Weakened growth of cropland N2o emissions in China associated with nationwide policy interventions

Authors: SHANG, ZIYIN - Peking University; ZHOU, FENG - University Of Aberdeen; SMITH, PETER - University Of Aberdeen; SAIKAWA, ERI - Emory University; CIAIS, PHILIPPE - Laboratoire Des Sciences Du Climat Et De L'Environnement (LSCE); CHANG, JINFENG - Laboratoire Des Sciences Du Climat Et De L'Environnement (LSCE); TIAN, HANQIN - Auburn University; Del Grosso, Stephen - Steve; ITO, AIHIKO - University Of Toronto; CHEN, MINPENG - Renmin University Of China; WANG, QIHUI - Peking University; CUI, XIAOQING - Peking University; CASTALDI, SIMONA - Universita Degli Studi Di Salerno; JUSZCZAK, RADOSLAW - Poznan University Of Life Sciences; KASIMIR, ASA - University Of Gothenburg; MAGLIULO, VINCENZO - National Research Council - Italy; MEDINETS, SEGIY - Odessa Ii Mechnikov National University; MEDINETS, VOLODYMYR - Odessa Ii Mechnikov National University; REES, BOB - Sruc-Scotland'S Rural College; WOHLFART, GEORG - University Of Innsbruck; SABBATINI, SIMONE - University Of Tuscia; YAN, BO - Peking University

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2019
Publication Date: 6/24/2019
Citation: Shang, Z., Zhou, F., Smith, P., Saikawa, E., Ciais, P., Chang, J., Tian, H., Del Grosso, S.J., Ito, A., Chen, M., Wang, Q., Cui, X., Castaldi, S., Juszczak, R., Kasimir, A., Magliulo, V., Medinets, S., Medinets, V., Rees, B., Wohlfart, G., Sabbatini, S., Yan, B. 2019. Weakened growth of cropland N2o emissions in China associated with nationwide policy interventions. Global Change Biology. https://doi.org/10.1111/gcb.14741.
DOI: https://doi.org/10.1111/gcb.14741

Interpretive Summary: China has experienced rapid agricultural development in the last several decades, accompanied by increased N fertilizer consumptions in croplands. This trend for increased N fertilizer use and how that affects the emission of the important greenhouse gas nitrous oxide (N2O) is uncertain. The primary sources of this uncertainty are the coarse spatial aggregation of agricultural activity data and the incomplete model representation of N2O emissions in response to management. Here we provide a data-driven estimate of cropland N2O emissions across China from 1990 to 2014, compiled using a global monitoring network, nationwide survey-based reconstruction of N-fertilization and irrigation, and an updated version of spatially-referenced algorithm. We find that China’s annual cropland-N2O emissions increased on average by 11.2 Gg N per year from 1990 to 2003, after which such increase seems to have ceased until 2014 (2.8 Gg N per year). The slowdown of an increase in cropland-N2O emissions after 2003 was pervasive across the majority of croplands, accounting together for ~2/3 of total sowing areas. This change was mainly driven by the nationwide reduction of N-fertilizer application rates, partially due to the prevalence of the Nationwide Soil Testing and Formulation Fertilization Program, launched in the early 2000s. This reduction has almost offset the policy-driven expansion of sowing areas in major cropping regions, particularly the Northeast Plain and the lower Yangtze River Basin. Our results underline the importance of high-resolution activity data and of spatially-explicit response of N2O emission to management for capturing cropland-N2O emission patterns. The importance of this research is in quantifying and identifying how agricultural farm management (activity data) can reduce global N2O emissions. The work also provides useful data for leaders and policy makers who are developing intervention or mitigation recommendations on future emissions.

Technical Abstract: China has experienced a rapid agricultural development over the past decades, accompanied by increased fertilizer consumptions in croplands, but the trend and drivers of the associated nitrous oxide (N2O) emissions have remained uncertain. The primary sources of this uncertainty are the coarse spatial aggregation of agricultural activity data and the incomplete model representation of N2O emissions in response to management. Here we provide a data-driven estimate of cropland N2O emissions across China from 1990 to 2014, compiled using a global monitoring network, nationwide survey-based reconstruction of N-fertilization and irrigation, and an updated version of spatially-referenced nonlinear algorithm. In addition, we have evaluated the drivers behind changing cropland-N2O patterns using an index decomposition analysis approach. We find that China’s annual cropland-N2O emissions increased on average by 11.2 Gg N per year (P < 0.001) from 1990 to 2003, after which such increase seems to have ceased until 2014 (2.8 Gg N per year, P = 0.02), as found in an ensemble of process-based terrestrial biosphere models (TBMs). The slowdown of an increase in cropland-N2O emissions after 2003 was pervasive across the majority of croplands, accounting for ~2/3 of total sowing areas. This change was mainly driven by the nationwide reduction of N-fertilizer application rates, partially due to the prevalence of the Nationwide Soil Testing and Formulation Fertilization Program, launched in the early 2000s. This reduction has almost offset the policy-driven expansion of sowing areas in major cropping regions, particularly the Northeast Plain and the lower Yangtze River Basin. Our results underline the importance of high-resolution activity data and of spatially-explicit response of N2O emission to management for capturing cropland-N2O emission patterns. Improving the representation of policy interventions is also recommended for future projections.