Farm-level emission intensities of smallholder cattle (Bos indicus; B. indicus-B. taurus crosses) production systems in highlands and semi-arid regions.

Ruminants are central to the economic and nutritional life of much of sub-Saharan Africa, but cattle are now blamed for having a disproportionately large negative environmental impact through emissions of greenhouse gas (GHG). However, the mechanism underlying excessive emissions occurring only on some farms is imperfectly understood. Reliable estimates of emissions themselves are frequently lacking due to a paucity of reliable data. Employing individual animal records obtained at regular farm visits, this study quantified farm-level emission intensities (EIs) of greenhouse gases of smallholder farms in three counties in Western Kenya. CP was chosen as the functional unit to capture the outputs of both milk and meat. The results showed that milk is responsible for 80-85% of total CP output. Farm EI ranged widely from 20 to >1 000 kg CO2-eq/kg CP. Median EIs were 60 (Nandi), 71 (Bomet), and 90 (Nyando) kg CO2-eq/kg. Although median EIs referenced to milk alone (2.3 kg CO2-eq/kg milk) were almost twice that reported for Europe, up to 50% of farms had EIs comparable to the mean Pan-European EIs. Enteric methane (CH4) contributed >95% of emissions and manure ∼4%, with negligible emissions attributed to inputs to the production system. Collecting data from individual animals on smallholder farms enabled the demonstration of extremely heterogeneous EI status among similar geographical spaces and provides clear indicators on how low EI status may be achieved in these environments. Contrary to common belief, our data show that industrial-style intensification is not required to achieve low EI. Enteric CH4 production overwhelmingly drives farm emissions in these systems and as this is strongly collinear with nutrition and intake, an effort will be required to achieve an "efficient frontier" between feed intake, productivity, and GHG emissions.

Severe below-maintenance feed intake increases methane yield from enteric fermentation in cattle.

The relationship between feed intake at production levels and enteric CH4 production in ruminants consuming forage-based diets is well described and considered to be strongly linear. Unlike temperate grazing systems, the intake of ruminants in rain-fed tropical systems is typically below maintenance requirements for part of the year (dry seasons). The relationship between CH4 production and feed intake in animals fed well below maintenance is unexplored, but changes in key digestive parameters in animals fed at low levels suggest that this relationship may be altered. We conducted a study using Boran yearling steers (n 12; live weight: 162·3 kg) in a 4 × 4 Latin square design to assess the effect of moderate to severe undernutrition on apparent digestibility, rumen turnover and enteric CH4 production of cattle consuming a tropical forage diet. We concluded that while production of CH4 decreased (1133·3-65·0 g CH4/d; P < 0·0001), over the range of feeding from about 1·0 to 0·4 maintenance energy requirement, both CH4 yield (29·0-31·2 g CH4/kg DM intake; P < 0·001) and CH4 conversion factor (Ym 9·1-10·1 MJ CH4/MJ gross energy intake; P < 0·01) increased as intake fell and postulate that this may be attributable to changes in nutrient partitioning. We suggest there is a case for revising emission factors of ruminants where there are seasonal nutritional deficits and both environmental and financial benefits for improved feeding of animals under nutritional stress.

Land Use, Not Stream Order, Controls N2O Concentration and Flux in the Upper Mara River Basin, Kenya.

Anthropogenic activities have led to increases in nitrous oxide (N2O) emissions from river systems, but there are large uncertainties in estimates due to lack of data in tropical rivers and rapid increase in human activity. We assessed the effects of land use and river size on N2O flux and concentration in 46 stream sites in the Mara River, Kenya, during the transition from the wet (short rains) to dry season, November 2017 to January 2018. Flux estimates were similar to other studies in tropical and temperate systems, but in contrast to other studies, land use was more related to N2O concentration and flux than stream size. Agricultural stream sites had the highest fluxes (26.38 ± 5.37 N2O-N µg·m-2·hr-1) compared to both forest and livestock sites (5.66 ± 1.38 N2O-N µg·m-2·hr-1 and 6.95 ± 2.96 N2O-N µg·m-2·hr-1, respectively). N2O concentrations in forest and agriculture streams were positively correlated to stream carbon dioxide (CO2-C(aq)) but showed a negative correlation with dissolved organic carbon, and the dissolved organic carbon:dissolved inorganic nitrogen ratio. N2O concentration in the livestock sites had a negative relationship with CO2-C(aq) and a higher number of negative fluxes. We concluded that in-stream chemoautotrophic nitrification was likely the main biogeochemical process driving N2O production in agricultural and forest streams, whereas complete denitrification led to the consumption of N2O in the livestock stream sites. These results point to the need to better understand the relative importance of nitrification and denitrification in different habitats in producing N2O and for process-based studies.

Management intensity controls soil N2O fluxes in an Afromontane ecosystem.

Studies that quantify nitrous oxide (N2O) fluxes from African tropical forests and adjacent managed land uses are scarce. The expansion of smallholder agriculture and commercial agriculture into the Mau forest, the largest montane forest in Kenya, has caused large-scale land use change over the last decades. We measured annual soil N2O fluxes between August 2015 and July 2016 from natural forests and compared them to the N2O fluxes from land either managed by smallholder farmers for grazing and tea production, or commercial tea and eucalyptus plantations (n=18). Air samples from 5 pooled static chambers were collected between 8:00am and 11:30am and used within each plot to calculate the gas flux rates. Annual soil N2O fluxes ranged between 0.2 and 2.9kgNha-1yr-1 at smallholder sites and 0.6-1.7kgNha-1yr-1 at the commercial agriculture sites, with no difference between land uses (p=0.98 and p=0.18, respectively). There was marked variation within land uses and, in particular, within those managed by smallholder farmers where management was also highly variable. Plots receiving fertilizer applications and those with high densities of livestock showed the highest N2O fluxes (1.6±0.3kgN2O-Nha-1yr-1, n=7) followed by natural forests (1.1±0.1kgN2O-Nha-1yr-1, n=6); although these were not significantly different (p=0.19). Significantly lower fluxes (0.5±0.1kgNha-1yr-1, p<0.01, n=5) were found on plots that received little or no inputs. Daily soil N2O flux rates were not correlated with concurrent measurements of water filled pore space (WFPS), soil temperature or inorganic nitrogen (IN) concentrations. However, IN intensity, a measure of exposure of soil microbes (in both time and magnitude) to IN concentrations was strongly correlated with annual soil N2O fluxes.

Methane and Nitrous Oxide Emissions from Cattle Excreta on an East African Grassland.

Greenhouse gas (GHG) emission measurements from livestock excreta in Africa are limited. We measured CH and NO emissions from excreta of six Boran () and six Friesian () steers near Nairobi, Kenya. The steers were fed one of three diets (T1 [chaffed wheat straw], T2 [T1 + Meissner - 0.2% live weight per day], and T3 [T1 + calliandra - 0.4% live weight every 2 d]). The T1 diet is similar in quality to typical diets in the region. Calliandra is a leguminous fodder tree promoted as a feed supplement. Fresh feces and urine were applied to grasslands and emissions measured using static chambers. Cumulative 28-d fecal emissions were 302 ± 52.4 and 95 ± 13.8 mg CH-C kg dry matter for Friesen and Boran steers, respectively, and 11.5 ± 4.26 and 24.7 ± 8.32 mg NO-N kg dry matter for Friesian and Boran steers, respectively. For urine from Friesian steers, the NO emissions were 2.8 ± 0.64 mg NO-N 100 mL urine. The CH emission factors (EFs) (246 ± 49.5 and 87 ± 12.7 g CH-C yr animal for Friesan and Boran, respectively) were lower than the International Panel on Climate Change EFs (750 g CH-C animal yr), whereas the NO EFs (0.1 and 0.2% for the Friesian and Boran feces, respectively, and 1.2% for urine) were also lower than International Panel on Climate Change estimates. The low N content of the excreta likely caused the low emissions and indicates that current models probably overestimate CH and NO emissions from African livestock manure.

Sampling frequency affects estimates of annual nitrous oxide fluxes.

Quantifying nitrous oxide (N2O) fluxes, a potent greenhouse gas, from soils is necessary to improve our knowledge of terrestrial N2O losses. Developing universal sampling frequencies for calculating annual N2O fluxes is difficult, as fluxes are renowned for their high temporal variability. We demonstrate daily sampling was largely required to achieve annual N2O fluxes within 10% of the 'best' estimate for 28 annual datasets collected from three continents--Australia, Europe and Asia. Decreasing the regularity of measurements either under- or overestimated annual N2O fluxes, with a maximum overestimation of 935%. Measurement frequency was lowered using a sampling strategy based on environmental factors known to affect temporal variability, but still required sampling more than once a week. Consequently, uncertainty in current global terrestrial N2O budgets associated with the upscaling of field-based datasets can be decreased significantly using adequate sampling frequencies.

The complete nitrogen cycle of an N-saturated spruce forest ecosystem.

Long-term nitrogen deposition into forest ecosystems has turned many forests in Central Europe and North America from N-limited to N-saturated systems, with consequences for climate as well as air and groundwater quality. However, complete quantification of processes that convert the N deposited and contributed to ecosystem N cycling is scarce. In this study, we provide the first complete quantification of external and internal N fluxes in an old-growth spruce forest, the Höglwald, Bavaria, Germany, exposed to high chronic N deposition. In this forest, N cycling is dominated by high rates of mineralisation of soil organic matter, nitrification and immobilisation of ammonium and nitrate into microbial biomass. The amount of ammonium available is sufficient to cover the entire N demand of the spruce trees. The data demonstrate the existence of a highly dynamic internal N cycle within the soil, driven by growth and death of the microbial biomass, which turns over approximately seven times each year. Although input and output fluxes are of high environmental significance, they are low compared to the internal fluxes mediated by microbial activity.

Nitrogen dynamics of a mountain forest on dolomitic limestone--a scenario-based risk assessment.

The dominant nitrogen (N) fluxes were simulated in a mountain forest ecosystem on dolomitic bedrock in the Austrian Alps. Based on an existing small-scale climate model the simulation encompassed the present situation and a 50-yr projection. The investigated scenarios were current climate, current N deposition (SC1) and future climate (+2.5 degrees C and +10% annual precipitation) with three levels of N deposition (SC2, 3, 4). The microbially mediated N transformation, including the emission of nitrogen oxides, was calculated with PnET-N-DNDC. Soil hydrology was calculated with HYDRUS and was used to estimate the leaching of nitrate. The expected change of the forest ecosystem due to changes of the climate and the N availability was simulated with PICUS. The incentive for the project was the fact that forests on dolomitic limestone stock on shallow Rendzic Leptosols that are rich in soil organic matter are considered highly sensitive to the expected environmental changes. The simulation results showed a strong effect due to increased temperatures and to elevated levels of N deposition. The outflux of N, both as nitrate (6-25 kg N ha(-1)yr(-1)) and nitrogen oxides (1-2 kg N ha(-1)yr(-1)), from the forest ecosystem are expected to increase. Temperature exerts a stronger effect on the N(2)O emission than the increased rate of N deposition. The main part of the N emission will occur as N(2) (15 kg N ha(-1)yr(-1)). The total N loss is partially offset by increased rates of N uptake in the biomass due to an increase in forest productivity.

Effect of pH, temperature and substrate on N2O, NO and CO2 production by Alcaligenes faecalis p.

AIMS: To study the effect of pH, temperature and substrate on the magnitude of N(2)O and NO production by heterotrophic nitrifiers. METHODS AND RESULTS: The change in N(2)O and NO production by the heterotrophic nitrifiers Alcaligenes faecalis subsp. parafaecalis and Paracoccus pantotrophus because of variations in pH, temperature and substrate was studied in chemostat cultures under steady-state conditions. N(2)O, NO and CO(2) production increased with temperature between 4 and 32 degrees C. For N(2)O an optimum temperature of 28 degrees C was observed. No optimum temperature was found for NO. Highest N(2)O and CO(2) productions were observed at a pH of 7.0. However, besides having an optimum at pH 7.0, especially NO production but also N(2)O production increased significantly at pH