The beneficial effect goes beyond nature and agriculture: A study shows that the long-term binding of carbon in the form of humus is one of the ecological positive effects of species-rich flower strips on the edge of arable land. The contribution to climate protection is thus a further argument in the aim of making more area available for flower strips in agriculture, say the scientists.
They form oases in the deserts of monocultures: Strips of near-natural vegetation can provide a home for numerous plant and animal species and thus also increase the aesthetic recreational value of the agricultural landscape for people. Flowering mixtures grow in the strips, which are sown as part of agri-environmental or nature conservation measures and are primarily intended to increase the diversity of plants and pollinating insects. As studies have shown, flower strips can also have other beneficial effects in a variety of ways: They improve ecosystem services and thus contribute to sustainability in agriculture. This can even be economically worthwhile: by promoting pollinating insects and enemies of pests, yields can in some cases be increased in the cultivated areas flanked by flower strips.
Biomass in sight
So far, however, there have been no more detailed investigations into another positive effect: flower strips produce biomass in which carbon is bound, which comes from the processing of the greenhouse gas carbon dioxide from the atmosphere. In contrast to harvested crops, the plant material above and below ground is not removed from the field and processed, but is usually worked back into the soil through agricultural measures. There it is then partly converted into humus, in whose organic compounds the carbon remains bound in the long term. A research team led by the Thünen Institute in Braunschweig has now investigated how much biomass is formed in flower strips and to what extent they can thereby contribute to binding carbon in the form of humus.
As part of their study, the scientists first examined the composition of species and the formation of biomass above and below ground in 23 test flower strips at various locations in Germany. "In doing so, we laboriously washed out the roots from hundreds of soil samples," reports senior author Christopher Poeplau from the Thünen Institute. For the first time, the team was able to estimate the biomass growth of flower strips on the basis of valid data.
They came to the conclusion that these plant stands produce an average biomass of almost eight tons per hectare per year. At some locations it can even be 19 tons. The connection between plant biodiversity and total biomass was interesting: the more grasses mixed into the flower strips, the higher the total biomass and thus the humus effect. However, it should be emphasized that the biodiversity in the mixtures and the "blooming factor" decrease when grasses spread rapidly. "It is therefore probably not possible to maximize both plant biodiversity and carbon sequestration within a flowering strip," the researchers write.
Previously overlooked positive aspect
In principle, however, there is a significant positive effect of flower strips, as further study results have shown. Using data and models, the researchers calculated how much of the biomass is actually converted into humus. In order to assess the long-term effect across Germany, the team also integrated information into its models that was obtained as part of the agricultural soil survey. They include the management of numerous arable sites over the last ten years as well as data on soil carbon stocks. The scientists then allowed flower strips to grow "fictitious" on a total of 1,500 fields and recorded the effects.
On average, this resulted in an annual accumulation of 0.5 tons of carbon per hectare of flowering strips over the next 20 years. This in turn corresponds to 1.8 tons of carbon dioxide removed from the atmosphere, the researchers explain. "Currently around one percent of German arable land is covered with flower strips," says Poeplau. The researchers' projections now show that if a large percentage of German arable land were converted into flower strips, an additional 240,000 tons of carbon dioxide could be bound in the soil every year. "This corresponds to almost 0.5 percent of annual greenhouse gas emissions from agriculture," says Poeplau. According to the principle "every contribution counts", the researchers come to the conclusion: The positive climate effect now makes flowering strips appear even more attractive.
Source: Johann Heinrich von Thünen Institute, Federal Research Institute for Rural Areas, Forests and Fisheries, specialist article: Plant Soil, doi: