The efficiency of long-term straw return to sequester organic carbon in Northeast China＇s cropland

Black soil is one of the most precious soil resources on earth because it has abundant carbon stocks and a relatively high production capacity. However, decreasing organic matter after land reclamation, and the effects of long-term inputs of organic carbon have made it less fertile black soil in Northeast China. Straw return could be an effective method for improving soil organic carbon（SOC） sequestration in black soils. The objective of this study was to evaluate whether straw return effectively increases SOC sequestration. Long-term field experiments were conducted at three sites in Northeast China with varying latitudes and SOC densities. Study plots were subjected to three treatments： no fertilization（CK）; inorganic fertilization（NPK）; and NPK plus straw return（NPKS）. The results showed that the SOC stocks resulting from NPKS treatment were 4.0 and 5.7% higher than those from NPK treatment at two sites, but straw return did not significantly affect the SOC stocks at the third site. Furthermore, at higher SOC densities, the NPKS treatment resulted in significantly higher soil carbon sequestration rates（CSR） than the NPK treatment. The equilibrium value of the CSR for the NPKS treatment equated to cultivation times of 17, 11, and 8 years at the different sites. Straw return did not significantly increase the SOC stocks in regions with low SOC densities, but did enhance the C pool in regions with high SOC densities. These results show that there is strong regional variation in the effects of straw return on the SOC stocks in black soil in Northeast China. Additional cultivations and fertilization practices should be used when straw return is considered as an approach for the long-term improvement of the soil organic carbon pool.

Challenges to increasing the soil carbon pool of agro-ecosystems in China

Climate change will place agro-ecological systems and food security at serious risk. At the 21 st Conference of the Parties（COP21） in Paris in December of 2015, parties to the United Nations Framework Convention on Climate Change（UNFCCC） reached a historic agreement（Paris Agreement） to combat climate change and to accelerate and intensify the actions and investments needed for a sustainable low carbon future. An initiative named the "4‰ initiative: Soils for food security and climate" was proposed by the French Minister of Agriculture, and this initiative was launched officially at the COP21 and adopted by many global organizations. The aim of this initiative was to increase carbon sequestration in soil to mitigate fossil fuel combustion emissions of greenhouse gasses. The present study found that China has high CO;emissions but a low soil carbon pool, and indicates that 4‰ increments of the soil carbon pool will not be sufficient to offset national CO;emissions. The current soil carbon sequestration rate would also not reach the mean level requested by the initiative. Therefore, China faces big challenges to achieve this initiative. An integrated use of straw technology may be used more widely to improve carbon sequestration, and other opportunities include improved fertilizer use efficiency and greenhouse gas mitigation through the waste management project under construction in China. This paper suggests that China may put forward the biomass treatment centered high yield and fertilizer-carbon sequestration project to enhance resilience of agro-ecosystems to climate change.

SOC storage and potential of grasslands from 2000 to 2012 in central and eastern Inner Mongolia, China

Grassland ecosystem is an important component of the terrestrial carbon cycle system. Clear comprehension of soil organic carbon（SOC） storage and potential of grasslands is very important for the effective management of grassland ecosystems. Grasslands in Inner Mongolia have undergone evident impacts from human activities and natural factors in recent decades. To explore the changes of carbon sequestration capacity of grasslands from 2000 to 2012, we carried out studies on the estimation of SOC storage and potential of grasslands in central and eastern Inner Mongolia, China based on field investigations and MODIS image data. First, we calculated vegetation cover using the dimidiate pixel model based on MODIS-EVI images. Following field investigations of aboveground biomass and plant height, we used a grassland quality evaluation model to get the grassland evaluation index, which is typically used to represent grassland quality. Second, a correlation regression model was established between grassland evaluation index and SOC density. Finally, by this regression model, we calculated the SOC storage and potential of the studied grasslands. Results indicated that SOC storage increased with fluctuations in the study area, and the annual changes varied among different sub-regions. The SOC storage of grasslands in 2012 increased by 0.51×1012 kg C compared to that in 2000. The average carbon sequestration rate was 0.04×1012 kg C/a. The slope of the values of SOC storage showed that SOC storage exhibited an overall increase since 2000, particularly for the grasslands of Hulun Buir city and Xilin Gol League, where the typical grassland type was mainly distributed. Taking the SOC storage under the best grassland quality between 2000 and 2012 as a reference, this study predicted that the SOC potential of grasslands in central and eastern Inner Mongolia in 2012 is 1.38×1012 kg C. This study will contribute to researches on related methods and fundamental database, as well as provide a reference for the protection of grassland ecosystems and the formulation of local policies on sustainable grassland development.

中国旱作区土壤有机碳密度三维模拟与固碳潜力估算

Soil organic carbon density(SOCD)and soil organic carbon sequestration potential(SOCP)play an important role in carbon cycle and mitigation of greenhouse gas emissions.However,the majority of studies focused on a two-dimensional scale,especially lacking of field measured data.We employed the interpolation method with gradient plane nodal function(GPNF)and Shepard(SPD)across a range of parameters to simulate SOCD with a 40 cm soil layer depth in a dryland farming region(DFR)of China.The SOCP was estimated using a carbon saturation model.Results demonstrated the GPNF method was proved to be more effective in simulating the spatial distribution of SOCD at the vertical magnification multiple and search point values of 3.0×106 and 25,respectively.The soil organic carbon storage(SOCS)of 40 cm and 20 cm soil layers were estimated as 22.28×10^(11)kg and 13.12×10^(11)kg simulated by GPNF method in DFR.The SOCP was estimated as 0.95×10^(11)kg considered as a carbon sink at the 20–40 cm soil layer.Furthermore,the SOCP was estimated as–2.49×10^(11)kg considered as a carbon source at the 0–20 cm soil layer.This research has important values for the scientific use of soil resources and the mitigation of greenhouse gas emissions.