Cover crop residue decomposition in no-till cropping systems: Insights from multi-state on-farm litter bag studies

Authors: THAPA, RESHAM - North Carolina State University; TULLY, KATHERINE - University Of Maryland; Schomberg, Harry; REBERG-HORTON, CHRIS - North Carolina State University; DAVIS, BRIAN - North Carolina State University; PONCET, AURELIE - University Of Arkansas; HITCHCOCK, RICK - University Of Georgia; GASKIN, JULIA - University Of Georgia; CABRERA, MIGUEL - University Of Georgia; Mirsky, Steven; SEEHAVER, SARAH - North Carolina State University; Timlin, Dennis; Fleisher, David

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2021
Publication Date: 12/12/2021
Citation: Thapa, R., Tully, K., Schomberg, H.H., Reberg-Horton, C., Davis, B., Poncet, A., Hitchcock, R., Gaskin, J.W., Cabrera, M., Mirsky, S.B., Seehaver, S., Timlin, D.J., Fleisher, D.H. 2021. Cover crop residue decomposition in no-till cropping systems: Insights from multi-state on-farm litter bag studies. Agriculture Ecosystems and the Environment. https://doi.org/10.1016/j.agee.2021.107823.
DOI: https://doi.org/10.1016/j.agee.2021.107823

Interpretive Summary: In the mid-Atlantic and Southeastern US regions, farmers plant cover crops during the winter fallow periods or between cash crops to provide living roots and to protect soil and water quality for extended time periods. After cover crops are terminated, residues are left on the soil surface in conservation tillage (no-till or reduced) systems. The rate of surface residue decomposition determines both N availability and the longevity of residue cover for effective soil protection, water conservation, and weed suppression. Therefore, it is crucial to investigate factors controlling residue decomposition to assist producers and land managers with evidence-based management practices in conservation tillage systems. Multi-state litter bag studies across 105 farmers' fields were conducted to determine the dynamics of surface cover crop residue decomposition and its controlling factors. We found that decomposition is not limited by temperature during the summer. Maintaining surface residues in humid environments and frequent rain events strongly influenced its decomposition rates. Among cover crop variables, decomposition rates decreased with increasing biomass and metrics of poor quality (i.e., C:N, lignin:N, and holo-cellulose), but increased with increasing labile C fractions (i.e., carbohydrates). An empirical equation was developed to predict residue decomposition rates based on cover crop residue quality and climatic variables. This work provides an accurate estimation of residue decomposition rates, and will be integrated into a decision support tool used by researchers, agricultural professionals, and farmers. Such a tool will allow evidence-based recommendations to farmers and land managers regarding residue persistence and nitrogen release from surface cover crops in conservation tillage systems.

Technical Abstract: Cover crop (CC) residue decomposition influences the provisioning of agroecosystem services. While several laboratory and field studies have investigated processes and mechanisms of CC residue decomposition at specific point or plot scales, regional assessment of factors controlling decomposition rates (i.e. k-values) in no-till corn (Zea mays L.) systems are currently lacking. Here, we conducted the first multi-state on-farm litter bag studies over 105 site-years in the mid-Atlantic and Southeastern US states to determine the independent and combined effect of factors intrinsic to the field (soil and climate) and extrinsic or management factors (CC quantity and quality) on k-values. In the coastal plain regions, the k-values decreased as the underlying soils became sandier. Among climatic variables, mean daily air relative humidity (RH) and number of rainy days showed stronger control on k-values than cumulative rainfall. This suggests faster decomposition of CC residues in humid environments and in site-years with frequent rain-events. Among extrinsic factors, the k-values decreased with higher CC biomass, C:N, residue holo-cellulose concentrations, and lignin:N, but increased with higher residue carbohydrate concentrations. The combination of CC residue quality (C:N and holo-cellulose) and climatic (RH and rainy days) variables accounted in total for 69% of the variability in k-values with CC residue quality having a greater control over k-values than does climate in the mid-Atlantic and Southeastern US states. Therefore, our study emphasizes the necessity to update current process-based decomposition models to explicitly consider both CC residue quality (C:N, holo-cellulose) and climate factors (RH, rainy days), when predicting CC residue decomposition in no-till cropping systems.