Biochar used in this study was commercially purchased from Sonnenerde company, Riedlingsdorf, Austria. It was produced by the pyrolysis of mixed paper fibre sludge and grain husks (in a ratio of 1:1 by mass) at 550 °C for 30 min in a Pyreg reactor (Pyreg GmbH, Dörth, Germany) .
The seller also provided information on the biochar properties such as specific surface area that was measured according to DIN 66132/ISO 9277 and the contents of cations (Ca, Mg, K, and Na) which were determined according to DIN EN ISO 11885. The biochar contained 53.1% C, 1.4% N (DIN 51732), 38.3% ash (DIN 51719). The C: N ratio of biochar was 37.9 and biochar pH was 8.8. Biochar contained particles with size ranging between 1-5 mm. The specific surface area of biochar particles was 21.7 m 2 g -1 . Further, biochar contained 57 g Ca kg -1 , 3.9 g Mg kg -1 , 15 g K kg -1 and 0.77 g Na kg -1 (Horák et al. 2020; (link)Aydin et al. 2020b ).
The seller also provided information on the biochar properties such as specific surface area that was measured according to DIN 66132/ISO 9277 and the contents of cations (Ca, Mg, K, and Na) which were determined according to DIN EN ISO 11885. The biochar contained 53.1% C, 1.4% N (DIN 51732), 38.3% ash (DIN 51719). The C: N ratio of biochar was 37.9 and biochar pH was 8.8. Biochar contained particles with size ranging between 1-5 mm. The specific surface area of biochar particles was 21.7 m 2 g -1 . Further, biochar contained 57 g Ca kg -1 , 3.9 g Mg kg -1 , 15 g K kg -1 and 0.77 g Na kg -1 (Horák et al. 2020; (link)Aydin et al. 2020b ).
