Nitrous oxide emissions in Chinese vegetable systems: A meta-analysis.

China accounts for more than half of the world's vegetable production, and identifying the contribution of vegetable production to nitrous oxide (N2O) emissions in China is therefore important. We performed a meta-analysis that included 153 field measurements of N2O emissions from 21 field studies in China. Our goal was to quantify N2O emissions and fertilizer nitrogen (N) based-emission factors (EFs) in Chinese vegetable systems and to clarify the effects of rates and types of N fertilizer in both open-field and greenhouse systems. The results indicated that the intensive vegetable systems in China had an average N2O emission of 3.91 kg N2O-N ha-1 and an EF of 0.69%. Although the EF was lower than the IPCC default value of 1.0%, the average N2O emission was generally greater than in other cropping systems due to greater input of N fertilizers. The EFs were similar in greenhouse vs. open-field systems but N2O emissions were about 1.4 times greater in greenhouses. The EFs were not affected by N rate, but N2O emissions for both open-field and greenhouse systems increased with N rate. The total and fertilizer-induced N2O emissions, as well as EFs, were unaffected by the type of fertilizers in greenhouse system under same N rates. In addition to providing basic information about N2O emissions from Chinese vegetable systems, the results suggest that N2O emissions could be reduced without reducing yields by treating vegetable systems in China with a combination of synthetic N fertilizer and manure at optimized economic rates.