Fertilizer-induced emission factors and background emissions of N2O from vegetable fields in China

The estimation of nitrous oxide (N2O) emissions based on specific cropping systems is important for accurate national N2O budgets. Intensively managed vegetable cultivation is responsible for large N2O emissions in mainland China. However, little information can be obtained on the nationwide estimation of direct N2O emissions from vegetable fields. Estimates of fertilizer-induced direct N2O emissions from vegetable fields in mainland China were thus obtained by compiling and analyzing reported data in peer-reviewed journals and research reports. The results indicated that the seasonal N2O emissions from vegetable fields significantly increased with nitrogen (N) fertilizer application (p < 0.0001). According to the ordinary least squares (OLS) model, the fertilizer-induced emission factor (EF) and background emissions of N2O were estimated to be 0.55 +/- 0.05% and 1.067 +/- 0.277 kg N ha(-1) yr(-1), respectively. The EF was reduced and the background emission of N2O increased when the measurement duration was prolonged from <= 100 d to >100 and <= 200 d. Comparable results were obtained by the maximum likelihood (ML) model, with an EF of 0.49 +/- 0.06% and background N2O emissions of 1.228 +/- 0.189 kg N ha(-1) yr(-1). Based on the OLS-derived parameters, the fertilizer-induced direct emissions and background emissions of N2O were estimated to be 66.95 Gg N and 19.63 Gg N, respectively, in 2009, and the annual N2O emissions were much higher in the provinces of Shandong, Henan, Hebei and Sichuan. The estimated N2O emissions from vegetable fields accounted for 21.4% of the total direct N2O emissions from Chinese croplands, with large uncertainties. Therefore, the EF and background emissions of N2O for each cropping system, particularly for intensively managed vegetable fields, should be specifically determined for accurate national N2O inventories. (C) 2011 Published by Elsevier Ltd.