Soils play a pivotal role in major global biogeochemical cycles (carbon, nutrient, and water), while hosting the largest diversity of organisms on land. Because of this, soils deliver fundamental ecosystem services, and management to change a soil process in support of one ecosystem service can either provide co-benefits to other services or result in trade-offs. In this critical review, we report the state-of-the-art understanding concerning the biogeochemical cycles and biodiversity in soil, and relate these to the provisioning, regulating, supporting, and cultural ecosystem services which they underpin. We then outline key knowledge gaps and research challenges, before providing recommendations for management activities to support the continued delivery of ecosystem services from soils. We conclude that, although soils are complex, there are still knowledge gaps, and fundamental research is still needed to better understand the relationships between different facets of soils and the array of ecosystem services they underpin, enough is known to implement best practices now. There is a tendency among soil scientists to dwell on the complexity and knowledge gaps rather than to focus on what we do know and how this knowledge can be put to use to improve the delivery of ecosystem services. A significant challenge is to find effective ways to share knowledge with soil managers and policy makers so that best management can be implemented. A key element of this knowledge exchange must be to raise awareness of the ecosystems services underpinned by soils and thus the natural capital they provide. We know enough to start moving in the right direction while we conduct research to fill in our knowledge gaps. The lasting legacy of the International Year of Soils in 2015 should be for soil scientists to work together with policy makers and land managers to put soils at the centre of environmental policy making and land management decisions.
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Acknowledgements. The input from P. Smith and P. J. Kuikman contributes to the EU-funded FP7 project SmartSOIL (grant agreement no. 289694), and that from P. Smith and R. I. Griffiths to the NERC-funded U-Grass project (NE/M016900/1). The input from P. C. West and J. S. Gerber was supported by the Gordon and Betty Moore Foundation, and that from P. Smith, J. S. Gerber, and P. C. West contributes to the Belmont Forum/FACCE-JPI-funded DEVIL project (NE/M021327/1). Input from G. Pan was supported by funding from the Priority Academic Program Development of Jiangsu Higher Education Institutions, China. J. I. House was funded by a Leverhulme early career research fellowship.