Comparisons of two soil water flow models under variable irrigation

Performance of WATCOM (a numerical model) and CRPSM (a simple water balance model) were assessed in simulating root zone water storage and water balance components under cowpea in Nigeria using a line source sprinkler system. Three sets of field data were collected: the first was used for calibration and model parameters’ estimation and the other two for testing and comparisons. The simulated soil water storage and crop evapotranspiration with WATCOM and CRPSM were in good agreement with field-measured data though WATCOM performed significantly better (P < 0.05) under the stressed condition. The maximum average error between predicted and measured soil water storage was −0.95 and +1.47 mm for WATCOM and CRPSM, respectively, while that between measured and predicted actual crop evapotranspiration was +2.7 and +11.38 mm, respectively, for the two models. WATCOM gave generally higher cumulative deep percolation and lower evapotranspiration than that of CRPSM for all irrigation levels (P < 0.05), and values of deep percolation for WATCOM were in better agreement with field data than that of CRPSM. This suggests that drainage below the field capacity needs to be included in CRPSM and that WATCOM will be a more useful management tool when detailed soil parameter is required and under variable water regime.