Intercropping of Gliricidia to Supply Nitrogen to Citrus Orchards in a Kaolinitic Soil in Northeastern Brazil.

Despite its positive results, the use of annual legume as green manures to citrus orchards has not been adopted in the Brazilian Coastal Tablelands, especially due to the need of sowing the legumes every year. The use of tree legumes, as Gliricidia sepium, has been proposed as an alternative to this drawback. To evaluate the viability of intercropping gliricidia with citrus and to compare the effect of this practice with that of N fertilizer, an experiment was carried out in an Ultisol in a randomized block design with seven treatments and four replications. The orchard had seedlings of 'Pera' orange budded on Rungpur lime. Treatments were: no mineral N fertilization (T1), 1/3, 2/3 and 3/3 of the recommended N dose as urea (T2, T3 and T4, respectively) and N supplied by the shoot residues of two, five and eight plants of gliricidia per citrus tree (T5, T6 and T7). Two rows of gliricidia spaced by 1 m were planted in the center of every other line of citrus. Within-row spaces between gliricidia seelings were 2, 0.8 and 0.5 m for T5, T6 and T7, respectively. Gliricidia was pruned every four months at a height of 50 cm and residues deposited on the soil around the orange within a 1-m radius. Shoot mass and N content were evaluated in all pruning events. Twenty months after planting, citrus plants were evaluated regarding the variables height, stem diameter, and crown diameter.  At this stage of development, the response of citrus to gliricidia deposition was highest when 5 plants were used (T6). In terms of effect on citrus growth, adding residues from five gliricidias per citrus plant was equivalent to 1/3 of the recommended N dose.