SR11 Which agricultural management interventions are most influential on soil organic carbon (using time series data)?
Various farmland management activities can alter the carbon storage potential of agricultural soils. Farmers are often faced with a variety of choices of land management practices, but little is known about their relative impacts on long-term conservation of soil carbon. Continuing from a systematic map published in 2015, EviEM is undertaking a systematic review to estimate the relative effects of a variety of farming practices on soil organic carbon using long-term time series data.
A map of knowledge on farming and soil organic carbon
On farmland that is harvested annually, the carbon content of the soil declines as organic compounds are broken down, removed in the form of crops, leached out by run-off or lost by erosion. Globally, the top one metre of soil contains roughly three times as much carbon as the above-ground biomass of plants, and twice as much as the atmosphere. Changes in the stock of soil carbon can therefore cause significant changes in the atmospheric concentration of carbon dioxide. On a global scale, the losses of carbon from agricultural soils have been estimated at roughly 100 to 1,000 million tonnes of carbon every year.
However, there are methods that can reduce carbon losses or even increase the sequestration (capture) of carbon in arable soils, even though the land continues to be farmed. Increased carbon sequestration in arable soils offers major benefits: It improves yields owing to better soil structure and fertility, and it reduces greenhouse gas levels in the atmosphere, helping to mitigate the threat of global warming.
Little is currently known about how different farming activities can affect soil organic carbon. To clarify the state of knowledge, EviEM recently published a systematic map of all evidence relating to the impacts of arable farmland management on soil organic carbon in temperate regions.
Review of how different farming practices affect long-term soil carbon sequestration
The systematic map identified 53 studies that presented long-term time series data (studies lasting 30 years or more with 3 or more measurements of soil carbon over time). Such data provides detailed information on the rates of change of carbon storage, and will allow us to examine which individual and combined practices are best for preserving or increasing soil organic carbon.
This review will examine studies that provide long-term continuous measurements of soil organic carbon for various different agricultural practices on arable land. Following critical appraisal of study reliability, data will be extracted and complex statistical tools will be used to compare carbon accumulation or loss curves using meta-analysis.
This review is also currently underway, and the systematic review protocol has been published in the journal Environmental Evidence (see link in the margin at right).
Katarina Hedlund (Chair), Centre for Environmental and Climate Research, Lund University, Sweden
Helene Bracht Jørgensen, Department of Biology, Lund University, Sweden
Louise E. Jackson, Department of Land, Air and Water Resources, University of California, Davis, USA
Thomas Kätterer, Department of Ecology, SLU Uppsala, Sweden
Emanuele Lugato, Joint Research Center (IES – Soil action), Ispra, Italy
Ingrid K. Thomsen, Department of Agroecology, University of Aarhus, Denmark
Per-Erik Isberg, Department of Statistics, Lund University, Sweden
Neal Haddaway (Project Manager), EviEM, Stockholm, Sweden