Modelling the effective rainfall on maize

Abstract

A model was developed to simulate the effective rainfall for supplementary irrigation purposes. The model was based on physical-hydric properties 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 percolation losses. The unsaturated hydraulic conductivity of the soil was calculated by the Campbell equation. A potential equation was adjusted to simulate the interception losses, from measured data of interception losses of 21 rainfalls events, measured in the period between December 7, 1991, and January 22, 1992, in Viçosa, MG, Brazil. Total rainfall 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 the measured and the simulated moisture were lower than 10%, wich indicates that the model could be used to calculate the effective rainfall for irrigation planning of intervals equal to or greater than 30 days.