Meteorological Limits to Winter Wheat Productivity in the Southern Great Plains: A Simulation Analysis.

Wheat (Triticum aestivum L.) yields in the southern Great Plains have been nearly stagnant for the last 30-yr, and some of the yield stagnation may be caused by the meteorological characteristics of the region. Our objectives were to identify geospatial gradients in key weather variables and to assess the meteorological drivers of wheat productivity and resource-use efficiency across Texas, Oklahoma, and Kansas. Water-limited wheat aboveground biomass and grain yield (Y_w) were simulated for 28 consecutive years at 37 locations across the southern Great Plains using Simple Simulation Modeling – Wheat (SSM-Wheat), actual soil and weather data, planting date, and population density. Regional gradients in meteorological variables were determined for (i) the entire crop cycle, (ii) pre- and post- anthesis, or (iii) jointing-anthesis interval, and Y_w were related back to these variables using linear and stepwise multiple regression. Boundary function analysis determined water productivity (WP), and transpiration- and radiation- use-efficiency (TE and RUE). Strong latitudinal gradients occurred for temperatures and longitudinal gradients for precipitation, evapotranspirative demand, and solar radiation. Wheat Y_w averaged 6.0 Mg ha^-1 and followed the longitudinal precipitation gradient increasing from west (3.5 Mg ha^-1) to east (6.9 Mg ha^-1). Interannual Y_w variability was large with coefficient of variation (CV) ranging from 0.11 to 0.5 from east to west. Meteorological variables accounting for major portions of the Y_w variability were water supply (precipitation + PAW_s) in the west (81.7%) and cumulative solar radiation (R_s) during the anthesis – physiological maturity in the east (86.9%). Temperatures during the anthesis-physiological maturity phase negatively affected grain yields across all locations and years (8% of Y_w variability). Wheat WP (19.1 kg ha^-1 mm^-1), TE (24.2 kg ha^-1 mm^-1), and RUE (0.86 g MJ^-1 based on incident R_s) compared well with published literature and can be used as benchmarks for other studies in the region.