Quantifying the Yield Gap for Winter Wheat in West-Central Oklahoma.

In Oklahoma’s rainfed wheat systems, average grain yield progressively increased from the 1950s to the 1980s. However, yields have remained stagnant in the last 30 years, and current wheat grain yields likely remain far below potential yields. The objective of this study was to determine the wheat grain yield gap between current yields, maximum attainable yields, and water-limited yield potentials in central and western counties of Oklahoma. Current yield was determined as the county average grain yield of last 10 years. Maximum attainable yield was determined using a frontier production function approach based on more than 50 years of yield and growing season rainfall data for 20 counties in Oklahoma. Water-limited yield potential was determined using a wheat variety trial network with more than 130 site-years. Yield gaps respective to maximum attainable yield and water-limited yield potential were calculated using total production for each county. Rainfall amount proved to be a limiting factor in counties with growing season rainfall <300 mm. Current wheat production represents 57% of the water-limited potential and 77% of  the maximum attainable production. State average yield was 2.1 Mg ha^-1 and the maximum recorded yield was 6.5Mg ha^-1, three times higher than the state average. We conclude that in central-western Oklahoma the average yield gap with respect to water-limited yield potential is 43% of that potential.