Feasibility of Organic Fertilization for Reducing Greenhouse Gas Emissions Compared to Mineral Fertilization

The objective of this study was to evaluate the impact of different nitrogen sources (urea, compost, and digestate) on N2O and CH4 emissions and the forage production of Piatã grass in tropical pastures, with the aim of identifying the fertilization practices that can balance productivity with environmental mitigation. The experiment included 10 forage cuts over a period of 14 months, from January 2017 to February 2018. The CH4 and N2O emissions were monitored using closed chambers and analyzed by gas chromatography. The forage production was assessed by weighing and drying the material. The emission intensity was calculated based on the global warming potential of the gases. The data were analyzed using ANOVA and compared by Tukey’s test (p ≤ 0.05). Fertilizer application increased the N2O emissions, with the highest flux (79.56 mg N-N2O/m2/day) observed for the digestate treatment (p < 0.01). The N2O consumption was the most significant for the control treatment (−5.90 mg N-N2O/m2/day) in July. The CH4 oxidation was prevalent across all the treatments, with the highest oxidation for the urea treatment (−49.80 µg C-CH4/m2/day) two days after fertilization. The dry matter production (DMP) was the highest with urea during the summer (16.9 t/ha; p < 0.01). The emission intensity values were 243.41 kg CO2eq/t DM for urea, 103.44 kg CO2eq/t DM for digestate, and 27.35 kg CO2eq/t DM for compost (p < 0.01). The compost application stimulated CH4 oxidation. In conclusion, compost can be considered an important alternative for fertilizing pasture areas, both from a productive and environmental perspective.