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Can biochar reduce soil greenhouse gas emissions from a Miscanthus bioenergy crop?

GCB Bioenergy (Impact Factor: 4.71). 01/2014; 6(1):76-89. DOI: 10.1111/gcbb.12052

ABSTRACT Energy production from bioenergy crops may significantly reduce greenhouse gas (GHG) emissions through substitution of fossil fuels. Biochar amendment to soil may further decrease the net climate forcing of bioenergy crop production, however, this has not yet been assessed under field conditions. Significant suppression of soil nitrous oxide (N2O) and carbon dioxide (CO2) emissions following biochar amendment has been demonstrated in short-term laboratory incubations by a number of authors, yet evidence from long-term field trials has been contradictory. This study investigated whether biochar amendment could suppress soil GHG emissions under field and controlled conditions in a Miscanthus × Giganteus crop and whether suppression would be sustained during the first 2 years following amendment. In the field, biochar amendment suppressed soil CO2 emissions by 33% and annual net soil CO2 equivalent (eq.) emissions (CO2, N2O and methane, CH4) by 37% over 2 years. In the laboratory, under controlled temperature and equalised gravimetric water content, biochar amendment suppressed soil CO2 emissions by 53% and net soil CO2 eq. emissions by 55%. Soil N2O emissions were not significantly suppressed with biochar amendment, although they were generally low. Soil CH4 fluxes were below minimum detectable limits in both experiments. These findings demonstrate that biochar amendment has the potential to suppress net soil CO2 eq. emissions in bioenergy crop systems for up to 2 years after addition, primarily through reduced CO2 emissions. Suppression of soil CO2 emissions may be due to a combined effect of reduced enzymatic activity, the increased carbon-use efficiency from the co-location of soil microbes, soil organic matter and nutrients and the precipitation of CO2 onto the biochar surface. We conclude that hardwood biochar has the potential to improve the GHG balance of bioenergy crops through reductions in net soil CO2 eq. emissions.

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    ABSTRACT: Most studies looking into the effect of amendment of biochar on soil microbial functioning employ shortterm laboratory studies and probably describe relatively transient phenomena. Multi-year experiments, spanning beyond initial degradation of biologically labile biochar constituents, on the other hand are more scarce, although these are much needed to establish the medium-term effect of biochar on soil organisms. In the present study, soil was sampled from biochar-amended and control plots of four biochar field trials at Lincoln (UK), Rivignano, Rocca Bernarda and Beano in Italy. Air-dried pre-incubated soil samples were incubated at 15 �C for 8e9 weeks to follow-up carbon dioxide (CO2) emissions. We then determined soil b-glucosidase and dehydrogenase enzyme activity, and used PLFA analysis to quantify the total soil microbial biomass and community structure. The analysis indicated that soil microbial activity was either not affected or inhibited to different extents in the biochar-amended plots. At Lincoln, with the highest application rate (49 t ha�1), an overall inhibition of all investigated measures of microbial activity, a lower sum of extracted PLFAs and lower fungal abundance were observed. On the other end at Beano, depth dispersion of biochar by deep tillage and a lower application rate (20 t ha�1) probably explain the absence of any significant effect on microbial activity in that experiment. At Rivignano and Rocca Bernarda, dehydrogenase activity was lower in the biochar amended soil and Cmineralization was lower as well for Rivignano. Interestingly, however, b-glucosidase activity and the sum of extracted PLFAs was not affected by biochar treatment. Several mechanisms could reconcile the different effect of biochar application on overall microbial activity on the one hand and microbial abundance and rate of cellulose degradation on the other. Biochar amendment led to a lowered or equal soil microbial activity and abundance in most field site. In contrast to many short-term laboratory studies, it therefore seems unlikely that biochar would still function as a substrate 1e4 years after incorporation in the field.
    Soil Biology and Biochemistry 11/2014; 78:95-203. · 3.65 Impact Factor

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May 28, 2014