Investigating uptake of N2O in agricultural soils using a high-precision dynamic chamber method

Uptake (or negative flux) of nitrous oxide (N2O)in agricultural soils is a controversial issue which has proved difficult to investigate in the past due to constraints such as instrumental precision and methodological uncertainties. Using a recently developed high-precision quantum cascade laser gas analyser combined with a closed dynamic chamber, a well-defined detection limit of 4 μg N2O-N m could be achieved for individual soil flux measurements. 1220 mea- surements of N2O flux were made from a variety of UK soils using this method, of which 115 indicated uptake by the soil (i.e. a negative flux in the micrometeorological sign convention). Only four of these apparently negative fluxes were greater than the detection limit of the method, which suggests that the vast majority of reported negative fluxes from such measurements are actually due to instrument noise. As such, we suggest that the bulk of negative N2O fluxes reported for agricultural fields are most likely due to limits in detection of a particular flux measurement methodology and not a result of microbiological activity consuming atmospheric N2O

Difference in soil methane (CH4) and nitrous oxide (N2O) fluxes from bioenergy crops SRC willow and SRF Scots pine compared with adjacent arable and fallow in a temperate climate

Soil greenhouse gas (GHG) fluxes of methane (CH4) and nitrous oxide (N2O) were measured over a two year period from several land-use systems on adjacent sites under the same soil and climatic conditions to assess the influence of the transition from arable agricultural (barley) and fallow to perennial bioenergy crops short rotation coppice (SRC) willow (Salix spp.) and short rotation forest (SRF) Scots pine (Pinus silvestris). There were no significant differences between CH4 and N2O fluxes measured from the SRC, SRF and fallow but the arable agricultural site showed an order of magnitude larger N2O emissions compared with the others. Fertiliser application to the arable crop was the major factor influencing N2O emissions and both air and soil temperature showed no significant effects on fluxes between the different land-use systems. Soil moisture was significantly different from the arable crop, showing a greater range than from SRF and SRC. Hence these bioenergy crops might be viable options for water stressed areas

Nitrous oxide emissions from managed grassland: a comparison of eddy covariance and static chamber measurements

Managed grasslands are known to be an important source of N2O with estimated global losses of 2.5 Tg N2O-N yr−1. Chambers are to date the most widely used method to measure N2O fluxes, but also micrometeorological methods are successfully applied. In this paper we present a comparison of N2O fluxes measured by non-steady state chambers and eddy covariance (EC) (using an ultra-sonic anemometer coupled with a tunable diode laser) from an intensively grazed and fertilised grassland site in South East Scotland. The measurements were taken after fertilisation events in 2003, 2007 and 2008. In four out of six comparison periods, a short-lived increase of N2O emissions was observed after mineral N application, returning to background level within 2–6 days. Highest fluxes were measured by both methods in July 2007 with maximum values of 1438 ng N2O-N m−2 s−1 (EC) and 651 ng N2O-N m−2 s−1 (chamber method). Negative fluxes above the detection limit were observed in all comparison periods by EC, while with chambers, the recorded negative fluxes were always below detection limit. Median and average fluxes over each period were always positive. Over all 6 comparison periods, 69% of N2O fluxes measured by EC at the time of chamber closure were within the range of the chamber measurements. N2O fluxes measured by EC during the time of chamber closure were not consistently smaller, neither larger, compared to those measured by chambers: this reflects the fact that the different techniques integrate fluxes over different spatial and temporal scales. Large fluxes measured by chambers may be representing local hotspots providing a small contribution to the flux measured by the EC method which integrates over a larger area. The spatial variability from chamber measurements was high, as shown by a coefficient of variation of up to 139%. No diurnal pattern of N2O fluxes was observed, possibly due to the small diurnal variations of soil temperature. The calculation of cumulative fluxes using different integration methods showed EC data provide generally lower estimates of N2O emissions than chambers

The impact of ploughing intensively managed temperate grasslands on N2O, CH4 and CO2 fluxes

Background and aims: Temperate grasslands are a globally important component of agricultural production systems and a major contributor to the exchange of greenhouse gases (GHG) between the biosphere and atmosphere. Many intensively managed grazed grasslands in NW Europe are ploughed and reseeded occasionally in order to improve their productivity. Here, we examined the impact of ploughing on the emission of GHGs a grassland. Methods: To study these interactions we measured soil GHG fluxes using the static chamber method in addition to the net ecosystem exchange (NEE) of CO2 by eddy covariance from two adjacent fields. Until ploughing one field in 2012 and the other in 2014, management of these intensively grazed grasslands was almost the same and typical for the study region. Results: The effect on N2O is small, but distinguishable from the effects of N fertilisation, soil temperature and soil moisture. Tillage-induced N2O fluxeswere close to expectations based on the IPCC default methodology. By far the dominant effect on the GHG balance was the temporary reduction in GPP. Conclusions: Ploughing and reseeding can substantially influence short-term GHG emissions. Therefore tillageinduced fluxes ought to be considered when estimating greenhouse gas fluxes or budgets from grasslands that are periodically ploughed

Methane flux measurements along a floodplain soil moisture gradient in the Okavango Delta, Botswana

Data-poor tropical wetlands constitute an important source of atmospheric CH4 in the world. We studied CH4 fluxes using closed chambers along a soil moisture gradient in a tropical seasonal swamp in the Okavango Delta, Botswana, the sixth largest tropical wetland in the world. The objective of the study was to assess net CH4 fluxes and controlling environmental factors in the Delta's seasonal floodplains. Net CH4 emissions from seasonal floodplains in the wetland were estimated at 0.072 ± 0.016 Tg a−1. Microbial CH4 oxidation of approximately 2.817 × 10−3 ± 0.307 × 10−3 Tg a−1 in adjacent dry soils of the occasional floodplains accounted for the sink of 4% of the total soil CH4 emissions from seasonal floodplains. The observed microbial CH4 sink in the Delta's dry soils is, therefore, comparable to the global average sink of 4–6%. Soil water content (SWC) and soil organic matter were the main environmental factors controlling CH4 fluxes in both the seasonal and occasional floodplains. The optimum SWC for soil CH4 emissions and oxidation in the Delta were estimated at 50% and 15%, respectively. Electrical conductivity and pH were poorly correlated (r2 ≤ 0.11, p < 0.05) with CH4 fluxes in the seasonal floodplain at Nxaraga

River Tay, Scotland, water chemistry and greenhouse gas measurements 2009-2010

This dataset contains concentrations of dissolved organic carbon, dissolved inorganic carbon, nutrients and concentrations of greenhouse gases CO2, CH4 and N2O from nine sites across the River Tay catchment. Water was sampled on a monthly basis between February 2009 and December 2010. The locations of sampling sites were based on existing flow gauging and water sampling sites of the Scottish Environment Protection Agency (SEPA).,These data were collected as part of a PhD project funded by the CEH Integrating fund. Water and headspace samples were collected from nine sites within the Tay catchment on a monthly basis between 2009 and 2010 by James Harley. Sample analysis was undertaken at CEH Edinburgh, again by James Harley. A detailed description of sample collection methods and analytical measurements can be found in the supporting information document supplied with the data.

Emissão de óxidos de nitrogênio associada à aplicação de uréia sob plantio convencional e direto Nitrogen oxides emission related to urea broadcasting fertilization under conventional and no-tillage systems

O objetivo deste trabalho foi avaliar emissões de NO e N2O até cinco dias após a primeira fertilização de cobertura com uréia em milho, em Latossolo Vermelho argiloso distrófico, sob plantio convencional e direto. A adubação de cobertura foi de 60 kg ha-1 de N. O experimento foi conduzido na Embrapa Cerrados, Planaltina, DF, com delineamento de blocos ao acaso, com três repetições, sendo o terceiro cultivo de milho, em rotação com soja. Os fluxos de NO e N2O foram medidos em câmaras de PVC instaladas em cada parcela. Houve emissão alta de NO imediatamente após (5,4 ng N cm-2 h-1) e no terceiro dia (4,8 ng N cm-2 h-1) após aplicação de uréia e irrigação. Um dia após fertilização, a emissão de NO reduziu-se a 1,9 ng N cm-2 h-1, e cinco dias depois, alcançou 1,2 ng N cm-2 h-1. Os fluxos de N2O ficaram abaixo do limite de detecção de 0,6 ng N cm-2 h-1. Não houve diferença significativa entre os plantios convencional e direto quanto à emissão dos óxidos de nitrogênio.<br>The objective of this work was to evaluate the NO and N2O emissions up to five days after the first nitrogen broadcasting fertilization with urea in a cornfield, in a Red Latosol, under conventional and no-tillage systems. The level of nitrogen broadcasting fertilization was of 60 kg ha-1. The experiment was conducted at Embrapa Cerrados, Planaltina, DF, Brazil, in a randomized block design, with three replications, beeing the third corn crop in rotation with soybean. NO and N2O fluxes were measured using PVC chambers installed in each plot. Higher NO fluxes were found immediately after (5.4 ng N cm-2 h-1) and three days (4.8 ng N cm-2 h-1) after N fertilization and irrigation. In the first day after fertilization, the NO emission decreased significantly to 1.9 ng N cm-2 h-1, and after five days, reached 1.2 ng N cm-2 h-1. N2O fluxes values were below the detection limit of 0.6 ng N cm-2 h-1. No significant differences in nitrogen oxides fluxes were found between plots under conventional and no-tillage systems