Abstract

Greenhouse gas emissions and peat subsidence are major concerns both from an environmental perspective and for farmers with declining soil production capacity. Agricultural databases, digitised maps of quaternary deposits and 40K radiation have been used in a GIS analysis to estimate the distribution and land use of agricultural organic soils in Sweden. The total area of agricultural land in Sweden is estimated to be 3,525,259 ha and 7.6% (267,990 ha) of this area is classified as agricultural organic soil. One-quarter of the agricultural area of peat soils is intensively cultivated with annual crops and the remainder is sparsely used, predominantly for managed grasslands and pastures. These data on the acreage and cultivation intensity of agricultural peat soils were used to calculate annual greenhouse gas emissions, which were estimated to be between 3.1 and 4.6 M ton CO₂ eq. (6-8% of total national emissions). Lysimeters with undisturbed soil columns (50 cm high, 29.5 cm in diameter) from two sites sown with ryegrass (Lolium perenne) were used to investigate the effects of water table depth and soil properties on soil organic matter decomposition and greenhouse gas emissions. The water table depth was set to either 40 cm or 80 cm. Dark static chambers were used to measure gas emissions from the soil surface. CO₂ emissions were greater with the water table at 40 cm than at 80 cm, and the plant contribution to CO₂ flux was 47-57%. N₂O emissions peaked in springtime and CH₄ emissions were very low or negative. The differences observed in GHG emissions between the soils were attributed to differences in organic matter resilience and soil physical properties.