Vol. 9, Special Issue 12, Part G (2025)

Phosphorus fixation in alkaline calcareous soils represents a critical constraint limiting onion (Allium cepa L.) seed production productivity across semi-arid regions of the Indian peninsula. While foliar nutrient application has demonstrated yield benefits, quantitative evidence regarding whole-plant nutrient uptake dynamics, nutrient use efficiency, and post-harvest soil fertility status remains limited. This investigation quantified the effect of ten foliar nutrient management treatments on nitrogen (N), phosphorus (P), and potassium (K) uptake, nutrient use efficiency, and residual soil fertility in onion seed production. The experiment was conducted at the Centre for Advanced Agricultural Science and Technology (CAAST), Mahatma Phule Krishi Vidyapeeth (MPKV), Rahuri (19°47′ N, 74°19′ E), Maharashtra, India during the 2022-2023 rabi season, using a randomized block design with three replications. Treatment T₈ (GRDF + Monoammonium Phosphate 12:61:0 @ 0.5% applied as foliar spray at 45, 60, and 90 days after planting) recorded the highest total nutrient uptake: 45.24 kg N ha⁻¹, 15.24 kg P ha⁻¹, and 40.41 kg K ha⁻¹, representing 58.2%, 82.7%, and 80.7% increases respectively over the absolute control (T₁). Phosphorus use efficiency in T₈ reached 32.9%, substantially exceeding T₁ (18.2%). Post-harvest soil fertility assessment revealed that phosphorus-enriched foliar treatments (T₈ and T₄) resulted in lower residual Olsen-extractable phosphorus (17.65 and 18.45 kg ha⁻¹ respectively) compared to potassium-dominant treatments (T₁₀: 21.12 kg ha⁻¹), directly reflecting superior phosphorus acquisition by the crop. Nutrient concentration in plant tissue at harvest demonstrated phosphorus concentration of 0.69% in T₈, compared to 0.34% in T₁, indicating substantially enhanced phosphorus accumulation in reproductive organs. The data conclusively demonstrate that in alkaline soils (pH 8.20), foliar phosphorus application fundamentally alters nutrient bioavailability pathways, circumventing soil-matrix phosphorus fixation mechanisms and enabling superior nutrient acquisition during phenologically-critical reproductive stages. This investigation provides mechanistic evidence that targeted foliar nutrient management, particularly phosphorus-enriched formulations applied during critical reproductive windows (60-90 days after planting), represents a sustainable strategy for optimizing nutrient use efficiency and maintaining soil fertility in semi-arid alkaline agricultural systems.