Deficit Irrigation Combined with Jeevamrutha-Based Nutrient Management Enhances Rhizosphere Microbial Abundance, Agronomic Performance, and Economic Returns of African Marigold Under Semi-Arid Conditions

Abstract Sustainable floriculture in semi-arid regions needs irrigation and nutrient management that conserve water and soil biological function, yet whether deficit irrigation and organic biostimulation act additively or interactively on rhizosphere microbiology remains untested. This two-season (2023–2025) split-plot trial grew African marigold (Tagetes erecta L.) under three irrigation levels (full, I₁, 1.0 ETc; mild deficit, I₂, 0.8 ETc; moderate deficit, I₃, 0.6 ETc) crossed with four nitrogen regimes: a fully chemical dose (N₁) and Jeevamrutha meeting 100% (N₂), 75% (N₃) or 50% (N₄) of crop nitrogen, with supplementary chemical P and K. Moderate deficit gave the highest rhizosphere bacterial, fungal and actinomycete counts (6.67 × 10⁷, 3.99 × 10⁵ and 2.92 × 10⁶ cfu g⁻¹), 11.5–11.9% above full irrigation; full Jeevamrutha-N substitution raised these counts 26.9–27.8% above chemical fertiliser, with a significant irrigation × nutrient interaction. These responses accompanied improved performance: moderate deficit gave the tallest plants (67.72 cm), longest longevity (22.17 days) and highest yield (14.76 t ha⁻¹), while full Jeevamrutha-N gave the widest canopy (47.74 cm) and highest yield (14.98 t ha⁻¹). Their combination (I₃N₂) ranked highest overall (16,909 kg ha⁻¹ yield, ₹3.38 lakh ha⁻¹ gross and over ₹2.21 lakh ha⁻¹ net returns, and a benefit–cost ratio of 1.90) while cutting seasonal irrigation by 38.6%. Deficit irrigation thus amplified, not merely coexisted with, the response to Jeevamrutha nutrition. By advancing water conservation (SDG 6), reduced synthetic-input use (SDG 12) and soil biological health (SDG 15), the approach offers a scalable pathway to sustainable, water- and input-efficient floriculture.