MOBILITY OF ROOT AND LEAF ABSORBED BORON IN ORANGE TREES

Boron deficiency is widespread in Brazilian citrus orchards and decreases yield of the main varieties. The prevention or correction of B deficiency is usually done by soil or foliar application. The B mobility depends on formation of polyol-B-polyol complexes that are phloem-translocated and occurs mainly in the species which produce significant amounts of polyols (sorbitol, manitol and dulcitol). The objective of this work was to study B absorption by roots and leaves of orange trees and to quantify the contribution to fruits. The experiment was conducted in a “fertigated” 4-year-old Valencia on Swingle Citrumelo block in the State of São Paulo, Brazil. Treatments consisted in application of isotopically-enriched ¹⁰B in soil (fertigation) and leaves. B distribution within trees was evaluated four months after of ¹⁰B application, in different parts of the branches: new (leaves, twigs and fruits developed after the treatment with 10B) and old parts (leaves and twigs already existing before the treatment with 10B). Samples were analyzed by total B content and ¹¹B/¹⁰B isotope ratio (ICP-MS). The results showed that the percentage of B derived from fertilizer in the new branches and fruits were 60-65% when B was applied in the soil, and 10-20% when sprayed foliarly.