Food security requires more than simply meeting the caloric requirement; proper dietary needs, including sufficient proteins and vitamins must be met. An additional problem for some regions studied in the paper is that agricultural land is utilized for tobacco production rather than food crops. The authors point out that any change is unlikely to be implemented on a wide scale without significant policy changes, providing incentives for adoption. Interventions are suggested by the United Nations that detail initially subsidizing costly mineral fertilizers, replacing them after a few crop seasons with legume cover crops and agroforestry practices as a source of N.
Sub-Saharan Africa faces the potential situation of deforestation and land degradation, intersecting with hunger and poverty. The clearing of forests and woodlands for agricultural use is the primary cause of deforestation. Agriculture practices can be linked to the climate mitigation strategy of Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (REDD). Palm et al. (2010) develop four scenarios for increasing agricultural production by differing supplies of nitrogen, and compare the effects to food production, basic caloric needs, and greenhouse gas emissions. The study found that crop surplus area for reforestation is achieved at low population densities where there is high land availability. Conversely, to realize food security and reduce greenhouse gases in highly populated areas with small farm sizes, mineral fertilizers are necessary to make land available for reforestation. The authors believe that agricultural intensification in sub-Saharan Africa with mineral fertilizers, green manures, or improved tree fallows needs policies addressing costs, and incentives to escalate. The authors suggest carbon financing for small-holder agriculture to reduce emissions due to deforestation.—Whitney Dawson
Palm, C.A., Smukler, S.A., Sullivan, C.C., Mutuo, P.K., Nyadzi, G.I., Walsh, M.G., 2010. Identifying Potential Synergies and Trade-offs for Meeting Food Security and Climate Change Objectives in Sub-Saharan Africa. PNAS 107:46, 19661-19666.
Palm et al. study how the increase of biological nitrogen (N) and fertilizers from mineral sources can reverse the nutrient depletion in farm soils due to decades of crop harvest and erosion. Four scenarios for increasing food production are examined in two SSA sites where food security, poverty, and land degradation are high. The sites differ in rainfall, population density, degree of deforestation, and amount of land used for crops. The four different N sources are extensification by clearing additional land, fertilizers, green manure through legume cover crops, and improved tree fallow. Palm et al. used an accounting model for estimating and comparing each scenario to crop productivity, determining if deforestation is needed to meet basic caloric needs or if reforestation is able to occur.
Ideally, a greater N input directs emissions of nitrous oxide from soils, and yields improve simultaneously, reducing the need to clear forest for food security. Where landscapes are already heavily used by agricultural production, tree fallows can be used for biomass production to mitigate GHG emissions while still retaining food security. It is assumed that organic sources of N produce lower emissions than mineral sources, and also lower nitrous oxide emissions.
The study showed that in cases of high population density and small farm sizes, green manure and improved tree fallows do not suffice in achieving necessary crop yields to permit reforestation, and fertilizers are needed to reach food security and reduce greenhouse gas emissions. However, in lower populated areas, there is more abundance of land, and larger areas for crops to grow. In these areas, no additional cropland was needed for food security, and yields proved to be highest with fertilizer use, the only scenario that actually freed cropland for reforestation and carbon sequestration. For each scenario, the N supplied from tree fallow improvement was significantly greater than from green manure. The global warming potential was only positive where the population densities are lower and reforestation from use of fertilizer was possible.