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[en] Improving food security, environmental preservation and enhancing livelihood should be the main targets of the innovators of today's farming systems. Conservation agriculture (CA), based on minimum tillage, crop residue retention and crop rotations, has been proposed as an alternative system combining benefits for the farmer with advantages for the society. This paper reviews the potential impact of CA on C sequestration by synthesizing the knowledge of carbon and nitrogen cycling in agriculture, summarizing the influence of tillage, residue management and crop rotation on soil organic carbon stocks and compiling the existing case study information. To evaluate the C sequestration capacity of farming practices, their influence on emissions from farming activities should be considered together with their influence on soil C stocks. The largest contribution of CA to reducing emissions from farming activities is made by the reduction of tillage operations. The soil C case study results are not conclusive. In 7 of the 78 cases withheld, the soil C stock was lower in zero compared to conventional tillage, in 40 cases it was higher and in 31 of the cases there was no significant difference. The mechanisms that govern the balance between increased or no sequestration after conversion to zero tillage are not clear, although some factors that play a role can be distinguished e.g. root development and rhizodeposits, baseline soil C content, bulk density and porosity, climate, landscape position and erosion/deposition history. Altering crop rotation can influence soil C stocks by changing quantity and quality of organic matter input. More research is needed, especially in the tropical areas where good quantitative information is lacking. However, even if C sequestration is questionable in some areas and cropping systems, CA remains an important technology that improves soil processes, controls soil erosion and reduces tillage-related production costs. (author)
[en] Observations worldwide are providing an increasing amount of atmosphere–ecosystem flux data. Thus, the establishment of a data mining methodology to detect significant trends and attribute changes to specific factors is important. This study examined the possibility of detecting significant trends in observed data at a test site with one of the longest records of flux measurements (Takayama, Japan). Statistical tests using non-parametric methods showed a ‘likely’ trend (i.e., detected at 66–90% confidence level) of increasing carbon sequestration. To investigate the change in carbon sequestration in relation to biological and environmental factors (ambient CO2, temperature, radiation, precipitation and disturbance), mechanistic and numerical methods were applied. A process-based model was used for the mechanistic attribution of change, and an optimal fingerprinting method in combination with model-based sensitivity simulations was used for numerical attribution. At the study site, local disturbances appeared to exert an impact on the observed carbon sequestration, whereas climatic factors made moderate contributions. These results indicate the feasibility of detection and attribution using current flux measurement data, although more evidence is needed to confirm global coherence. (letter)
[en] The variations of vegetation carbon sequestration have become a gauge for evaluating the ecological effect of vegetation restoration. In this study, the spatiotemporal patterns of the net ecosystem production (NEP) were simulated using an improved CASA model and GSMSR model. It showed that the NEP markedly increased in the tableland of Loess Plateau during 2003–2012, with an annual average growth of 3.65 g C·m−2 a−1. The mixed broadleaf-conifer forest ranked first (127.23 g C·m−2 a−1) while the bare land and sparse vegetation presented the lowest carbon sequestration (14.64 g C·m−2 a−1). The NEP manifested a significantly uneven overall spatial distribution: high in the southwest and low in the northeast. The spatial variations of NEP resulted from the combined effects of geographic position, terrain, meteorology, and soil and vegetation, respectively. Quantitative isolation revealed that the most dominant factor of vegetation carbon sequestration was soil and vegetation, while terrain exerted insignificant impacts on the NEP.