Utilization by early harvest sugar cane ratoon of the nitrogen from 15N-aqua ammonia and 15N-urea applied to the soil as vinasse N-complement

Abstract

The utilization of nitrogen from aqua ammonia and urea applied to the soil as vinasse N-complement by early harvest sugar cane ratoon was, evaluated using ¹⁵N tracer technique. The experiment was conducted in São Paulo State on a commercial sugar cane field planted with the variety SP 70-1143, first ratoon crop. Two treatments of nitrogen fertilizer (urea and aqua ammonia) were used. Each treatment consisted of 19 neighbouring rows of sugar cane, 10 m long and 1.4 m apart. After vinasse application to the soil surface at a rate of 100 m³/ha, the N-fertilizers; (100 kg/ha of N) were manually applied and buried to 15 cm deep in furrows located 25 cm from both sides of all cane rows. The ¹⁵N-fertilizers were applied to subplots of 2 linear meter row segments (4 replicates). The results of fresh and dry matter yield and nitrogen derived from the fertilizer in the shoots (12-13 kg/ha of N-fertilizer recovery) were the same for both treatments (aqua ammonia and urea), 12 months after N fertilization. Six months after fertilization the estimates of nitrogen recovery from the aqua ammonia and urea in the shoot of the ratoon crop were 24 and 19 kg/ha of N, respectively. The total N in the shoot decreased from the 6^th to the 9^th month, possibly indicating translocation to the roots, or even volatilization losses; by the sugar cane foliage.