Irrigação com águas salinas e adubação nitrogenada no cultivo de goiabeira.

Abstract

Guava is among the fruit species of high social and economic importance for the Northeast of Brazil, with great potential for expansion through irrigated plantations; however, in this region, the water sources available for irrigation have high concentrations of salts, which may compromise the exploitation of fruits, including guava in a rational way, especially of those considered sensitive and moderately sensitive to salinity. In this context, the objective of present study was to evaluate the growth, physiological aspects, production and quality of guava fruits cv. Paluma under irrigation with waters of different salinity and nitrogen doses. The experiment was carried out in the experimental area of the Center for Science and Agrifood Technology (CCTA) of the Federal University of Campina Grande (UFCG), Pombal, PB. The experimental design was performed in randomized blocks, with treatments arranged in a factorial scheme 5 x 4, related to the electrical conductivity levels of the irrigation water - ECw of 0.3; 1.1; 1.9; 2.7 and 3.5 dS m-1 and four nitrogen doses 70, 100, 130 and 160% of the recommended dose of N being the standard dose of 100% corresponding to 541.1 mg of N dm-3 of soil with three replicates and two plants per plot. The effects of the different treatments were evaluated by growth variables at 90, 120, 150, 255 and 300 days after transplanting (DAT) and physiology at 210, 255 and 300 DAT and 180 days after pruning (580 DAT); fruit production and quality were evaluated at the time of harvest. The interactive effect was significant at 150 DAT for the number of leaves and leaf area indicating decreased effect for the factor salinity levels of the irrigation water within each dose of nitrogen. Guava growth in number of leaves and branches, stem diameter, leaf area, absolute and relative growth rates, dry matter of leaf, branches and shoot decreased linearly with increase in salinity of irrigation water from 0.3 dS m-1. The stomatal conductance, internal CO2 concentration, CO2 assimilation rate, transpiration, instantaneous water use efficiency and relative water content in leaf were linearly affected by salinity of xviii irrigation water, regardless of the dose of nitrogen used; the increase in salinity from 0.3 dS m-1 promoted an increase in the percentage of electrolyte leakage at 210 and 300 DAT. The number of fruits, average fruit mass, yield per plant, polar diameter and equatorial fruit diameter were linearly affected by the salinity of the irrigation water in the two production cycles. The salinity of irrigation water negatively affects the soluble solids and ascorbic acid levels of guava fruits. The use of ECw of up to 0.96 dS m-1, promotes an acceptable reduction of 10% in production.