Grain yield and biomass relationship for crops in the Inland Pacific Northwest United States

Abstract

Interest in improving the performance of water and wind erosion prediction models, such as the Revised Universal Soil Loss Equation (RUSLE), the Water Erosion Prediction Project (WEPP), and the Wind Erosion Prediction System (WEPS), led to this study of the relationship between the mass of crop residue and crop yield produced on nonirrigated cropland of the Inland Pacific Northwest United States, consisting of eastern Washington, northern Idaho, and northcentral Oregon. Retaining postharvest crop residues as soil surface cover is a primary method for controlling wind and water erosion; accordingly, erosion prediction models are highly sensitive to the amount of surface residue retained as soil cover. Traditionally, crop biomass calculations and erosion prediction models used expected or modeled crop yields and a fixed residue/grain index (R/G Index) value to determine residue quantity. Literature search indicated that cereal breeding efforts that emphasize yield have reduced the amount of residue for each unit of grain produced. In order to fulfill our objective of improving the relationship between grain yield and residue production, we assembled and examined a large set of regional crop yield and residue production data collected in research plot studies, on-farm field studies, and in available literature from eastern Washington and northcentral Oregon. Results of the study indicated that the R/G Index varies with yield. We also found that residue production versus grain yield for major nonirrigated crops of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) cereals, as well as for annual legumes and brassicas, can be fit with a linear relationship with a positive intercept and that the slope and intercept of the line are crop specific. Parameter values for specific crops are given. Using the historical fixed R/G Index can result in overestimating residue production of high-yielding winter wheat by as much as 35% and underestimating residue production for low spring wheat yields by as much as 66%. The results provide improved residue-to-grain yield relationships for use in water and wind erosion prediction models applied to the conditions of the Inland Pacific Northwest and adjacent areas. They provide a basis for estimating crop residue production in the region, and in conjunction with carbon sequestration models, a basis for determining if and where residues can be harvested for biomass in the region.