SIMULATION OF SURFACE-ENERGY BALANCE AND SOIL-TEMPERATURE UNDER STRIP TILLAGE .1. MODEL DESCRIPTION

Conservation-tillage practices that reduce soil erosion and conserve moisture are becoming more widespread. In northern latitudes, germination and early crop development may be hindered due to slower soil warming under mulched surfaces. Strip tillage, in which mulch or stubble strips alternate with bare planting strips, represents a compromise between conservation of soil and water by mulch or stubble and more rapid spring warming of bare soil. The object of our research was to identify the processes that determine surface energy-balance components and soil temperatures under strip tillage and simulate them using a physically based numerical model, which consists of soil-temperature and surface-energy-balance submodels. Dynamic inputs to the model are solar irradiances, air temperatures, water-vapor densities, and wind speeds measured above the surface. The energy-balance model determines radiation, heat, and water-vapor transfers within the mulch and between the mulch surface and atmosphere, as well as the surface energy balance in the bare strip, including shading, shortwave and longwave reflection, and emission effects of the mulch sides. An explicit finite-difference numerical technique is used to predict soil temperatures and heat fluxes. The soil-temperature model was in excellent agreement with analytical solutions to periodic heat-transfer problems in one-dimensional nonhomogeneous and two-dimensional homogeneous semi-infinite soils with surface boundary conditions of the third kind (linear combination of soil heat flux and temperature specified at the surface).