WATER APPLICATION SCHEDULING BY PAN EVAPORATION FOR DRIP-IRRIGATED TOMATO

Tomatoes (Lycopersicon esculentum Mill.) were grown on an Arredondo fi ne sandy soil to evaluate the effects of water quantity applied by dri p irrigation scheduled by pan evaporation in a 3-year study. Water was applied to polyethylene-mulched tomatoes at 0, 0.25, 0.50, 0.75, and 1.0 times pan evaporation in one application per day. Irrigation was a lso scheduled with tensiometers to apply water to maintain soil mater tension above 10 cb. The response to irrigation varied with rainfall d uring the three seasons. In an extremely dry season, fruit yields were doubled by irrigation. Total fruit yields were highest with irrigatio n quantities of 0.75 and 1.0 times pan and significantly lower with 0. 25 and 0.50 times pan. In an extremely wet season, fruit yields were n ot influenced by water quantities from 0 to 1.0 timespan. In a third s eason that was wet from the middle to the end of the season, irrigatio n more than doubled the marketable fruit yield. However, with an incre ase in water quantity from 0.25 to 0.75 times pan, yield increased onl y from 65.9 to 74.1 t-ha(-1). Water uses during the three seasons with 0.75 pan were 31.8, 31.1, and 29.6 cm, respectively. Fruit yields wer e similar with the 0.75-pan and 10-cb tensiometer treatments, but wate r uses with the latter treatment were 15.8, 17.0, and 18.4 cm during t he three seasons, respectively. Tomato leaf N concentrations were redu ced slightly with each increase in water quantity applied, even though N was applied with drip irrigation. Leaf N concentrations with the 10 -cb treatment were generally equal to or higher than the concentration s with 0.75 pan.