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: To improve our ability to predict SOC mineralization response to residue and N additions in soils with different inherent and dynamic organic matter properties, a 330-day incubation was conducted using samples from two long-term experiments (clay loam Mollisols in Iowa [IAsoil] and silt loam Ultisols in Maryland [MDsoil]) comparing conventional grain systems (Conv) amended with inorganic fertilizers with 3 yr (Med) and longer (Long), more diverse cropping systems amended with manure. A double exponential model was used to estimate the size (Ca, Cs) and decay rates (ka, ks) of active and slow C pools which we compared with total particulate organic matter (POM) and occluded-POM (OPOM). The high-SOC IAsoil containing highly active smectite clays maintained smaller labile pools and higher decay rates than the low-SOC MDsoil containing semi-active kaolinitic clays. Net SOC loss was greater (2.6 g kg-1; 8.6%) from the IAsoil than the MDsoil (0.9 g kg-1, 6.3%); fractions and coefficients suggest losses were principally from IAsoil's resistant pool. Cropping history did not alter SOC pool size or decay rates in IAsoil where rotation-based differences in OPOM-C were small. In MDsoil, use of diversified rotations and manure increased ka by 32% and ks by 46% compared to Conv; differences mirrored in POM- and OPOM-C contents. Residue addition prompted greater increases in Ca (340% vs 230%) and Cs (38% vs 21%) and decreases in ka (58% vs 9%) in IAsoil than MDsoil. Reduced losses of SOC from residue-amended MDsoil were associated with increased OPOM-C. Nitrogen addition dampened CO2-C release. Clay type and C saturation dominated the IAsoil's response to external inputs and made labile and stable fractions more vulnerable to decay. Trends in OPOM suggest aggregate protection influences C turnover in the low active MDsoil. Clay charge and OPOM-C contents were better predictors of soil C dynamics than clay or POM-C contents.
    PLoS ONE 01/2014; 9(7):e103720. · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Conservation agriculture (CA) systems composed of intercropping and strip tillage practices were evaluated on marginalized maize-based farming system in hill region of Nepal. On-farm experimental trials were conducted on the field of 25 smallholder farmers in three villages of central mid-hill region. Results indicated that although CA systems did not increase crop yields; higher return and revenue were generated due to increased number of crop harvests and higher price of the cash crops used in intercropping. Therefore, it was concluded that smallholder farmers should adopt CA system for increasing return and improving sustainability of the farming system.
    Procedia Engineering 01/2014; 78:327–336.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background/Question/Methods Recent studies show that earthworms can considerably increase emissions of the greenhouse gas nitrous oxide (N2O). However, the extent of this effect varies widely with earthworm ecological group, and exact pathways remain unclear. Here we determined to what extent the earthworm-induced N2O effect is related to the incorporation depth of residue by different ecological groups. We hypothesized that (i) N2O emissions reduce with incorporation depth in the absence of earthworms, as more N2O is reduced to N2 while diffusing upwards; (ii) effects of a deep-burrowing (anecic) earthworms that are confined to various burrowing depths show a similar pattern; and (iii) the effects of an anecic and a topsoil-dwelling (epigeic) earthworm species are therefore identical when they are both confined to the topsoil. In a mesocosm (50 cm depth, sandy soil) study we measured cumulative N2O emissions. In experiment A, maize residue was manually incorporated at a depth of 0, 10, 30 and 50 cm. In experiment B, 13C-labeled maize residue was applied on top, but individuals of the anecic species Lumbricus terrestris (L.) were confined to 10, 30 or 50 cm with a nylon mesh, and individuals of the epigeic species Lumbricus rubellus (Hoffmeister) to 10 cm. Results/Conclusions After 83 days, L. terrestris biomass was decreased with 25.3%, without a significant effect of confinement depth. L. rubellus had lost significantly more weight (48.0%; p=0.015). In experiment A, N2O emissions decreased with incorporation depth (p<0.001) from 4.91 to 2.69 mg N2O-N kg-1 soil. In experiment B, N2O emissions differed with earthworm treatment (p<0.001). Highest emissions were observed for the L. rubellus treatment at 10 cm confinement (5.05 mg N2O-N kg-1 soil). Although confining L. terrestris to 10 cm resulted in lower emissions (3.85 mg N2O-N kg-1 soil), this was not significantly different from L. rubellus. Confinement depth significantly affected emissions of L. terrestris (p<0.001), but lowest emissions were found for 30 rather than 50 cm incorporation depth. With regard to our hypotheses, we postulate that (i) N2O emission decreases as expected with residue incorporation depth in the absence of earthworms; (ii) in the presence of earthworms this effect was obfuscated by changed gas diffusion properties through burrowing activity; and (iii) no significant differences were observed between an epigeic and anecic earthworm that were both confined to the topsoil. We conclude that earthworm-induced N2O emissions are indeed related to residue incorporation depth, albeit in more intricate ways than previously assumed.
    95th ESA Annual Convention 2010; 08/2010

Full-text (4 Sources)

Available from
Aug 25, 2014