THE INFLUENCE OF SOIL MOISTURE ON THE VEGETATIVE AND REPRODUCTIVE GROWTH OF ORANGE TREES UNDER TROPICAL CONDITIONS

The effect of 4 different levels of water stress on the balance of vegetative and reproductive activity of 'Valencia' orange trees were compared. Irrigation was withheld after the end of the rainy season allowing the soil to dry out to matric potentials of -0.07, -0.16, -0.18 and -0.32 MPa which produced predawn leaf water potentials of -0.45, -0.50, -0.65, and -0.85 MPa, respectively.

Vegetative activity following rewatering was higher in trees that had undergone lower water stress. Values of 23.1, 44.7 and 51.2 % of nonbearing shoots were produced in the wettest treatment in the growth flushes of February, April and July, respectively, vs. 13.2, 24.4 and 20.2 % in the driest one. Reproductive activity was favored by the driest treatment in the flushes of February and April originating 45.8 and 64.4 % of flowering shoots vs. 33.4 and 40.5 % in the wettest one. In the flush of July, however, the trend was reversed, with values of 6.9 % vs. 16.2 %, respectively. Intermediate treatments, correspondingly, showed intermediate values of activity. No significant differences were found on yield or fruit quality, except for acidity.

In general, it was shown that previous water stress, within limits, tended to decrease vegetative activity but favored reproductive activity, at least in the first two growth flushes following the resumption of irrigation.