Conservation Agriculture and Soil Carbon Sequestration: Between Myth and Farmer Reality

Critical Reviews in Plant Sciences (Impact Factor: 5.44). 05/2009; 28(3):97-122. DOI: 10.1080/07352680902776358


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 production cost.

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    • "No-Till (NT) is defined as disturbing the soil as little as possible – only up to 20%–25% (Govaerts et al. 2009:98) – by using tine planters or combination tine and disc planters. Govaerts et al. (2006:99) described the conversion from conventional tillage to NT and/or CA as a gradual or step-wise process with minimum tillage (MT), NT and CACHEMICAL+ (High External Inputs) and CA (Low External Inputs) as phases in the process. "
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    • "However, the general hypothesis that no-till is always followed by SOC sequestration is still controversial since in most of the studies comparing the effects of different tillage systems on soil C, only the surface soil (0–30-cm depth) has been taken into account (Govaerts et al. 2009; Palm et al. 2013). Furthermore, attention has to be paid to a possible increase in the emission of N 2 O when using low-intensity soil management systems, as a result of the greater amount of water stored in the soil. "
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    ABSTRACT: Dryland areas cover about 41 % of the Earth’s surface and sustain over 2 billion inhabitants. Soil carbon (C) in dryland areas is of crucial importance to maintain soil quality and productivity and a range of ecosystem services. Soil mismanagement has led to a significant loss of carbon in these areas, which in many of them entailed several land degradation processes such as soil erosion, reduction in crop productivity, lower soil water holding capacity, a decline in soil biodiversity, and, ultimately, desertification, hunger and poverty in developing countries. As a consequence, in dryland areas proper management practices and land use policies need to be implemented to increase the amount of C sequestered in the soil. When properly managed, dryland soils have a great potential to sequester carbon if financial incentives for implementation are provided. Dryland soils contain the largest pool of inorganic C. However, contrasting results are found in the literature on the magnitude of inorganic C sequestration under different management regimes. The rise of atmospheric carbon dioxide (CO2) levels will greatly affect dryland soils, since the positive effect of CO2 on crop productivity will be offset by a decrease of precipitation, thus increasing the susceptibility to soil erosion and crop failure. In dryland agriculture, any removal of crop residues implies a loss of soil organic carbon (SOC). Therefore, the adoption of no-tillage practices in field crops and growing cover crops in tree crops have a great potential in dryland areas due to the associated benefits of maintaining the soil surface covered by crop residues. Up to 80 % reduction in soil erosion has been reported when using no-tillage compared with conventional tillage. However, no-tillage must be maintained over the long term to enhance soil macroporosity and offset the emission of nitrous oxide (N2O) associated to the greater amount of water stored in the soil when notillage is used. Furthermore, the use of long fallow periods appears to be an inefficient practice for water conservation, since only 10–35 % of the rainfall received is available for the next crop when fallow is included in the rotation. Nevertheless, conservation agriculture practices are unlikely to be adopted in some developing countries where the need of crop residues for soil protection competes with other uses. Crop rotations, cover crops, crop residue retention, and conservation agriculture have a direct positive impact on biodiversity and other ecosystem services such as weed seed predation, abundance and distribution of a broad range of soil organisms, and bird nesting density and success. The objective of sequestering a significant amount of C in dryland soils is attainable and will result in social and environmental benefits.
    Agronomy for Sustainable Development 09/2015; DOI:10.1007/s13593-015-0326-x · 3.99 Impact Factor
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    • "soil erosion in CT and BL plot and minimized the difference between tillage types. In addition, minimum tillage practices in BL plots might have raised erosion-resistance by improving the soil structure (Curci et al. 1997; Spaan et al. 2005; Govaerts et al. 2009). On the other hand, SNTR treatment also had the risk of causing even larger soil erosion than CT treatment when rainfall intensity was high, for example, during the event on July, 29 th , 2011 with Imax30 of 56 mm, SNTR had higher erosion than other two treatments. "
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    ABSTRACT: Under global warming, storm events tend to intensify, particularly in monsoon-affected regions. As an important agricultural area in China, the purple soil region in the Sichuan Basin, where it has a prevailing monsoon climate, is threatened by serious soil erosion. Tillage operations alter runoff and soil erosion processes on croplands by changing the physical properties of the soil surface. To clarify the relationship between tillage and soil erosion in the purple soil region, three different tillage practices in this region were investigated at the plot scale over 4 years: bare land with minimum tillage (BL), conventional tillage (CT) and seasonal no-tillage ridges (SNTR) which was initially designed to prevent soil erosion by contoured ridges and no-tillage techniques. The results showed that although there were no significant differences in the surface runoff and soil erosion among the three practices, BL caused relatively high surface runoff and soil erosion, followed by CT and SNTR. Classification and comparison of the rainfall events based on cluster analysis (CA) verified that the surface runoff was not significantly different between most intensive event and long intensive events but was significantly different between most intensive and short and medium-duration events. Only the rainfall events with the highest rainfall intensity could trigger serious soil erosion, up to 1000 kg ha-1 in the region. Further detailed investigations on the effects of tillage operations on the soil erosion in a subtropical region with a monsoon climate are needed to provide a basis for modeling catchments and designing better management practices.
    Journal of Mountain Science 02/2015; 12(1):134-144. DOI:10.1007/s11629-014-3241-8 · 0.96 Impact Factor
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