Effects of Plant Spacing and Harvest Stage on Dry Matter Production, Sennoside Yield of Senna (Cassia angustifolia Vahl.) under Arid Conditions

Abstract

Senna (Cassia angustifolia Vahl.; syn. Senna alexandrina Mill.) is an important medicinal crop cultivated for its leaves and pods, which are rich in sennosides A and B, the principal anthraquinone glycosides used in pharmaceutical laxative formulations. Optimising agronomic practices that enhance both biomass production and sennoside yield is essential for improving the productivity and profitability of senna cultivation in arid and semi-arid regions. A three-year field experiment was conducted under rainfed conditions at the ICAR–Central Arid Zone Research Institute (CAZRI), Jodhpur, India, to evaluate the effects of plant spacing and harvest stage on dry matter production, dry leaf yield, sennoside content, sennoside yield and water-use efficiency. The experiment was laid out in a split-plot design with three replications, comprising three plant spacings (30 × 30, 45 × 30 and 60 × 30 cm) as main-plot treatments and three harvest stages (pre-flowering, 50% flowering and maturity) as sub-plot treatments. Plant spacing influenced biomass production and sennoside yield. The 45 × 30 cm spacing recorded the highest mean total dry matter yield (1251 kg ha⁻¹), dry leaf yield (705 kg ha⁻¹) and sennoside yield (18.3 kg ha⁻¹). Harvest stage exerted a greater influence on sennoside accumulation than plant spacing. Although harvesting at the pre-flowering stage resulted in the highest mean sennoside concentration (2.78%), harvesting at 50% flowering produced the greatest sennoside yield because of higher leaf biomass. Total crop water use varied little among treatments; however, water-use efficiency was greatest under the combination of 45 × 30 cm spacing and harvesting at 50% flowering. The findings indicate that adopting an intermediate plant spacing together with harvesting at 50% flowering provided the optimum balance between biomass production, phytochemical quality and efficient water use under arid rainfed conditions.