Simulations of water and thermal dynamics for soil surface with residue mulch and surface runoff

Authors: WANG, ZHUANGJI - University Of Maryland; THAPA, RESHAM - University Of Maryland; Timlin, Dennis; LI, SANAI - Forest Service (FS); SUN, WENGGUANG - University Of Nebraska; BEEGUM, SAHILA - University Of Nebraska; Fleisher, David; Mirsky, Steven; CABRERA, MIGUEL - University Of Georgia; Sauer, Thomas; Reddy, Vangimalla; HORTON, ROBERT - Iowa State University; TULLY, KATHERINE - University Of Maryland

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2021
Publication Date: 10/13/2021
Citation: Wang, Z., Thapa, R., Timlin, D.J., Li, S., Sun, W., Beegum, S., Fleisher, D.H., Mirsky, S.B., Cabrera, M., Sauer, T.J., Reddy, V., Horton, R., Tully, K. 2021. Simulations of water and thermal dynamics for soil surface with residue mulch and surface runoff. Water Resources Research. 57. https://doi.org/10.1029/2021WR030431.
DOI: https://doi.org/10.1029/2021WR030431

Interpretive Summary: Knowledge of the impacts on residue mulch and surface runoff on surface soil is important for agricultural field management. We developed a new method to simulate the moisture and thermal regimes on soil surface with residue mulch and/or surface runoff using a computer program. The computer program can also present the surface air stability, runoff flux and residue decomposition. The program can estimate the nitrogen and carbon (organic matter) exchanges between residue mulch and surface soil. This information will be useful to scientists, agricultural managers and consultants as well as policy makers.

Technical Abstract: Moisture and thermal dynamics on soil surfaces can be influenced by multiple factors, such as weather conditions, soil properties, residue mulch, surface runoff, and additional anthropic field managements. Because of the difficulties in direct measurements, numerical simulations become an effective method to analyze water and heat, as well as their fluxes on soil surface. Factors mentioned above and their effects on soil moisture and temperature have been studied in existing models. However, (1) those effects may be transient or long-lasting and occur simultaneously or asynchronously; (2) effects from individual factors may be constant or varying with respect to time; (3) interactions or derivatives may appear, e.g., ponded water may submerge a portion of residue mulch, while residue mulch may decompose and induce carbon and nitrogen exchanges between soil and mulch. Therefore, a model that can perform convoluted simulations of surface moisture and temperature should be able to dynamically manage multiple factors, interactions and derivatives; while comprehensive simulations can provide completed results not only including surface moisture and temperature regimes, but also the factor-related quantities, such as surface runoff fluxes, residue decomposition and deformation. In this study, the objective is to develop a convoluted process-based model for surface moisture and temperature, where residue mulch and surface runoff are the two main ambient factors included. Mulch effects are estimated based on a modified coupled water and heat movement model, with precipitation interception and radiation attenuation depending on residue properties; surface runoff is simulated with Saint-Venant equation; residue decomposition as a derivative process is computed via a modified CERES-N model. The interaction between surface runoff and residue mulch, and the derivative effect due to residue decomposition are also included. The model is deployed with a modularized design and a “layered module architecture”, such that the main ambient factors, interactions, and derivatives can be activated or deactivated adaptively based on ambient conditions or user settings. Two illustrative examples including the scenarios of rigid (non-decomposable) residue mulch, surface runoff and mulch decomposition are presented. Results demonstrate mulch effects on conserving soil water and stabilizing soil surface temperature, as well as the occurrence of surface runoff; residue decomposition, nitrogen mineralization and mulch shrinkage are also reported. The flux regimes on soil surface, measured by Rayleigh number and Richardson number, and the decomposition results are of the same scale as literature results. This study demonstrates the workability of the proposed model in simulating moisture and temperature on soil surface with residue mulch and surface runoff. The proposed model can be implemented in existing soil-crop packages, e.g., MAIZSIM, to support Soil-Vegetation-Atmosphere-Transfer (SVAT) modelling. This study also suggests the feasibility of convoluting multiple factors via a modularized model design. Although only residue mulch and surface runoff are included as main ambient factors in this study, the “layered module architecture” provides a generic framework for future model expansion.