Yield gap analysis for rainfed grain sorghum in Kansas

In the United States, grain sorghum [Sorghum bicolor (L.) Moench] production is concentrated in the US Great Plains region, with the state of Kansas accounting for ∼50% of the planted area. In Kansas, state-level grain yields steadily increased at a rate of 0.07 Mg ha⁻¹ year⁻¹ from 1957 to 1990. However, since 1990, sorghum yield trends across the United States and Kansas have been exhibiting signs of yield stagnation. The objectives of this study were to (1) quantify the magnitude of the yield gap and (2) identify possible reasons for yield stagnation of rainfed sorghum in Kansas. Current yield (Y_c) was estimated as the average yield of the most recently reported 10 years. Maximum attainable yield (Y_a) and water-limited potential yield (Y_w) were estimated with a frontier yield function using an extensive dataset of crop performance trials, yield contest data, and county-level survey yield data totaling 2997 site-years. State-level Y_c was 4.7 Mg ha⁻¹, which represents 77% of Y_a and 49% of Y_w. At a regional level, there is a trend of increasing yield gap in central and western Kansas sorghum-producing regions. Sorghum yield in Kansas appears to be stagnant due to a small exploitable yield gap relative to Y_a rather than Y_w, a statewide shift in planting area to environments more vulnerable to water deficits, and cultivation in soils with moderate to severe limitations.