Eficiência de uso do nitrogênio e emissão de gases de efeito estufa na cultura do trigo sob fontes de adubação nitrogenada

Abstract

In Brazil, more than 80% of nitrous oxide emissions come from the agricultural sector, with synthetic nitrogen fertilizers being the main source. These fertilizers are intensifying this natural process and raising concerns within the scientific community. This study aimed to evaluate the effects of different nitrogen fertilizer sources on N₂O emissions, nitrogen losses, and nitrogen use efficiency (NUE) in wheat cultivation. The experiment was conducted at UTFPR, Dois Vizinhos Campus, from June to September 2023. The experimental design was a randomized block design with four replications. The treatments evaluated were urea (UR), urea with a urease inhibitor (UR+NBPT), ammonium nitrate (AN), ammonium nitrate at 70% of the dose (NA70), and a control (C). The application was carried out as a topdressing 37 days after planting, with a nitrogen rate of 75 kg ha⁻¹. N₂O flux was analyzed using the closed static chamber methodology, and the concentration was determined by gas chromatography. Soil parameters (WFPS, NH₄⁺, and NO₃⁻) were also measured during the evaluations. Grain yield was obtained by measuring the grain mass in an area of 1.36 m². N₂O emissions remained low for most of the evaluation period, with emission peaks occurring shortly after fertilizer application, between 7 and 30 days, with lower fluxes in UR+NBPT and UR compared to NA70%. Additionally, NA70% had the highest values for WFPS (81%), cumulative N₂O emissions (0.15 kg N-N₂O ha⁻¹), emission intensity (19.05 kg CO₂eq Mg grain⁻¹), and emission factor (0.10%). Urea showed the highest ammonia volatilization rate on the third day (2.69 kg N-NH₃ ha⁻¹ day⁻¹), with cumulative emissions of 8.70 kg N ha⁻¹, corresponding to 9.23% of the applied nitrogen. Grain yield was similar across treatments, with averages of 2.30, 2.92, 3.15, 3.73, and 3.28 Mg ha⁻¹ for T, NA, NA70, UR, and UR+NBPT, respectively. Urea had the highest nitrogen use efficiency at 37.91%, with no statistical difference. It was concluded that N₂O fluxes did not exceed 30 μg N m⁻² h⁻¹, cumulative emissions did not surpass 1% of the applied nitrogen, and emission factors were below the 1.6% threshold set by the IPCC, highlighting the significance of these region-specific studies.