Automatgenererad bild.

18 February 2016

Can ploughing help to combat climate change? Mapping: an initial stage in systematic review

Can arable land be farmed in such a way as to store more carbon? The question is important both for food production and for the climate. Mistra EviEM is reviewing the body of scientific findings in this area, and recently issued an initial report.

‘Retaining carbon in farmland is important. First, it makes for fertile soils that yield abundant food and, second, it means avoiding release of carbon into the atmosphere where it exacerbates the greenhouse effect,’ says Professor Katarina Hedlund of Lund University.

Hedlund chairs an international research group that, on behalf of the Mistra Council for Evidence-Based Environmental Management (EviEM), is examining how various cultivation methods affect carbon content in arable soils. Carbon is an essential substance for all living things, and the more carbon there is in arable land the better the crops grow. The problem is that all cultivated soils constantly lose their carbon content: the rate varies, but the downward trend is the same all over the world. There are several reasons, such as that carbon is washed away in runoff and through erosion, but also that it leaves the soil when crops are harvested.

In Sweden, the carbon content of arable soils is decreasing at a rate of some 0.5–1% annually, according to Katarina Hedlund. However, there are methods that can slow down carbon losses. One is changed ploughing routines. Some trials indicate that it might even be possible, in some cases, to boost storage (sequestration) of carbon in the soil. The results are mixed, and clear recommendations on what works best are lacking.

Scrutinising hundreds of studies

EviEM has therefore appointed an international research group, comprising biologists, soil scientists and agricultural researchers, to evaluate how farming methods affect the carbon content of arable soils.

Of the total of some 25,000 scientific studies that were initially identified as potentially relevant, 735 were selected as usable in the survey. These have since been revised, categorised and inserted into an interactive map that is available online. This map shows clearly that the majority of the studies come from Europe and North America. Surveys from Russia, for example, are lacking. The data quality and methods of the studies investigated also have shortcomings, Hedlund points out, but she hopes that the interactive map will be disseminated and continue to expand and be updated.

‘Just since our survey started in 2014, thousands of articles have been published in the area. Our hope is that other researchers will enter their results on the map and build further on our findings.’

Many reports in the spring

During the spring, the group’s work will continue. Currently, there are two systematic reviews under way in which the researchers are looking closely at the 735 studies. There is particular interest in what answers they find to two questions: how rapidly carbon is lost from arable soils and how carbon content is affected by ploughing. Later in the spring, the group will report its conclusions.

‘We expect to be able to provide documentation for concrete recommendations to farmers and government agencies on how to work the land so that the soil retains as much as possible of its carbon,’ Hedlund says.

On another controversial environmental issue, too, Mistra EviEM’s experts will announce their conclusions later this year. Here, the questions are whether protected forests should be left entirely untouched or whether they need some form of active management to preserve their biodiversity. In this case, too, work has begun on a survey of the scientific literature.

Thus, there are several interesting reports to look forward to in the spring. In August, Mistra EviEM will be among the organisers of Better Evidence, Better Decisions, Better Environment, an international conference in Stockholm that will focus on how systematic reviews can be used for better environmental management.

Text: Henrik Lundström

Mistra Webbredaktör