Nitrous oxide emissions from fertilized and unfertilized grasslands on peat soil

Abstract

Emissions of nitrous oxide (N 2 O) from managed and grazed grasslands on peat soils are amongst the highest emissions in the world per unit of surface of agriculturally managed soil. According to the IPCC methodology, the direct N 2 O emissions from managed organic soils is the sum of N 2 O emissions derived from N input, including fertilizers, urine and dung of grazing cattle, and a constant 'background' N 2 O emission from decomposition of organic matter that depends on agro-climatic zone. In this paper we questioned the constant nature of this background emission from peat soils by monitoring N 2 O emissions, groundwater levels, N inputs and soil NO 3 --N contents from 4 grazed and fertilized grassland fields on managed organic peat soil. Two fields had a relatively low groundwater level ('dry' fields) and two fields had a relatively high groundwater level ('wet' fields). To measure the background N 2 O emission, unfertilized sub-plots were installed in each field. Measurements were performed monthly and after selected management events for 2 years (2008)(2009)). On the managed fields average cumulative emission equaled 21 ± 2 kg N ha -1 y -1 for the 'dry' fields and 14 ± 3 kg N ha -1 y -1 for the 'wet' fields. On the unfertilized sub-plots emissions equaled 4 ± 0.6 kg N ha -1 y -1 for the 'dry' fields and 1 ± 0.7 kg N ha -1 y -1 for the 'wet' fields, which is below the currently used estimates. Background emissions were closely correlated with groundwater level (R 2 = 0.73) and accounted for approximately 22% of the cumulative N 2 O emission for the dry fields and for approximately 10% of the cumulative N 2 O emissions from the wet fields. The results of this study demonstrate that the accuracy of estimating direct N 2 O emissions from peat soils can be improved by approximately 20% by applying a background emission of N 2 O that depends on annual average groundwater level rather than applying a constant value.

Response of N 2 O emission to water and nitrogen addition in temperate typical steppe soil in Inner Mongolia, China

“…The functions of N and water addition in improving soil N 2 O effluxes are described as follows: (1) N input provides sufficient substrate for the N 2 O generation processes; (2) the drying-rewetting transformation after water addition allows the release of several organic and inorganic substances into the soil, which provides sufficient substrates and energy for nitrification and denitrification (Mummey et al, 1994;Bollmann and Conrad, 1998;Beare et al, 2009); and (3) the variations in soil NO 3 À and NH 4 + contents suggest that water addition facilitates the immediate transfer of fertilizers to mineral N from surface soil to the 0-10 cm soil layer, which also provides ample substrate for nitrification and denitrification (Goldberg et al, 2010;Kim et al, 2010). Short bursts of N 2 O emissions after fertilization were also observed in previous studies (Dobbie and Smith, 2003;Jones et al, 2007); however, the highest effluxes observed in our study was in the lower range relative to the peak values of N 2 O obtained by some other N addition experiments in temperate grasslands abroad (ranged from 100 to 7500 mg m À2 h À1 N 2 O-N) (e.g., Kim et al, 2010;Pinto et al, 2004;Van Beek et al, 2011). In this study, the highest peak efflux among different treatments was only (Peng et al, 2011).…”

Reducing nitrous oxide emissions by changing N fertiliser use from calcium ammonium nitrate (CAN) to urea based formulations

“…The HB soil texture was classified as a clay loam (gleysol) and was imperfectly drained with evidence of gleying (at 0.3m depth). In addition, drainage impeded soils tend to be low in oxygen and tend to lose a greater percentage of N as N 2 O (Dennis et al, 2012) compared to well drained soils, with emissions from managed and grazed grasslands on peat soils among the highest emissions in the world (van Beek et al, 2011). Results from the current study demonstrated that emissions from CAN at HB were significantly higher than the other two sites, probably due to the higher denitrification potential of these soils combined with higher precipitation at this location especially in 2013.…”

Evaluating effects of land management on greenhouse gas fluxes and carbon balances in boreo-temperate lowland peatland systems

“…However, whilst the results are from three different studies, the data are collected from the same peatland area. Furthermore, during the critical appraisal process, these studies were classified as unclear [63,64] and high [65] in their susceptibility to bias. The results should therefore be treated with caution.…”