ABSTRACT
Agriculture, at all scales of production, is dependent on the natural capital of soils which yield a flow of services upon which humans depend, not only for food, fibre and biomass production, but also for other ecosystem services such as provision of fresh water, regulation of nutrient cycling, flood mitigation, water purification, carbon sequestration and climate regulation (Kibblewhite, Ritz & Swift 2008; Haygarth & Ritz 2009; Dominati, Patterson & Mackay 2010; Robinson et al. 2013). During the 20th century, the rising demand for food globally was met by conversion of natural and semi-natural habitats into agricultural land, and the intensification of farming methods, including mechanization and use of synthetic fertilizers (Robinson & Sutherland 2002; Haygarth & Ritz 2009). However, intensification of agriculture has depleted the natural capital of soil organic
carbon (SOC) and nutrients resulting in serious losses of regulating and supporting ecosystem services (Franzluebbers 2002). These include impaired water and nutrient holding capacity, reduced pollutant immobilization and water filtration, loss of soil aggregates and strength (Watts & Dexter 1997) leading to increased erosion, CO2 release to the atmosphere and eutrophication of aquatic ecosystems (Robinson & Sutherland 2002; Loveland & Webb 2003; Dominati, Patterson & Mackay 2010; Robinson et al. 2013). Loss of organic matter (OM) content is of particular concern for food security as yields of staple cereal crops typically increase linearly with SOC concentration (Lal 2010).
