Nitrous oxide emission factor from cattle urine and dung in native grassland of the Pampa biome, South Brazil
Résumé
Native grassland supports extensive livestock production in the Pampas of South America, but the impact of cattle excreta on nitrous oxide (N 2 O) emissions remains unknown in this biome. The objective of this study was to determine the N 2 O emission factor (EF-N 2 O, % of N applied that is emitted as N 2 O) for urine and dung from beef cattle grazing on native grasslands. A field trial was conducted under low and moderate forage allowances (FA4 and FA12; i.e. 4 and 12 kg dry matter/100 kg live weight respectively) during the 30th year of a long-term grassland experiment on a Typic Paleudult in South Brazil. Urine and dung were applied onto separate patches, at rates equivalent to one average urination or defecation; and N 2 O fluxes were monitored with closed static chambers over 338 days. In adjacent microplots receiving the same excreta treatment, water-filled pore space, nitrate, ammonium and extractable dissolved organic carbon were monitored in the top 0.1 m of soil. Averaged across the forage allowances, daily soil N 2 O fluxes were low in the control without excreta (1.3 g N ha-1), but increased upon application of dung (3.8 g N ha-1) and urine (66 g N ha-1). The annual N 2 O emission and the EF-N 2 O for urine were greater under FA12 than FA4, but no difference was observed for dung. The positive relationships between N 2 ON emissions and ammonium intensity and nitrate intensity suggest that N 2 O may have been produced concurrently by nitrification, nitrifier/denitrification and denitrification. On average, the EF-N 2 O was almost 10 times higher for urine than for dung (0.74% vs 0.08%), both much lower than the IPCC's Tier 1 default value of 2%. Our findings reinforce the need for disaggregating the EF-N 2 O for urine and dung and of revising the IPCC's Tier 1 EF-N 2 O.
Domaines
Science des sols
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