Simultaneous heat and water model of a snow-residue-soil system.

摘要

Frozen soil is a major cause of runoff and erosion from many watersheds. Pore-blockage by ice greatly decreases the permeability of soil, causing large runoff and erosion rates from otherwise mild rainfall or snowmelt events. Tillage and residue management greatly affect frost occurrence and depth in agricultural soils, but their effects have been difficult to predict.; A Simultaneous Heat And Water (SHAW) model for evaluating the effects of tillage and residue management on soil freezing has been developed and verified. The SHAW model uses a finite-difference approach to simulate the physics of a one-dimensional snow-residue-soil system. The interrelated processes of heat, water, vapor and solute transfer are calculated through the system from specified atmospheric conditions at the upper boundary to soil conditions at the lower boundary. The model uses inputs of measured or estimated hourly air temperature, wind speed, relative humidity, solar radiation and precipitation to predict snowmelt, evaporation, and profiles of temperature, moisture, ice and solute through the snow-residue-soil system.; Climatic and soil profile data were collected over two winter seasons (1985-86 and 1986-87) on six plots with three tillage treatments and two residue loadings. Maximum frost depth on bare-surface, tilled plots was approximately 30 cm the first year, and 12 cm the second year. Frost depth in residue-covered, no-till plots was about half that of bare-surface, tilled plots.; Data collected over the two winter seasons were used to calibrate and verify the SHAW model. Data for December 1986 from two plots representing the extremes in residue and tillage treatments were used for minor calibration of the model. The model was then verified using data from all six plots over both winter seasons. Soil temperatures, snowmelt, frost depth and moisture contents were predicted quite well for all treatments. The model's capabilities to predict the impacts of different residue, tillage, topographic and environmental conditions are quite good and can be used to evaluate tillage-residue management options for hydrologic and crop production purposes.