Irrigation small grain residue management effects on soil properties

The effects of straw removal from fields under irrigated wheat and barley on soil properties has become a potential concern in Idaho. The demand of straw for animal bedding and feed, and the potential development of cellulosic ethanol production will likely increase in the future. This paper reviews published research assessing the effects of wheat and barley straw removal on soil organic carbon (SOC), and analyzes changes in nutrient cycling within wheat and barley production systems. Six studies compared SOC changes with time in irrigated systems in which wheat was removed or retained. These studies indicate that reductions in SOC due to removal may not be a concern. Soil OC either increased with time or remained constant when residues were removed. It is possible that belowground biomass is supplying C to soils at a rate sufficient to maintain or in some cases, slowly increase SOC with time. A separate research review calculated the minimum aboveground residue required to maintain SOC levels from nine wheat system studies. Eight of the studies were dryland production systems. The grain yields required to produce sufficient above ground biomass to maintain SOC levels ranged from 9 to 122 bu acre-1 for wheat and 14 to 185 bu acre-1 for barley. Wheat straw contains approximately 15, 3.4, and 33 lbs nitrogen (N), phosphorus (P2O5), and potassium (K2O) ton-1, respectively. Barley straw contains approximately 12, 3.9, and 38 lbs N, P2O5, and K2O ton-1, respectively. The calculated total economic value of the N, P2O5, and K2O in one ton of wheat and barley straw is $17.91 and $18.18, respectively, based on average nutrient costs in the Pacific Northwest in 2007. Rotations including wheat and barley in the irrigated agriculture of Idaho and many other states in the Pacific Northwest are much different than what was reported in the reported studies. There is very little reported data that can be directly related the irrigated rotations in Idaho that include wheat or barley. To fully understand the impacts of crop residue removal from soils in Idaho, research projects need to be conducted on crop rotations that include wheat and barley under irrigated conditions in Idaho. Otherwise the best data available for dissemination is from research conducted in different environments and systems.