Characterizing Spatial and Temporal Variations in N 2 O Emissions from Dairy Manure Management in China Based on IPCC Methodology

The emission factor method (Tier 1) recommended by the Intergovernmental Panel on Climate Change (IPCC) is commonly used to estimate greenhouse gas (GHG) emissions from livestock and poultry farms. However, the estimation accuracy may vary due to practical differences in manure management across China. The objectives of this study were to estimate the direct and indirect nitrous oxide (N 2 O) emissions from dairy manure management between 1990 and 2021 in China and characterize its spatial and temporal variations following IPCC guideline Tier 2. The N 2 O emission factor (EF) of dairy cow manure management systems was determined at the national level and regional level as well. The results showed that the national cumulative N 2 O emission of manure management from 1990 to 2021 was 113.1million tons of CO 2 equivalent, ranging from 90.3 to 135.9 million tons with an uncertainty of ±20.2%. The annual EF was 0.021 kg N 2 O-N (kg N) −1 for total emissions, while it was 0.014 kg N 2 O-N (kg N) −1 for direct emissions. The proportions of N 2 O emissions in North China, Northeast China, East China, Central and Southern China, Southwest China and Northwest China were 32.3%, 18.6%, 11.4%, 5.8%, 6.1% and 25.8%, respectively. In addition, N 2 O emissions varied among farms in different scales. The respective proportions of total N 2 O emissions from small-scale and large-scale farms were 64.8% and 35.2% in the past three decades. With the improvement in farm management and milk production efficiency, the N 2 O emissions per unit mass of milk decreased from 0.77 × 10 −3 kg to 0.48 × 10 −3 kg in 1990–2021. This study may provide important insights into compiling a GHG emission inventory and developing GHG emission reduction strategies for the dairy farming system in China.