Synergistic effect of compost and PGPR in improving Mentha longifolia in newly reclaimed soil

For medicinal plants such as Mentha longifolia (horsemint), the quality of the final product is just as important as the yield quantity. As global demand drives cultivation into sandy, nutrient-poor soils, it becomes essential to develop sustainable methods that preserve high product quality despite these harsh conditions. In this context, the current study was conducted to assess the potential role of compost at different doses, with PGPR, as an eco-friendly practice on horsemint productivity. In a factorial design with three replications per treatment, the experiment tested varying compost application rates (0, 18.8, 37.5, and 56.3 tons/ha) with or without 100 ml of each microbe of PGPR in a factorial randomized block design with three replicates. Compared to untreated plants, compost at 37.5 tons/ha with PGPR (B1T2) improved plant length, No. of branches, fresh weight per plant, and dry weight per plant by 34%, 46.9%, 49.6%, and 48.4%, respectively. It also significantly boosted essential oil yield by 81.3%. Analysis of the essential oil profile across all treatments revealed levomenol (13.8–19.9%), isomenthone (3.6–4.6%), and eucalyptol (4.4–5.4%) as the primary chemical constituents. Furthermore, B1T2 increased total nitrogen uptake and carbohydrate content by 15.7% and 39.8%, respectively. These outcomes emphasize the importance of organic amendments and biofertilizers as an effective strategy for eco-friendly cultivation of horsemint and other medicinal and aromatic herbs in reclaimed soil. Further research is required to assess how this sustainable method can be applied to other medicinal crops to increase production in recently reclaimed soils.