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Abstract: 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. [Copyright &y& Elsevier]

The fruit has become the third-largest agricultural planting industry after cereals and vegetables in China. Fertilization regimes (e.g., application rate and method) in fruit orchards typically differ from cereal croplands, which would incur a pronounced difference in fertilizer-induced nitrous oxide (N 2 O) emissions between them. However, fertilizer-induced direct N 2 O emissions from orchard fields remain poorly understood. We conducted a field experiment in a peach orchard and a global meta-analysis of N 2 O emissions from fruit orchards. The emission factor (EF) of fertilizer N for N 2 O averaged 0.81%, with a background N 2 O emission of 3.4 kg N ha–1 yr-1 in our field study. A global meta-analysis suggested that the linear regression model was the best to fit N 2 O emissions by fertilizer N input for most fruit types compared to the nonlinear models. When averaging all global data, the linear model projected the EF of N 2 O from orchards to be 0.84%, with the background emission of 1.96 kg N ha–1. The estimate of direct N 2 O derived from the orchard-specific nonlinear model was substantially lower than those from the nonlinear model with global cropland measurements. The fertilizer-induced direct N 2 O emission from Chinese orchards during the 2000s was estimated to be 32–49 Gg N yr–1, equivalent to about 14% of total direct N 2 O emissions from Chinese uplands. Therefore, orchard cultivation constitutes a hotspot of N 2 O emissions in the agricultural sector, and priority should be given to emissions reduction to achieve the transition to climate-smart agriculture. [Display omitted] • N 2 O emissions from global orchards were summarized and meta-analyzed. • N 2 O emission was 32–49 Gg N yr–1 from Chinese orchards during the 2000s. • Orchard cultivation is one of the hotspots of agricultural N 2 O emissions. • Orchard N 2 O emissions were similar to emissions from vegetables and tea cultivation. [ABSTRACT FROM AUTHOR]