Impact of Plant Density and Irrigation Regimes on Physiological and Biochemical Responses of Cumin (Cuminum cyminum)

Cumin (Cuminum cyminum L.) is a medicinal plant, and its quality and quantity are notably affected by agricultural practices such as plant density and irrigation. A split-plot experiment was conducted using a randomized complete block design (RCBD) with three replications for two crop years (2018–2020) at the Sistan Agricultural and Natural Resources Research and Education Center, Iran. The irrigation methods included: I₁, which involved irrigation during vegetative, flowering, and seed-filling stages; I₂, which involved irrigation during vegetative and flowering stages; I₃, which involved irrigation during flowering and seed-filling stages; I₄, which involved irrigation only during flowering stage; and I₅, which involved no irrigation at all. The experiment also included testing plant density at 30, 50, and 100 plants per m². The study found that different irrigation regimes significantly impacted seed yield, relative water content, chlorophyll, proline, total carbohydrate, antioxidant activities, and essential oil content. The maximum seed yield was attained with I₁ (control) and a planting density of 100 plants per m², resulting in 651.9 kg ha⁻¹ and 672.4 kg ha⁻¹ in the first and second years, respectively. The irrigation during flowering and seed filling (I₃) with 50 and 100 plants per m² also showed a high seed yield in the first year. Non-irrigation and 30 plants per m² density resulted in the highest catalase, peroxidase, and superoxide dismutase activities. The essential oil content varied depending on irrigation and planting density, with the highest content achieved with I₄ irrigation and a planting density of 50 and 30 plants per m² in the first and second years (5.44 and 4.5%), respectively. The essential oil compounds with the highest mean values were β-pinene and safranal, while cuminaldehyde and sabinene had the lowest mean values. The research findings suggest that for optimal plant performances, it is advisable to use a planting density of 50 plants per m² and implement two irrigation stages during vegetative growth and flowering.