Modeling water potential of cover crop residues on the soil surface

Authors: DANN, CARSON - University Of Georgia; CABRERA, MIGUEL - University Of Georgia; THAPA, RESHAM - University Of Maryland; Mirsky, Steven; TULLY, KATHERINE - University Of Maryland; REBERG-HORTON, CHRIS - North Carolina State University; HITCHCOCK, RICK - University Of Georgia; GASKIN, JULIA - University Of Georgia; MORARI, FRANCESCO - Universita Di Padova

Submitted to: Ecological Modeling
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2021
Publication Date: 8/30/2021
Citation: Dann, C., Cabrera, M., Thapa, R., Mirsky, S.B., Tully, K., Reberg-Horton, C., Hitchcock, R., Gaskin, J., Morari, F. 2021. Modeling water potential of cover crop residues on the soil surface. Ecological Modeling. https://doi.org/10.1016/j.ecolmodel.2021.109708.
DOI: https://doi.org/10.1016/j.ecolmodel.2021.109708

Interpretive Summary: Farmers plant cover crops to achieve a myriad of ecosystem services in cropping systems. While a slow-decomposing cover crop maintains a thick and persistent residue layer for a longer duration to effectively protect soil, conserve water, and control weeds, a fast-decomposing cover crop releases nitrogen quickly from their tissues and meets all or part of the nitrogen requirements of the subsequent cash crops. Therefore, decomposition and subsequent release of nitrogen from cover crop residues need to be accurately modeled to assist farmers and land managers in their residue management decisions. Since decomposition is highly influenced by residue environment, a simple mechanistic model was developed to estimate hourly changes in the water potential of surface residues. The surface residue water potential model requires hourly information on air relative humidity, air temperature, and rainfall as inputs. We found that the model simulates well observed diurnal patterns in the water potential of surface residues, with greater values in early morning hours and lesser values in the afternoon. We believe that the integration of the newly developed residue water potential model into existing residue decomposition models will greatly reduce the uncertainty in the accuracy of model simulations. A more accurate simulation of residue persistence and nitrogen release from surface cover crop residues will ultimately assist farmers and land managers in making better cover crop and cash crop management decisions and hence, make their cropping systems more profitable and environment-friendly.

Technical Abstract: Cover crops are usually planted between cash crops to protect the soil, take up residual soil nitrate, and release nitrogen (N) to subsequent crops. Following cover crop termination, residues may be incorporated into the soil or left on the soil surface depending on tillage system used. When residues remain on the soil surface, decomposition is largely dependent on residue temperature and water potential. While it is possible to continuously measure residue temperature, continuous measurements of residue water potential are not yet practical. Thus, a model to estimate residue water potential would be useful for models of residue decomposition. To obtain data for a model of residue water potential for cereal rye (Secale cereale L.), red clover, (Trifolium pratense L.), and crimson clover (Trifolium incarnatum, the objectives of this work were to evaluate the effects of (1) residue stage of decomposition on water release curve; (2) relative humidity (RH) on residue water potential; (3) soil moisture on residue gravimetric water content; (4) precipitation on residue gravimetric water content; and (5) diurnal changes in RH and temperature on residue water potential. Results showed that water release curves for cereal rye and crimson clover changed as decomposition progressed, and that parameters for these curves could be estimated from residue lignin content. Both types of residues rewetted rapidly when exposed to high RH, and cereal rye required a lower amount of rainfall than crimson clover to reach maximum water content. These results were used to develop, calibrate, and validate a model of residue water potential for surface residues. Comparison of observed vs. simulated data indicated the model simulates reasonably well the observed diurnal patterns in surface residue water potential with R2=0.84. Because residue water potential is central to microbial activity and residue decomposition, the developed model could be a useful component of decomposition models that simulate decay of cover crop residues remaining on the soil surface.