Department of Plant Sciences

The utilization of nitrogen by sugar cane (Saccharum officinarum L.) fertilized with sunn hemp (Crotalaria juncea L.) as green manure and ammonia sulfate and its residual effect during two cuts were evaluated using 15N tracer technique. The amounts of 195.8 kg and 70 kg of N by hectare were added respectively as sunn hemp (SH) and ammonium sulfate (AS), in the following treatments: Control; AS-15N; SH-15N + AS; SH-15N; AS-15N + SH. Five samples of +3 leaves were collected and two meters of the sugar cane plants were cut to estimate the productivity. The experiments were set in randomized blocks design with four replicates. The cane stalk yields in the first cut were higher in the treatment with two both N sources (organic and mineral), however not differing between them. The highest fertilizer contributions on nitrogen to sugarcane crop were observed eight months after sugarcane planting for treatments containing green manure without mineral N, and green manure with mineral N. The largest nitrogen recovery was observed during the first harvest, 18 months after planting: 34.4% in the treatment containing mineral fertilizer and 40.0% in the mineral N plus green manure N treatment. It more nitrogen in the sugar cane ratoon was originated from the green manure treatment 4.8%, while only 1.7% was observed in mineral N source. The presence of green manure crop and mineral N applied together promoting increases in Ca and Mg contents, Sum of Bases, pH, and Base Saturation, with a decline in potential acidity.