Nitrogen Leaching from Soil and Uptake by Sugarcane from Various Urea-based Fertilizers

Two greenhouse experiments were conducted to determine the relative efficiencies of SCU (sulfur-coated urea) and urea with and without N-Serve [2-chloro-6-(trichloromethyl)pyridine] or S on growth, uptake and subsequent losses of N from sugarcane (a trispecies hybrid of Saccharum) grown on Arredondo fs (a loamy, siliceous, hyperthermic Grossarenic Paleudult). In the first experiment, three SCU products, with initial dissolution rates of 32.5, 29.6, and 26.8% of the total N in water during a 7-day period were compared with urea, urea applied in two application, urea + N-Serve, and urea + powdered S at the equivalent amount of S in SCU. In the second experiment SCU-30 was compared with urea, urea applied in two applications, urea + N-Serve, and urea + powdered S at two irrigation regimes (36 and 48 mm/week). Nitrogen fertilizers were applied at rates of 1.78 g/pot of N. Growth and uptake of N by sugarcane plants were not significantly different among treatments, but there were significant differences in leached and residual N. Nitrogen leaching varied from 6 to 24% of applied N depending on the fertilizer treatment and irrigation level. Leaching of the applied N was mainly in the NO₃⁻ form, but when irrigation took place before the N hydrolyzed from urea was completely nitrified, leaching in the NH₄⁺ form was of considerable magnitude. The least N leaching resulted from application of SCU. Inclusion of N-Serve with urea did not improve fertilizer efficiency. Under the conditions of these experiments, SCU was more promising for commercial use than was granular urea mixed with N-Serve. Leaching losses of N from all the sources increased with irrigation but to a varying degree. Eleven to fifteen percent of the applied N was not accounted for by the plant, leachate or soil. These results generally agree with those of a previous field experiment conducted by the authors on the same soil.