Nitrogen turnover and N2O/N2 ratio of three contrasting tropical soils amended with biochar.

Biochar has been reported to reduce emission of nitrous oxide (N2O) from soils, but the mechanisms responsible remain fragmentary. For example, it is unclear how biochar effects on N2O emissions are mediated through biochar effects on soil gross N turnover rates. Hence, we conducted an incubation study with three contrasting agricultural soils from Kenya (an Acrisol cultivated for 10-years (Acrisol10); an Acrisol cultivated for over 100-years (Acrisol100); a Ferralsol cultivated for over 100 years (Ferralsol)). The soils were amended with biochar at either 2% or 4% w/w. The 15N pool dilution technique was used to quantify gross N mineralization and nitrification and microbial consumption of extractable N over a 20-day incubation period at 25 °C and 70% water holding capacity of the soil, accompanied by N2O emissions measurements. Direct measurements of N2 emissions were conducted using the helium gas flow soil core method. N2O emissions varied across soils with higher emissions in Acrisols than in Ferralsols. Addition of 2% biochar reduced N2O emissions in all soils by 53 to 78% with no significant further reduction induced by addition at 4%. Biochar effects on soil nitrate concentrations were highly variable across soils, ranging from a reduction, no effect and an increase. Biochar addition stimulated gross N mineralization in Acrisol-10 and Acrisol-100 soils at both addition rates with no effect observed for the Ferralsol. In contrast, gross nitrification was stimulated in only one soil but only at a 4% application rate. Also, biochar effects on increased NH4 + immobilization and NO3 -consumption strongly varied across the three investigated soils. The variable and bidirectional biochar effects on gross N turnover in conjunction with the unambiguous and consistent reduction of N2O emissions suggested that the inhibiting effect of biochar on soil N2O emission seemed to be decoupled from gross microbial N turnover processes. With biochar application, N2 emissions were about an order of magnitude higher for Acrisol-10 soils compared to Acrisol-100 and Ferralsol-100 soils. Our N2O and N2 flux data thus support an explanation of direct promotion of gross N2O reduction by biochar rather than effects on soil extractable N dynamics. Effects of biochar on soil extractable N and gross N turnover, however, might be highly variable across different soils as found here for three typical agricultural soils of Kenya.

Emissions intensity and carbon stocks of a tropical Ultisol after amendment with Tithonia green manure, urea and biochar.

Biochar has been shown to reduce soil emissions of CO2, CH4 and N2O in short-term incubation and greenhouse experiments. Such controlled experiments failed to represent variable field conditions, and rarely included crop growth feedback. The objective of this study was to assess the effect of biochar, in comparison to green manure and mineral nitrogen, on greenhouse gas Emissions Intensity (EI = emissions in CO2 equivalents per ton of grain yield) in a low-fertility tropical Ultisol. Using a field trial in western Kenya, biochar (0 and 2.5 t ha-1; made from Eucalyptus wood) was integrated with urea (0 and 120 kg N ha-1) and green manure (Tithonia diversifolia; 0, 2.5 and 5 t ha-1) in a factorial design for four consecutive seasons from October 2012 to August 2014. Compared to the control, biochar increased soil CO2 emissions (9-33%), reduced soil CH4 uptake (7-59%) and reduced soil N2O emissions (1-42%) in each season, with no seasonal differences. N2O emissions increased following amendment with T. diversifolia (6%) and urea (13%) compared to the control. Generally, N2O emissions decreased where only biochar was applied. The greatest decrease in N2O (42%) occurred where all three amendments were applied compared to when they were added separately. EI in response to any of the amendments was lower than the control, ranging from 9 to 65% (33.0 ± 3.2 = mean ± SE). The amendments increased SOC stocks by 0.1-1.2 t ha-1 year-1 (mean ± SE of 0.8 ± 0.09 t ha-1 year-1). The results suggest decreased net EI with biochar in low fertility soils mainly through greater net primary productivity (89% of the decrease).

Aggregate size distribution in a biochar-amended tropical Ultisol under conventional hand-hoe tillage.

Biochar (or pyrogenic organic matter) is increasingly proposed as a soil amendment for improving fertility, carbon sequestration and reduction of greenhouse gas emissions. However, little is known about its effects on aggregation, an important indicator of soil quality and functioning. The aim of this study was to assess the effect of Eucalyptus wood biochar (B, pyrolyzed at 550 °C, at 0 or 2.5 t ha-1), green manure (T, from Tithonia diversifolia at 0, 2.5 or 5.0 t ha-1) and mineral nitrogen (U, urea, at 0, or 120 kg N ha-1) on soil respiration, aggregate size distribution and SOC in these aggregate size fractions in a 2-year field experiment on a low-fertility Ultisol in western Kenya under conventional hand-hoe tillage. Air-dry 2-mm sieved soils were divided into four fractions by wet sieving: Large Macro-aggregates (LM; >1000 µm); Small Macro-aggregates (SM, 250-1000 µm); Micro-aggregates (M, 250-53 µm) and Silt + Clay (S + C, < 53 µm). We found that biochar alone did not affect a mean weight diameter (MWD) but combined application with either T. diversifolia (BT) or urea (BU) increased MWD by 34 ± 5.2 µm (8%) and 55 ± 5.4 µm (13%), respectively, compared to the control (P = 0.023; n = 36). The B + T + U combination increased the proportion of the LM and SM by 7.0 ± 0.8%, but reduced the S + C fraction by 5.2 ± 0.23%. SOC was 30%, 25% and 23% in S + C, M and LM/SM fractions, and increased by 9.6 ± 1.0, 5.7 ± 0.8, 6.3 ± 1.1 and 4.2 ± 0.9 g kg-1 for LM, SM, M and S + C, respectively. MWD was not related to either soil respiration or soil moisture but decreased with higher SOC (R2  = 0.37, P = 0.014, n = 26) and increased with greater biomass production (R2  = 0.11, P = 0.045, n = 33). Our data suggest that within the timeframe of the study, biochar is stored predominantly as free particulate OC in the silt and clay fraction and promoted a movement of native SOC from larger-size aggregates to the smaller-sized fraction in the short-term (2 years).

Traditional medicine as an alternative form of health care system: a preliminary case study of Nangabo sub-county, central Uganda.

This study was conducted in Nangabo sub-county of Wakiso district. The purpose was to document the common Traditional Medicine (TM) practices; assess the local people's preferences for TM versus western medicine (WM) and lastly to determine the awareness about the importance of TM by local people. Data were collected using semi-structured administered face-to-face with respondents. A total of 120 interviewed. Six focused group discussions (FGDs) were held to validate the questionnaire responses. Data were analyzed descriptively using Statistical Package for Social Sciences (SPSS). The findings indicated that most (43%) respondents derive their livelihoods from traditional medicine practices. Three forms of TM were reported-herbalism (67%), spiritual counseling (23%) and bone setting (10%). Although the majority (81%) of respondents were quite aware of the importance of TM in the sustenance of health care system, majority (55%) of them shunned TM in preference to WM, largely because of the belief that TM is evil-founded and devilish in nature. Only 45% of the respondents preferred TM to WM. The main reasons given for visiting TM practioners rather than western medical practitioners were that TM is sometimes more effective than WM and that in many instances it has very minimal side effects on the human body. There is, however, a need for Ugandan government to legitimize the practice of TM since it contributes a lot to health care needs in areas where western medicine is insufficiently provided. In addition, there is a need for further research into the efficacy and safety of traditional medicines if it is to be adequately integrated into western medicine.