Stratified dispersive model for material characterization using terahertz time-domain spectroscopy

We propose a novel THz material analysis approach which provides highly accurate material parameters and can be used for industrial quality control. The method treats the inspected material within its environment locally as a stratified system and describes the light-matter interaction of each layer in a realistic way. The approach is illustrated in the time-domain and frequency-domain for two potential fields of implementation of THz technology: quality control of (coated) paper sheets and car paint multilayers, both measured in humid air.Comment: 4 pages, 4 figure

Spatial and temporal variation of CO₂ efflux along a disturbance gradient in a miombo woodland in Western Zambia

Carbon dioxide efflux from the soil surface was measured over a period of several weeks within a heterogeneous Brachystegia spp. dominated miombo woodland in Western Zambia. The objectives were to examine spatial and temporal variation of soil respiration along a disturbance gradient from a protected forest reserve to a cut, burned, and grazed area outside, and to relate the flux to various abiotic and biotic drivers. The highest daily mean fluxes (around 12 mu mol CO2 m(-2) s(-1)) were measured in the protected forest in the wet season and lowest daily mean fluxes (around 1 mu mol CO2 m(-2) s(-1)) in the most disturbed area during the dry season. Diurnal variation of soil respiration was closely correlated with soil temperature. The combination of soil water content and soil temperature was found to be the main driving factor at seasonal time scale. There was a 75% decrease in soil CO2 efflux during the dry season and a 20% difference in peak soil respiratory flux measured in 2008 and 2009. Spatial variation of CO2 efflux was positively related to total soil carbon content in the undisturbed area but not at the disturbed site. Coefficients of variation of efflux rates between plots decreased towards the core zone of the protected forest reserve. Normalized soil respiration values did not vary significantly along the disturbance gradient. Spatial variation of respiration did not show a clear distinction between the disturbed and undisturbed sites and could not be explained by variables such as leaf area index. In contrast, within plot variability of soil respiration was explained by soil organic carbon content. Three different approaches to calculate total ecosystem respiration (R-eco) from eddy covariance measurements were compared to two bottom-up estimates of R-eco obtained from chambers measurements of soil-and leaf respiration which differed in the consideration of spatial heterogeneity. The consideration of spatial variability resulted only in small changes of R-eco when compared to simple averaging. Total ecosystem respiration at the plot scale, obtained by eddy covariance differed by up to 25% in relation to values calculated from the soil-and leaf chamber efflux measurements but without showing a clear trend

Soil Nitrous Oxide (N\u3csub\u3e2\u3c/sub\u3eO) Emission from Integrated Soil Fertility Management in Maize (\u3ci\u3eZea mays\u3c/i\u3e L.) Cropping Systems

Integrated Soil Fertility Management (ISFM) has been recommended to address challenges of low soil fertility by incorporating locally available organic resources (ORs) together with inorganic nitrogen (N) fertilizers. Despite ISFM success in field trials, there is limited information on ORs contribution to atmospheric greenhouse gas concentrations through N2O emission. A short-term field study was conducted at two sites with different soil types; silt loam (Aludeka) and silty-clay soil (Sidada) to assess the influence of selected ORs on soil N2O emissions. The ORs treatments included; Calliandra carothyrsus (CL), farmyard manure (FYM) and maize stover (MS) with (+N) and without (-N) inorganic N fertilizer. The study also evaluated the relationship between N2O emissions and soil organic carbon, mineral N, total nitrogen, soil temperature, moisture content, soil nitrate (NO3-) and ammonium (NH4+). Relative to the control (0.19±0.1 Kg N2O-N ha-1), cumulative N2O emissions were significantly (P= 0.01) higher by 6, 9 and 13 fold under MS +N (1.05±0.8 Kg N2O-N ha-1), FYM +N (1.74±0.8 Kg N2O-N ha-1) and CL +N (2.54±1.2 Kg N2O-N ha-1), respectively at the Aludeka site. At Sidada, cumulative N2O emissions were similar across all the treatments (P = 0.149). Approximately 240% and 411% of increase in cumulative N2O emissions across treatments at Sidada and Aludeka, respectively, was related to inorganic N fertilizer application. At Aludeka, cumulative N2O emissions exhibited significant positive relationship with soil NO3-(r = 0.894, P = 0.03) and NH4+ (r = 0.817, P = 0.013), and negatively correlated with soil C: N ratio (r = -0.710, P = 0.049). While at Sidada soil properties did not exhibit significant relationship with cumulative N2O emissions. The study suggests that influence of OR on N2O emissions in maize based-cropping system vary depending on the type of soil and increases when OR are applied in combination with inorganic N fertilizers

Closing maize yield gaps in sub-Saharan Africa will boost soil N2_{2}O emissions

In sub-Saharan Africa (SSA), the most important staple crop is maize; the production of which is dominated by smallholder farming systems using low external inputs (<10 kg N ha$^{−1}$) resulting in low crop yields and large yield gaps (difference between actual and potential yields). To assess increases in soil N$_{2}$O emissions when closing maize yield gaps by increased fertilizer use, we reviewed the literature, developed a relationship between yield gaps and soil N$_{2}$O emissions, and used it to scale across SSA. According to our analysis, N$_{2}$O emissions from maize production will increase from currently 255 to 1755 ± 226 Gg N$_{2}$O-N year$^{−1}$ (+589%) if existing maize yield gaps are closed by 75%, increasing total anthropogenic N$_{2}$O emissions for SSA by c. 50%

A simplified approach for producing Tier 2 enteric-methane emission factors based on East African smallholder farm data

Context: Accurate reporting of livestock greenhouse-gas (GHG) emissions is important in developing effective mitigation strategies, but the cost and labour requirements associated with on-farm data collection often prevent this effort in low- and middle-income countries. Aim: The aim of this study was to investigate the precision and accuracy of simplified activity data collection protocols in African smallholder livestock farms for country-specific enteric-methane emission factors. Method: Activity data such as live weight (LW), feed quality, milk yield, and milk composition were collected from 257 smallholder farms, with a total herd of 1035 heads of cattle in Nandi and Bomet counties in western Kenya. The data collection protocol was then altered by substituting the actual LW measurements with algorithm LW (ALG), feed quality (FQ) data being sourced from the Feedipedia database, reducing the need for daily milk yield records to a single seasonal milk measurement (MiY), and by using a default energy content of milk (MiE). Daily methane production (DMP) was calculated using these simplified protocols and the estimates under individual and combined protocols were compared with values derived from the published (PUBL) estimation protocol. Key results: Employing the algorithm LW showed good agreement in DMP, with only a small negative bias (7%) and almost no change in variance. Calculating DMP on the basis of Feedipedia FQ, by contrast, resulted in a 27% increase in variation and a 27% positive bias for DMP compared with PUBL. The substitutions of milk (MiY and MiE) showed a modest change in variance and almost no bias in DMP. Conclusion: It is feasible to use a simplified data collection protocol by using algorithm LW, default energy content of milk value, seasonal single milk yield data, but full sampling and analysis of feed resources is required to produce reliable Tier 2 enteric-methane emission factors. Implications: Reducing enteric methane emissions from the livestock is a promising pathway to reduce the effects of climate change, and, hence, the need to produce accurate emission estimates as a benchmark to measure the effectiveness of mitigation options. However, it is expensive to produce accurate emission estimates, especially in developing countries; hence, it is important and feasible to simplify on-farm data collection

A simplified approach for producing Tier 2 enteric methane emission factors based on East African smallholder farm data

Context: Accurate livestock greenhouse gas (GHG) emissions reporting is important in developing effective mitigation strategies, but the cost and labor requirements associated with on-farm data collection often prevent this effort in low-and-middle-income countries. Aim: The aim of this study was to investigate the precision and accuracy of simplified activity data collection protocols in African smallholder livestock farms for country-specific enteric methane emission factors. Method: Activity data such as live weight (LW), feed quality, milk yield, and milk composition were collected from 257 smallholder farms with a total herd of 1,035 heads of cattle in Nandi and Bomet counties in Western Kenya. The data collection protocol was then altered by substituting actual LW measurements with algorithm LW (ALG), feed quality (FQ) data sourced from the Feedipedia database, reducing the need for daily milk yield records to a single seasonal milk measurement (MiY), and using a default energy content of milk (MiE). Daily methane production (DMP) was calculated using these simplified protocols and the estimates under individual and combined protocols were compared with values derived from the published (PUBL) estimation protocol. Key results: Employing the algorithm LW showed good agreement in DMP with only a small negative bias (7%) and almost no change in variance. Calculating DMP based on Feedipedia FQ, by contrast, resulted in a 27% increase in variation and a 27% positive bias for DMP compared to PUBL. The substitutions of milk (MiY and MiE) showed a modest change in variance and almost no bias in DMP. Conclusion: It is feasible to use a simplified data collection protocol by using algorithm LW, default energy content of milk value, seasonal single milk yield data, but full sampling and analysis of feed resources is required to produce reliable Tier 2 enteric methane emission factors. Implications: Reducing enteric methane emissions from the livestock is a promising pathway to reduce the effects of climate change hence the need to produce accurate emissions estimates as benchmark to measure the effectiveness of mitigation options. However, it is expensive to produce accurate emission estimates especially in developing countries, hence important and feasible to simplify on-farm data collection

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 CO$_{2}$-eq/kg CP. Median EIs were 60 (Nandi), 71 (Bomet), and 90 (Nyando) kg CO$_{2}$-eq/kg. Although median EIs referenced to milk alone (2.3 kg CO$_{2}$-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 (CH$_{4}$) 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 CH$_{4}$ 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

Weight gain and enteric methane production of cattle fed on tropical grasses

Context: Planted grasses are becoming an increasingly important feed resource for tropical smallholder ruminant production; yet, limited research has been conducted to quantify productivity or enteric methane (CH$_4$) production of animals consuming these grasses. Aim: An experiment was conducted to assess yields and nutritional attributes of the following three tropical grasses: Cenchrus purpureus var. Kakamega 1 (Napier), Chloris gayana var. Boma (Rhodes) and Urochloa brizantha var. Xaeres (Brachiaria), and quantify enteric CH$_4$ production of cattle fed on them. Methods: Yearling Boran steers (n:18; initial liveweight 216 ± 5.8 kg (mean ± s.e.m.) were allocated to one of three grasses, in a completely randomised design and fed ad libitum for two feeding periods, each period lasting for 70 days. Intake, liveweight (LW), apparent total-tract digestibility and enteric CH$_4$ production were assessed. The grasses used were grown on site and biomass yields were monitored over a 2-year period. Animal growth was also simulated to a final weight of 350 kg, and the amount of feed and size of land required to produce, and days to reach final weight, were estimated. Key results: Mean voluntary dry-matter intake (DMI) and ADG were higher (P 0.05) within period. Methane yield (MY; CH$_4$ g/DMI kg) was similar among treatments (26.7–28.5, P = 0.26) but Napier had a higher CH$_4$ conversion factor [Ym; CH$_4$ (MJ)/gross energy intake (MJ)] than did Rhodes and Brachiaria (0.0987 vs 0.0873 and 0.0903 respectively; P = 0.013). Our modelling indicated that steers consuming Rhodes took at least 30 more days to reach the target LW, required larger land area for feed production and produced more enteric CH$_4$ than did the other two diets. Conclusion: Even though animal performance and MY among treatments did not differ, the animals had higher MY and Y$_m$ than currently estimated by the Intergovernmental Panel on Climate Change. Implication: The three grasses supported similar animal growth rate, implying that growing of higher-yielding grasses such as Napier offers an opportunity to optimise land productivity in the tropics. However, suitable feeding practices such as protein supplementation need to be explored to enhance ruminant production and reduce enteric CH$_4$ production