Biochar has the potential to store carbon (C), mitigate greenhouse gas (GHG) emissions from soil, and affect soil microbial biomass (SMB) involved in carbon (C) and nitrogen (N) dynamics. Laboratory incubation studies were conducted to compare the effects of amendments with biochar and biochar feedstocks on SMB, C and net N mineralization, as well as GHG (CO₂, N₂O and CH₄) emissions from soil. Biochar feedstocks were coffee grounds, wood pellets, and horse manure and bedding compost. The biochar was prepared from these feedstocks by gasification at 700ºC. Biochar and raw feedstocks amendments were incorporated into a silt loam soil at a rate of 0.75% by weight at 22 % gravimetric water content and incubated for 175 days. GHG emissions were sampled 17 times and measured by gas chromatography (GC), while net N mineralization (ammonium and nitrate-N) and MB-C and MB-N were measured weekly for up to 70 days by colorimetric and fumigation extraction methods. The data has shown that amendments with biochar feedstocks significantly increased CO₂ emission rate and SMB in contrast to treatments with biochars which were not different from the unamended soil. Mineralized C from biochar feedstocks was 13, 37 and 51 % of initially added C for horse manure and bedding compost, coffee grounds and wood pellets, respectively. By contrast, biochar treatments mineralized only around 0.5 % of initially added C, suggesting biochar did not significantly increase microbial activity. Moreover, mineral N immobilization was evident in the biochar feedstocks amendments whereas biochar treatments did not have a significant effect on net N mineralization and nitrification rates. Finally, biochar had no effect on N₂O and CH₄ emissions from soil. In conclusion, high temperature biochar as a soil amendment, appears to be rather inert, showing no effect on either soil microbial biomass and inorganic N dynamics or GHG emissions.

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