Selected soil and biochar properties¹.

<p>¹TN = Total nitrogen, TOC = Total organic carbon, TH = Total hydrogen, H/C = molar ratio, LOI = Loss on ignition. Untreated BC properties (Ash, CEC & base cations) and surface area data were obtained from Martinsen, Alling [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138781#pone.0138781.ref041" target="_blank">41</a>] and Smebye, Alling [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138781#pone.0138781.ref042" target="_blank">42</a>] respectively. All the other soil and BC data were measured in sub-samples from homogenized bulk samples used in the study. Soil and BC pH was measured in a 1:2.5 v/v slurry in water (n = 2) using a pH meter (Orion 2 Star, Thermo Fisher Scientific, Fort Collins, CO, USA) after overnight sedimentation and shaking. Base cations were measured in the eluate of ammonium acetate at pH 7 for BC and ammonium nitrate for soil (n = 1), with a flame spectrophotometer (Perkin Elmer, AAS 3300). CEC was determined as sum of base cations and exchangeable acidity in ammonium acetate pH 7 and ammonium nitrate extract for BCs and soil respectively. TOC, TN and TH were determined using CHN analyzer (n = 1) (CHN-1000, LECO, USA). The TOC for BCs were determined after acidification to remove carbonates.</p><p>Selected soil and biochar properties<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138781#t001fn001" target="_blank">¹</a>.</p

Denitrification kinetics and CO₂ and O₂ concentrations in anoxic incubations of Lampung soil amended with increasing doses of untreated rice husk BC (upper 2 panels) and cacao shell BC (lower 2 panels).

<p>Shown are averages of three incubations; error bars denote SE. Approximately 6.1 μmol NO₃^--N g^-1 was added to 9.8 g soil in the bottles. Note the differences in the scale of y-axis.</p

Results from stepwise linear ANCOVA showing the importance of labile C and pH for BC effect on denitrification rate, product ratio and maximum NO accumulation.

<p>Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ns ‘ 1, ‘:’ means interaction of factors.</p><p>Results from stepwise linear ANCOVA showing the importance of labile C and pH for BC effect on denitrification rate, product ratio and maximum NO accumulation.</p

Effect of Soil pH Increase by Biochar on NO, N₂O and N₂ Production during Denitrification in Acid Soils

<div><p>Biochar (BC) application to soil suppresses emission of nitrous- (N₂O) and nitric oxide (NO), but the mechanisms are unclear. One of the most prominent features of BC is its alkalizing effect in soils, which may affect denitrification and its product stoichiometry directly or indirectly. We conducted laboratory experiments with anoxic slurries of acid Acrisols from Indonesia and Zambia and two contrasting BCs produced locally from rice husk and cacao shell. Dose-dependent responses of denitrification and gaseous products (NO, N₂O and N₂) were assessed by high-resolution gas kinetics and related to the alkalizing effect of the BCs. To delineate the pH effect from other BC effects, we removed part of the alkalinity by leaching the BCs with water and acid prior to incubation. Uncharred cacao shell and sodium hydroxide (NaOH) were also included in the study. The untreated BCs suppressed N₂O and NO and increased N₂ production during denitrification, irrespective of the effect on denitrification rate. The extent of N₂O and NO suppression was dose-dependent and increased with the alkalizing effect of the two BC types, which was strongest for cacao shell BC. Acid leaching of BC, which decreased its alkalizing effect, reduced or eliminated the ability of BC to suppress N₂O and NO net production. Just like untreated BCs, NaOH reduced net production of N₂O and NO while increasing that of N₂. This confirms the importance of altered soil pH for denitrification product stoichiometry. Addition of uncharred cacao shell stimulated denitrification strongly due to availability of labile carbon but only minor effects on the product stoichiometry of denitrification were found, in accordance with its modest effect on soil pH. Our study indicates that stimulation of denitrification was mainly due to increases in labile carbon whereas change in product stoichiometry was mainly due to a change in soil pH.</p></div

Plots of N₂O product ratio of denitrification against BC dose (upper panel—A1, B1, C1 & D1) and against average effective soil pH (lower panel—A2, B2, C2 & D2) of BC, uncharred cacao shell and NaOH amended soil.

<p>Plots of N₂O product ratio of denitrification against BC dose (upper panel—A1, B1, C1 & D1) and against average effective soil pH (lower panel—A2, B2, C2 & D2) of BC, uncharred cacao shell and NaOH amended soil.</p

Regression coefficients of N₂O product ratios explained by dose effect (w/w %) or by pH effect of different amendments added to Lampung soil.

<p>Intercept = value of product ratio at 0% BC and uncharred cacao shell addition or if pH of the soil would be zero. Slope = unit decrease in product ratio per percent increase of BC or uncharred cacao shell added or per unit increase in soil pH due to amendment added. Numbers in brackets are the standard errors.</p><p>Regression coefficients of N₂O product ratios explained by dose effect (w/w %) or by pH effect of different amendments added to Lampung soil.</p

Mean soil slurry pH after treatment with various doses of the amendments at the start and end of incubation.

<p>SE is standard error calculated from all doses of each amendment for either start or end pH.</p><p>Mean soil slurry pH after treatment with various doses of the amendments at the start and end of incubation.</p

Environmental and Socioeconomic Impacts of Utilizing Waste for Biochar in Rural Areas in Indonesia–A Systems Perspective

Biochar is the product of incomplete combustion (pyrolysis) of organic material. In rural areas, it can be used as a soil amendment to increase soil fertility. Fuel-constrained villagers may however prefer to use biochar briquettes as a higher-value fuel for cooking over applying it to soils. A systems-oriented analysis using life cycle assessment (LCA) and cost benefit analysis (CBA) was conducted to analyze these two alternative uses of biochar, applying the study to a rural village system in Indonesia. The results showed soil amendment for enhanced agricultural production to be the preferential choice with a positive benefit to the baseline scenario of −26 ecopoints (LCA) and −173 USD (CBA) annually pr. household. In this case, the positive effects of carbon sequestration to the soil and the economic value of the increased agricultural production outweighed the negative environmental impacts from biochar production and the related production costs. Use of biochar in briquettes for cooking fuel yielded negative net effects in both the LCA and CBA (85 ecopoints and 176 USD), even when positive health effects from reduced indoor air pollution were included. The main reasons for this are that emissions during biochar production are not compensated by carbon sequestration and that briquette making is labor-intensive. The results emphasize the importance of investigating and documenting the carbon storage effect and the agricultural benefit in biochar production-utilization systems for a sustainable use. Further research focus on efficient production is necessary due to the large environmental impact of biochar production. In addition, biochar should continue to be used in those soils where the agricultural effect is most beneficial

Aerosol–Water Distribution of PCDD/Fs and PCBs in the Baltic Sea Region

Atmospheric deposition is a major pathway of PCDD/Fs to the Baltic Sea. We studied the aerosol–water distribution for aerosols collected close to the Baltic Sea in order to investigate the availability of pollutants sorbed to aerosols deposited on water. Aerosols were analyzed for both total concentration (Soxhlet extraction) and the freely dissolved water concentration (extraction with 17-μm polyoxymethylene equilibrium passive samplers). Concentrations of PCDD/F and sum PCB-7 in aerosols were 65–1300 pg/g dw TEQ and 22–100 ng/g dw, respectively. Organic carbon (OC)-normalized aerosol–water distribution ratios (<i>K</i>_{aer‑water,OC}) were consistently lower (factor 2–60) than previously determined sediment organic carbon–water distribution ratios (<i>K</i>_sed,OC). Hence PCDD/Fs and PCBs entering the Baltic Sea through aerosol deposition seem to be more available for desorption to the water phase than PCDD/Fs and PCBs sorbed to sediment. Further, we investigated whether aerosol–water distribution may be predicted from the air–aerosol partitioning constant multiplied by the Henry’s Law constant. This proposed model for aerosol–water distribution underestimated measured values for PCBs by factors of 1–17 and for PCDD/Fs by more than a factor 10. These findings can be used to improve future fate modeling of PCBs and PCDD/Fs in marine environments and specifically the Baltic Sea

Life Cycle Assessment to Evaluate the Environmental Impact of Biochar Implementation in Conservation Agriculture in Zambia

Biochar amendment to soil is a potential technology for carbon storage and climate change mitigation. It may, in addition, be a valuable soil fertility enhancer for agricultural purposes in sandy and/or weathered soils. A life cycle assessment including ecological, health and resource impacts has been conducted for field sites in Zambia to evaluate the overall impacts of biochar for agricultural use. The life cycle impacts from conservation farming using cultivation growth basins and precision fertilization with and without biochar addition were in the present study compared to conventional agricultural methods. Three different biochar production methods were evaluated: traditional earth-mound kilns, improved retort kilns, and micro top-lit updraft (TLUD) gasifier stoves. The results confirm that the use of biochar in conservation farming is beneficial for climate change mitigation purposes. However, when including health impacts from particle emissions originating from biochar production, conservation farming plus biochar from earth-mound kilns generally results in a larger negative effect over the whole life cycle than conservation farming without biochar addition. The use of cleaner technologies such as retort kilns or TLUDs can overcome this problem, mainly because fewer particles and less volatile organic compounds, methane and carbon monoxide are emitted. These results emphasize the need for a holistic view on biochar use in agricultural systems. Of special importance is the biochar production technique which has to be evaluated from both environmental/climate, health and social perspectives