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

Critical Reviews in Plant Sciences (Impact Factor: 4.36). 05/2009; 28:97-122. DOI: 10.1080/07352680902776358

ABSTRACT 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.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background and aims Conservation agriculture, the combination of minimal soil movement (zero or reduced tillage), crop residue retention and crop rotation, might have the potential to increase soil organic C content and reduce emissions of CO2. Methods Three management factors were analyzed: (1) tillage (zero tillage (ZT) or conventional tillage (CT)), (2) crop rotation (wheat monoculture (W), maize monoculture (M) and maize-wheat rotation (R)), and (3) residue management (with (+r), or without (−r) crop residues). Samples were taken from the 0–5 and 5–10 cm soil layers and separated in micro-aggregates (< 0.25 mm), small macro-aggregates (0.25 to 1 mm) and large macro-aggregates (1 to 8 mm). The carbon content of each aggregate fraction was determined. Results Zero tillage combined with crop rotation and crop residues retention resulted in a higher proportion of macro-aggregates. In the 0–5 cm layer, plots with a crop rotation and monoculture of maize and wheat in ZT+r had the greatest proportion of large stable macro-aggregates (40%) and highest mean weighted diameter (MWD) (1.7 mm). The plots with CT had the largest proportion of micro-aggregates (27%). In the 5–10 cm layer, plots with residue retention in both CT and ZT (maize 1 mm and wheat 1.5 mm) or with monoculture of wheat in plots under ZT without residues (1.4 mm) had the greatest MWD. The 0–10 cm soil layer had a greater proportion of small macroaggregates compared to large macro-aggregates and micro-aggregates. In the 0–10 cm layer of soil with residues retention and maize or wheat, the greatest C content was found in the small and large macro-aggregates. The small macro-aggregates contributed most C to the organic C of the sample. For soil cultivated with maize, the CT treatments had significantly higher CO2 emissions than the ZT treatments. For soil cultivated with wheat, CTR-r had significantly higher CO2 emissions than all other treatments. Conclusion Reduction in soil disturbance combined with residue retention increased the C retained in the small and large macro-aggregates of the top soil due to greater aggregate stability and reduced the emissions of CO2 compared with conventional tillage without residues retention and maize monoculture (a cultivation system normally used in the central highlands of Mexico).
    Plant and Soil 355(1-2). · 3.24 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we argue that over the last 40 years the context of agronomic research in the developing world has changed significantly. Three main changes are identified: the neoliberal turn in economic and social policy and the rise to prominence of the participation and environmental agendas. These changes have opened up new spaces for contestation around the goals, priorities, methods, results and recommendations of agronomic research. We suggest that this dynamic of contestation is having important effects on how agronomic research is planned, managed, implemented, evaluated and used, and is therefore worthy of detailed study. This is particularly so at a time when food security, rising food prices and the potential impacts of climate change on agriculture are in the policy spotlight. We outline a research agenda that should help illuminate the drivers, dynamics and impacts of this new ‘political agronomy’.
    Agriculture and Human Values 30(1). · 1.36 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Agriculture production in developing countries must be increased to meet food demand for a growing population. Earlier literature suggests that sustainable land management could increase food production without degrading soil and water resources. Improved agronomic practices include organic fertilization, minimum soil disturbance, and incorporation of residues, terraces, water harvesting and conservation, and agroforestry. These practices can also deliver co-benefits in the form of reduced greenhouse gas emissions and enhanced carbon storage in soils and biomass. Here, we review 160 studies reporting original field data on the yield effects of sustainable land management practices sequestering soil carbon. The major points are: (1) sustainable land management generally leads to increased yields, although the magnitude and variability of results varies by specific practice and agro-climatic conditions. For instance, yield effects are in some cases negative for improved fallows, terraces, minimum tillage, and live fences. Whereas, positive yield effects are observed consistently for cover crops, organic fertilizer, mulching, and water harvesting. Yields are also generally higher in areas of low and variable rainfall. (2) Isolating the yield effects of individual practices is complicated by the adoption of combinations or “packages” of sustainable land management options. (3) Sustainable land management generally increases soil carbon sequestration. Agroforestry increases aboveground C sequestration and organic fertilization reduces CO2 emissions. (4) Rainfall distribution is a key determinant of the mitigation effects of adopting specific sustainable land management practices. Mitigation effects of adopting sustainable land management are higher in higher rainfall areas, with the exception of water management.
    Agronomy for Sustainable Development · 3.57 Impact Factor

Full-text (4 Sources)

Available from
Aug 25, 2014