Impact of Dual-Purpose Management On Wheat Grain Yield.

Farmers in the Southern Great Plains utilize wheat (Triticum aestivum L.) as a forage and grain crop (dual-purpose), and there is debate among farmers and researchers as to what extent grazing impacts final wheat grain yield. The objective of this study was to evaluate the impact of grazing and dual-purpose management on wheat grain yield using two multi-year data sets that included a diverse group of commercially-released hard red winter wheat cultivars and a limited number of advanced experimental breeding lines. Paired experiments were conducted each year from 1991 to 2009 at the Wheat Pasture Research Unit near Marshall, OK. Simple linear regression was used to determine the relationship between grazed (dependent variable) and non-grazed (independent variable) wheat yield data. When grazed and non-grazed plots were both sown in early September, grazing improved wheat grain yield if yield of the non-grazed plots did not exceed 1,143 kg ha^-1; grazing decreased grain yield when yield exceeded this amount. When planting was manipulated to allow comparison of dual-purpose and grain-only systems , the dual-purpose system had an inherent yield disadvantage of 411 kg ha^-1 which was primarily attributed to early sowing. Following adjustment for this planting date penalty, wheat yield in the dual-purpose system was approximately 96% of that in the grain-only system. Ultimately, our data indicate that once a producer has made the decision to plant early and implement the dual-purpose system, the grain-yield impact of grazing by livestock is minimal.