RESPONSE OF YOUNG CLEMENTINE CITRUS TREES TO DRIP IRRIGATION .1. IRRIGATION AMOUNT AND NUMBER OF DRIPPERS

Growth, evapotranspiration, water relations and yield components of clementine trees (Citrus clementine, Hort ex Tan) subjected to differential drip-irrigation treatments were investigated during two seasons (1990-1992). Irrigation treatments were applied in a factorial design of two or four emitters per tree and four amounts of water (50, 80, 110 and 140% of tree evapotranspiration measured by a large weighing lysimeter located in the same plot). Seasonal water use in the lysimeter was 290 and 397 mm per year for 1990 and 1991, respectively, and the corresponding crop coefficient values were 0.25 and 0.31. Soil evaporation during selected periods of 1991 ranged from about 50% of evapotranspiration in months with frequent rainfall to 8-30% in rainless months. The number of emitters per tree did not significantly affect soil matric tension, tree water status or tree growth, nor flowering, fruit-set or yield. Irrigation amount, however, significantly affected all these variates. Irrigation with 50% ET was insufficient in both seasons, producing high water stress and reducing tree growth. Yield was also reduced by a reduction in fruit number per tree. Optimum growth of the trees was obtained with irrigation at 110% ET which did not differ from that at 140%.