ABSTRACT
In citrus, many years ago, quantitative determinations of nutrients consumptions were determined through chemical analysis of young or aerial tree tissues Smith, [87]. However, these data did not properly refl ect the annual nutritional needs of the tree since neither elements accumulated in perennial tissues (roots, trunk and older branches) nor the nutrients supplied by the storage tissues (internal remobilization) can be determined without extracting trees from soil. Legaz and Primo-Millo [42] and Martínez-Alcántara et al. [47] determined the total amount taken up by a citrus tree along one-year vegetative cycle by means of sequential destructive harvests of trees of different ages (2-, 6-and 12-years-old) along the cycle. In the case of N, these data were obtained by supplying nitrogen heavy isotope (15N) in an inert soil-free medium (sand) or in soil. Annual nutrient requirements indicated that some nutrients are provided by the reserves of old leaves, except for Fe, which is scarcely mobile in the tree and its translocation from old leaves to new developing organs can be considered negligible. The difference between new and old organs nutrient demand and that covered by old leaves reserves represents net annual needs for the citrus tree.
