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Title (Primary) Ammonia volatilisation is not the dominant factor in determining the soil nitrate isotopic composition of pasture systems
Author Wells, N.S.; Baisden, W.T.; Clough, T.J.;
Journal Agriculture Ecosystems & Environment
Year 2015
Department CATHYD;
Volume 199
Language englisch;
POF III (all) T31;
Keywords Nitrate; Grazed pastures; Ammonia volatilisation; Nitrogen mineralisation; Denitrification; Nitrification
UFZ wide themes RU2;
Abstract Nitrate dual isotopes (d15N—NO3 and d18O—NO3) are increasingly used to assess the sources and sinks
of nitrogen (N) pollution in freshwater systems. However, the application of this methodology to pasture
agroecosystems is currently limited by the lack of information on how, or even if, the primary N inputs to
the systems (livestock urine and urea fertiliser) are expressed in the isotopic signature of exported NO3.
To remedy this gap, direct measurements of fractionation during ammonia volatilisation were linked
with changes in the concentration and isotopic composition of the residual soil inorganic N pool (NO3,
nitrite, and ammonium) following the addition of differing levels of bovine urine and urea fertiliser.
Ammonia volatilisation, with a d15N enrichment factor of +35  5m, removed from 5 to 40% of N inputs
from the different treatments, which should have enriched the residual inorganic N pool to 25m and 3m,
respectively. However, this fractionation did not propagate into the soil NO3 pool due to a combination
of urine-induced mineralisation (up to 120 mg N g soil1 day1 in the high urine treatment) and on-going
nitrification. Consequently, NO3 measured within the treatments was not as enriched in 15N as the
values typically ascribed to excreta-N sources. Up-scaling these results, the whole-pasture NO3 isotopic
composition primarily reflected time since fertilisation, regardless of urine inputs. These
findings
necessitate expanding the range of d15N—NO3 values ascribed to livestock sources to encompass values
as low as 10m, highlighting the need to account for post-deposition soil N cycling in order to accurately
define NO3 isotopic source ranges.
ID 15829
Persistent UFZ Identifier http://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=15829
Wells, N.S., Baisden, W.T., Clough, T.J. (2015):
Ammonia volatilisation is not the dominant factor in determining the soil nitrate isotopic composition of pasture systems
Agric. Ecosyst. Environ. 199 , 290 - 300