World’s Soil Resources

Research in tropical and semi-tropical lands has established that inputs of organic material through the
return of residues and manure to the soil are essential for fertility restoration in degraded soils, but that low
residue production and competing uses for residues and manure limit the adoption of these SOC-aggrading
approaches (e.g. Lal, 2006; Rusinamhodzi et al., 2013; Palm et al. 2014). Sustainable soil management that
increases SOM levels will assist in maintaining productivity, but the specific measures taken to increase SOM
must be locally developed.
Establishing a direct, quantitative link between soil biodiversity and increasing food production is even more
elusive. Sylvain and Wall (2011) observe that “the total invertebrates found in a soil will interact to provide many
services and participate in several ecosystem functions, but it is unlikely that a single species will influence all
services and functions that influence plant growth or composition at the same time or in the same manner”.
Biodiversity beyond the soil plays an important role in regulating services such as biological pest control and
crop pollination (Bommarco, Kleijn and Potts, 2013), and public concerns about the effects of pesticides on key
species continues to grow.
A final role for SOC enhancement and maintenance of soil biodiversity is to increase the resilience of the soil
for food production, especially its ability to withstand disruption due to human-induced climate change. SOC
buffers the impact of climate extremes on soils and crops by: (i) regulating water supply by reducing runoff
and increasing soil-water holding capacity; (ii) reducing erosion through runoff reductions and improved
aggregation; and (iii) providing sites for nutrient retention and release (Loveland and Webb, 2003; Lal, 2006).
The combined role of soil organic matter and biodiversity in nutrient cycling ensures a continuing supply of
nutrients for crop growth. It is difficult to quantify this relationship, especially in the light of the uncertainties
associated with human-induced climate change, but the existing qualitative understanding is sufficient to
establish the importance of SOC and biodiversity in sustainable soil management.
Summary
The importance of soil degradation and soil rehabilitation are highlighted in principles eight and nine of the
proposed World Soil Charter:
Soil degradation inherently reduces or eliminates soil functions and their ability to support ecosystem
services essential for human well-being. Minimizing or eliminating significant soil degradation is essential
to maintain the services provided by all soils and is substantially more cost-effective than rehabilitating
soils after degradation has occurred.
Soils that have experienced degradation can, in some cases, have their core functions and their contributions
to ecosystem services restored through the application of appropriate rehabilitation techniques. This
increases the area available for the provision of services without necessitating land use conversion.
Our ability to predict the effect of soil degradation on food security is very limited for two main reasons. First,
there is a lack of up-to-date knowledge both on the area affected by degradation and on the linkages between
degradation and soil functions (and ultimately plant production). The research community continues to cite
research summaries on the effects of soil degradation on crop yields from the 1990s based on data gathered in
the 1980s. Yet crop production in many regions has undergone profound change since the 1980s – for example,
the widespread adoption of conservation tillage in many regions occurred during the 1990s and 2000s. There
is a pressing need for meta-analyses on all of the soil threats discussed here. This in-depth review of existing
work needs to be complemented by new research to address major information gaps, and in particular to
prove more conclusively the functional relationships between soil attributes and plant production.
Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services
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