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The use of livestock manure as an organic fertiliser on agricultural land is an attractive alternative to synthetic fertiliser. The type of manure and the timing and method of application can however be crucial factors in reducing the extent of nitrogen lost from the system. This is important not only to enhance crop production, but in controlling gaseous emissions, including nitrous oxide (N 2 O) and ammonia (NH 3 ). Emissions of N 2 O and NH 3 were measured for 12 months from two experiments at an arable site in Scotland, to determine the effect of manure type and the timing (season) of application. Emission factors (EFs) were calculated for each manure applied in each season, and compared to IPCC standard EFs of 1% for N 2 O and 20% for NH 3 . Cattle farmyard manure, broiler litter, layer manure, and cattle slurry by surface broadcast and trailing hose application were applied to one experiment in October 2012 (autumn applications) and one in April 2013 (spring applications). Experimental areas were sown with winter wheat ( Triticum aestivum ) and manures were applied at typical rates. Crop yield was recorded to allow calculation of N 2 O and NH 3 emission intensities. Mean annual N 2 O emissions across all manure treatments were greater from autumn (2 kg N 2 O–N ha − 1 ) than spring (0.35 kg N 2 O–N ha − 1 ) applications, and in the spring experiment were significantly lower from cattle slurry than other treatments. Ammonia emissions were generally greater (though not significantly) from spring than autumn applications. Significantly greater NH 3 emissions were measured from layer manure than all other manures at both times of application. N 2 O and NH 3 EFs were highly variable depending on the season of application and manure type. The mean autumn and spring N 2 O EFs across all manure treatments were 1.72% and − 0.33% respectively, and mean NH 3 EFs across all treatments were 8.2% and 15.0% from autumn and spring applications, respectively. These results demonstrate large deviation from the IPCC default values for N 2 O and NH 3 EFs, and the considerable effect that manure type and time of application have on N 2 O and NH 3 emissions. [ABSTRACT FROM AUTHOR]

Cultivated agricultural soils are the largest anthropogenic source of nitrous oxide (N 2 O), a greenhouse gas approx . 298 times stronger than carbon dioxide. As agricultural land covers 40–50% of the earth’s surface agricultural N 2 O emissions could significantly influence future climate. The timing, amount and form of manufactured nitrogen (N) fertiliser applied to soils are major controls on N 2 O emission magnitude, and various methods are being investigated to quantify and reduce these emissions. A lack of measured N 2 O emission factors (EFs) means that most countries report N 2 O emissions using the IPCC’s Tier 1 methodology, where an EF of 1% is applied to mineral soils, regardless of soil type, climate, or location. The aim of this research was to generate evidence from experiments to contribute to improving the UK’s N 2 O agricultural inventory, by determining whether N 2 O EFs should vary across soil types and agroclimatic zones. Mitigation methods were also investigated, including assessing the impact of the nitrification inhibitor (NI) dicyandiamide (DCD), the application of more frequent smaller doses of fertiliser, and the impact of different rates and forms of manufactured N fertiliser. Nitrous oxide emissions were measured at one cropland site in Scotland and two in England for 12 months in 2011/2012, along with soil and environmental variables. Crop yield was also measured, and emission intensities were calculated for the contrasting fertiliser treatments. The greatest mean annual cumulative emissions from a range of ammonium nitrate (AN) fertiliser rates were measured at the Scottish site (2301 g N 2 O-N ha −1 ), which experienced 822 mm rainfall compared to 418 mm and 472 mm at the English sites, where cumulative annual emissions were lower (929 and 1152 g N 2 O-N ha −1 , respectively). Climate and soil mineral N influenced N 2 O emissions, with a combination of factors required to occur simultaneously to generate the greatest fluxes. Emissions were related to fertiliser N rate; however the trend was not linear. EFs for AN treatments varied between sites, but at both English sites were much lower than the 1% value used by the IPCC, and as low as 0.20%. DCD reduced AN- and urea-generated N 2 O emissions and yield-scaled emissions at all sites. AN application in more frequent smaller doses reduced emissions at all sites, however, the type of fertiliser (AN or urea) had no impact. A significant difference in mean annual cumulative emissions between sites reflected differences in rainfall, and suggests that location specific or rainfall driven emission estimates could be considered. [ABSTRACT FROM AUTHOR]