A SIMPLE NUMERICAL-SOLUTION FOR 2-DIMENSIONAL MOISTURE DISTRIBUTION UNDER TRICKLE IRRIGATION

An analytical solution (Warrick 1974) for time-dependent infiltration of water under point source was suggested for a narrow soil moisture range at or near saturation. An attempt has been made by the authors to validate numerically Warrick's (1974) theory for a wide range of soil moisture conditions by dividing the hydraulic conductivity-moisture relationship into small segments of 0.02 cc/cc. The outputs were compared with the numerical outputs of Brandt et al. (1971), widely used by various workers, and also with the experimental data generated for four soils of widely different textures under both on- and off-cycles of irrigation. Relative comparison between the theoretical and experimental data also was made quantitatively by Relative Error Percent, defined as the percent difference of the two, in relation to the experimental value. Agreements of both models with the experimental data were entirely satisfactory for Ghatakpukur and Baruipur soils that have lower silt and clay contents. For heavier soils, viz. Canning-A and Canning-B, the agreements for both models with the experimental data were relatively less satisfactory at 15-cm depth and beyond. This may be due to errors in (i) experimental observations (by neutron counts at 10-cm depth intervals) at lower moisture regimes, i.e., at the sub-surface depths, due to the influence of the "sphere of influence," which is larger at the lower moisture regime and (ii) theoretical outputs in the case of the heavier soils as a result of neglecting the swelling nature of the soil and hysteresis of soil moisture for estimation of the hydraulic conductivity as the input parameter. The theoretical model proposed by the authors thus behaved similarly to that of Brandt et al. (1971). In view of the simple mathematics and much less computer time involved compared with Brandt et al. (1971), our model should be more useful in computing moisture flux for the entire saturated-unsaturated moisture regime.