Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2006
Publication Date: 9/20/2007
Citation: Kozak, J.A., Aiken, R.M., Flerchinger, G.N., Nielsen, D.C., Ma, L., and Ahuja, L.R. 2007, Comparison of modeling approaches to quantify residue architecture effects on soil temperature and water. International Journal of Soil and Tillage Research.95:84-96.
Interpretive Summary: Residue and tillage management are important tools for soil and water conservation. The presence of residue and its orientation, i.e. standing stubble or distributed flat residues, significantly impacts evaporation, soil water storage, soil temperature, soil freezing and associated frozen-soil runoff. RZ-SHAW, a computer model which can simulate the effects of crop residues on soil temperature and water, allows different methods to simulate crop residues. The objective of this study was to compare the predictive accuracy of the three RZ-SHAW methods to simulate effects of residue architecture and no residue on soil temperature, and water near the surface. Overall, RZ-SHAW offers a flexible model to simulate diurnal changes in energy balance and air temperature needed for simulating surface residue effects on soil temperature and water content. Results from this study can be used by managers to make more informed decisions concerning the effects of tillage and residue management on soil and water conservation.
Technical Abstract: RZ-SHAW is a hybrid model, comprised of the Simultaneous Heat and Water (SHAW) module and the Root Zone Water Quality Model (RZWQM) with enhanced simulation of different residue types and architectures that affect heat and water transfer at the soil surface. RZ-SHAW allows different methods of surface energy flux evaluation to be used: (1) The SHAW module; (2) the Shuttleworth-Wallace (S-W) module; and (3) the PENFLUX module. The objective of this study was to compare the predictive accuracy of the three RZ-SHAW modules to simulate effects of residue architecture and no residue on net radiation, soil temperature, and water kinetics near the soil surface. The model was tested in Akron, Colorado: in either soil with standing and flat wheat residue, no-till (NT) or soil with stubble-mulch incorporated residue, reduced-till (RT). Temperature gradients between the soil surface and ambient air frequently exceeded 17C under RT and NT conditions, invalidating the isothermal assumption employed in the S-W module. The S-W module exhibited positive bias for Rn and negative biases for 3-cm soil temperature and 30-cm water content; these were attributed to consequences of the isothermal assumption. Under radiative loading, both SHAW and PENFLUX modules overestimated 3-cm soil temperature for RT conditions but underestimated it for NT conditions. Mean bias error for 30-cm water content was within 0.015 m/m under NT for SHAW and PENFLUX modules; and within 0.01 m/m under RT for the PENFLUX module. Better performances of the SHAW and PENFLUX surface energy evaluations are to be expected as both approaches are more detailed and consider a more discretized domain. Overall, RZ-SHAW offers a flexible model to simulate diurnal changes in energy balance and air temperature needed for simulating surface residue effects on soil temperature and water content