Nutritional diagnosis in carob-tree:: Relationships between yield and leaf mineral concentration

Reliable fruit production of carob-tree (Ceratonia siliqua L.) in the Mediterranean region may be linked to nutrient availability and nutrient status of the trees. The objectives of this study were to determine relationships between yield and leaf nutrient concentrations, determine limits of nutrient concentration required for maximum yield, and establish yield prediction models for carob-tree. The study was conducted in a mature carob-tree orchard established on an acid soil, with low organic matter content. Treatments consisted of two N rates (as ammonium nitrate), 0.3 and 0.9 kg N tree(-1) yr(-1) and three irrigation levels (0, 50, and 100% of Class A pan evaporation). Each tree also received 0.6 kg K after the second year of the experiment. The field trial was conducted during the 4 yr from 1992 to 1995, and leaf N, P, K, Ca, Mg, Fe, Mn, and Zn concentrations were analyzed in autumn (40 d after full bloom) and winter (90 d after full bloom). A nonbearing year (third year of experiment) was excluded from this study. Each nutrient concentration value obtained on both sampling rates was correlated with fruit production and subsequently several multiple regressions were tested. The best estimation model indicated that 92% of yield variation may be related to N, P, K, Mn, and Fe leaf concentration values. This model was validated against independent data. The optimal leaf nutrient limits were established corresponding to maximum yields obtained under the conditions of this site.