The current notion that food security is determined by household income, poverty, and access to resources rather than by aggregate increased food production puts the potential role of carbon sequestration in small-scale farming systems in a broad and complex context. One or two 'best' management practices that simultaneously boost soil carbon and crop yields, but fail to address any of the other multiple social goals of rural households, are most likely not the alternatives that are likely to be adopted by resource-poor farmers.
It has been shown that carbon stocks in the central part of Senegal are relatively low (on average, less than 20 metric tons C ha-1), and that they are expected to remain at risk without adequate management practices. The same is true for crop yields. Results from CENTURY simulations indicated that improvements in C stocks in agricultural systems are possible but, that the overall rate of increase is likely to be modest. For soils, annual gains on croplands over 25 years amounted to 0.02 to 0.42 metric tons C ha-1 year-1, which is slightly higher than other existing estimates of 0.1 to 0.3 metric tons C ha-1 year-1 (Lal, 1999a; Batjes, 2001). "Best" C management practices for soils included plantations with nitrogen-fixing trees (Faidherbia albida), the application of 4 to 10 metric tons of manure with and without fertilizer, agricultural intensification with manure, fertilizer, green manure from agroforestry, and short-term fallow, as well as 6 to 10 years of improved fallows in rotation with millet and groundnuts. The same practices, with the exception of tree plantations, would also result in increased crop yields, ranging from +50% to +200% compared to current average yields. However, the impacts of climate change could seriously jeopardize gains in both soil carbon and crop yields, and losses over the next 100 years could be as high as 40% and 93% for both, respectively.
It may very well be in the interest of farmers to improve carbon stocks and, hence, soil fertility, especially if they are subsistence farmers. However, cropping is only one of multiple household livelihood strategies associated with flexible and adaptable risk management in drylands (Scoones et al., 1996;
Mortimore and Adams, 1999). For instance, only 6% of all sample households in the Old Peanut Basin obtained most of their income from farming. Most rely on remittances, which account for one-third of total average household revenue. Thus, in a complex livelihood system, a 50% to 200% increase in food production through 'best' carbon sequestration practices does not automatically mean enhanced food security. If applied on a larger scale, these practices might in fact compete with or undermine other livelihood practices that also contribute to food and livelihood security. In a risk-prone environment, such as the Sahel, secure livelihoods are those that are flexible and resilient.
In terms of economic feasibility, the results from this case study suggest that there may not be any significant low-cost options with ancillary benefits as indicated in preliminary studies (Ringius, 2002). For resource-poor farmers, only one simulated practice, namely live hedges with highly valuable seeds, would be profitable after 25 years. From a 'tradeoff' perspective, management options involving 4 to 10 metric tons of manure and short-term improved fallows would satisfy global needs and local economic interests, at least for better-endowed farmers. However, given the low investment capital of most smallholders and the high upfront costs associated with most 'best' practices, most will probably not be able to afford their implementation. Hence, carbon activities will not automatically reduce poverty. If, however, external and well-targeted funding or cost-sharing mechanisms are set in place to cover initial investment costs, as also proposed by Izac (1997) and Ayuk (2001), household budgets are likely to increase with time. In some cases, the increases may be substantial, thus playing a major role in rural poverty reduction.
The study suggests that increasing C stocks, improving food security, and reducing rural poverty are inevitably linked. The key to achieve all three is to strengthen and diversify local livelihoods. The premise, then, is twofold. First, carbon sequestration should be perceived as an additional element in people's livelihood portfolios and not as a goal per se. Whether the main objective is improved soil fertility, increased yields, additional income, enhanced food security, or the restoration of degraded lands will depend on the specific priorities of a household. Second, the fact that farmers are not a homogeneous group should be acknowledged. It is highly unlikely that one and the same 'best' practice will work for every single participant. As observed in other cases of farming system research in the Sahel, well-intentioned technologies for an 'average' farmer on an 'average' field are not only inappropriate, but also counterproductive since they risk undermining the very flexibility of the system (Defoer et al., 1998).
In order to address complex and multiple livelihood needs through carbon sequestration, a basket of management choices rather than one 'best' practice will be required. This includes a mix of farm and nonfarm activities. One possibility is to actually shift the emphasis on food crops to other income-generating activities that could be used to purchase food, thereby also broadening livelihood strategies. These income-generating activities could include cash cropping, the sale of wood products and valuable seeds, and animal fattening. Under conditions of land scarcity, smallholders may be very reluctant to convert their cropland to alternative types of land use, even if this conversion results in increased C stocks. Other sources of income and reliable food programs will be crucial.
Carbon sequestration in drylands can be a win-win strategy. It has the potential to address global needs of reduced C2 concentration and livelihood needs of rural populations. Focusing on merely one or two aspects, for the sake of simplicity — accountability and verification — may satisfy the needs of external agencies. Complex livelihoods, however, require complex solutions.
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