SLU news

Not an effective climate strategy to leave fallow agricultural land on drained peat

Published: 14 February 2024

Agriculture on drained peatlands results in significant carbon dioxide emissions. Under the EU Common Agricultural Policy, direct payments are offered to farms that set aside (leave fallow) agricultural land on drained peat, in order to reduce greenhouse gas emissions. Hannes Keck's thesis from SLU questions this strategy. In his study, carbon dioxide emissions were higher from set-aside grasslands than from nearby arable land.

Peatlands form over a long period when materials from dead plants do not break down in wet and oxygen-poor conditions. This organic material consists largely of carbon. Peatlands are a globally important carbon store, holding about 21 percent of total soil carbon. In their natural state, most peatlands act as a sink for atmospheric carbon dioxide (CO2) and a source for methane (CH4) and small amounts of nitrous oxide (N2O).

Large areas of natural peatlands are drained for peat extraction, agriculture, or forestry. Drainage allows oxygen to come into contact with the organic material, leading to significant carbon dioxide emissions.

Farmers in the EU can receive support to set aside agricultural land on drained peat. The goal is to reduce greenhouse gas emissions. However, an increasing number of scientific studies have shown that this may be an ineffective climate mitigation strategy.

Hannes Keck, a doctoral student at SLU, has measured greenhouse gas fluxes from two adjacent fields, one being cultivated and the other grassland left fallow for over six years. He found that the fallow grassland was a larger source of carbon dioxide, a smaller source of N2O, and a larger sink for CH4 compared to the cultivated arable land. The N2O and CH4 fluxes, however, had only little impact on the sites' global warming effect.

“Based on our results and in line with other recently conducted studies, setting-aside farmland on drained peat is probably not an effective way to reduce agricultural greenhouse gas emissions, as long as the peatland remains drained”, says Hannes Keck.

He has also improved the technology to measure nitrous oxide and methane fluxes, which can be used to improve the monitoring of greenhouse gas fluxes.

“My work is a small but important contribution to ongoing efforts to mitigate climate change and preserve critical carbon stores in the ecosystem" says Hannes Keck.

More knowledge is needed. Multi-seasonal and continuous greenhouse gas flux measurements at several peatland sites under different land use and management intensities, ideally paired with rewetting experiments, would provide valuable insights into management alternatives for agricultural peatlands aimed at reducing greenhouse gas emissions.

The thesis

Greenhouse gas fluxes from drained peatland Measurement techniques and management impacts

Public defense

Welcome to the defense 16 February 9:00

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Thomas Kätterer, professor systems ecology
Department of Ecology, SLU +46 (0)18-672425