Biochemical composition of cover crop residues determines water retention and rewetting characteristics

When cover crop residues are left on the soil surface, their decomposition is mainly influenced by environmental conditions in residue layers, particularly residue water potential (& psi;residue). Thus, models for surface residue decomposition in conservation tillage systems should include a sub-module that can simulate hourly changes in & psi;residue using available weather variables. The main goal of this study was to collect data to further improve a previously developed sub-module within the Cover Crop Nitrogen Calculator (CC-NCALC) that simulates water content and & psi;residue in cover crop residues left on the soil surface. Specific objectives were to (1) evaluate the effect of degree of residue decomposition on the characteristic water release curves for cereal rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.) residues, and (2) model the rate of rewetting of cereal rye and crimson clover residues by rainfall. Our results extended the data needed for equations to estimate regression parameters for water release curves of cereal rye and crimson clover residues based on changes in lignin concentration as residue decompose. Our results also indicated that the parameters of an equation describing residue wetting as a function of cumulative rainfall could be estimated from soluble carbohydrate concentrations in the residue. These results will be integrated into the & psi;residue sub-module of CC-NCALC to further improve the estimation of hourly changes in & psi;residue${\psi }_{{\mathrm{residue}}}\ $of cover crop residues remaining on the soil surface. Water release curves of cereal rye and crimson clover residues change with the stage of decomposition.Parameters for the water release curve can be estimated from residue lignin concentration.The rate of rewetting of residues by the rain depends on soluble carbohydrate concentrations.