Biochar usually has a large specific surface area, and due to this, it increases the sorption capacity of the soil where it was applied. The objectives of this study were to (i) quantify the effects of biochar and biochar in combination with N fertilizer on the soil sorption parameters and (ii) quantify the effects of soil organic matter on the sorption parameters after application of biochar with and without N fertilizer.

The experiment was established on Haplic Luvisol at the locality of Dolná Malanta (Slovakia) in 2014. The soil samples were collected once a month from the depth 0–0.2 m during 2014 to 2016. The field experiment included three rates of biochar application (B0?=?no biochar, B10?=?biochar at the rate of 10 t ha^?1, B20?=?biochar at the rate of 20 t ha^?1) and three levels of N fertilization (N0?=?no nitrogen, N40?=?nitrogen at the rate of 40 kg ha^?1, N80?=?nitrogen at the rate of 80 kg ha^?1).

Overall, the decrease of the average values of hydrolytic acidity due to biochar and biochar combined with N fertilization resulted on average in an increase of sum of basic cation (SBC), cation exchange capacity (CEC), and sorption capacity of soil organic matter (CEC_SOM) in all treatments. However, this effect was the most intensive in B10N40. Despite the fact that the average values of sorption parameters improved, its dynamics during the investigated period were different. A significant decrease in CEC was observed from 2014 to 2016 in all treatments, except B0N0 and B10N0. A stable trend in CEC_SOM was observed only in B10N40. Humic substances and humic acids had a statistically significant positive effect on the SBC, CEC, and CEC_SOM only in B20N0 treatment. Negative correlations between the above mentioned parameters were observed in B10N80 treatment.

We conclude that the application of biochar and biochar combined with N fertilization had a positive influence on sorption parameters. However, its effects on SBC, CEC, and CEC_SOM decreased over time after its application.