Abstract
Abstract. Twelve cattle were kept for three days in a circular area of 16 m radius on short pasture and fed with freshly-cut pasture. Ammonia (NH3) emissions from the urine and dung excreted by the cattle were measured with a micrometeorological mass-balance method, during the cattle presence and for 10 subsequent days. Daily-integrated emission rates peaked on Day 3 of the experiment (last day of cattle presence) and declined steadily for five days thereafter. Urine patches were the dominant sources for these emissions. On Day 9, a secondary emissions peak occurred, with dung pats likely to be the main sources. This interpretation is based on simultaneous observations of the pH evolution in urine patches and dung pats created next to the circular plot. Feed and dung samples were analysed to estimate the amounts of nitrogen (N) ingested and excreted. Total N volatilised as NH3 was 19.8 (± 0.9)% of N intake and 22.4 (± 1.3)% of N excreted. The bimodal shape of the emissions time series allowed to infer separate estimates for volatilisation from urine and dung, respectively, with the result that urine accounted for 88.6 (± 2.6)% of the total NH3 emissions. The emissions from urine represented 25.5 (± 2.0)% of the excreted urine-N, while the emissions from dung amounted to 11.6 (± 2.7)% of the deposited dung-N. Emissions from dung may have continued after Day 13 but were not resolved by the measurement technique. A simple resistance model shows that the magnitude of the emissions from dung is controlled by the resistance of the dung crust.
Highlights
Ammonia (NH3) is generated at the soil surface, often in abundant quantities, shortly following the surface application of any source of ammoniacal-N (NHx-N, combining NH3-N and NH+4 -N) that induces an increase in soil-surface pH
Sources include urea and other ammoniacal fertilisers, ammoniacal wastes and ruminant urine (Sherlock et al, 1995). Such NH3 is susceptible to volatilisation at rates which can vary extensively depending on the crop, cultural conditions, soil properties, dung or urine deposition rates and method of fertiliser application: e.g. for urea from 1.7 % to 56 % of the applied N (Ryden et al, 1987; Jarvis et al, 1989; Sherlock et al, 1989, 2008), or for slurry from 4 % to over 60 % (Sintermann et al, 2012)
Ammonia volatilisation from agricultural soils is a dominant factor in the formation of atmospheric secondary aerosols due to its reaction with nitric and sulphuric acids in the atmosphere (Nemitz et al, 2009)
Summary
Ammonia (NH3) is generated at the soil surface, often in abundant quantities, shortly following the surface application of any source of ammoniacal-N (NHx-N, combining NH3-N and NH+4 -N) that induces an increase in soil-surface pH. Sources include urea and other ammoniacal fertilisers, ammoniacal wastes and ruminant urine (Sherlock et al, 1995) Such NH3 is susceptible to volatilisation at rates which can vary extensively depending on the crop, cultural conditions, soil properties, dung or urine deposition rates and method of fertiliser application: e.g. for urea from 1.7 % to 56 % of the applied N (Ryden et al, 1987; Jarvis et al, 1989; Sherlock et al, 1989, 2008), or for slurry from 4 % to over 60 % (Sintermann et al, 2012). Ammonia volatilisation from agricultural soils is a dominant factor in the formation of atmospheric secondary aerosols due to its reaction with nitric and sulphuric acids in the atmosphere (Nemitz et al, 2009) These aerosols contribute to the formation of acid rain (Bobbink et al, 1992). These conditions are far removed from those typically experienced under laboratory conditions and emissions under field conditions can differ substantially from NH3 volatilisation losses measured in the laboratory (Fenn and Hossner, 1985)
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