Small Grain Residue Management Effects on Soil Organic Carbon: A Literature Review

Impact of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) straw removal from fields on soil organic C (SOC) is a concern. Increased animal populations and potential development of cellulosic ethanol production could increase the removal of straw from fields. This paper focuses on the effects of wheat and barley straw removal on SOC in irrigated production systems, and related the results to estimates of the minimum straw C inputs required to maintain SOC (MSC) from rain-fed systems. Six studies compared SOC changes with time in irrigated systems in which wheat straw was removed or retained. These studies indicated that SOC did not decline when residues were removed. Apparently belowground biomass is supplying C to irrigated soils at a rate sufficient to maintain SOC with time. However, under rain-fed systems, returning residue to the soil was required to maintain SOC. Estimates of MSC were obtained from nine rain-fed wheat system studies. Averaged across all rain-fed MSC values, 4.14 Mg more straw per ha was required to maintain SOC in rain-fed than in irrigated systems. Presently, the rain-fed based MSC values are the best information available to evaluating residue removal effects but caution should be used in applying these in irrigated systems. The results from this limited number of irrigated studies suggest that rain-fed estimates of MSC will overestimate the MSC in irrigated systems and underestimate the available irrigated straw resources. There is need to evaluate the effect of residue removal on SOC for diverse irrigated systems