Crescimento e absorção de macronutrientes pelo meloeiro fertirrigado com diferentes doses de nitrogênio e potássio.

Abstract

The region of Chapada do Apodi in the state of Rio Grande do Norte leads Brazilian production and exportation of melon, a entirely fertigated crop. The importance of fertigation technique is attributed to the fractionation of nutrient dose in several applications during crop cycle. The need for field studies to define doses of nitrogen and potassium to be applied via fertigation was the cause of this study, which objectives were: to determine the influence of different doses of nitrogen and potassium applied via fertigation on the yield, growth and macronutrient uptake by plants of "pele de sapo" melon; and to make a balance of the nutrients applied in the soil-plant system. The experimental design was an entirely randomized blocks with three replications in a factorial scheme. Factors studied were three doses of N (83, 119 and 156 kg/ha) and three doses of K 2 0 (190, 271 and 352 kg/ha). Soil and plants were sampled at 22, 33, 43, 54 and 69 days after seeding (DAS) to determine plant dry matter, plant contents of N, P, K, Ca and Mg, and soil contents of N, P and K. Yield of melon fruits was not influenced by potassium doses but decreased linearly as nitrogen doses increased. The higher fruit production was obtained with a dose of 83 kg/ha of N and 190 kg/ha of K 20. Melon plants accumulated low amounts of nitrogen, high amounts of potassium and yielded little dry matter. Plant growth rate showed a minimum in the first 33 DAS, a maximum between 44 and 55 DAS, and a decrease in the final stage of the crop. The increase in nitrogen dose increased soil nitrogen losses, but the increase in potassium dose caused accumulation in the soil. Higher losses of nitrogen, phosphorus and potassium occurred in the stage of higher nutritional needs of the crop.