UTILIZATION BY LATE HARVEST SUGAR-CANE RA TOON OF 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 late harvest sugar cane ratoon was eva luated using N-15 tracer technique. The experiment was conducted in Sa o 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 (90 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-fe rtilizers were applied to single microplots of 2 linear meter row segm ents (4 replicates). The sugar cane yield and N derived from the ferti lizer (40% of N-fertilizer recovery) were similar for both treatments of N-fertilizer (aqua ammonia and urea), 12 months after fertilization (final harvest). The results of accumulated nitrogen in the shoot, at different growing stages and up to the harvest time, strongly indicat ed the occurrence of biological nitrogen fixation (BNF). The BNF toget her with the nitrogen taken up from the soil resulted in a total of 26 0 kg/ha of N accumulated in the shoot of ratoon crop after 12 months g rowing period.