Simulation of Water State and Flow in the Soil-Plant-Atmosphere System by a Model Named Hejmdal

Abstract

Appreciating that water available to crops is one of the most yield determining environmental factors within a region, a continuous dynamic model describing water state and fluxes in soil and plant to atmosphere has been constructed, tested in the field, and is being applied for evaluation of quality of arable land. The model was established on soil physical and plant physiological parameters determined in laboratories, and on climatic parameters. Soil physical input parameters of the plants are: soil water characteristic curve, soil hydraulic conductivity, root growth and distribution, plant resistance to water uptake, plant water characteristic curves, leaf area index, plant resistance to water-vapour flux, plant growth (i.e. photosynthesis + respiration). Climatic input parameters are: global and net radiation, temperature, air humidity, wind velocity, rate and amount of precipitation. The soil profile is divided into 10 cm thick compartments with root and soil characteristics assumed to be evenly destributed. Time intervals are of 0.002 days. The output potentials are many, the most important perhaps being evapotranspiration, soil and plant water status, and plant growth. A two-seasonal field test has been carried out. Change in soil water content was measured by a neutron probe, evapotranspiration and photosynthesis by the Bowen Ratio Method, and plant water status by the Pressure Bomb Technique. Inputs were the actual climatic parameters measured. Simulated and measured results of evapotranspiration fitted closly, both on accumulated basis and on halfhour basis during both wet and dry periods.