Physiological and economic optimization of onion (Allium cepa L.) seed production through targeted foliar nutrient supplementation in semi-arid tropics

Onion (Allium cepa L.) seed production in semi-arid tropics remains constrained by poor nutrient availability, particularly phosphorus fixation in alkaline calcareous soils. The crop’s shallow root system and high reproductive nutrient demand further limit seed yield and quality under conventional soil fertilization. This study evaluated the physiological, yield, seed quality, and economic responses of onion to targeted foliar nutrient supplementation using ten nutrient treatments under a randomized block design at MPKV, Rahuri. Results demonstrated that phosphorus-enriched foliar formulations significantly improved reproductive architecture, umbel formation, seed filling, and physiological vigor. Among treatments, foliar application of monoammonium phosphate (12:61:0) at 0.5% (T₈) was superior, producing the highest umbels per plant (7.51), primary umbel diameter (7.81 cm), 1000-seed weight (3.91 g), seed germination (90.90%), and seed yield (7.66 q ha⁻¹). The economic analysis revealed that T₈ achieved the maximum net returns (₹ 8,69,176 ha⁻¹) and the highest benefit-cost ratio (4.52), indicating strong profitability and high adoption potential for farmers. The findings confirm phosphorus as the principal limiting nutrient and demonstrate that foliar supplementation effectively bypasses soil fixation constraints, enhancing source-sink dynamics and reproductive efficiency. This study recommends foliar application of 12:61:0 at critical growth stages (45, 60, and 90 DAP) as an agronomically and economically optimal strategy for improving onion seed productivity in semi-arid, phosphorus-limited soils.