Regional N₂O emission differences and the mitigation measurements in the vegetable production systems of China

Objectives We studied the N₂O-N emission factors in various vegetable species, cultivation modes, and regions in China, and assessed the effects of often used measurements on reducing N₂O emission.

Methods Field observation data were collected from research papers focusing on N₂O emission and emission reduction in vegetable production areas in China. The emission factors (EF) were calculated according to the vegetable species and production areas under greenhouse and open field conditions, respectively. The effect of managements on reducing soil N₂O emission were summarized. The correlation between N₂O emission reduction and vegetable yields were studied as well.

Results The EF of open field vegetable production in North China, Northwest China, the middle and lower reaches of the Yangtze River, Southwest China, and South China were 1.27%, 0.83%, 1.20%, 1.54%, and 5.57%, respectively, with an average of 1.23% across the whole country. Notably, the EF in South China was 6.7 times higher than that in Northwest China. For greenhouse vegetable production, the EF in North China, Northwest China, and the middle and lower reaches of the Yangtze River were 0.99%, 0.65%, and 1.13%, with an average of 0.88% across the whole country. Furthermore, the EF in leafy, fruit, tuber, and root vegetable production were 1.72%, 1.03%, 0.92%, and 1.28% in open field, and in leafy, fruit and tuber vegetable production were 0.44%、0.95% and 0.41% in greenhouse fields, respectively. Compared to conventional fertilization methods, N rate reduction, biochar application, optimized irrigation, and nitrification inhibitor application reduced N₂O emissions by 41.3%, 29.1%, 37.4%, and 27.9%, respectively. Combination of optimized irrigation with N rate reduction, and nitrification inhibitor with N rate reduction achieved N₂O emission reduction ranging from 45.8% to 57.3%. All the nitrification inhibitors displayed comparable N₂O reduction rates of 26.5% to 29.7%. Application of biochar in rates of ≤10, 10−20, 20−30 and 30−40 t/hm² could reduce N₂O emission by 31.7%, 24.3%, 38.0%, and 26.8%, respectively; Reducing nitrogen input rate of ≤20%, 20%−30%, 30%−40%, 40%−50%,>50% were observed N₂O emission reductions of 36.9%, 37.5%, 29.7%, 71.3%, and 39.4%, respectively, compared to conventional N rate and management practices.

Conclusions The N₂O-N emission factors are significantly different among vegetable production areas and vegetable species under both green house and open field conditions in China. More attention to N₂O emission should be paid in the multi-maturing vegetable systems in the subtropical climate areas. EF reducing measurements should be made according to vegetable species for relatively constant effect across the whole country. Reducing 40%−50% of conventional N fertilizer input, nitrification inhibitors and biochar application could reduce N₂O emission effectively, and their combining use can achieve a win-win scenario, without obvious influence on vegetable yields.