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

Authors: MEEKS, CARLEY - University Of Georgia; CABRERA, MIGUEL - University Of Georgia; THAPA, RESHAM - Tennessee State University; REBERG-HORTON, S. CHRIS - North Carolina State University; Mirsky, Steven

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2023
Publication Date: 8/22/2023
Citation: Meeks, C., Cabrera, M., Thapa, R., Reberg-Horton, S., Mirsky, S.B. 2023. Biochemical composition of cover crop residues determines water retention and rewetting characteristics. Agronomy Journal.6:3173-3187. https://doi.org/10.1002/agj2.21451.
DOI: https://doi.org/10.1002/agj2.21451

Interpretive Summary: Cover crops can provide benefits to cropping systems after they are terminated by way of the mulch they create. These benefits depend on the amount of mulch left behind, whether or not it is left on the surface, and how it breaks down. Mulch decomposition, in turn, is affected by environmental conditions within the mulch, especially with regard to water dynamics. The purpose of this work was to improve the model underlying the Cover Crop Nitrogen Calculator (CC-NCALC) to make the tool useful for, and relevant to, farmers who use soil-protective conservation tillage (i.e. low or no till methods that leave cover crop mulch on the soil surface). We evaluated how residue decomposition affected water release from the mulch and how rainfall affected residue decomposition. Our findings will allow us to to further improve our estimation of hourly changes in water dynamics of cover crop residues remaining on the soil surface. This will benefit farmers by making the CC-NCALC tool, which facilitates cover crop management, more useful to those who use conservation tillage methods.

Technical Abstract: When cover crop residues are left on the soil surface, their decomposition is heavily influenced by environmental conditions in residue layers, particularly residue water potential ('_residue). Thus, models for surface residue decomposition in conservation tillage systems should include a sub-module that can simulate hourly changes in '_residue using easily available weather variables. The main goal of this study was to collect additional data with which to further improve a previously developed sub-module within the Cover Crop Nitrogen Calculator (CC-NCALC) for simulating water content and '_residue in the cover crop residue layer left on the soil surface. The specific objectives were to 1) evaluate the effect of degree of residue decomposition on its characteristic water release curves for cereal rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.) residues, and 2) model wetting of surface cover crop residues by rainfall. Our results extended the data needed for equations to estimate regression parameters for the water release curves of cereal rye and crimson clover based on changes in lignin content as residue decompose. Furthermore, our results 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 '_residue sub-module to further improve our estimation of hourly changes in water content or water potential of cover crop residues remaining on the soil surface.