Two-dimensional energy balance model for ridge-furrow tillage

Typescript (photocopy).Ridge-furrow tillage systems establish heat and moisture fluxes in two dimensions. However, no models had been developed previously which permitted quantitative investigations of temperature fluctuations, redistribution and evaporation of soil water, and radiation exchanges within such systems. Therefore, a one-dimensional soil surface energy balance submodel was developed and coupled with a two-dimensional finite element soil heat and moisture transport submodel to simulate moisture and energy fluxes within and above a soil with a ridge-furrow configuration. The finite element procedures of the model allow irregularly shaped boundaries and varying physical properties within the soil to be more easily incorporated into the model than with other techniques such as finite differences. Soil heat and moisture fluxes were determined using the soil heat and moisture transport submodel. A Newton-Raphson convergence technique was used to estimate the energy balance and return initial estimates of soil surface temperatures at the surface nodes. The soil heat and moisture transport and soil surface energy balance submodels alternated calculating the soil surface temperature and energy balance until convergence between submodels was found. Backward substitutions into the systems of simultaneous equations produced the temperature and moisture nodal values at the next time step. Model verification against measured field data indicate that the model adequately simulated soil temperature and moisture profiles, and evaporation amounts. Simulated reflected irradiances from the artificial, white furrow experiment overestimated by 20% measured reflected irradiances for slopes facing away from the sun, and underestimated by 40% that for slopes facing the sun. However, errors of this magnitude would only slightly influence the total energy balance. Soil temperatures were simulated generally to within [plus or minus] 2-4°C of values measured from the experimental plot row orientation. Soil volumetric water contents from the same orientation were simulated mostly within [plus or minus]20% of measured values, the exception being the uppermost positions of the ridge and southwest facing slope which were overestimated greatly due to the extensive soil cracking and erosion at these positions during field measurements..