objective is not only to produce a maximum yield silage system with full water supplies, but to develop systems which produce acceptable yield and quality under water deficits. Results from 2014 suggested that sorghum produced more biomass than corn, except in the treatment with the lowest water applied, where no difference was found. The in vitro digestibility at 30 hours of both species was found to be reduced significantly with increasing water supply. Digestibility of conventional sorghum was significantly lower than that of Brown Midrib Sorghum and Corn. Data on yield response and forage quality to irrigation treatment, and interactions between variety and irrigation treatment of both years will be presented.