Soil natural capital
The recognition of soil as a component of the earth’s natural capital creates new avenues for integration of soil science with other environmental sciences, and with economics.
Soil natural capital has emerged as a useful concept to analyse environmental and resource management problems, and although soil science provides an understanding of the links between soil properties and processes, soil natural capital provides the key to putting a real value on soils and the many services they provide to society.
The concept of soil natural capital helps convey the value of soil services to communities and policymakers, making the discipline of soil science relevant to current political decision-making timescales. It potentially enables the “greening” of existing economic indicators such as GDP (Gross Domestic Product), which at present ignore impacts on human well-being such as flood control and nutrient filtering. Recently, researchers have begun to reveal relationships between soil natural capital, soil properties, processes and the provisioning and regulating of services provided by soils.1,2
We are developing a method to estimate and map soil natural capital using commonly available soil information. We define the soil natural capital “stocks” by soil properties that can be either directly or indirectly measured or estimated within a soil profile, facilitating the mapping of soil natural capital stocks, using normal soil mapping techniques.
There are four kinds of soil stocks: inherent stocks (e.g. clay content); manageable dynamic stocks (e.g. soil water content); energy stocks (e.g. stored heat); soil fabric (e.g. total porosity).
Our “stock adequacy” method quantifies soil natural capital relative to the requirements of a specified land-use type. We propose that for adequate sustainable production, a land-use type requires a specific set of soil services, which need to draw on a specific set and level of soil stocks. If these stocks are adequate then the soil services can operate to their full potential, and in turn, the land-use type can operate to its potential, as far as the soil is concerned. If the soil stocks are not adequate then the provision of soil services, and in turn the land-use type, will not perform adequately.
The stock adequacy method has the following steps (outlined in Figure 1).
- Define the land-use type.
- Select the soil services required.
- Determine the soil stocks, represented by soil properties, needed to sustain each soil service.
- Quantify the soil stocks.
- Estimate the quality of each stock to adequately support a specified level of soil service in a percentage scale.
- Define stock quantity–quality curves.
- Derive an aggregated stock adequacy across all stocks.
Because quantification of soil natural capital has many valuable applications, e.g. applied to resource-use efficiency, and land-use trade-off analysis, we are continuing to develop this method.
1 Dominati et al. (2010) Ecological Economics 69: 1858–1868
2 Robinson et al. (2011) Vadose Zone J. doi:10.2136/vzj2011.005
Allan Hewitt, Trevor Webb & Carolyn Hedley