Impact of soil incorporation of biochar on radon emission

Biochar (charcoal made from biomass in the pyrolysis process) has found broad application in agriculture. The research performed with biochar revealed the positive impact of biochar application for chemical and physical properties of soil. Biochar was also used as an material for decontamination of soil from heavy metals and pesticides. The improved water retention of soil after biochar application was shown as well. There are particular research concerning the usage of biochar as an material for decontamination of soil from anthropogenic radioactive material including Cs-137 and Sr-90 deposited after nuclear weapon test. However, the biochar find the most practical application in agriculture for improvement of crops efficiency and water retention of soils. The typical application amount of biochar for agricultural purpose varies from 40 to 100 Mg ha^-1.

Actually, there are numerous research activities focused on the direct impact of biochar on physical and chemical soil properties. Simultaneously lack of information are available for issue if and how biochar impact for environment radioactivity. As one of that impact could be  the influence on radon emission from soil surface. The aim of presented work was to investigate the impact of biochar application into the soil for the radon emission process.

The research objects were soil samples collected from experimental fields with biochar applied at doses from 1 to 100 Mg ha^-1. Two type of biochar were investigated – first biochar produced from sunflower husk at temperature of 650°C and second biochar produced from wood chips at temperature of 650°C. The radon emanation coefficient were assessed using active cumulative technique incorporating AlphaGUARD instrument equipped with sealed accumulation box.  In addition, we directly measured radon exhalation rate at the experimental fields. As the emanation coefficient calculation require the information on Ra-226 activity concentration, the gamma spectrometry analysis using HPGe detector were performed for samples collected on particular field.  

The results of activity concentration assessments shown that the most visible effect of biochar application into the soil is associated with the reduction of soil bulk density by this material. No significant changes in activity concentration depending on the biochar dose applied were observed for Ra-226. Fluctuation in radon exhalation rate as well as in emanation coefficient, depending on the biochar dose (from 1 to 100 Mg ha^-1) were observed and presented.

The research was partially conducted under the projects “Water in soil – satellite monitoring and improving the retention using biochar” no. BIOSTRATEG3/345940/7/NCBR/2017, which was financed by the Polish National Centre for Research and Development in the framework of “Environment, agriculture and forestry” – BIOSTRATEG strategic R&D programme.