Changes in the essential oil, fixed oil constituents, and phenolic compounds of ajowan and fenugreek in intercropping with pea affected by fertilizer sources

Abstract

Intercropping systems combined with the application of organic and biofertilizers can create more sustainable and cleaner plant production systems. This study investigated the effect of organic/biofertilizers and intercropping patterns on the seed yield of ajowan (Carum copticum L.), fenugreek (Trigonella foenum-graecum L.), and pea (Pisum sativum L.) and the essential oil and fatty acid profiles and phenolic compounds of the two medicinal and aromatic plants. The five fertilizer treatments were: no fertilizer (control), 100% chemical fertilizer (NPK), 50% chemical fertilizer+ 100% biofertilizer (CH+B), 50% chemical fertilizer + 100% humic acid (CH+H), and 100% biofertilizer + 100% humic acid (B+H). The six intercropping treatments were ajowan pure stand (Aps), fenugreek pure stand (Fps), pea pure stand (Pps), intercropping one row each of fenugreek + ajowan + pea (1 F:1 A:1 P), intercropping two rows each of fenugreek + ajowan + pea (2 F:2 A:2 P) and intercropping three rows each of fenugreek + ajowan + pea (3 F:3 A:3 P). The results showed that pure stands with CH+H fertilizer produced the highest seed yields for ajowan, fenugreek, and pea, being 29%, 25%, and 30% higher than the unfertilized control. The 2 F:2 A:2 P intercropping ratio fertilized with CH+H had the highest concentrations of ajowan essential oil (3.9%) and main chemical constituents, including thymol (51.3%) and p-cymene (19.6%). The main oil chemical constituents of ajowan included petroselinic acid (69–75.7%) oleic acid (18–23.9%), and palmitic acid (2.1–5.2%). The main chemical constituents of fenugreek oil were linoleic acid (32.4–38.9%), oleic acid (18–24.3%), linolenic acid (16.1–20.9%), and palmitic acid (7.2–14.1%). The 2 F:2 A:2 P intercropping ratio fertilized with CH+H and CH+B had the highest concentrations of coumaric and rosmarinic acids in ajowan and fenugreek, respectively. The results suggest that the 2 F:2 A:2 P intercropping ratio combined with chemical and organic fertilizer application is a more sustainable and cleaner strategy for improving secondary metabolites and fatty acid profiles in ajowan and fenugreek than pure stands.