Soil amendments with biochar
to improve soil fertility and increase soil carbon stocks have received some
high-level attention. Physical and chemical analyses of amended soils and biochars
from various feedstocks are reported, alongside some evaluations of plant
growth promotion capabilities. Fewer studies investigated the soil microbiota and
their potential to increase cycling and mobilization of nutrients in biochar
amended soils. This review is discussing the latest findings in the bacterial
contribution to cycling and mobilizing nitrogen, phosphorus and sulfur in
biochar amended soils and potential contributions to plant growth promotion.
Depending on feedstock, pyrolysis, soil type and plant cover, changes in the
bacterial community structure were observed for a majority of the studies using
amplicon sequencing or genetic fingerprinting methods. Prokaryotic
nitrification largely depends on the availability of ammonium and can vary
considerably under soil biochar amendment. However, denitrification to
di-nitrogen and in particular nitrous oxide reductase activity is commonly
enhanced, resulting in reduced nitrous oxide emissions. Likewise, bacterial
fixation of di-nitrogen appears to be regularly enhanced. A paucity of studies
suggests that bacterial mobilization of phosphorus and sulfur is enhanced as
well. However, most studies only tested for extracellular sulfatase and
phosphatase activity. Further research is needed to reveal details of the
bacterial nutrient mobilizing capabilities and this is in particular the case
for the mobilization of phosphorus and sulfur.