Nitrogen derived from fertilization and straw for plant cane nutrition

The objective of this work was to evaluate the recovery, by plant cane, of the nitrogen ((15)N) from urea and from sugarcane (Saccharum spp.) crop residues - straw and root system - incorporated into the soil. The experiment was settled in 2005/2006 with the sugarcane cultivar SP81 3250. At planting, microplots of 2 m length and 1.5 m width were installed, and N applications were done with 80 kg ha(-1) N (urea with 5.05% in (15)N atoms) and 14 Mg ha(-1) crop residues - 9 Mg ha(-1) of sugarcane straw (SS) and 5 Mg ha(-1) of root system (RS), labeled with (15)N (1.07 and 0.81% in (15)N atoms, respectively). The total N accumulation by plants was determined during the crop cycle. Although the N use by shoot from crop residue mineralization (PA and SR) increased significantly over time, this source hardly contributed to crop nutrition. The recovery of the (15)N-urea, (15)N-SS and (15)N-RS by plant cane was 30.3 +/- 3.7%, 13.9 +/- 4.5% and 6.4 +/- 0.9%, respectively, representing 15.9, 4.7 and 1.4% of total nitrogen uptake by shoot.