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 Yp 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 <250 mm wheat yields were often water-limited. However, average GSRF was 471 mm, and yield was typically limited by factors other than GSRF amount. Production exhibited greater temporal variability than yield, and production gap may be a better indicator than yield gap for regions with highest potential to increase production. Low yields and yield stagnation in Oklahoma cannot be attributed to a small remaining yield gap, nor to inadequate GSRF amount.