Microbial mineralization of biochar and wheat straw mixture in soil: A short-term study

A short-term incubation study was carried out to investigate the effect of biochar addition to soil on CO2 emissions, microbial biomass, soil soluble carbon (C) nitrogen (N) and nitrate–nitrogen (NO3–N). Four soil treatments were investigated: soil only (control); soil + 5% biochar; soil + 0.5% wheat straw; soil + 5% biochar + 0.5% wheat straw. The biochar used was obtained from hardwood by pyrolysis at 500 °C. Periodic measurements of soil respiration, microbial biomass, soluble organic C, N and NO3–N were performed throughout the experiment (84 days). Only 2.8% of the added biochar C was respired, whereas 56% of the added wheat straw C was decomposed. Total net CO2 emitted by soil respiration suggested that wheat straw had no priming effect on biochar C decomposition. Moreover, wheat straw significantly increased microbial C and N and at the same time decreased soluble organic N. On the other hand, biochar did not influence microbial biomass nor soluble organic N. Thus it is possible to conclude that biochar was a very stable C source and could be an efficient, long-term strategy to sequester C in soils. Moreover, the addition of crop residues together with biochar could actively reduce the soil N leaching potential by means of N immobilization.

► Biochar addition to soil with or without wheat straw residues.
► Only 2.8% of the C from biochar was respired, whereas 56% of the wheat straw C was decomposed.
► Wheat straw residues did not promote biochar C decomposition.
► Biochar did not influence microbial biomass nor soluble organic N.
► Plant residues and biochar could reduce the soil N leaching potential increasing N immobilization.