1) Tausta ja tavoitteet
Soil organic carbon (SOC) can act as both a source and a sink of atmospheric CO2. The pool size is larger than the carbon stored in living vegetation and the atmosphere combined, a small change in the pool size may cause significant variation in the atmospheric CO2 concentration (Schlesinger, 1997). In COP21 (UNFCCC 2015) in Paris, France made a 4 per mil initiative (http://4p1000.org/understand), since an annual increase of “4 per thousand” (0.4 ‰) each year of organic matter in soil would be enough to compensate for the global emissions of greenhouse gases (GHG).
China has a large land area, similar in size to that of the United States, comprises 130 Mha of cropland (Editorial Board of China Agriculture Yearbook, 2008), 400 Mha of grazing land and 134 Mha of forestland (Lal, 2002). Cropland is a major land use in China. SOC stock is about 3950 TgC in croplands of China (Yan et al., 2011) and 10500 TgC in grassland of northern China (Yang et al., 2010). Cropland management in China was estimated to have a carbon sequestration potential of 25–37 TgC yr-1 (Lal, 2002), while carbon sink of China’s forests is 180 TgC yr-1(Pan et al., 2011). Annual total GHG emissions in China are about 2490 Tg C) (Liu et al., 2015).
SOC is directly disturbed by human activities such as land use change, agronomic management practices, and indirectly affected by CO2, fertilization, N deposition, and climate change (Smith et al., 2005). Cropland management, such as fertilization and cultivation has changed considerably during the last 30 years, resulting in dramatically increased crop yields. Meantime, crop growth and productivity has been affected notably by climate change since the 1980s (Tao et al., 2012). There may have been significant changes in SOC of Chinese croplands over the last 30 years. There have been several attempts to estimate SOC changes in Chinese croplands, which have given contrasting results. Modelling and literature survey studies have yielded contrasting results of SOC stock change, ranging from -2.0 to 0.6% of total SOC per year (Yan et al., 2011). Furthermore, the insights on changes of croplands soil organic carbon in China and their controlling factors have important implications for increasing the sequestration of the atmospheric CO2, and for developing climate smart agriculture.
To better understand the storage, patterns and changes of croplands soil organic carbon in China, as well as the controlling factors and their impacts, we intend to conduct a meta-analysis to understand the three important questions:
- How did croplands SOC change in China spatially and temporally since 1980
- What are the agronomic management practices and potentials to increase soil organic carbon of croplands in China? Are there any success stories from China where the 4 ‰ increases in the soil C stock is achieved?
- How did changes in SOC affect crop yields?
An integrated review will be conducted based on papers published in the peer-reviewed journals
-Identify the agronomic management practices or success stories that increase cropland SOC, as well as the relation between SOC change and crop yield, in China
-Submit a research report to LUKE
-Submit a review paper to a scientific journal
4) Vaikuttavuus ja käytäntöön vienti
Result are relevant to international climate negotiations and to the cropland management in China
Users of the croplands in China and international climate negotiations.