Comparative effects of walnut, apricot, and almond shell biochars on in vitro rumen fermentation and methane production.

An alternative strategy to reduce methane (CH₄) emissions from livestock is biochar, a porous carbonaceous material produced through the pyrolysis of biomass. This study aimed to evaluate the effects of biochars derived from walnut shell, almond shell, and apricot shell on rumen fermentation and CH₄ production under in vitro conditions. The experiment used a completely randomized design in an in vitro fermentation system with four treatments: a control diet without biochar and the control diet supplemented with 1% (based on total substrate dry matter) walnut, almond, or apricot shell biochar. Gas production was measured at multiple time points, and fermentation parameters were analyzed after 24 h of incubation. Walnut shell biochar increased gas production throughout the incubation period, whereas apricot shell biochar decreased it compared to the control (P < 0.05). While pH remained unaffected, apricot shell biochar significantly reduced ammonia nitrogen (NH₃-N) (P < 0.05). Furthermore, apricot and almond shell biochars significantly reduced protozoa counts (P < 0.05). Notably, walnut shell biochar significantly increased total volatile fatty acids (VFA) and propionate concentrations (P < 0.05), and enhanced in vitro dry matter degradability (DMD) (72.3% vs. 65.3% in the control) (P < 0.05). All biochar treatments significantly reduced CH₄ production (P < 0.05), with the greatest reduction observed with walnut shell biochar (77.2 vs. 90.9 mL/g DM; approximately 15% reduction). Overall, walnut shell biochar showed the most favorable effects by enhancing in vitro DMD, increasing total VFA and propionate concentrations, and achieving the greatest reduction in CH₄ production.