Microwave-assisted combustion to produce benzene polycarboxylic acids as molecular markers for biochar identification and quantification

Biochar is a promising carbon dioxide removal(CDR)technology for climate change mitigation.Current procedures for its determination are lengthy,labor-intensive,and difficult to conduct.Benzene polycarboxylic acids(BPCA)are the most promising molecular markers for identification and quantification of biochar and its quality as they specifically represent the stable polyaromatic backbone of biochar.Therefore,using the BPCA method,its stability and,thus,its C sequestration potential could be used for CDR accounting.The current BPCA method relies on a specific high-pressure digestion apparatus,which is not available around the world.Therefore,the aims of the present work were(i)to compare the conventional high-pressure nitric acid oxidation with a microwave-assisted digestion technique and optimize the oxidation conditions in such a way that previous results are comparable with future ones,and(ii)to significantly reduce the digestion time of soil samples of 8 h and to develop a suitable routine method that produces comparable and reproducible results.For this purpose,soil and control sample series were prepared for different temperature-time-program.Obtained results were compared with the values of the conventional method both for individual samples and for the whole dataset separately.To ensure the representative-ness of the results,in addition to various soil samples with different properties,we included two reference materials into our data set,one without biochar(wheat flour)and a biochar sample.Our results showed that conventional nitric acid oxidation in the BPCA determination at 170°C and 8 h can be substituted by digestion in a microwave reaction system(CEM Mars6)at 190°C and 1 h.Our results further showed that this condition needs to be strictly matched,because,otherwise,over-or underestimation of biochar quantity and/or quality will be the consequence.The goal of a less time-consuming BPCA extrac-tion from soil samples was achieved by reducing the extraction time from 8 to 1 h using the microwave-assisted method.However,one disadvantage of the new method is that five times more sample material and chemicals are needed for further BPCA analysis,compared to the original method.

Biochar and sugar cane filter cake interaction on physical and hydrological soil properties under tropical field conditions

Biochar is known for its effects on carbon sequestration and soil fertility.However,there is a lack of information about its effects on soil physical and hydraulic properties for tropical soils.We assessed the effects of biochar(BC)plus sugar cane filter cake(FC)rate,and time of interaction on soil physical and hydraulic properties under humid tropical conditions.For this purpose,a field experiment was installed at a loamy sandy soil with five treatments and four replicates:control(only soil),25 Mg ha^(−1) sugar cane filter cake,and 25 Mg ha^(−1) sugar cane filter cake plus 6.25,12.5,and 25 Mg ha^(−1) Miscanthus biochar,respectively,two soil depths(0-10 and 10-20 cm)and two times of interaction(9 and 18 months).Physical prop-erties(aggregate stability,bulk density,total porosity,pores size distribution)and hydraulic properties(soil water holding capacity,hydraulic conductivity,plant-available water holding capacity)were measured after nine and eighteen months.The bulk density decreased slightly,and the porosity increased after nine months,for the biochar plus sugar cane filter cake(both 25 Mg ha^(−1)).After 18 months,biochar plus filter cake interaction increase micropores,aggregate stability,and plant-available water content.Saturated hydraulic conductivity was not influenced by sugar cane filter cake.However,biochar significantly reduced saturated hydraulic conductivity when combined with sugar cane filter cake after 18 months.We concluded that sugar cane filter cake in combination with biochar modified the pore size distribution,slightly increased plant-available water holding capacity,and significantly decreased saturated hydraulic conductivity.

Effect of biochar fertilizers on amino acid variability of Secale cereale and Lupinus angustifolius

Little is known on the effects of biochar on N uptake and amino acid variability in crops such as winter rye and narrow-leafed lupine despite the fact that amino acids are important indicators,for food quality and plant stress.N uptake of both crops showed contrasting results when treated with different biochar fertilizers.Total amino acid contents referred to total nitro-gen generally tend to decrease in rye grains in the presence of biochar;whereas lupine seeds were more or less unaffected by biochar combined with mineral fertilizer or compost.In lupine seeds,total amino acid contents significantly increased when biochar was mixed with digestate but decreased when mixed with fermented digestate.Lysine,one of the most limiting amino acids in cereals,reached the recommended value of 4 g kg^(−1) in rye grain for most biochar fertilizers.In lupine seeds,lysine decreased when biochar had been applied but were still in the recommended range when used as animal feed.Proline,an indicator for plant stress,significantly decreased(−49%)in rye when 2 Mg biochar ha^(−1) was added in combination with mineral fertilizer.In contrast,proline increased when biochar was added to organic(digestate and compost)fertilizers(up to 43%).Further biochar research should focus much more on food quality,which is a key challenge for global food production.