Abstract

Accurate estimates of crop evapotranspiration ET_c, that quantify the total water used by a crop, are needed to optimize irrigation scheduling for horticultural crops and to minimize water degradation. During early growth, accurate assessments of ET_c are difficult in vegetable crops because of high soil evaporation due to frequent irrigation. A model to estimate ET_c for vegetable crops, using only daily reference evapotranspiration data as an input parameter, was developed. It calculates crop transpiration and soil evaporation based on ground cover and daily radiation intercepted by the canopy. The model uses a two-stage soil evaporation method adapted to conditions of variable reference evapotranspiration. The model was evaluated against data using measurements from two seasons of lettuce crop, two tomato fields in the same season, and one season of broccoli crop production. Using all of the crop data, the root–mean–square error for measured versus modeled daily ET_c was 0.72 mm day^-1, indicating that the model works well.

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