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

Authors: THAPA, RESHAM - University Of Maryland; TULLY, KATHERINE - University Of Maryland; CABRERA, MIGUEL - University Of Georgia; DANN, CARSON - University Of Georgia; Schomberg, Harry; Timlin, Dennis; GASKIN, JULIA - University Of Georgia; REBERG-HORTON, CHRIS - North Carolina State University; DAVIS, BRIAN - University Of Maryland; Mirsky, Steven

Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2021
Publication Date: 2/4/2021
Citation: Thapa, R., Tully, K.L., Cabrera, M.L., Dann, C., Schomberg, H.H., Timlin, D.J., Gaskin, J., Reberg-Horton, C., Davis, B.W., Mirsky, S.B. 2021. Effects of moisture and temperature on C and N mineralization from surface-applied cover crop residues. Biology and Fertility of Soils. 57:485-498. https://doi.org/10.1007/s00374-021-01543-7.
DOI: https://doi.org/10.1007/s00374-021-01543-7

Interpretive Summary: Cover crops are non-cash crops that play a dual role in soil nitrogen (N) management in cropping systems. Cover crops serve as soil N scavengers while growing and reduce nutrient loadings into water bodies. Following termination, decomposition of legume cover crop residues provide all or part of the N requirement of the subsequent cash crops. Whereas, grass cover crops immobilize soil N during decomposition. Therefore, farmers should adjust N fertilizer needs of the subsequent cash crops based on N availability from decomposing cover crop residues. Moisture and temperature in the surface cover crop residues fluctuate dramatically and diurnally. In this study, we developed a response surface model to describe the effect of residue environmental conditions on the decomposition and N release from surface-applied cover crop residues. Researchers can integrate the response surface model developed in this study into existing computer simulation models to better predict decomposition and N released from surface-applied cover crop residues. Ultimately, farmers and land managers can use the modified tool to adjust N fertilizer needs of subsequent cash crops in no-till cropping systems where cover crop residues are left on the soil surface.

Technical Abstract: Cover crop (CC) decomposition and subsequent release of nitrogen (N) in no-till systems is highly influenced by CC residue moisture/water potential and temperature (T). To evaluate how carbon (C) and N mineralization from surface-applied CC residues responds to changes in moisture/water potential and T, a controlled microcosm experiment was conducted for 150 d 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 (-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. Total inorganic N was determined by destructive sampling at 15, 30, 60, 100, and 150 d. 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 ratio) residues decompose quickly and mineralized N, whereas, late-killed rye residue (high fiber content and C:N ratio) immobilized N. The normalized values of C and N mineralized from surface-applied CC residues increased exponentially with increasing moisture/water potential from -10.0 to -0.03 MPa. Increasing T from 15 to 35°C further amplified the effect of moisture/water potential, suggesting a strong interactive effect of moisture/water potential 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.