Decomposition and Carbon Dynamics of Crop Residue Mixtures in a Semiarid Long Term No-Till System: Effects on Soil Organic Carbon

Abstract

Plant residues decomposition transfers organic matter and nutrients to soil, and plays a decisive role in carbon (C) cycling. The aims of our study were to analyze under realistic field conditions the annual decomposition and C dy- namics of crop residues mixtures under long-term no-till management and their effect on soil organic carbon (SOC). Three treatments were evaluated: soybean monoculture, soybean rotation (maize as preceding crop), and maize rotation (soybean as preceding crop). In each treatment soil samples and crop residue samples were collected. In crop residues samples we determined: total residue mixture biomass, soybean residue biomass, maize residue biomass, non identifiable residue biomass, total C, soluble C, insoluble fiber. In soil samples, SOC were analyzed. Decomposition rates were calcu- lated for residues mixture, soybean and maize residue before and after deposition of fresh residue. Decomposition rates of all residues analyzed showed a high variability between treatments. Total C, soluble C and insoluble fiber concentrations of the residues mixtures showed a great similarity among treatments. Contrarily, their annual dynamics differed between sampling dates in all treatments. We concluded that decomposition and C dynamics of crop residues mixtures in long- term no-till systems in the semiarid central Argentina are strongly influenced by: the interaction of the chemical quality of the residues, the proportion of the residues from different crops and/or with different decomposition degree,and the sea- sonal effect. The greater C amount in residues mixture of rotation was not reflected in SOC contents, and further studies are recommended.