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Organic matter influences virtually all of the physical, chemical and biological properties of soil that are of importance for either agriculture or environmental functions. The properties influenced by soil organic matter (SOM, usually measured and expressed as content of organic carbon, C) include the formation and stability of aggregates, development or pores spaces, water holding capacity, the content and cycling of nutrients such as nitrogen, phosphorus and sulphur and the size and activity of the soil microbial population.

Soil organic C content is influenced by cropping and management practices. However changes in the total content usually occur slowly over periods of years or decades whereas some fractions within the total respond more rapidly to changes in management. We use a wide range of approaches to study soil C dynamics. These include long-term experiments in which slow changes can be studied – using experiments at Rothamsted and other sites world-wide through collaborations, many of which are through the IGBP Soil Organic Matter Network (SOMNET). We also use a range of physical fractionation and spectroscopic techniques to identify pools within SOM of potential interest, including light fractions and “black carbon”. Some years ago research at Rothamsted led to methods for measuring soil microbial biomass, and this work is being taken forward to understand carbon turnover from the microbial perspective (see microbial biomass group website). We make extensive use of modelling, including the long-established Rothamsted Carbon Model (RothC) and the recently developed SOMA model.

In addition to influencing soil quality, the quantity of organic carbon in soils globally is very significant within the global carbon cycle with consequences for climate change. The total stock of organic C in the world’s soils is approximately 1500 Gt, more than twice the amount currently in CO2 in the atmosphere. We have made estimates of the capacity of soils in the UK and Europe to lock up or “sequester” carbon. We have also collaborated with the Hadley Centre to quantify the risks of carbon being released as CO2 from soils worldwide through climate change, thus adding further to climate forcing.

Also see 'Climate Change and Land Management - A Rothamsted publication' for more information.