A thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1981

A computer based moisture simulation model is developed, taking into account nonhomogeneous soil properties, the effects of the rate of root growth and the effects of soil moisture depletion on evaporation and transpiration. Nonhomogeneous soil properties are taken into account by considering the soil as consisting of a number of soil layers acting in parallel. The growth of the roots is taken to be a function of the time as well as the soil moisture content. In evaluating the actual evaporation and transpiration from that of the potential evaporation and transpiration, the twin effects of the crop canopy as well as of the actual soil moisture contents are considered. Using the soil and meteorological data as input parameters, a computer based moisture simulation model provides daily simulated moisture values as well as quantitatively evaluating the evaporation, transpiration, root depth and drainage. The information obtained from the simulation model is used to test a simple water balance model with two types of root water extraction terms. The simple model paves an easier way to evaluate the response of the model to various sets of input parameters. This simple model gave satisfactory results for nonhomogeneous soil. The calibration of the model is done by data obtained for sorghum grown on an Alfisol,