How do emission rates and emission factors for nitrous oxide and ammonia vary with manure type and time of application in a Scottish farmland?

• N2O and NH3 emissions from cropland treated with livestock manures were measured.
• The effect of manure type and timing of application on emissions was assessed.
• Mean annual N2O emissions were greatest following manure applications in autumn.
• Mean annual NH3 emissions were greatest following manure applications in spring.
• There were large variation in EFs depending on manure type and time of application.

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 (N2O) and ammonia (NH3). Emissions of N2O and NH3 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 N2O and 20% for NH3. 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 N2O and NH3 emission intensities. Mean annual N2O emissions across all manure treatments were greater from autumn (2 kg N2O–N ha− 1) than spring (0.35 kg N2O–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 NH3 emissions were measured from layer manure than all other manures at both times of application. N2O and NH3 EFs were highly variable depending on the season of application and manure type. The mean autumn and spring N2O EFs across all manure treatments were 1.72% and − 0.33% respectively, and mean NH3 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 N2O and NH3 EFs, and the considerable effect that manure type and time of application have on N2O and NH3 emissions.