Soil biochemical activities after the application of pyroligneous acid to soil

Pyroligneous acid (PA) is produced during the combustion of woody biomass and is a complex aqueous fraction resulting from the thermochemical rupture of the components of vegetable biomass. We evaluated the effect of PA on the soil microbial community and activity in order to assess the applicability of this acid in soil and to gather further information on the mechanisms of its toxicity or stimulation. Five concentrations of PA solution (0, 0.5, 1, 2 and 5%) were selected to monitor the biochemical parameters of the soil. The respirometric test showed that the increase in the evolved carbon dioxide-carbon (C) was not due to a release of the native organic C from the soil, but only from the organic compounds of PA. The highest values of microbial biomass content were found in the soil treated with the lowest PA doses, but decreased with increased doses. At higher application doses (2 and 5%), there was a decrease in most enzymatic activities and a loss of soil quality. When PA was applied in doses of up to 1%, our results indicated no negative effects on soil biology and that there was even an improvement.