|MCCLELLEN, RON - Natural Resources Conservation Service (NRCS, USDA)
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2011
Publication Date: 1/15/2012
Citation: McClellen, R.C., McCool, D.K., Rickman, R.W. 2012. Grain yield and biomass relationship for crops in the Inland Pacific Northwest United States. Journal of Soil and Water Conservation. 67(1):42-50. doi:10.2489/jswc.67.1.42.
Interpretive Summary: Crop residue is essential in preventing wind and water erosion, sequestering carbon, and maintaining soil organic matter. Residue also has commercial value for livestock bedding, energy production, and other uses. Knowing the quantity of residue produced by a crop is important in balancing residue use for resource maintenance with the potential for a needed source of farm income. Historically, residue production has been estimated as a crop-specific fixed ratio of residue to crop yield, determined before crop breeding programs developed semi-dwarf cereals and other crops that reduced plant size while increasing grain yield. We used residue and yield data from current crop varieties to develop new relationships between residue production and grain yield for dominant crops in the Inland Pacific Northwest. The study produced new relationships that indicated lower residue quantities at current high yields than predicted by previous ratios. For example, using the historical fixed residue to grain ratio for winter wheat can result in over-estimating residue from high-yielding (130 bushels per acre) winter wheat by over 50%, (4,800 pounds or almost 2.5 tons per acre). Our results provide improved residue to grain yield relationships for estimating crop residue production in the region, and in conjunction with erosion prediction and carbon sequestration models, a basis for determining if and where residues can be harvested for off-field use. The new relationships will be important to conservation agencies and planners in federal, state, and consulting firms who estimate available fuel resources when locating biomass-based power generation stations.
Technical 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 in the Inland Pacific Northwest. Retaining post-harvest crop residues as soil surface cover is a primary method for controlling wind and water erosion, and 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 a fixed residue-to-grain index value to determine amounts of residue. We assembled a large set of crop yield and residue production data to examine and improve this relationship. The study indicates that crop breeding efforts that emphasized yield have reduced the amount of residue for each unit of grain produced, that residue production versus grain yield data for major dry-farmed crops of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) cereals as well as annual legumes and brassicas can be fit with a linear relationship with a positive intercept, and that the slope of the line and intercept are crop specific. Using the historical fixed residue to grain ratios can result in over-estimating residue quantity of high-yielding winter wheat by over 50%. The results provide improved residue to grain yield relationships for use in water and wind erosion prediction models applied to the conditions of the NWRR. 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.