Use of Biochar and Lime to Reduce the Acidity of Agrosoddy-Podzolic Soils in a Laboratory Experiment

Liming is the main method for eliminating excessive soil acidity. Biochar has been proposed as an alternative liming agent. The liming capacity of biochar has remained largely unstudied in the Northwestern region of Russia. The objective of this study is to evaluate the potential for separate and combined use of biochar and lime to neutralize the acidity of agrosoddy-podzolic soils. The acid–base properties (pH, exchangeable and total (hydrolytic) acidity, exchangeable Al3+ content, sum of exchangeable bases, cation exchange capacity, and base saturation) were determined in the course of a 30-day laboratory experiment with samples from the arable horizon (0–20 cm) of strongly acid loamy sandy and medium acid loamy agrosoddy-podzolic soils in Leningrad oblast. Biochar was obtained by fast pyrolysis of birch wood at 600°C. The liming effect of biochar was compared to that of a traditional calcium-containing ameliorant, CaCO3. Biochar was added to soils at the rates of 5 and 10 g/kg, while CaCO3 was added at the rates of 0.5 and 1.0 g/kg. We also tested various combinations of lime and biochar applied at the same rates. Biochar was shown to significantly reduce soil acidity and increase the concentration of basic cations more effectively than CaCO3 in the model experiment. The mechanisms of action of biochar and CaCO3 differed, which was particularly evident with respect to their influence on the reduction in the content of mobile aluminum: biochar was 8–11% more effective than lime in sandy loam soils and 22–29% more effective in loamy soils. The combined effect of lime and biochar was comparable to or superior to their separate application. Compared to lime application, base saturation increased by 5–10% upon biochar application and and by 15–20% upon application of both ameliorants. The greatest positive changes were observed in sandy loam soil.