Grazing Intensity and Wheat Growth Habit Affect Wheat Grain Yield in a Dual-Purpose System.

Cattle stocking density and variety selection influence dual-purpose winter wheat growth and grain yield. The objectives of this study were to determine the effects of growth habit and simulated grazing intensity on dual-purpose, hard red winter wheat canopy closure, fertile spike number, and grain yield. Experiments were conducted during the 2009-2010 and 2010-2011 wheat production seasons at Stillwater and Lahoma, OK. Grazing intensity was simulated by mowing two hard red winter with differing growth habits (prostrate or erect) to 3, 7.5, and 12-cm heights at approximately four-week intervals. Mowing was initiated in early November and terminated at first hollow stem (Feekes 5-6) in the spring, which correspond to typical cattle placement and removal from wheat pasture in the region. Simulated grazing to a 12-cm height did not affect winter wheat grain yield at either location, but the 3-cm mowing height reduced grain yield of winter wheat compared with the non-defoliated treatment regardless of growth habit or variety. Fractional canopy closure of at least 0.53 prior to winter dormancy (Feekes 3-4) or 0.62 at grazing termination was required to obtain 95% of asymptotic yield potential within an early-sown, dual purpose production system. Grazing to a height of 3-cm significantly reduced wheat ability to achieve these critical values and grazing at a 12-cm height generally ensured that these critical fractional canopy closure values would be maintained.