CO2 emissions of peat soils in agricultural use

calculation and prevention

Resumo

About 9% of the area of the Netherlands is covered by peat soils (about 290,000 ha), mainly drained and in use for dairy farming (about 223,000 ha). Decomposition (oxidation) of peat soils used in dairy farming causes subsidence rates of 12 mm.y^-1 The objective of the research was to develop a method to calculate from subsidence the CO₂ emissions of peat soils in agricultural use and to test the possibilities of submerged drains to raise groundwater levels and diminish subsidence and CO₂ emissions. One mm subsidence by oxidation equals a CO₂ emission of about 2.3 tons of CO₂ per year per hectare. We calculated that about 3% of the annual anthropological CO₂ emission in the Netherlands can be accounted to the oxidation of peat soils. This is about 4.2 Mton CO₂ per year. In dry summers the groundwater level lowers well below ditchwater levels, exposing easily biological degradable peat to oxidation. Raising groundwater levels up to ditchwater levels by subsurface irrigation by submerged drains with a spacing from drain to drain of 4 to 6 meters is tested as a possibility to reduce subsidence and CO₂ emissions. The experiments started in 2003. Subsidence and so CO₂ emissions proved to be reduced by more than 80%. A disadvantage of the use of submerged irrigation might be the increased water usage. Model calculations showed that the amount of inlet water increased on average up to 30%, however, intelligent water management can be a possibility to reduce the extra water usage to about 5%. The modeled reduction in subsidence (and so the CO₂ emission) was about 40% of the subsidence in the situation without submerged drains. We concluded that the use of submerged drains can reduce subsidence and CO₂ emissions with at least 50%.