Emissions of N2O from fertilized and grazed grassland on organic soil in relation to groundwater level

Intensively managed grasslands on organic soils are a major source of nitrous oxide (N 2 O) emissions. The Intergovernmental Panel on Climate Change (IPCC) therefore has set the default emission factor at 8 kg N–N 2 O ha −1 year −1 for cultivation and management of organic soils. Also, the Dutch national reporting methodology for greenhouse gases uses a relatively high calculated emission factor of 4.7 kg N–N 2 O ha −1 year −1 . In addition to cultivation, the IPCC methodology and the Dutch national methodology account for N 2 O emissions from N inputs through fertilizer applications and animal urine and faeces deposition to estimate annual N 2 O emissions from cultivated and managed organic soils. However, neither approach accounts for other soil parameters that might control N 2 O emissions such as groundwater level. In this paper we report on the relations between N 2 O emissions, N inputs and groundwater level dynamics for a fertilized and grazed grassland on drained peat soil. We measured N 2 O emissions from fields with different target groundwater levels of 40 cm (‘wet’) and 55 cm (‘dry’) below soil surface in the years 1992, 1993, 2002, 2006 and 2007. Average emissions equalled 29.5 kg N 2 O–N ha −1 year −1 and 11.6 kg N–N 2 O ha −1 year −1 for the dry and wet conditions, respectively. Especially under dry conditions, measured N 2 O emissions exceeded current official estimates using the IPCC methodology and the Dutch national reporting methodology. The N 2 O–N emissions equalled 8.2 and 3.2% of the total N inputs through fertilizers, manure and cattle droppings for the dry and wet field, respectively and were strongly related to average groundwater level ( R 2 = 0.74). We argue that this relation should be explored for other sites and could be used to derive accurate emission data for fertilized and grazed grasslands on organic soils.