Numerical Analysis of Water and Heat Transport in Vegetated Soils Using HYDRUS-1D.

Evaluating water contents and soil temperature in the root zone is important for water management of agricultural fields. For accurate numerical analyses of the simultaneous movement of water and heat in vegetated soils, the boundary condition at the soil-plant-atmosphere interface is critical. Although water and energy balance for arid or semi-arid regions is well used as upper conditions, vegetated soils are rarely considered.
 In this study, we implemented in the HYDRUS-1D code the double-source model that includes separate water and energy balance equations for the vegetation canopy and the underlying soil surface. The transpiration rate is calculated from the balance equation for the vegetation canopy, while the evaporation rate and soil heat flux are calculated from the balance equation for the soil surface. The model is evaluated using field soil temperature and pressure head data from different depths collected at the alfalfa field in San Jacinto, California, from September 3rd 2008 when the alfalfa was harvested to October 16th 2008. Soil temperatures (10, 15, 30, and 100 cm depth) and pressure heads (30, 135, 160 cm depth) were simulated using applied irrigation fluxes, measured meteorological data (solar radiation, air temperature, relative humidity, and wind speed), and crop information (crop height, LAI, and root depth). Simulated temperature and pressure head closely agreed with measured values.