Yield Gap and Production Gap of Rainfed Winter Wheat in the Southern Great Plains

Since 1980, average wheat (Triticum aestivum L.) yields have remained nearly stagnant in the southern Great Plains (SGP) and stagnant in the state of Oklahoma. Yield stagnation can sometimes be attributed to a relatively small gap between current and potential yields, but the magnitude of the yield gap for this region has not been well quantified. The objective of this study was to determine the wheat yield and production gaps in Oklahoma at state and county levels. This involved estimation of attainable yield (Y a ) using a frontier yield function and water-limited potential yield (Y p ) using estimated transpiration and transpiration efficiency. Yield gap and production gap relative to Y a and Y p were calculated using grain yields and harvested area for 19 counties. Current average yield (Y c ) was 2.06 Mg ha –1 at the state level, well below the maximum recorded yield at the plot level of 6.59 Mg ha –1 . The Y p of current wheat varieties is far above Y c in Oklahoma, and Y c represents 74% of Y a but only 30% of Y p at state level. For growing season rainfall (GSRF) amount