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The Palgrave Handbook of Critical Physical Geography pp 421–441Cite as

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Questions of Imbalance: Agronomic Science and Sustainability Assessment in Dryland West Africa

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Abstract

Nutrient budgeting has become a common tool to assess the sustainability of African agriculture, calculated by subtracting estimates of flows of nutrients out from the flows coming in. More negative budgets for a field, village territory, county, country, or region are seen as evidence for unsustainable “nutrient mining” leading to land degradation. This chapter places this approach within the traditions of agronomic science of dryland Africa. A basic limitation of this tradition is its recurrent attempts to avoid engaging seriously with the dynamics and heterogeneities of farmers’ practices. This chapter concludes by presenting a critical physical geographical alternative that seeks to understand how social and biophysical landscapes are co-produced involving high rates of soil sampling and analysis; interviews of farmers about the management history of sampled fields; and assessment of field managers’ access to productive resources (land, labor, livestock).

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Notes

  1. 1.

    This characterization is based on decades of working with agronomists in the region. It is important to state clearly that it would be a gross simplification that the abstraction from farmers’ practices is solely driven by an embrace of neo-Malthusianism. Prior training (controlled field experimentation) and an understandable interest to transform unproductive farming systems through modern inputs (why study something that will be replaced) also play important roles in the common practice of abstracting from the everyday constraints, decisions, and practices of smallholder farmers. Moreover, there is a long history of using biophysical signs of environmental decline or degradation without any consideration of how farmers and pastoralists engage materially with their environments to produce (or not) these symptoms (e.g. desertification).

  2. 2.

    These factors influence each other. For instance, moisture availability increases rates of mineralization particularly at the beginning of the rainy season (Powell et al. 1999).

  3. 3.

    Each agropastoral territory encloses not only the croplands of central villages and associated cultivation hamlets but also the pastures utilized by villagers’ livestock.

  4. 4.

    Nutrient losses from cropping stem from the removal of the crop (grain or fruit) from the cropped area. The nutrients in the harvest are therefore lost to the local farming system either from actual physical export of crops, burial of nutrients in latrines and graves, or the loss of nutrients to the atmosphere (e.g. volatilization of nitrogen). Crop residue can be harvested and stocked elsewhere for animal feed, incorporated back into the soil, or grazed in place by livestock. These different management options have a significant effect on the flows of nutrients and the chemical forms in which they return to the soil (affecting their availability to plants).

  5. 5.

    Agronomists’ focus on chemical rather than physical changes to soils reflects the perceived timescales of anthropogenic changes to soils (Duvall 2011). The lack of horizon development of these soils means that their vulnerability to structural changes is minimal. Their structure is strongly shaped by the development of impermeable ferricrete crusts which are seen as developing over long time periods. The texture of upland soils in the region is composed largely of medium-to-coarse sands, lowering their potential for compaction (e.g. trampling of livestock). Silt and clay contact increases in lower-lying depressions and active or fossil floodplains. These soils are more sensitive to compaction during short windows of time between inundation and full drying (Valentin 1985). There has been some work on micro-crust formation, which may reduce infiltration to some extent, on sandy soils with more silt/clay content (wide particle size distribution) associated with grain sorting with rain impact (Hoogmoed and Stroosnijder 1984). One could argue that human activities, by removing litter layer, increase the vulnerability to such micro-crusts. Still, the development of litter layers is rare (except under strong protection from termites, grazing, and fire), making most soils with the appropriate particle size distribution susceptible to such micro-crust forming during early rains. It could be argued that livestock trampling and cultivation, by breaking up these crusts, could improve rainfall infiltration.

  6. 6.

    For a general history of understandings of African soils, see Showers (2006).

  7. 7.

    An example is the influential work performed at ICRISAT’s Sahelian Center at Sadoré, Niger, located south of the capital city of Niamey. Agronomists at the center conducted their experiments within the research station under the assumption that nitrogen was the major limiting factor affecting crop production in the region. To clarify the effect of nitrogen fertilization on crop yields, control and treatment plots were fertilized with all other nutrients that could influence crop response. With the realization that phosphorus is another macronutrient limiting crop productivity, agronomists and soil scientists had to look outside the station to perform their work while planting cover crops on test plots within the station to remove phosphorus from their soils.

  8. 8.

    Turner (1995) discusses how most of parameters in equations used to generate estimates of sustainable rangeland-to-cropland ratios show a wide range of variation with much of the variation due to known differences in how different people manage their fields and livestock. Scoones and Toulmin (1998) likewise describe the many ways in which crop management can affect nutrient balances. Thus, to understand the sustainability of mixed farming systems, one needs to understand a broader set of institutional and political economic factors that affect resource management.

  9. 9.

    See Cobo et al. (2010) for an excellent review of the findings of nutrient-balance estimates across Africa.

  10. 10.

    These approaches are tied to the coupling of neo-Malthusian approaches for environmental assessment with the tradition of human ecological systems analysis of tracing nutrients through economies (e.g. Odum 1971; Moran 1990; Grote et al. 2005).

  11. 11.

    As described by Prudencio (1993), infields are those that tend to be more heavily manured and cultivated continuously within a short radius of the village. Outfields are areas that are not continuously cultivated and receive much more limited nutrient amendments.

  12. 12.

    Most of these researchers have mixed training in both the physical and social sciences with geographers constituting a large fraction of these.

  13. 13.

    This discussion also points to the sensitivity of such studies to the monitoring time frame (growing season, year, multiple years).

  14. 14.

    This finding is consistent with the conservative nature of phosphorus in the system with gradients of phosphorus availability positively associated with the long-term history of manure application which is negatively correlated with distance from village.

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  1. Department of Geography, University of Wisconsin, Madison, WI, USA

    Matthew D. Turner

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  1. Indiana University Bloomington, Bloomington, IN, USA

    Rebecca Lave

  2. University of Washington, Seattle, WA, USA

    Christine Biermann

  3. Université de Lausanne, Gryon, Switzerland

    Stuart N. Lane

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Turner, M.D. (2018). Questions of Imbalance: Agronomic Science and Sustainability Assessment in Dryland West Africa. In: Lave, R., Biermann, C., Lane, S. (eds) The Palgrave Handbook of Critical Physical Geography. Palgrave Macmillan, Cham. https://doi.org/10.1007/978-3-319-71461-5_20

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