Irrigated Small-Grain Residue Management Effects on Soil Chemical and Physical Properties and Nutrient Cycling

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The effects of straw removal from irrigated fields cropped to wheat and barley on soil properties and nutrient cycling are a concern because of its potential impact on the sustainability of agricultural fields. The increasing demand of straw for animal bedding and the potential development of cellulosic ethanol production will likely increase the demand in the future. Previous reviews addressing changes in soil properties when crop residues are removed focused primarily on rain-fed systems. This article reviews published research assessing the effects of wheat and barley straw removal on soil organic carbon (SOC) and analyzes changes in nutrient cycling within irrigated wheat and barley production systems. The effects of straw removal on bulk density, saturated hydraulic conductivity, and other properties are reported from selected studies. Six studies compared SOC changes with time in irrigated systems in which wheat straw was removed or retained. These studies indicated that SOC either increased with time or remained constant when residues were removed. It is possible that belowground biomass was 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 annual carbon inputs needed to maintain SOC levels from nine wheat system studies. Calculations of the minimum aboveground annual C source inputs needed to maintain SOC levels were from rain-fed systems and are some of the best information presently available for use in evaluating residue removal effects in irrigated systems. However, long-term studies are needed to obtain reliable data for diverse irrigated systems. Significant amounts of nutrients are removed from the soil/plant system when straw is removed. Producers will need to determine the cost of the nutrient removal from their systems to determine the value of the straw.

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