Previous studies suggest that biochar has potential to benefit soil when used as an amendment, but only few studies have investigated how the different biochars affect the microbial activity of soil in a calcareous soil. Hence, to study the effect of the biochars obtained from wheat straw and cow manure and produced under different production conditions on two biological soil indicators, dehydrogenase activity and soil respiration, after 0, 60, and 120 days of incubation (DOI), an incubation experiment as a completely randomized design with factorial arrangement in three replicates was conducted in a calcareous soil. The results of the study showed that with increasing the pyrolysis temperature (300 and 500 °C) and pyrolysis residence times (1, 3, and 6 h) of biochars, regardless of feedstock source, the dehydrogenase activity and soil respiration decreased. Both maximum activity of dehydrogenase (20.93 μg TPF g-1 24 h-1) and maximum soil respiration (0.26 mg CO2 g-1 24 h-1) were found in the biochar produced from wheat straw at 300 °C, and the residence time of 1 h at the level of 10 t ha-1 and minimum of these soil biological traits was observed in control treatments (soil). Moreover, the maximum activity of dehydrogenase and soil respiration was observed in 60 DOI. Therefore, when applying biochar as an amendment for increasing microbial activity in calcareous soil, the production conditions of biochar, type of biochar, and long- and short-term effects of different biochars should be taken into consideration.
Keywords: Biochar; Calcareous soil; Dehydrogenase activity; Pyrolysis temperatures; Soil respiration.