Soil formation and nutrient cycling

Abstract

Soil is the foundation of terrestrial life – a complex ecosystem that supports plant growth and a living filter that binds and removes contaminants. Soil is also a fragile natural resource, and its mismanagement leads to lost productivity and a degraded environment. Soils play a critical role in a range of ecosystem services. These services include production of raw materials such as food and fiber, supporting natural processes including nutrient cycling, cultural services, and regulating services including waste treatment and air and water regulation (Costanza et al. 1997). Each of these can be related directly or indirectly to soil. A soils’ ability to hold and store water, to transform wastes and nutrients, to store carbon (soil is the third largest carbon sink, behind oceanic reserves and fossil fuels), and to support plant growth are clear services attributed to soils (Clothier et al. 1997; Costanza et al. 1997; Doran 2002; Robinson et al. 2013). There have been recent efforts to quantify the value of soils in relation to these services. One study attributed 17 % of the gross national product of New Zealand directly to soil resources (Kirkham and Clothier 2007). The value of macropores; the larger void spaces in soils that allow for movement of water and diffusion of gas to and from the atmosphere into the soil, in soils and the services associated with those pores was valued at $304 billion annually (Clothier et al. 2008). Soil valuation has not progressed to the point where the value of a particular soil can be quantified. While tools like life cycle assessment have enabled a fuller understanding of the environmental ramifications of different systems, no comparable tools have been developed for soils and their associated services. Despite the growing recognition of the importance and value of soils for supporting ecosystem services, there are very few to no incentives in the US that encourage soil preservation and improvement. Currently the best tool available in the US for quantifying the value of soils is the USDA Conservation Reserve Program (CRP) that pays farmers to leave sensitive soils fallow in order to preserve and protect them. The program currently includes 140,000 km2 with annual payments of $1.8 billion (Robinson et al. 2013). This is equivalent to a payment of $241,000 to develop 15 cm of topsoil at a soil formation rate of 0.008 cm year (Brown et al. 2014).