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Glob Chang Biol. 2018 Dec;24(12):5590-5606. doi: 10.1111/gcb.14425. Epub 2018 Sep 14.

Chinese cropping systems are a net source of greenhouse gases despite soil carbon sequestration.

Gao B1,2,3, Huang T3,4, Ju X3, Gu B5,6, Huang W1,2, Xu L1,2, Rees RM7, Powlson DS8, Smith P9, Cui S1,2.

Author information

1
Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China.
2
Xiamen Key Lab of Urban Metabolism, Xiamen, China.
3
College of Resources and Environmental Sciences, Key Laboratory of Plant-soil Interactions of MOE, China Agricultural University, Beijing, China.
4
College of Geography Science, Nanjing Normal University, Nanjing, China.
5
Department of Land Management, Zhejiang University, Hangzhou, China.
6
School of Agriculture and Food, The University of Melbourne, Melbourne, Victoria, Australia.
7
SRUC, Edinburgh, Scotland, UK.
8
Department of Sustainable Agriculture Sciences, Rothamsted Research, Harpenden, UK.
9
Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, UK.

Abstract

Soil carbon sequestration is being considered as a potential pathway to mitigate climate change. Cropland soils could provide a sink for carbon that can be modified by farming practices; however, they can also act as a source of greenhouse gases (GHG), including not only nitrous oxide (N2 O) and methane (CH4 ), but also the upstream carbon dioxide (CO2 ) emissions associated with agronomic management. These latter emissions are also sometimes termed "hidden" or "embedded" CO2 . In this paper, we estimated the net GHG balance for Chinese cropping systems by considering the balance of soil carbon sequestration, N2 O and CH4 emissions, and the upstream CO2 emissions of agronomic management from a life cycle perspective during 2000-2017. Results showed that although soil organic carbon (SOC) increased by 23.2 ± 8.6 Tg C per year, the soil N2 O and CH4 emissions plus upstream CO2 emissions arising from agronomic management added 269.5 ± 21.1 Tg C-eq per year to the atmosphere. These findings demonstrate that Chinese cropping systems are a net source of GHG emissions and that total GHG emissions are about 12 times larger than carbon uptake by soil sequestration. There were large variations between different cropping systems in the net GHG balance ranging from 328 to 7,567 kg C-eq ha-1  year-1 , but all systems act as a net GHG source to the atmosphere. The main sources of total GHG emissions are nitrogen fertilization (emissions during production and application), power use for irrigation, and soil N2 O and CH4 emissions. Optimizing agronomic management practices, especially fertilization, irrigation, plastic mulching, and crop residues to reduce total GHG emissions from the whole chain is urgently required in order to develop a low-carbon future for Chinese crop production.

KEYWORDS:

N2O and CH4 emission; agronomic management; life cycle analysis; net greenhouse gas balance; soil organic carbon; upstream CO2 emissions

PMID:
30118572
DOI:
10.1111/gcb.14425

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