Irrigated Small Grain Residue Management Effects On Soil Properties and Nutrient Cycling.

The effects of straw removal from irrigated wheat and barley fields on soil properties and nutrient cycling is a concern due to its potential impact on the sustainability of agricultural production.  The demand for animal bedding and the potential development of cellulosic ethanol production will likely increase straw demand in the future.  Previous reviews addressing changes in soil properties when crop residues are removed focused primarily on rain-fed systems. 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 irrigated wheat and barley production systems.  Six studies compared SOC changes with time in irrigated systems in which wheat straw was either 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 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 (MCS) from nine wheat system studies.  Calculations of the MCS values were from rain-fed systems and are likely the best information available presently, for use in evaluating residue removal effects in irrigated systems. However, long-term studies are needed to obtain reliable data for diverse irrigated systems.  Nutrients removed from the soil/plant system with straw can be worth $7 to $20 per Mg of straw removed.  Producers will need to determine the cost of the nutrient removal from their systems to determine the value of the straw.