SEASONAL-VARIATIONS OF LEAF WATER POTENTIAL AND GROWTH IN FERTIGATED CAROB-TREES (CERATONIA-SILIQUA L)

Variations of predawn and midday leaf water potential and relative gro wth rates were studied in mature carob trees (Ceratonia siliqua L. cv ''Mulata'') submitted to a fertigation experiment. Three levels of irr igation were tested: 0%, 50% and 100%, based on daily standard evapora tion values. For each irrigation level two nitrogen amounts were appli ed - 21 and 63 kg N ha(-1) year(-1) as ammonium nitrate. The experimen t was run between July 91 and August 1993. Measurements of leaf water potential and absolute branch length increments were made at monthly i ntervals, during the entire experimental period or during seasonal gro wth, respectively. Leaf water potential was related to soil volumetric water content, maximum and minimum air temperature and daily evaporat ion. Predawn leaf water potentials were always higher than -1.1 MPa. M idday leaf water potential values presented very large seasonal variat ions and very low values independent of treatments. The low leaf water potentials observed for the fertigated trees during summer, suggest t hat this parameter may be related not only to the evaporative demand b ut also to growth investment. The amount of fertigation was positively correlated with vegetative growth increment and fruit production. Pra ctical implications for irrigation schedules of leaf water potential p atterns together with drought adaptation mechanisms of carob tree are discussed.