Eficiência da adubação nitrogenada foliar na cana-de-açúcar

Abstract

The productive sustainability of sugarcane fields depends on adequate nutritional management of sugarcane. Among the nutrients, Nitrogen (N) is the second most absorbed and the one that most limits crop productivity. Leaching losses that occur in sugarcane fields reduce the availability of N for the crop. To meet the need for sugarcane, doses of up to 200 kg ha-1 of mineral N are applied to sugarcane fields, but the recovery of fertilizer N has been limited to 50%. Foliar fertilization can be an alternative to compose more efficient fertilization managements. Whereas, up to 70% of N in the form of N-urea can be recovered by sugarcane within 24 hours. The objective of this work is to evaluate the efficiency of foliar fertilization with N-urea solution in increasing the recovery of N-fertilizer and reducing its leaching losses during sugarcane development. Seven N application managements with doses of 60 kg ha-1, combining reduced fertilization via soil and supplementation on the leaf, plus an extra treatment with application of 120 kg ha-1N via soil, were tested and arranged in three blocks by chance. In the first seven months, N leaching was evaluated. At 162 Day After Planting (DAP), 194 DAP and 224 DAP, the fertilization efficiency, growth and accumulation of aboveground biomass in sugarcane were evaluated. Nitric-N had the greatest participation in the leached solution. The smallest concentrations of N in the leachate and the smallest losses of N by leaching were verified in managements with a dose reduction of 50% (30 kg ha-1) and 25% (45 kg ha-1). In these managements, the N-nitric had greater participation in the leached solution. Foliar fertilization optimized 15N-fertilizer uptake and increased N content and accumulation, biomass production, plant height, and number of internodes. The best responses were identified in the management with a 50% reduction of the dose in the soil with the complementation of two 15 kg ha-1 N applications. In this context, it is concluded that it is possible to reduce the input of N in the soil and complement it via the leaves without compromising the development and accumulation of biomass in the aboveground part of the sugarcane in the sugarcane plant cycle.