Do Permanent Grasslands Contribute to Climate Protection?
Photo: Gabriela Brändle,
Agroscope
Do soils under meadows and pastures in Switzerland take up more carbon than they release, thus contributing to climate protection? According to a new study from Agroscope, they currently do not. Measures to promote carbon storage do, however, exist.
Seventy-five per cent of Swiss agricultural land consists of permanent grassland, i.e. meadows, year-round pastures and summer pastures. These soils naturally contain a high amount of carbon, as grasses form a dense mesh of roots which are very important for carbon input in soils.
The dead roots, together with dead microbes, fungi and their decomposition products, form the soil organic matter. Farmyard manure also contributes to the formation of soil carbon stocks.
Is there additional carbon storage?
‘Carbon sequestration’, however, only occurs when organic matter is retained over a longer period, and this organic matter formation is associated with a net uptake of carbon dioxide from the atmosphere. For this, carbon inputs must be greater than carbon losses. Carbon losses occur mainly when soil microorganisms decompose organic matter (mineralisation).
Do Swiss grassland soils have a positive carbon balance? Is carbon storage therefore increasing, and are soils thus contributing to climate protection? Using existing data, a team from Agroscope reviewed how the carbon stocks of permanent-grassland soils have changed over the last 30 years.
Neutral carbon balance over the past 30 years
The researchers came to the conclusion that over the past 30 years meadows and pastures on mineral soils have been neither carbon sinks nor sources. Hence, the available data offer no indication of increased carbon storage on permanent grassland under the current management. However, available data is insufficient to answer this question conclusively. Moreover, data on the subsoil, where large quantities of carbon can be stored, and are stored for longer periods than in the topsoil, are at best scant. It is therefore vital to include the subsoil in all future investigations.
Possible measures for increasing carbon storage
Could soil carbon storage be increased by implementing specific management measures? Since data on this topic is scarce in Switzerland, the researchers are discussing methods that have been successful in other countries. Among these are increased pasture management, moderate management intensity and mineral fertilisation.
According to the current state of knowledge, the planting of trees and shrubs and the use of biochar in the Swiss context are most likely to lead to additional soil carbon storage. By contrast, the spreading of organic fertilisers such as manure and slurry seldom leads to additional carbon storage, since this usually only involves the displacement of organic matter, which does not lead to a net carbon-dioxide uptake. Soil quality can, however, be improved through organic fertilisation.
A comparison with the current greenhouse-gas emissions from livestock shows that Swiss permanent grasslands cannot offset these emissions, even when optimistic storage rates are assumed. However, since permanent-grassland soils store large amounts of carbon, the preservation of these stores is vital for preventing losses and maintaining soil quality.
Conclusions
- The carbon stores of Swiss permanent grasslands – i.e. meadows, year-round pastures and summer pastures– have neither increased nor decreased over the past 30 years.
- According to the current state of knowledge, the planting of trees and shrubs as well as the use of biochar are the most suitable measures for increasing carbon storage in Switzerland.
- Evaluations of further measures such as increased pasture management and moderate management intensity under Swiss conditions is recommended.
- Even based on very optimistic assumptions, Swiss permanent grassland soils cannot store enough additional carbon to offset livestock greenhouse-gas emissions.
- Since permanent-grassland soils store large amounts of carbon, preserving these stores is vital for preventing losses and maintaining soil quality.
Bibliographical reference
Dauergrünlandböden der Schweiz: Quelle oder Senke von Kohlendioxid?.