Qualidade de frutos da goiabeira ‘paluma’ sob adubação nitrogenada e potássica

Abstract

Brazil has been consolidating in recent years as the third largest producer of fruit in the world. Specifically for guava, Brazilian production in 2011 was 342,528 t, with a highlight in the Northeast region that produced 151,903 t, which represents 44% of the national production. In addition to the production should also be highlighted the quality of these fruits. Thus, the preharvest factors have a great influence on the postharvest quality of agricultural products. Among these factors, the fertilization and, consequently, the nutritional status of the crops can affect the productivity, the quality and the postharvest conservation of the fruits. Based on that, the objective of this experiment was to evaluate the quality of the guava fruits of the Paluma variety, through the physical and physicochemical characteristics, as well as to determine, for the conditions of the Paraiba Coast, the economic doses of nitrogen and potassium that allow to meet the quality requirements market with maximum productivity. The experimental design was a randomized complete block, in a split plot scheme with five replications. The experimental unit consisted of five fruits. The treatments corresponded to the combinations of four nitrogen doses, corresponding to 50, 100, 150, 200 g.plant-1, and four doses of potassium: 50, 100, 150, 200 g.plant-1. The subplots covered the five ripening stages characteristic of guava. For each maturation stage, the response surface technique was applied for N and K doses. For the choice of models, the criterion of determination coefficients (R2) of at least 50% was adopted. The variables evaluated were: fresh mass, transverse diameter, axial length, mesocarp thickness, placenta thickness in the pulp, pulp firmness, soluble solids (SS), titratable acidity (TA), reducing sugars, SS/AT ratio, pH and ascorbic acid content. For the fresh mass, the demand for nitrogen doses increased from 50 g.plant-1 in stage 2 to 100 g.plant-1 in stage 4. These doses promoted the largest fresh masses for these maturity stages.For potassium this requirement was 183 g.plant-1 in stage 2, while in stage 4 it decreased to 100 g.plant-1. This demonstrated a greater need for potassium at the onset of maturation, which declines as it progresses. This also points out an inversely proportional relation of the nitrogen and potassium demands for the accumulation of fresh mass during maturation. In relation to the thickness of the mesocarp, the demand for nitrogen was increasing while for the potassium was constant during the maturation. The N dose of 100 g.plant-1 and that of K 183 g.plant-1 resulted in better quality fruits with respect to physical characteristics. In turn, the physicochemical characteristics were maximized by the N dose of 100 g.plant-1 and K of 150 g.plant-1 of “Paluma” guava. Based on N and K fertilization, the main quality changes in “Paluma” guava occurred between the maturity stages 3 and 5, when fruits presented ideal conditions for fresh consumption, due to the accumulation of soluble solids and soluble sugars. For the physical variables, the application of 100 g of N. plant-1 and up to 183 g of K. plant-1 maximizes the evaluated parameters. For the physicochemical variables it is recommended to apply 100 g plant-1 of nitrogen and 150 g of plant-1 of potassium.