In recent years, international energy policy has placed great emphasis on increasing the share of renewable energy in gross final energy consumption, which contributes to the growing importance of alternative energy sources and the search for new energy resources. The paper deals with the refinement of plant biomass by pyrolysis of residues from selected agricultural crops for the production of high-enriched biochar materials. In addition, the effect of the length of the pyrolysis process on the basic energy parameters of biochars obtained from buckwheat and low-morphine poppy crop residues was evaluated. Buckwheat husk and poppy residues of poppy plants were subjected to anaerobic thermal modification at 400°C and process times of 2, 4, 6, 8, 10, 12, 14, 16, and 18 min. It was found that the optimal roasting time for the modified biomass is 2 min. For this process variant, the maximum heating values of pyrolysates were 28.52 and 24.7 MJ kg-1 for buckwheat and poppy, respectively. The study also showed that biochar obtained from buckwheat has a significantly higher total carbon content (max. 76.71%) compared to biochar materials obtained from poppy (max. 58.86%). Biochar materials from buckwheat crop residues and low-morphine poppy can be an alternative to other biomass and biochar fuels.