A diffusion based simulation model was tested on groundnut (Arachis Hypogaea L) in a lateritic sandy loam soil (Oxic-Haplustalf) of eastern India. Two moisture regimes, wet and dry, were induced by recharging the soil profile (1.2 m depth) to field capacity storage, whenever soil water pressure reached -0.078 m at 0.225 m (wet) and 0.6 m (dry) soil depths, respectively. Moisture retention characteristics and hydraulic conductivity curves were measured for three distinct soil layers of the experimental soil profile. Readily available meteorological, soil and plant data were used as input parameters of the model. The simulated cumulative ET (ET s ) closely corresponded with the field observed cumulative ET (ET f ) in the early part of the drying cycle following irrigation. However at the later part of the drying cycle ET s deviated from the ET f , this being particularly true under wet regime. The closest match between ET s and ET f was observed under dry soil water regime 50-70 days after sowing (DAS). The model underestimated the field observed ET up to 50 DAS and there after overestimated it.