Short-Term Assessment of Nitrous Oxide and Methane Emissions on a Crop Yield Basis in Response to Different Organic Amendment Types in Sichuan Basin

Agriculture’s goal to meet the needs of the increasing world population while reducing the environmental impacts of nitrogen (N) fertilizer use without compromising output has proven to be a challenge. Manure and composts have displayed the potential to increase soil fertility. However, their potential effects on nitrous oxide (N₂O) and methane (CH₄) emissions have not been properly understood. Using field-scaled lysimeter experiments, we conducted a one-year study to investigate N₂O and CH₄ emissions, their combined global warming potential (GWP: N₂O + CH₄) and yield-scaled GWP in a wheat-maize system. One control and six different organic fertilizer treatments receiving different types but equal amounts of N fertilization were used: synthetic N fertilizer (NPK), 30% pig manure + 70% synthetic N fertilizer (PM30), 50% pig manure + 50% synthetic N fertilizer (PM50), 70% pig manure + 30% synthetic N fertilizer (PM70), 100% pig manure (PM100), 50% cow manure-crop residue compost + 50% synthetic N fertilizer (CMRC), and 50% pig manure-crop residue compost + 50% synthetic N fertilizer (PMRC). Seasonal cumulative N₂O emissions ranged from 0.39 kg N ha⁻¹ for the PMRC treatment to 0.93 kg N ha⁻¹ for the NPK treatment. Similar CH₄ uptakes were recorded across all treatments, with values ranging from −0.68 kg C ha⁻¹ for the PM50 treatment to −0.52 kg C ha⁻¹ for the PM30 treatment. Compared to the NPK treatment, all the organic-amended treatments significantly decreased N₂O emission by 32–58% and GWP by 30–61%. However, among the manure-amended treatments, only treatments that consisted of inorganic N with lower or equal proportions of organic manure N treatments were found to reduce N₂O emissions while maintaining crop yields at high levels. Moreover, of all the organic-amended treatments, PMRC had the lowest yield-scaled GWP, owing to its ability to significantly reduce N₂O emissions while maintaining high crop yields, highlighting it as the most suitable organic fertilization treatment in Sichuan basin wheat-maize systems.