Predicting straw yield of hard red spring wheat

Accurate estimates of straw production for spring wheat (Triticum aestivum L.) are important in the Great Plains for conservation planning, nutrient cycling, and fertilizer recommendations. Frequently, these estimates are based on grain yield and the assumption of a Constant ratio between straw and grain. This approach may not always be accurate because straw/grain ratios can vary greatly across environments and genotypes. Spring wheat studies were conducted to contrast straw/grain ratios over diverse water and N environments and to determine if plant height and grain protein at maturity, in addition to grain yield, would significantly improve predictions of straw production. A 3-yr field study consisting of four cultivars, three water regimes' and a wide range of N levels served as a database for this analysis. Straw/grain ratios ranged from 0.91 to 2.37 and were affected by water, N, and cultivar selection. Extended periods of water stress during grain fill and/or vegetative growth and improved N fertility I generally resulted in wider ratios. Stability of straw/grain ratios over the diverse environments improved as cultivar height decreased. Straw yield models that considered only grain yield provided a modest fit to the data (R-2 = 0.66. SE = 701 kg ha(-1)). Prediction models that included terms for plant height and plant N status (straw N or grain protein) in addition to grain yield provided a considerably better fit to the experimental data (R-2 = 0.88, SE = 425). Observations from validation data sets confirmed that inclusion of plant height (two of two data sets) and grain protein (one of two data sets) improved accuracy, of straw yield predictions.