Objective The study was carried out to alleviate the allelopathic effects of phenolic acids in soil on patchouli (Pogostemon cablin) and to investigate the impact of biochar-urea peroxide composite granules on the agronomic traits and physiological-biochemical indicators of patchouli cuttings under phenolic acid stress, with an aim to provide a reference for the research and development of soil conditioners for the continuous cropping of Chinese medicinal herbs.

Method A pot experiment was conducted with five treatments: conventional cultivation (CK), phenolic acid stress (PhA), phenolic acid stress with biochar-urea peroxide composite particles (PhA+BC-UP), phenolic acid stress with biochar granules (PhA+BC), and phenolic acid stress with urea peroxide granules (PhA+UP), respectively. After transplanting the patchouli cuttings for 30 days, 15 indicators were measured, including agronomic traits, root phenotypes, root activity, and leaf antioxidant enzymes, etc. Additionally, the residual total phenolic acid content in rhizosphere soil was determined, and the differences among different treatments were compared.

Result Compared with the PhA treatment, the PhA+BC-UP treatment resulted in a 28.8% increase in the aboveground biomass and a 21.4% increase in the height of patchouli seedlings, the increases in root length, root surface area, root volume, root tip number, branch number, and root crossing number ranged from 20.1% to 70.6%, and the root vitality was improved by 23.6%, while the MDA content decreased by 33.6%. Compared with CK, the PhA treatment significantly inhibited the activity of superoxide dismutase (SOD) in patchouli leaves, while simultaneously inducing increases in the activities of peroxidase (POD) and catalase (CAT). In contrast to the PhA treatment, the PhA+BC-UP treatment exhibited an opposite regulatory effect on the leaf antioxidant enzyme activity. Furthermore, compared with the individual application of biochar or urea peroxide granules, the biochar-urea peroxide composite granules showed a better regulatory effect on the growth indicators of patchouli cuttings under phenolic acid stress. The increase in growth indicators, such as fresh weight of both aerial and underground parts, plant height, and root length, exceeded 8.3% and 15.9%, respectively, root vitality improved by 18.2% and 41.2%, while MDA content decreased by 14.9% and 95.8%, respectively.

Conclusion The biochar-urea peroxide composite granules can effectively reduce the phenolic acid content in the soil, thereby alleviating the allelopathic stress of phenolic acids on patchouli cuttings. This promotes root morphological development and regulates the antioxidant enzyme activity in the plants, ultimately enhancing the growth of patchouli.