Abstract
Basil (Ocimum basilicum L.) and fenugreek (Trigonella foenum-graecum L.) are essential oil-bearing medicinal plants that could be used for food spice, antimicrobial and antioxidant properties. Plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) promote crop growth and yield through different mechanisms. A two-year study was conducted to investigate the effects of fertilizer treatments on growth characteristics, essential oil (EO) yield and compositions of basil in intercropping with fenugreek. A factorial experiment was arranged in a randomized complete block design with three replicates in 2021 and 2022 in West Azarbaijan, Iran. The first factor was cropping pattern including sole cropping of basil and fenugreek, strip intercropping of basil (B)-fenugreek (F) with replacement method in the ratios of 2B:2 F, 4B:2 F, 5B:3 F and an additive intercropping of 100% basil + 50% fenugreek (100B:50 F). The second factor was fertilizer at three levels including application of local recommended dose of chemical fertilizer (RDF), 50% RDF + biofertilizer of AMF + PGPR (50% RDF + Bio) and biofertilizer of AMF + PGPR (Bio). The greatest basil height was observed in 2B:2 F cropping pattern and 50% RDF + Bio treatment (50.39 cm). The greatest yield of dry herbage was observed in 5B:3B cropping pattern with RDF and 50% RDF + Bio treatments. The highest yields of EO were observed in sole basil (0.85 g m(− 2)) and 5B:3 F intercropping (0.72 g m(− 2)), in 50% RDF + Bio treatment. Methyl chavicol, methyl eugenol, β-caryophyllene and 1,8-cineole, were the main chemical constitutes of EO. The contents of major components of EO were affected differently by cropping pattern and fertilizer. The greatest content of methyl chavicol (53.7%), was observed in 2B:2 F and Bio fertilizer treatment. Also, the highest content of methyl eugenol was obtained in 4B:2 F and 50% RDF + Bio fertilizer treatment. The results of EO compositions also were approved by principal component analysis (PCA). At all treatments, the land equivalent ratios (LER(T)) were more than 1.0 that indicates the advantage of intercropping patterns compared with sole crops. The highest LER(T) (1.99) was obtained in 2B:2 F intercropping with 50% RDF + Bio treatment. We can conclude that application of 50% RDF + Bio fertilizer treatment in 2B:2 F intercropping, increased the productivity of basil-fenugreek intercropping, improved the EO compositions and could be recommended to the growers in sustainable production of basil. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-026-39446-y.