Optimization of Sowing Window and Plant Geometry for Enhanced Nutrient Assimilation in Cassia angustifolia Vahl.

A field investigation was conducted at Herbal Garden, College of Agriculture, Raichur in the year 2023-24 to assess the influence of different sowing windows and planting densities on nitrogen, phosphorus and potassium uptake in senna (Cassia angustifolia Vahl.), an important medicinal plant valued for its sennoside-rich foliage. Five sowing windows (S1: September II fortnight to S5: November II fortnight) and three planting densities (D1: 30 × 30 cm, D2: 45 × 30 cm and D3: 60 × 30 cm) were evaluated in a split plot design. The results revealed significant variations in nutrient uptake across sowing windows, planting densities and their interactions. Early sowing (S1) recorded the highest uptake of N, P and K (59.57, 33.54 and 10.08 mg plant⁻¹), while late sowing (S5) showed the lowest values. Among planting densities, the intermediate spacing D2 (45 × 30 cm) enhanced nutrient assimilation, registering maximum uptake (58.60, 34.18 and 9.99 mg plant⁻¹). The interaction effect S1D2 proved superior, achieving the highest N, P and K uptake (64.50, 40.01 and 11.42 mg plant⁻¹), whereas S5D1 performed the poorest. Percent increase analysis further confirmed the agronomic advantage of early sowing and optimum spacing, with S1 outperforming S5 by 42.75%, 76.53% and 33.16% for N, P and K uptake, respectively, and S1D2 surpassing S5D1 by 87.50%, 166.73% and 63.14%. The findings emphasize that timely sowing in the second fortnight of September coupled with a planting density of 45 × 30 cm significantly improves nutrient uptake efficiency in senna, thereby enhancing crop growth, biomass productivity and potential sennoside yield. These results provide valuable insights for refining nutrient and crop management strategies for commercial senna cultivation in semi-arid ecologies.