Simulation of maize yield under water stress with the EPICphase and CROPWAT models

Models that simulate the effects of water stress on crop yield ran be valua ble tools in irrigation, We evaluated the crop growth simulation model EPIC phase and the model CROPWAT on their ability to simulate maize (Zea mays L. ) grain yield reduction caused by water stress under semiarid conditions. T he simulation of evapotranspiration (ET), harvest index (HI), Leaf area ind ex (LAI), and final biomass was also evaluated. Data from three held experi ments were used to test the models. In one sprinkler-irrigated experiment, different water amounts (0-592 mm) were applied, producing a continuous wat er deficit. The other two experiments were flood-irrigated and water stress was imposed at given development stages of maize. EPICphase simulated the ET with a root mean square error (RMSE) of 40 mm. The regression of the EPI Cphase simulated vs. measured values of tit and yield had intercepts that w ere not significantly different from ii and slopes not different from 1. EP ICphase overestimated the biomass in the more water-stressed treatments (in tercept of simulated vs. measured values = 5.25 t ha(-1)) due to overestima tion of LAI, Modifications of EPICphase relative to the effect of water str ess on LAI growth and on the light extinction coefficient improved the simu lations of LAI, biomass, HI, and yield. CROPWAT calculated maize grain yiel d with a RMSE of 14% but overestimated ET in the flood-irrigated treatments (bias = 58 mm and 31 mm). Better simulation of ET by EPICphase makes this model more consistent for calculating yield reduction due to water stress.