versão On-line ISSN 1996-7489
S. Afr. j. sci. vol.110 no.5-6 Pretoria Mar. 2014
NEWS AND VIEWS
Schalk v.d.M. LouwI; John R.U. WilsonII, III; Charlene JanionIII; Ruan VeldtmanII, IV; Sarah J. DaviesIII; Matthew AddisonIV, V
IDepartment of Zoology and Entomology, University of the Free State, Bloemfontein, South Africa
IISouth African National Biodiversity Institute, Kirstenbosch National Botanical Gardens, Cape Town, South Africa
IIICentre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Stellenbosch, South Africa
IVDepartment of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch, South Africa
VHortgro Science, Stellenbosch, South Africa
Keywords: soil signature; edaphic factors; sustainability; food security; sustainable agriculture
The need to provide food security to a growing human population in the face of global threats such as climate change, land transformation, invasive species and pollution1 is placing increasing pressure on South African soils. South Africa is losing an estimated 300-400 million tonnes of soil annually2, while soil degradation is a major threat to agricultural sustainability3. In spite of these problems, treatment of soil health in biodiversity assessment and planning in South Africa has been rudimentary to date.4,5
Defining soil health
Soil is a crucial component of the pedosphere, which sustains life, and should therefore be regarded as one of the most important assets held by South Africans. However, in South Africa, soil is a highly neglected research focus in ecosystem service delivery. Studies of ecosystem services often focus on more elegant and tractable systems, such as pollination networks.6 Currently in South Africa, soils are viewed in certain sectors as resources that can be used to generate short-term gains, rather than assets to be protected and developed. Soils form the basis for food security through agriculture, where processes taking place in the pedosphere result in water retention, nutrient augmentation and soil biodiversity proliferation.
In an effort to facilitate research on soil health, or at least stimulate debate on the topic, we propose that soil health be measured by a combination of abiotic (A) and biotic (B) and socio-economic (S) aspects relative to a benchmark measure, i.e.
Soil health =
where A is measured by a subset of soil physicochemical indicators (with subsets determined on the basis of variable thresholds relating to soil type and soil usage); B is determined by standard biodiversity metrics (e.g. species richness, abundance, network or species assemblage connectedness), incorporating biodiversity in the context of applied strategies (e.g. agricultural push-pull systems and mixed cropping) and S is determined by socio-economic values (e.g. monetary value, equity, human well-being). In order to scale each component, benchmark values will also have to be determined that will serve as the denominator for calculation of changing component values over time.7,8
Here we use a similar model to that used in above ground environmental analyses (e.g. the lUCN's system analysis in Leverington et al.9), but we recognise that the below ground 'closed' medium functions at different tempos and scales. As such, this model is simplistic, yet a degree of ignorance exists about 'understanding' soils,10 strengthening the notion that soils need to be elevated to mainstream research foci where interactions among the physical, chemical and biological components of soils receive precedence and serve as a point of departure.
For soils to operate in a complex, interacting total system manner, biodiversity in different environments serving different socio-economic requirements can potentially be temporally and spatially separated, e.g. hydroponic farms and conservation areas or an ecological network in which all aspects are incorporated. In some cases this can lead to an overall greater soil health set-up than if all elements were combined in one area at a specific time period (e.g. debate on conservation versus agriculture, or conservation and agriculture11 and landscape-scale analysis over seasons12).
The three components of soil defined here all contribute to ecosystem services and intersect to provide healthy soils. The model for this soil health index (Figure 1), supported by intersection descriptions and more detailed relevant examples (Figure 2), serves to emphasise that soils are extremely complex and function in multiple roles, and as such have a pivotal role in ecological function. Based on this framework, we formulated several key research questions (Table 1).
The need for foundational work on soil organisms
In the last decade, the diverse roles of soil communities in the ecological function of soils has gained global recognition.13 Several large multidisciplinary projects in Europe (such as ENVASSO and EcoFINDERS) now focus on soil organisms using holistic approaches incorporating traditional taxonomy14 and modern molecular techniques15. However, in South Africa, like elsewhere in the world, research in the field of soil biology has been neglected compared with research in soil chemistry or soil physics. This scenario has started to change over the past decade or two and South Africa is no exception in this regard. Research on a broad biological basis regarding South African soils has increased since the mid-1990s and these outcomes are published in journals such as the European Journal of Soil Science, Soil Biology and Biochemistry, Biogeochemistry, Soil Research, Geoderma and the South African Journal of Plant and Soil. Sadly, however, this cannot be said of pure foundational research on soil organisms and, despite some notable pioneering experts (e.g. Lawrence16), our knowledge of South African soil organisms is largely restricted to taxonomically well-known groups such as ants17-19 and spiders20, and even then this knowledge is often fragmented and poorly documented. The need to integrate existing research initiatives was unanimously expressed at a Soil Health Workshop at the XVII Congress of the Entomological Society of Southern Africa in July 2011. This expression led to the formation of SERG (Soil Ecosystem Research Group) - a soil biodiversity research group that provides a platform for linking and promoting research on soil organisms.
One of the first priorities identified by SERG was the need to collate and mobilise data and collections to consolidate and compare the state of knowledge of each group.
We anticipate that research on soils will be a major initiative linking fundamental and applied research endeavours in the times ahead, especially in the context of climate smart management strategies. Having said this, we do recognise that the establishment of thresholds for biological indicators of soil health is a far greater challenge than the establishment of thresholds for either chemical or physical indicators of soil health, simply because biological indicators are too variable over short periods. Future research endeavours will therefore have to breach this complication.
We thank our respective institutions and departments for support in terms of funding and facilities. We also thank the NRF for funding. An anonymous reviewer is gratefully acknowledged for providing many positive and thought-provoking comments which helped improve the manuscript.
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Department of Zoology and Entomology
University of the Free Sate, PO Box 339
Bloemfontein 9300, South Africa