Nitrogen Utilization from Ammonium Nitrate and Urea Fertilizer by Irrigated Sugarcane in Brazilian Cerrado Oxisol

Sugarcane is the most promising among renewable biofuel-producing crops. An adequate availability of water and nutrients, especially nitrogen (N), is of utmost importance. From the hypothesis that the source and the rate of N fertilization influence the N use efficiency of an irrigated soil-sugarcane system, this study aimed to evaluate the stalk and crop residues (pointer and leaves) yield, as well as the N utilization, from different rates of ammonium nitrate and urea by irrigated sugarcane in the cane plant cycle, using an N-15 isotopic dilution technique. The soil used for the experiment was an Oxisol (Rhodic Haplustox) Cerrado (savannah) phase. The experiment was carried out at a farm of the Raizen Mill, which was located in the municipality of Jatai, Goias State, Brazil. The sugarcane variety IACSP95-5000 was used in a randomized block design, with three replicates, four N rates (30, 60, 120, and 180 kg ha(-1)), and two fertilizer sources labeled with N-15 isotopes (urea and ammonium nitrate). The average value for N utilization was 60.17% for the ammonium nitrate source and 44.95% for urea. The responses in the percentage and quantity of N in the sugarcane from the fertilizer increase with the increasing N rate. The soil was the main N source for sugarcane. The higher stalk and pointer yield was recorded at the average rate of 143.61 kg N ha(-1). Further studies are needed to evaluate the residual effect of N in the next cycles.