Model for estimating evaporation and transpiration from row crops

Accurate estimates of crop evapotranspiration ETc, that quantify the total water used by a crop, are needed to optimize irrigation scheduling for hort icultural crops and to minimize water degradation. During early growth, acc urate assessments of ETc are difficult in vegetable crops because of high s oil evaporation due to frequent irrigation. A model to estimate ETc for veg etable crops, using only daily reference evapotranspiration data as an inpu t parameter, was developed. It calculates crop transpiration and soil evapo ration based on ground cover and daily radiation intercepted by the canopy. The model uses a two-stage soil evaporation method adapted to conditions o f variable reference evapotranspiration. The model was evaluated against da ta using measurements from two seasons of lettuce crop, two tomato fields i n 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 dail y ETc was 0.72 mm day(-1), indicating that the model works well.