Quantification of reductions in ammonia emissions from fertiliser urea and animal urine in grazed pastures with urease inhibitors for agriculture inventory: New Zealand as a case study
Authors: Saggar, S; Singh, J; Giltrap, DL; Zaman, M; Luo, J; Rollo, M; Kim, DG; Rys, G; Der Weerden, TJ
Science of the Total Environment.
HERO ID: 1510889
Urea is the key nitrogen (N) fertiliser for grazed pastures, and is also present in excreted animal . . .
Urea is the key nitrogen (N) fertiliser for grazed pastures, and is also present in excreted animal urine. In soil, urea hydrolyses rapidly to ammonium (NH(4)(+)) and may be lost as ammonia (NH(3)) gas. Unlike nitrous oxide (N(2)O), however, NH(3) is not a greenhouse gas although it can act as a secondary source of N(2)O, and hence contribute indirectly to global warming and stratospheric ozone depletion. Various urease inhibitors (UIs) have been used over the last 30years to reduce NH(3) losses. Among these, N-(n-butyl) thiophosphoric triamide (nBTPT), sold under the trade name Agrotain®, is currently the most promising and effective when applied with urea or urine. Here we conduct a critical analysis of the published and non-published data on the effectiveness of nBTPT in reducing NH(3) emission, from which adjusted values for Frac(GASF) (fraction of total N fertiliser emitted as NH(3)) and Frac(GASM) (fraction of total N from, animal manure and urine emitted as NH(3)) for the national agriculture greenhouse gas (GHG) inventory are recommended in order to provide accurate data for the inventory. We use New Zealand as a case study to assess and quantify the overall reduction in NH(3) emission from urea and animal urine with the application of UI nBTPT. The available literature indicates that an application rate of 0.025% w/w (nBTPT per unit of N) is optimum for reducing NH(3) emissions from temperate grasslands. UI-treated urine studies gave highly variable reductions (11-93%) with an average of 53% and a 95% confidence interval of 33-73%. New Zealand studies, using UI-treated urea, suggest that nBTPT (0.025% w/w) reduces NH(3) emissions by 44.7%, on average, with a confidence interval of 39-50%. On this basis, a New Zealand specific value of 0.055 for Frac(GASF) FN(UI) (fraction of urease inhibitor treated total fertiliser N emitted as NH(3)) is recommended for adoption where urea containing UI are applied as nBTPT at a rate of 0.025% w/w. Only a limited number of published data sets are available on the effectiveness of UI for reducing NH(3) losses from animal urine-N deposited during grazing in a grazed pasture system. The same can be said about mixing UI with urine, rather than spraying UI before or after urine application. Since it was not possible to accurately measure the efficacy of UI in reducing NH(3) emissions from animal urine-N deposited during grazing, we currently cannot recommend the adoption of a Frac(GASM) value adjusted for the inclusion of UI.