Greenhouse gas emissions and crop-specific emission factors of eight upland crops based on a six-year field experiment in the North China Plain

Nitrous oxide is a significant greenhouse gas (GHG) contributor in crop production, yet detailed documentation, including crop yields and specific emission factors (EF_d of N₂O), are lacking for the North China Plain. A six-year (2016–2022) diversified crop rotation experiment in this region examined GHG emissions from eight crops (sweet potato, peanut, soybean, spring maize, sweet sorghum, ryegrass, summer maize, and winter wheat) and fallow seasons. The results revealed that summer maize had the highest cumulative soil N₂O emissions (5.07 kg N ha⁻¹), with an average flux value of 225.3 μg N₂O-N m⁻² h⁻¹ during the growing season. Summer maize emitted 16–75 % more N₂O than spring crops and winter wheat and 85–86 % more than ryegrass (cover crop) and the winter fallow season. All eight crops acted as weak net CH₄ sinks. Annual average CO₂-equivalents of N₂O and CH₄ emissions reflected N₂O emissions from all crops and fallow seasons. In addition, GHG footprint metrics (GF_a, per unit area; GF_y, per kg equivalent yield; GF_b, per kg biomass; GF_e, per unit economic benefit) based on life cycle assessment thinking showed that intensive cereal crops (winter wheat and summer maize) had the highest GHG footprints, while sweet potato had the lowest due to its greater biomass and lower N input. Other crops had 19–90 % lower GHG footprints than wheat and maize. Furthermore, we also quantified specific-crop EF_d of N₂O, with ryegrass having the lowest EF_d (0.48 ± 0.02 %), followed by winter wheat (0.81 ± 0.43 %), and other crops ranging from 1.00 ± 0.13 % to 2.36 ± 0.85 %. This study provides important emissions data for different crops and winter fallow periods, enhancing our understanding of GHG footprints and emission factors, which are essential for the advancement of sustainable agriculture practices.