Legume-based intercropping systems have been proposed as sustainable and eco-friendly systems with potential to improve crop production and soil fertility. A field experiment was conducted in two growing seasons (2017 and 2018) to determine optimal intercropping patterns of ajowan (Trachyspermum ammi L.) and fenugreek (Trigonella foenum-graecum L.) to increase yield and quality of ajowan and to improve soil properties. The treatments evaluated in this study were sole cropping of ajowan (A) and fenugreek (F), replacement intercropping series of A:F (1:1, 4:4, 3:1, and 1:3 ratios) and additive intercropping series of A:F (100:12.5, 100:25, 100:37.5, 100:50, 100:62.5, 100:75, and 100:87.5 ratios). The results showed that the highest biological yield (4172.7 kg ha-1), seed yield (1009.7 kg ha-1), and essential oil yield (42.0 kg ha-1) of ajowan were obtained in the additive pattern of A:F 100:25. The highest concentrations of thymol and γ-terpinene as the major chemical components of ajowan essential oil was recorded for the A:F 100:25 intercropping pattern. Total LER and ATER indices were more than one in all of the intercropping patterns. The concentrations of soil total organic carbon (TOC) and nitrogen (TON), available forms of NO3- and NH4+, Mg2+, K+, as well as basal respiration (BR) and substrate-induced respiration (SIR) in the A:F 100:25 intercropping pattern were greater than for the fenugreek and ajowan sole crops. Overall, the analysis showed that A:F 100:25 additive intercropping pattern had positive and strong effects in terms of increased yield and quality of ajowan and improvement of soil fertility.
