Nitrate and Ammonium Content in Degraded Pasture Area Fertilized with Rates and Sources of Nitrogen.

The reconstruction of soil fertility is a major tool for the recovery of degraded pastures and nitrogen fertilizer application assumes a fundamental importance in the production process. This study aimed to determine the nitrate and ammonium content from the soil, as a function of fertilization with rates and sources of nitrogen. The research was conducted with grass Brachiaria in degraded pasture area in an Ultisol in the Cerrado biome. Nitrogen sources (ammonium sulfate, ammonium nitrate and urea) were tested with rates of nitrogen (0, 150, 300, 450 and 600 kg ha^-1 yr^-1). The nitrate content and ammonium were evaluated in the spring. The results were submitted to analysis of variance for the sources and nitrogen rates and when the results was significance at 5%, Tukey test or polynomial regression was applied. The initial contents of nitrate and ammonium in the soil were 3.8 and 4.5 mg kg^-1 of soil, respectively. In the first two samplings was not observed significance for nitrate and ammonium content in the soil with an average content of 31.6 and 51.5 mg kg^-1 of soil, respectively. In the third sampling of soil interaction rates x sources nitrogen wasn’t observed, but the significance was observed separately. The highest nitrate (38.9 mg kg^-1) and ammonium content (42.1 mg kg^-1) were observed for urea and ammonium sulfate, respectively. In case of nitrogen rates linear fit was observed for nitrate (y=0.04+0.1032x, R²=0.94**) and ammonium content (y=1.66+0.0789x, R² = 0.94 **). In general, nitrogen fertilization sources and rates of nitrogen promotes variation in nitrate content and ammonium in the soil.