Vol. 25, No. 2 (2026), Bio26755 https://doi.org/10.24275/rmiq/Bio26755

Phytoregulators production through anaerobic digestion of dairy manure: evaluation of initial pH and digestion time effect

 

Authors

M.M. Solís-Oba, J.J. Castro-Ramos, R. Castro-Rivera, A. Solís-Oba

Abstract

Phytoregulators are widely used in agriculture to improve crop quality and yield. Currently, they are produced mainly through aerobic axenic fermentation; however, anaerobic digestion presents a potentially viable alternative, as it reduces energy requirements and allows the use of waste substrates. The effect of initial pH and digestion time on gibberellic acid (GA3), indole-3-acetic acid (IAA), and abscisic acid (ABA) through anaerobic digestion (AD) of dairy manure (DM) was evaluated. A completely randomized factorial design was implemented using initial pH [5.5, 6.5 (control), 7.5, 8.5] and digestion time (0, 4, 8, 12, 16, 20 days) as factors. The ADs temperature was kept at 42 °C, the total solids was set at 7 %, and no external inoculum was added. Both main effects and their interaction showed a highly significant effect on GA3 and IAA production. The highest overall GA3 concentration (124.86 mg/L) was obtained at initial pH 8.5 and 8 days. IAA production occurs only in initial acid pH treatments, reaching a maximum concentration of 5.52 mg/L at initial pH 5.5 and 20 days. ABA was not detected under the evaluated conditions. The acidification behavior across all AD treatments suggests that GA3 and IAA were produced during the hydrolytic-acidogenic stage of AD. Initial pH and digestion time highly influenced the profile and production of phytoregulators from DM via anaerobic digestion.

Keywords

anaerobic digestion, dairy manure, gibberellic acid, indole-3-acetic acid, phytoregulators.

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