Decreased soil microbial biomass and nitrogen mineralisation with Eucalyptus biochar addition to a coarse textured soil
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Background and Aims
Biochar has been shown to aid soil fertility and crop production in some circumstances. We investigated effects of the addition of Jarrah (Eucalyptus marginata) biochar to a coarse textured soil on soil carbon and nitrogen dynamics.
Wheat was grown for 10 weeks, in soil treated with biochar (0, 5, or 25 t ha−1) in full factorial combination with nitrogen (N) treatments (organic N, inorganic N, or control). Samples were analysed for plant biomass, soil microbial biomass carbon (MBC) and nitrogen (MBN), N mineralisation, CO2 evolution, community level physiological profiles (CLPP) and ammonia oxidising bacterial community structure.
MBC significantly decreased with biochar addition while MBN was unaltered. Net N mineralisation was highest in control soil and significantly decreased with increasing addition of biochar. These findings could not be attributed to sorption of inorganic N to biochar. CO2 evolution decreased with 5 t ha−1 biochar but not 25 t ha−1. Biochar addition at 25 t ha−1 changed the CLPP, while the ammonia oxidising bacterial community structure changed only when biochar was added with a N source.
We conclude that the activity of the microbial community decreased in the presence of biochar, through decreased soil organic matter decomposition and N mineralisation which may have been caused by the decreased MBC.
KeywordsBlack carbon Fertility Surface area Sorption Nitrogen cycling Priming effect
analysis of variance
ammonia oxidising bacteria
community level physiological profile
Duncan’s multiple range test
infra-red gas analyser
microbial biomass carbon
microbial biomass nitrogen
polymerase chain reaction
permutational analysis of variance
terminal restriction fragment length polymorphism
water holding capacity
DND and DVM were funded by the Grains Research and Development Corporation (GRDC) and DBG by an Australian Research Council (ARC) Discovery Grant (DP0985832). DLJ was funded by the Welsh Assembly Government. The authors thank Prof. R.J. Gilkes for his characterisation advice and Dr Y. Sawada and Mr M.N. Smirk for their technical assistance. The authors also acknowledge Dr P.S. Blackwell, of the Department of Agriculture and Food, Western Australia (DAFWA), for providing the soil, biochar and advice.
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