Nitrogen Soil Transformation Affected By Nitrogen Sources in Sugarcane.

For better utilization of fertilization with nitrogen by crops is necessary broad understanding of the dynamics of this nutrient in soil. The estimate of mineralization can be used to adjust the nitrogen fertilization recommendations, since N of the more labile fraction is released at the initial periods of the mineralization process. Thus, aim of this study was to evaluate changes in rates of mineralization and immobilization-N due to the application of N sources and the incorporation of plant residue of high C/N ratio. The experiment was carried out under aerobic incubating for a period of 20 weeks. The experimental design was completely randomized with six treatments, three replications and eight evaluation times, amounting 144 experimental units. Nitrogen fertilizers (enriched with 2 atom % ¹⁵N) were applied on soil surface as ammonium or amidic-N at dose of 100 mg N kg^-1 and the sugarcane residue at dose of 5.2 g kg^-1 incorporated into the soil (referring to 15 Mg ha^-1 of dry matter of sugarcane shoots). The residue incorporation of sugarcane to the soil increased immobilization rates of available mineral nitrogen in soil. The nitrogen from ammonium sulfate showed higher immobilization rates in total soil organic fraction, but higher nitrogen mineralization from soil native nitrogen. The nitrogen from urea source showed higher immobilization rates in the fraction of soil organic nitrogen and lower rates of nitrogen mineralization from soil native nitrogen.