Green manure boosts biomass, essential oils, and chemical constituents in Origanum majorana L.: a sustainable fertilization approach

Green manure (GM) serves as an alternative to animal manure and organic compounds. Its use in sustainable agricultural practices helps enhance soil fertility and structure. Thus, this study aims to evaluate the potential of Cajanus cajan as a green manure to enhance the vegetative growth, essential oil metabolism, photosynthetic pigment levels, and antioxidant activity of Origanum majorana . The experiment was laid out in a randomized block design, with four replications (5 plants per replications) and six treatments: 0, 150, 300, 450 and 600 g plant −1 of C. cajan and one inorganic fertilizer control – NPK, 2.78 g plant −1 of urea (45 % N), 14.29 g plant −1 of single superphosphate (21 % P 2 O 5 ), and 3.77 g plant −1 of potassium chloride (60 % K 2 O). Various parameters were evaluated, including growth (dry matter), photosynthetic pigments, essential oil (EO) content and yield, chemical composition, nutrient accumulation, and antioxidant enzyme activity. The study demonstrated that all pigeon pea doses were effective as green manure, promoting greater dry matter accumulation than the control treatment. These results revealed that a 600 g plant −1 dose of C. cajan resulted in significant increases in dry matter accumulation in the leaves, stem, and shoot parts of 338 %, 555 %, and 414 %, respectively, compared to the 0 g plant −1 dose (control). The 450 g plant −1 dose of C. cajan resulted in a 14 % and 18 % increase in total chlorophyll content compared to the 150 g plant −1 dose and the control, respectively. The inorganic fertilizer recorded the lowest superoxide dismutase (SOD) activity, whereas the lowest doses (0 and 150 g plant −1 ) increased catalase (CAT) activity. Ascorbate peroxidase (APX) activity decreased in the absence of fertilization. Furthermore, the EO yield was significantly higher with 600 g plant −1 and inorganic fertilizer, reaching 0.050 and 0.056 mg plant −1 , an increase of 406 % and 471 %, respectively, compared to the control (no fertilization). In addition, α-Terpineol stood out as the major compound in the EO, since it reached higher concentrations in plants treated with 600 g plant −1 of green manure. The higher dose green manure not only resulted in the best performances in growth, nutrient accumulation, and antioxidant activity, but also consolidated C. cajan effectiveness as fundamental green manure strategy for the sustainable production of aromatic plants. This factor reinforced its potential benefit to sustainable agriculture and to the essential oil industry.