What is needed for reducing the greenhouse gas footprint?

Livestock production is responsible for a large amount of greenhouse gas (GHG) emissions. However, numerous approaches have been developed to reduce these emissions and thus lower environmental pollution caused by livestock husbandry. This article shows where interventions are possible and which hurdles have to be cleared in implementing the various measures needed

Estimating global terrestrial denitrification from measured N2_{2}O:(N2_{2}O + N2_{2}) product ratios

The use of nitrogen (N) fertilizers and cultivation of N-fixing crops has grown exponentially over the last century, with severe environmental consequences. Most of the anthropogenic reactive nitrogen will ultimately be returned by denitrification to the atmosphere as inert N$_{2}$, but the magnitude of denitrification and the ratio of N$_{2}$O to (N$_{2}$O + N$_{2}$) emitted (R$_{N_{2}O}$) is unknown for the vast majority of terrestrial ecosystems. This paper provides estimates of terrestrial denitrification and R$_{N_{2}O}$ by reviewing existing literature and compiling a N budget for the global land surface. We estimate that terrestrial denitrification has doubled from 80 Tg-N year$^{-1}$ in pre-industrial times to 160 Tg-N year$^{-1}$ in 2005 with a mean R$_{N_{2}O}$ of approximately 0.08. We conclude that upscaling of R$_{N_{2}O}$ can provide spatial estimates of terrestrial denitrification when data from acetylene inhibition methods are excluded. Recent advances in methodologies to measure N$_{2}$ emissions and R$_{N_{2}O}$ under field conditions could open the way for more effective management of terrestrial N flows

Soil N intensity as a measure to estimate annual N2_{2}O and NO fluxes from natural and managed ecosystems

As natural and managed terrestrial ecosystems are major sources of the potent greenhouse gas nitrous oxide (N$_{2}$O) and of the atmospheric pollutant nitric oxide (NO), predicting the source strengths of these ecosystems is central to understanding and sustainably managing the N-oxides fluxes. Here we reviewed 82 high temporal resolution datasets on N$_{2}$O and 57 on NO fluxes collected from multi-site and multi-year field measurements, including grasslands, forests, and agricultural crops, to assess whether soil N intensity, that is, the time-weighted sum of soil NH$_{4}$$^{+}$ and/or NO$_{3}$$^{-}$ concentrations, can be used to estimate annual N-oxides emissions. We show that soil N intensity alone can accurately predict annual N$_{2}$O and NO emissions, and that the N$_{2}$O emission strength is exponentially related to the soil inorganic N load. Thus, measuring soil inorganic N loads should improve current estimates of N-oxide emissions from global terrestrial ecosystems, and open possibilities for monitoring N$_{2}$O mitigation efforts

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

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

Global assessment of manure management policies and practices

In 2014 an assessment of livestock manure policies was performed in 34 countries in Asia, Africa and Latin America, followed by an in-depth assessment of manure management practices in Bangladesh, Viet Nam, Ethiopia, Malawi, Argentina and Costa Rica. The assessments revealed the key barriers for improving integrated manure management and identified six opportunities for actual practice changes to improve manure related policies as well as farm practices with the overall objective of improving food security while mitigating methane emissions at the same tim

Effect of feeding practices and manure quality on CH4_{4} and N2_{2}O emissions from uncovered cattle manure heaps in Kenya

Countries in sub-Saharan Africa (SSA) rely on IPCC emission factors (EF) for GHG emission reporting. However, these were derived for industrialized livestock farms and do not represent conditions of smallholder farms (small, low-producing livestock breeds, poor feed quality, feed scarcity). Here, we present the first measurements of CH$_{4}$ and N$_{2}$O emissions from cattle-manure heaps representing feeding practices typical for smallholder farms in the highlands of East Africa: 1) cattle fed below maintenance energy requirements to represent feed scarcity, and 2) cattle fed tropical forage grasses (Napier, Rhodes, Brachiaria). Sub-maintenance feeding reduced cumulative manure N$_{2}$O emissions compared to cattle receiving sufficient feed but did not change EF$_{N2O}$. Sub-maintenance feeding did not affect cumulative manure CH$_{4}$ emissions or EF$_{CH4}$. When cattle were fed tropical forage grasses, cumulative manure N$_{2}$O emissions did not differ between diets, but manure EF$_{N2O}$ from Brachiaria and Rhodes diets were lower than the IPCC EF$_{N2O}$ for solid storage (1%, 2019 Refinement of IPCC Guidelines). Manure CH$_{4}$ emissions were lower in the Rhodes grass diet than when feeding Napier or Brachiaria, and manure EF$_{CH4}$ from all three grasses were lower than the IPCC default (4.4 g CH$_{4}$ kg$^{-1}$ VS, 2019 Refinement of IPCC Guidelines). Regression analysis revealed that manure N concentration and C:N were important drivers of N$_{2}$O emissions, with low N concentrations and high C:N reducing N$_{2}$O emissions. Our results show that IPCC EFs overestimate excreta GHG emissions, which calls for additional measurements to develop localized EFs for smallholder livestock systems in SSA