Soil natural capital quantification by the stock adequacy method

A method is presented for assessing soil natural capital based on the principles of land evaluation. Policymakers are adopting concepts of flows of ecosystem services, and the natural capital stocks that support them, to provide more integrated analyses of the trade-offs between environmental, economic, social and cultural outcomes from land use. Soil is frequently overlooked in these analyses. Techniques are needed to quantify and map soil natural capital and their potential to provide ecosystem services to enable the soil science community to more effectively engage with decision-makers. To support this engagement, these techniques need to use available soil survey maps and databases to provide extensive geographic coverage of soil natural capital estimates. The method presented estimates the adequacy of soil natural capital stocks to support the soil processes behind the provision of ecosystem services under a specific land use. A stock adequacy index estimates the degree to which the provision of services is limited by soil natural capital stocks or advantaged by a stock surplus under a given land use. Reference values are derived from a curve of the response of the provision of the service to key soil stocks for a specified land use. These curves are determined from land evaluation and soil quality literature, or by modelling. The method is essentially an extension of land evaluation in which the evaluations are calibrated using an ecosystem approach. The output indices provide information about potential ecosystem services provision, land-use suitability, soil resource use efficiency, and environmental performance. Outputs from the method are demonstrated for a range of soils under pastoral dairy land use in Wairarapa, New Zealand.