MODELING THE EFFECTIVE RAINFALL ON MAIZE

A model was developed to simulate the effective rainfall for supplemen tary irrigation purposes. The model was based on physical-hydric prope rties of the soil, on rainfall characteristics, on evapotranspiration of the crop, and on leaf interceptation losses. The Darcy equation was used to calculate the re-distribution of water in the soil and the pe rcolation losses. The unsaturated hydraulic conductivity of the soil w as calculated by the Campbell equation. A potential equation was adjus ted to simulate the interception losses, from measured data of interce ption losses of 21 rainfalls events, measured in the period between De cember 7, 1991, and January 22, 1992, in Vicosa, MG, Brazil. Total rai nfall during the crop cycle (115 days) was 941.2 mm and the simulated losses due to interception were 243.2 mm, corresponding to 26% of the total rainfall. It was concluded that 75% of the differences between t he measured and the simulated moisture were lower than 10%, wich indic ates that the model could be used to calculate the effective rainfall for irrigation planning of intervals equal to or greater than 30 days.