Raise water table in peat soils
System: Dairy cattle
Mainly applicable for: Farms on drained peat soils
Not applicable or effective for: Farms on mineral soils
Description
Raising the water table in managed peat soils (“rewetting”) by reducing drainage and partially restoring natural water tables. In this factsheet we do not consider full restoration of natural peatlands, requiring strong increase of the water table, but only partial rewetting that still allows agricultural use.
While deep water tables allow intensive farming, shallower water tables will imply less intensive land use and less productive grassland. The higher water table reduces the soil’s load-bearing capacity, limiting opportunities for grazing and machinery use, and increases the risk of soil compaction or degradation due to trampling and machine traffic. This will lead to a reduction in net dry matter (DM) yield, primarily because grassland utilization is often substantially poorer under high water table conditions, for example due to increased grazing and conservation losses, and difficulties with manure application in spring.
An alternative use suitable for higher water tables is paludiculture (farming with water-tolerant crops like reeds or cattails), which is not covered in this factsheet.
Mechanism of effect
Rewetting peatlands reduces CO2 and N2O emissions from peat soils. Any increase in the water table, even 10-20 cm, can make a significant difference to reduce CO2 emissions. Raising the water table to the soil surface can even lead to a carbon “sink”, but does not allow agricultural use (thus not reported in this factsheet). As CH4 emissions increase with a higher water table (starting from about 40 cm depth) due to anaerobic conditions, there is an optimum in the net GHG (in CO2-equivalents) at a water table of 6 cm depth. Compared to 60 cm depth, this results in an average GHG saving potential of 25 t CO2-eq per ha and year (Torrus Castillo et al., 2024), but different land uses and peatland types and locations may respond differently. Rewetting can also reduce N2O, but this link is less clear (Lin et al., 2022).
Raising the water table, however, likely negatively impacts the net DM yield and can reduce the quality of the forage grown on the peat. As a result, to maintain the same herd size and animal productivity, additional forage and feed will need to be imported to compensate for these production losses. This can lead to higher GHG emissions from purchased feed, and possible changes in enteric CH4 emissions due a different feed ration composition and quality. However, effects of these changes on total GHG emissions are negligible compared to the large reduction of GHG emissions from the peat soils (e.g., Van Boxmeer et al., 2021).
Effects on GHG emissions from soils reported in this factsheet are based on the review by Torrús Castillo et al. (2024, Chapter 3).
Reference situation
Drained peat soils
Legend
| ● – Small effect (<5%) | o – No effect | o – no effect |
| ●● – Medium effect (5-20%) | ● – Unfavourable effect | ? – unknown effect |
| ●●● – Large effect (>20%) | ● – ● – Variable effect (depending on farm characteristics or way/level of implementation) |
Effect on total greenhouse gas (GHG) emissions
| Mean effect and range in kg CO2-equivalents: | per kg product | per farm | Level of evidence | ||
| Mean | (min-max) | Mean | (min-max) | ||
| Raise water table | ●●● | ●–●●● | ●●● | ● – ●● | High |
Effect per emission source
| Source | Manure storage | Animals | Feed and forage production | Barn | ||||
| Gas | CH4 | N2O | CH4 | CO2 | N2O | LUC | CO2 | |
| Raise water table | ●●● | ? | ? | |||||
*risk of an adverse effect (see ’cause of variable or unfavourable effect’)
Explanation of variable effect
Raise water table
The effect depends on the area of peat soils on the farm, the water table in the reference situation and amount of increase in water table (the larger the increase, the more reduction of CO2), the type of peat soil and climate, land uses, and any installed techniques for additional water infiltration. Effects will be time-dependent (studies from Switzerland show that the shift from source to sink can take up to 20 years).
| Literature references | Elevate water table |
|---|---|
| Renou-Wilson et al.,2016 | To graze or not to graze? Four years greenhouse gas balances and vegetation composition from a drained and a rewetted organic soil under grassland |
| Van Boxmeer et al., 2021 | Environmental and economic performance of Dutch dairy farms on peat soil |
| Torrús Castillo et al., 2024 | Carbon Farming mitigation potential: Evaluating the mitigation potential (and uncertainties) of carbon farming practices (Deliverable 4.1 of MARVIC project, v1.0; p111) |
| Bianchi et al. 2021 | Review of Greenhouse Gas Emissions from Rewetted Agricultural Soils. |
| Koch et al., 2023 | Water-table-driven greenhouse gas emission estimates guide peatland restoration at national scale |
| Tiemeyer et al., 2020 | A new methodology for organic soils in national greenhouse gas inventories: Data synthesis, derivation and application. |
| Aben et al., 2024 | Using automated transparent chambers to quantify CO2 emissions and potential emission reduction by water infiltration systems in drained coastal peatlands in the Netherlands. |
| Paul et al., 2021 | Carbon budget response of an agriculturally used fen to different soil moisture conditions. |
| Paul et al., 2024 | Can mineral soil coverage be a suitable option to mitigate greenhouse gas emissions from agriculturally managed peatlands? |
| Evans et al., 2021 | Overriding water table control on managed peatland greenhouse gas emissions. |