Re-assessing nitrous oxide emissions from croplands across Mainland China

Abstract

Reliable quantification of nitrous oxide emission is a key to assessing efficiency of use and environmental impacts of N fertilizers in crop production. In this study, N2O emission and yield were quantified with a database of 853 field measurements in 104 reported studies and a regression model was fitted to the associated environmental attributes and management practices from China's croplands. The fitted emission model explained 48% of the variance in N2O emissions as a function of fertilizer rate, crop type, temperature, soil clay content, and the interaction between N rate and fertilizer type. With all other variables fixed, N2O emissions were lower with rice than with legumes and then other upland crops, lower with organic fertilizers than with mineral fertilizers. We used the subset of the dataset for rice-covering a full range of different typical water regimes, and estimated emissions from China's rice cultivation to be 31.1 Gg N2O-N per year. The fitted yield model explained 35% of the variance in crop yield as a function of fertilizer rate, temperature, crop type, and soil clay content. Finally, the empirical models for N2O emission and crop yield were coupled to explore the optimum N rates (N rate with minimum N2O emission per unit yield) for combinations of crop and fertilizer types. Consequently, the optimum N application rate ranged between 100 kg N ha-1 and 190 kg N ha-1 respectively with organic and mineral fertilizers, and different crop types. This study therefore improved on existing empirical methods to estimate N2O emissions from China's croplands and suggests how N rate may be optimized for different crops, fertilizers and site conditions.

Variation of Greenhouse Gases Fluxes and Soil Properties with Addition of Biochar from Farm-Wastes in Volcanic and Non-Volcanic Soils

“…Emissions of N 2 O from soils depend on diverse factors such as soil water content, level of oxygen, soil pore space, sulphur and organic matter content, among other factors [48]. In agricultural soils, addition of organic residues [49] and nitrogen fertilization [50,51] produce relevant flush of N 2 O emissions to the atmosphere, mainly in the first days after application of fertilizers [52]. In the case of BCs, it has been acknowledged that thermic decomposition produce the stabilization of C-materials and the volatilization of labile forms of nutrients, for example, nitrogen loss with increased pyrolysis temperature due to the volatilization of organic matter, resulting in a reduction of half of their N at 400 • C [53].…”

Weakened growth of cropland‐N2O emissions in China associated with nationwide policy interventions

“…Over the past decades, this source in China increased with N‐fertilizer use, accounting for over 20% of global cropland‐N 2 O emissions from IPCC Tier 1 inventories (FAO, ; Janssens‐Maenhout et al, ; Winiwarter, Höglund‐Isaksson, Klimont, Schöpp, & Amann, ). China is a large country with contrasting crop production systems, climate, and soil types, where the patterns of N 2 O emissions are poorly understood compared to some developed countries (Yue et al, ; Zhou et al, ; Zou, Lu, & Huang, ). In the last decade, process‐based models (e.g., DNDC, DAYCENT, DLEM), used to produce Tier 3 IPCC estimates, simulated global and regional cropland‐N 2 O emissions using subnational N inputs from China (Li et al, ; Tian et al, ; Yue et al, ).…”

Predicting greenhouse gas benefits of improved nitrogen management in North American maize

“…Our recommended model structure is especially robust, as we developed models using a training dataset and subsequently tested model performance on a separate testing dataset. In addition, our recommended model for maize systems in the United States and Canada has similar parameters to a model developed to describe cropping systems in China (Yue et al, 2018). Overall, using minimal site-specific data, our model explains important variation in N 2 O emission, resulting in a model that is appropriate for predicting N 2 O emission from commercial maize fields in the United States and Canada.…”

“…In contrast, N 2 O emissions vary more uniformly for soil texture, soil organic C, soil pH, fertilizer type, and cropping system (Stehfest & Bouwman, 2006). Statistical models generally estimate N 2 O emissions from annual cropping systems based on N applied, N balance, or N use efficiency (Omonode, Halvorson, Gagnon, & Vyn, 2017;Van Groenigen et al, 2010), but more complex statistical models that combine management and environmental parameters improve regional estimates of N 2 O emission (Yue et al, 2018).…”