Fertilization Strategies for Peppermint (Mentha× piperita) Under Irrigation Patterns in Varamin, Iran: The Role of Mycorrhizae Depends on Chemical Phosphorus Availability

Peppermint (Mentha× piperita) stands as the predominant mint species cultivated across various global regions, owing to its superior quality and abundance of essential oil. The objective of this study was to investigate the impact of distinct biological fertilizers on physiological and morphological traits of peppermint. An experiment was conducted employing a split-plot design arranged within a randomized block framework. The experimental treatments encompassed varying irrigation intensities (full irrigation, and moderate and severe water-deficit stress, irrigation at 75%, 60%, and 45% of the field capacity, respectively), along with six combinations of phosphorus chemical fertilizers and arbuscular mycorrhizal fungi (Glomus intraradices). Inoculation with mycorrhiza exhibited a significant effect on leaf dry weight and essential oil yield, resulting in an augmentation of 5.3% and 10.7%, respectively, when contrasted with the non-fertilizer treatment. The results obtained show that moderate water stress elicited the highest essential oil content at 2.2%. The treatment combining 50% chemical phosphorus fertilizer with mycorrhiza inoculation yielded the highest leaf phosphorus content at 0.41%, while the lowest content of 0.21% was observed in the non-fertilizer treatment. Water restriction led to a reduction in gas exchange parameters; nevertheless, the application of fertilizers improved these attributes across all irrigation regimes. The highest proline content (0.036 μg g−1fresh weight) was detected in non-fertilizer peppermint subjected to severe water stress. The study unveiled that the combined application of phosphorus chemical fertilizer and biological fertilizer yielded superior outcomes compared to individual applications, even under stressful conditions. This approach holds promise for achieving heightened productivity while mitigating excessive use of phosphorus chemical fertilizers, thereby curbing environmental pollution and advancing toward sustainable agricultural practices.