Perdas de nitrogênio por volatilização em milho safrinha no sul da Amazônia

Abstract

Urea is the most widely used nitrogen fertilizer today, as it has characteristics such as high soil solubility, high nitrogen concentration, easy manufacture, and cheap, among many other favorable characteristics. However, urea applied to the soil surface is subject to high N losses from ammonia volatilization (NH3), which losses can be quite high in urea applications up to 20 to 30% of applied N. The objective of this study was to evaluate soil nitrogen losses by ammonia volatilization (NH3) in areas cultivated with corn, second crop. For this purpose urease inhibitor and nitrification additives incorporated into the urea used in fertilization were used and emissions were compared in seeds treated with seed inoculated Azospirillum brasilense. The inhibitor additives used were: N- (n-butyl) triamide thiophosphate (NBPT), urease inhibitor; and Dicyandiamide (DCD), nitrification inhibitor. The treatments were: T1: Witness (without additives); T2: Seed inoculated with Azospirillum brasilense; T3: 90 kg ha-¹ of nitrogen; T4: 90 kg ha-¹ of nitrogen + inoculation; T5: 90 kg ha-¹ nitrogen + DCD + NBPT; T6: 120 kg ha-¹ of nitrogen; T7: 120 kg ha-¹ of nitrogen + inoculation; T8: 120 kg ha-¹ nitrogen + NBPT; T9: 120 kg ha-¹ nitrogen + DCD; T10: 120 kg ha-¹ nitrogen + NBPT + DCD. NH3 was collected using a static free semi-open chamber (SALE) for a period of 77 days after fertilization. The data obtained indicated high volatilization in the treatment using the inoculant associated with the application of 120 kg of nitrogen per hectare. In the treatments that received urease and nitrification inhibitors, a reduction in volatilization wasobserved, indicating efficiency in reducing volatilization. Other efficient treatments were 90 kg of nitrogen per hectare, and the one treated with DCD, with the lowest volatilization values. The nitrification inhibitor (DCD) showed the greatest reduction in ammonia volatilization. The use of inoculant Azospirillum brasiliense associated with the application of urea in coverage resulted in higher ammonia volatilization rate. Although NBPT was a specific inhibitor of ammonia volatilization, it was not the inhibitor that most reduced ammonia volatilization. NBPT promoted a significant reduction in volatilization compared to treatments without inhibitors. The associations of NBPT with DCD showed good reduction of ammonia volatilization, indicating that DCD does not interfere with NBPT efficiency.