Efeito de sistemas de produ??o e doses de adubo de libera??o lenta no estado nutricional de porta-enxerto cítrico

摘要

The production system of citrus rootstock before the transplanting can modify the seedlings root system and the response of these to fertilization. The objective of this experiment was to evaluate the effects of three production systems of 'Rangpur' lime tree and five doses of a controlled-release fertilizer, applied after transplanting, on the nutritional status of rootstock in the grafting point. The experiment was carried out, under a screen-protected nursery, in a factorial scheme 3 x 5, with seven replicates and one plant per experimental plot. The production systems of citrus rootstock were: 1 - production in stiff plastic tubes filled up with commercial substrate constituted of pinus bark; 2 - production in stiff plastic tubes filled up with substrate constituted of industrial residues of the region, that is, sugarcane bagasse + industrial sugarcane plant residues, (3:2; v:v); and 3 - production in pressed blocks constituted of the pressed substrate used in system 2. The five doses of controlled-release fertilizer formula NPK 14-14-14 were 5, 10, 15, 20 and 25 g/plant. The production system of citrus rootstock before transplanting, influenced the plant response to the fertilization after transplanting. In the grafting point, the plants grown under the pressed block system presented smaller contents of P, K, and Fe in comparison to plants under grown in stiff plastic tubes system, but presented larger growth (root system dry matter, leaf dry matter, stem dry matter and stem diameter). Plants grown in system 1 presented iron deficiency symptoms in leaves, while plants from the other two systems presented magnesium deficiency symptoms in leaves.