Carbon dioxide, nitrous oxide and methane dynamics in boreal organic agricultural soils with different soil characteristics

The annual carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) dynamics were measured with static chambers on two organic agricultural soils with different soil characteristics. Site 1 had a peat layer of 30 cm, with an organic matter (OM) content of 74% in the top 20 cm. Site 2 had a peat layer of 70 cm but an OM content of only 40% in the top 20 cm. On both sites there were plots under barley and grass and also plots where the vegetation was removed. All soils were net sources of CO2 and N2O, but they consumed atmospheric CH4. Soils under barley had higher net CO2 emissions (830 g CO2–C m−2 yr−1) and N2O emissions (848 mg N2O–N m−2 yr−1) than those under grass (395 g CO2–C m−3 yr−1 and 275 mg N2O–N m−2 yr−1). Bare soils had the highest N2O emissions, mean 2350 mg N2O–N m−2 yr−1. The mean CH4 uptake rate from vegetated soils was 100 mg CH4–C m−3 yr−1 and from bare soils 55 mg CH4–C m−2 yr−1. The net CO2 emissions were higher from Site 2, which had a high peat bulk density and a low OM content derived from the addition of mineral soil to the peat during the cultivation history of that site. Despite the differences in soil characteristics, the mean N2O emissions were similar from vegetated peat soils from both sites. However, bare soils from Site 2 with mineral soil addition had N2O emissions of 2–9 times greater than those from Site 1. Site 1 consumed atmospheric CH4 at a higher rate than Site 2 with additional mineral soil. N2O emissions during winter were an important component of the N2O budget even though they varied greatly, ranging from 2 to 99% (mean 26%) of the annual emission.