『Abstract
Pristine peatlands have generally low nitrous oxide (N2O)
emissions but drainage and management practices enhance the microbial
processes and associated N2O emissions. It
is assumed that leaving peat soils from intensive management,
such as agriculture, will decrease their N2O
emissions. In this paper we report how the annual N2O
emission rates will change when agricultural peat soil is either
left abandoned or afforested and also N2O
emissions from afforested peat extraction sites. In addition,
we evaluated a biogeochemical model (DNDC) with a view to explaining
GHG emissions from peat soils under different land uses. The abandoned
agricultural peat soils had mower mean annual N2O
emissions (5.5±6.4 kg N ha-1) than the peat soils in
active agricultural use in Finland. Surprisingly, N2O
emissions from afforested organic agricultural soils (12.8±9.4
kg N ha-1) were similar to those from organic agricultural
soils in active use. These emissions were much higher than those
from the forests on nutrient rich peat soils. Abandoned and afforested
peat extraction sites emitted more N2O, (2.4±2.1
kg N ha-1), than the areas under active peat extraction
(0.7±0.5 kg N ha-1). Emissions outside the growing
season contributed significantly, 40% on an average, to the annual
emissions. The DNDC model overestimated N2O
emission rates during the growing season and indicated no emissions
during winter. The differences in the N2O
emission rates were not associated with the age of the land use
change, vegetation characteristics, peat depth or peat bulk density.
The highest N2O emissions occurred when the
soil C:N ratio was below 20 with a significant variability within
the measured C:N range (13-27). Low soil pH, high nitrate availability
and water table depth (50-70 cm) were also associated with high
N2O emissions. Mineral soil has been added
to most of the soils studied here to improve the fertility and
this may have an impact on the N2O emissions.
We infer from the multi-site dataset presented in this paper that
afforestation is not necessarily an efficient way to reduce N2O emissions from drained boreal organic fields.
Keywords: Agriculture; Forestry; N2O; Peatland;
Water table; Carbon; Nitrogen; Nitrate; pH; Winter 』
Introduction
Materials and methods
Study site
Soil chemical and physical characteristics and weather data
Plant coverage and composition of species
Cellulose decomposition
N2O flux measurements
In situ net nitrification
DNDC model
Statistical methods
Results
Weather conditions and soil temperature
N2O flux dynamics
N2O flux dynamics in abandoned and afforested
agricultural soils
N2O flux dynamics in afforested peat extraction
sites
Factors behind annual N2O emissions
Annual N2O losses
Water table level
Vegetation
Soil physical and chemical properties
In situ net nitrification
Modelling of N2O emission with DNDC
Discussion
Conclusion
Acknowledgments
References