Nitrification inhibitors and fertiliser nitrogen application timing strategies to reduce N2O. Site in Devon, 2010

N - Datasets

Misselbrook, T. H., Cardenas, L. M., Camp, V. and Donovan, N. 2017. Nitrification inhibitors and fertiliser nitrogen application timing strategies to reduce N2O. Site in Devon, 2010. Freshwater Biological Assoc. https://doi.org/10.17865/ghgno357

AuthorsMisselbrook, T. H., Cardenas, L. M., Camp, V. and Donovan, N.
Abstract

At Rothamsted Research, North Wyke, near Okehampton, south-west England (clay loam topsoil texture), direct nitrous oxide (N2O) and ammonia (NH3) emissions were measured from replicated (x3) plots (12 x 13 m) following spring applications of manufactured nitrogen (N) fertilisers to grassland. A control treatment was included where no N fertiliser was applied. Ammonium nitrate (AN) fertiliser (34.5% N) or urea fertiliser (46% N) was applied at a rate of 120 kg N ha-1 in two equal split applications (mid- and late April), with or without the commercially available nitrification inhibitor - dicyandiamide (DCD). The DCD was applied in a solution (15 kg DCD ha-1) and sprayed onto the plots immediately after N fertiliser application. The N supplied by the DCD was accounted for in the 120 kg N ha-1. As separate treatments, AN and urea fertiliser were also applied in four equal splits, 1 week apart from mid-April to early May i.e. 'little and often'. Following N fertiliser application, measurements of direct N2O-N were made over c.12 months, using 5 static chambers (0.8 m2 total surface area) per plot and analysed by gas chromatography. Ammonia-N emissions were measured for 3 weeks after each split N fertiliser application, using a wind tunnel technique (one per plot). Indirect N2O-N emissions were estimated from the measured NH3 losses and using the Intergovernmental Panel on Climate Change (IPCC) default emission factor; namely 1% of volatilised N is lost as N2O-N. Soil moisture (0-10 cm) content and soil mineral nitrogen content (0-10 cm from 2-split AN and control treatments only) were measured at every N2O sampling event, along with continuous measurements of rainfall, air and soil temperatures (5 cm). Grass yields and N offtakes were also measured following the first and second grass cuts in late May and early August 2010. The Devon, 2010 experiment contains data sets of; annual nitrous oxide emission, annual nitrous oxide emission factor, total ammonia loss, soil moisture, top soil mineral nitrogen (selected treatments), temperature, rainfall and associated crop (grass yield and nitrogen offtakes) and soil measurements.

Year of Publication2017
PublisherFreshwater Biological Assoc
Digital Object Identifier (DOI)https://doi.org/10.17865/ghgno357
Keywordsnitrous oxide
ammonium nitrate
ammonia
urea
nitrification inhibitors
grassland soils
clay soils
Publication dates
Online03 Feb 2017
FunderDepartment of Environment, Food and Rural Affairs
Data collection period13 Apr 2010 to end of 14 Mar 2011
Geographic location
Devon, South West England, United Kingdom
Geographic region bounding box
(50.68, -4.04) to (50.85, -3.75)
Geographic coverageDevon, South West England, United Kingdom
Data collection method

Direct N2O emissions were measured with five static flux chambers (40 cm wide x 40 cm long x 25 cm high) per plot, covering a total surface area of 0.8 m2. The chambers were of white (i.e. reflective) PVC and un-vented with a weighted lid and neoprene seal allowing an air-tight seal to form following chamber enclosure. Chambers were pushed into the soil up to a depth of 5 cm and remained in place throughout the experiment, except during fertiliser application and grass cutting when chambers were removed, locations were marked, and chambers were re-instated to the same position as prior to removal. Chambers remained open except for a short time on each sampling day. On that day, ten samples of ambient air were taken to represent time zero (T0) N2O samples. From each chamber, after a 40-minute enclosure period (T40) a headspace sample was taken using a 50-ml syringe. Using a double needle system the sample was flushed though a pre-evacuated 20-22 ml glass vial fitted with a chloro-butyl rubber septum and held at atmospheric pressure. The N2O flux was calculated using an assumed linear increase in N2O concentration from the ambient N2O concentration (T0) to the N2O concentration inside the chamber after 40-minutes enclosure (T40) (Chadwick et al., 2014). Throughout each experiment, the linearity of emissions through time was checked routinely from three chambers located on the highest N rate plots. A minimum of four samples were taken from each chamber at 20 min intervals commencing at closure i.e. T0 and spanning the T40 sampling time. In order to minimise the effect of diurnal variation, gas sampling was carried out between 10:00 am and 14:00 pm and where possible between 10:00 am and 12:00 pm as suggested by IAEA (1992) and referred to in the IPCC good practice guidance (IPCC, 2000). Gas samples were analysed as soon as possible after collection (to minimise potential leakage) using gas chromatographs fitted with an electron-capture detector and an automated sample injection system. Following receipt in the laboratory, three replicates of one standard N2O gas were kept with the samples and were used to verify sample integrity during storage. The gas chromatographs were calibrated on a daily basis using certified N2O standard gas mixtures. Following each fertiliser application, N2O flux measurements were carried out in line with the following sampling schedule until the next fertiliser application or for the final application until the end of the monitoring period; measurements were taken for 5 days immediately following fertiliser application, daily for a further 5 days during the next week, twice weekly for the next two weeks, every other week over the next c. four months, decreasing in frequency to monthly until the end of the 12 month sampling period. Prior to the first fertiliser application N2O measurements were taken to provide baseline information. This sampling schedule resulted in an annual total of c.40 sampling days starting from the day of the first fertiliser application. Measurements were taken over 12 months to follow IPCC good practice guidance and so that the results were directly comparable to the IPCC 2006 methodology default emission factor.

Data preparation and processing activities

Nitrous oxide fluxes from the five replicate chambers per plot were averaged. Cumulative fluxes were calculated using the trapezoidal rule to interpolate fluxes between sampling points.

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