UTILIZATION BY EARLY HARVEST SUGAR-CANE R ATOON OF THE NITROGEN FROM N-15-AQUA AMMONIA AND N-15-UREA APPLIED TO THE SOIL AS VINASSE N-COMPLEMENT

The utilization of nitrogen from aqua ammonia and urea applied to the soil as vinasse N-complement by early harvest sugar cane ratoon was ev aluated using N-15 tracer technique. The experiment was conducted in S b Paulo State on a commercial sugar cane field planted with the variet y SP 70-1143, first ratoon crop. Two treatments of nitrogen fertilizer (urea and aqua ammonia) were used. Each treatment consisted of 19 nei ghbouring rows of sugar cane, 10 m long and 1.4 m apart. After vinasse application to the soil surface at a rate of 100 m(3)/ha, the N-ferti lizers (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 N-15-f ertilizers were applied to subplots of 2 linear meter row segments (4 replicates). The results of fresh and dry matter yield and nitrogen de rived from the fertilizer in the shoots (12-13 kg/ha of N-fertilizer r ecovery) were the same for both treatments (aqua ammonia and urea), 12 months after N fertilization. Six months after fertilization the esti mates 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 b y the sugar cane foliage.