Increase in soil organic carbon by agricultural intensification in northern China

Agricultural intensification has contributed greatly to the sustained food supply of China's population of 1.3 billion over the 30-year period from 1982 to 2011. Intensification has several and widely recognized negative environmental impacts including depletion of water resources, pollution of water bodies, greenhouse gas emissions and soil acidification. However, there have been few studies over this period on the impacts of intensification on soil organic carbon (SOC) at the regional level. The present study was conducted in Huantai County, a typical intensive farming region in northern China, to analyze the temporal dynamics of SOC influenced by climate and farming practices. The results indicate that from 1982 to 2011, SOC content and density in the 0-20 cm layer of the cropland increased from 7.8 ± 1.6 to 11.0 ± 2.3 g kg^-1 (41%) and from 21.4 ± 4.3 to 33.0 ± 7.0 Mg ha^-1 (54%), respectively. The SOC stock (0-20 cm) of the farmland for the entire county increased from 0.75 to 1.2 Tg (59%). Correlation analysis revealed that incorporation of crop residues significantly increased SOC, while an increase in the mean annual temperature decreased the SOC level. Therefore, agricultural intensification has increased crop productivity and contributed to SOC sequestration in northern China. In the near future, more appropriate technologies and practices must be developed and implemented for a maintenance or enhancement of SOC in this region and elsewhere in northern China, which also reduce non-CO2 greenhouse gas emissions, since the climate benefit from the additional SOC storage is estimated to be smaller than the negative climate impacts of N2O from N fertilizer additions