Effects of moisture and temperature on C and N mineralization from surface-applied cover crop residues

Cover crop (CC) decomposition and subsequent release of nitrogen (N) are highly influenced by residue water potential (ψ) and temperature (T). To evaluate how carbon (C) and N mineralization from surface-applied CC residues responds to changes in ψ and T, a controlled microcosm experiment was conducted for 150 days with three CC residues (early-killed cereal rye (Secale cereale L.), late-killed cereal rye, late-killed crimson clover (Trifolium incarnatum L.), and a soil-alone control) under different ψ (−0.03, −1.5, −5, and −10 MPa) and T (15, 25, and 35 °C) conditions. Headspace gas was sampled periodically to determine carbon dioxide (CO2) and nitrous oxide (N2O) emissions. Soil inorganic N was determined by destructive sampling at 15, 30, 60, 100, and 150 days. Temporal dynamics in C and N mineralization from surface-applied CC residues were adequately described by first-order rate kinetic models. Early-killed rye and crimson clover (low C:N) residues decomposed quickly and mineralized N, whereas, late-killed rye residue (high fiber content and C:N) immobilized N. The normalized values of C and N mineralized from surface-applied CC residues increased exponentially with increasing ψ from −10.0 to −0.03 MPa. Increasing T from 15 to 35 °C further amplified the effect of ψ, suggesting a strong interactive effect of ψ and T on C and N mineralization from CC residues. Mathematical equations were developed to describe these interactive effects. Existing computer simulation models (e.g., CERES-N) could be improved by integrating these equations to simulate the effect of environmental conditions on surface-applied CC residue decomposition and N mineralization.