Effect of Simulated Grazing Intensity On Dual-Purpose Winter Wheat Grain Yield Potential in Oklahoma.

Dual-purpose winter wheat growth and grain yield are influenced by cattle stocking density and variety selection. We evaluated the effect of simulated grazing intensity on wheat canopy closure and grain yield of two varieties of wheat with different growth habits Fuller (prostrate) and Overley (upright).  Canopy closure was determined using a handheld NDVI sensor and digital photography. Grazing intensity was simulated by mowing wheat to heights of 3, 7.5, and 12 cm at approximately four week intervals. Mowing was initiated in late October, which is a typical date for initiation of grazing on wheat pasture in the Southern Great Plains, and terminated just before first hollow stem in the spring. Digital photographs and NDVI measurements were taken before and after each mowing treatment. Percent coverage calculated by digital photography and NDVI measurements were closely correlated, indicating that NDVI measurements can be used as a reliable means of determining canopy closure in winter wheat. Mid and late-season canopy closure was lowest for both varieties at the 3-cm mowing height and increased as mowing height increased. Grain yield decreased as simulated grazing intensified. The 3-cm mowing height reduced grain yield of the prostrate growth habit variety (Fuller) by 35%, but reduced grain yield of the upright growth habit variety (Overley) by 50%. The results of this study indicate that there is a grain yield loss associated with grazing wheat, and final yield loss is affected by grazing intensity and wheat growth habit.