Nitrous oxide emission factors for cattle dung and urine deposited onto tropical pastures: A review of field-based studies

Yuhao Zhu,Klaus Butterbach-Bahl,Lutz Merbold,Sonja Leitner,David E Pelster

doi:10.1016/j.agee.2021.107637

Yuhao Zhu, Klaus Butterbach-Bahl + Show 3 more

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https://doi.org/10.1016/j.agee.2021.107637

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Abstract

Livestock excreta on pastures is an important source of nitrous oxide (N2O) emissions, however studies measuring these emissions in tropical regions, particularly Africa, remain limited. Therefore we measured N2O emissions from different quantities of dung patches during three observation periods (dry, wet and transition from dry to wet season) and different volumes of urine patches during wet and dry seasons. Dung patches did not stimulate soil N2O emissions in any of the three observation periods, while urine application stimulated soil N2O emissions during both seasons, with higher emissions observed during the wet season. The dung EFs (0.00–0.03%) and the urine EFs (0.04–0.40%) showed no detectable effects of dung quantity or urine volume. We further synthesized observations from other studies in wet and dry tropical regions, which indicated that the excreta N2O EFs were similar to the default values provided in the IPCC 2019 refinement (0.11% vs 0.07% for dung and 0.41% vs 0.32% for urine in dry climates, and 0.13% vs 0.13% for dung and 0.65% vs 0.77% for urine in wet climates). However, sub-Saharan African (SSA) studies had consistently lower EFs, possibly due to the lower urine-N: dung-N ratio in SSA compared with the other tropical regions, suggesting that the refinement may still overestimate excreta emissions in SSA. Moreover, considering the large variations in the summarized tropical excreta N2O EFs, from -0.01 to 1.77% for dung and 0.00 to 4.90% for urine, more studies under diverse conditions across tropical regions are recommended.

Highlights

Grasslands used for livestock grazing are important nitrous oxide (N2O) sources (Jones et al, 2005)
We further synthesized observations from other studies in wet and dry tropical regions, which indicated that the excreta N2O EFs were similar to the default values provided in the IntergovernmentalPanel on Climate Change (IPCC) 2019 refinement (0.11% vs 0.07% for dung and 0.41% vs 0.32% for urine in dry climates, and 0.13% vs 0.13% for dung and 0.65% vs 0.77% for urine in wet climates)
In our synthesis of observations from tropical regions in sub-Saharan African (SSA) and LAM, we found that excreta N2O EFs were in line with the values provided in the recent IPCC 2019 re finements

Summary

Introduction

Grasslands used for livestock grazing are important nitrous oxide (N2O) sources (Jones et al, 2005). Estimated global N2O emissions from livestock excreta deposition on managed grasslands were 1.31 Tg N2O-N in 2014 (Dangal et al, 2019) and are expected to increase in the future due to increased livestock numbers and higher stocking rates (Tian et al, 2020; Smith et al, 2016). Stimulation of soil N2O emis sions following livestock excreta deposition to grasslands are due to the increased soil N availability for microbial processes involved in N2O production (e.g. nitrification and denitrification). Panel on Climate Change (IPCC) to help jurisdictions that lacked suffi cient information for the development of local emission factors estimate N2O emissions from livestock excreta deposition (IPCC, 2006). The IPCC developed a set of refinements with disaggregated EFs for urine and dung for both cattle and sheep under wet and dry climates to reduce uncertainties (Kristell et al, 2019)

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