Influence of Different Fertigation Levels and Nano-Nutrients on Growth, Yield and Quality of Onion (Allium cepa L.) cv. Bhima Super under Dryland Conditions

Onion (Allium cepa L.) is a major foreign-exchange-earning horticultural crop in India. However, its shallow root system and high NPK requirement make conventional soil-based fertilisation inefficient, particularly under water-scarce dryland conditions. Water-smart approaches such as fertigation enable precise, need-based nutrient delivery through drip irrigation, minimising nutrient losses, while nano-fertilisers such as Nano DAP can enhance nutrient-use efficiency through targeted foliar uptake. A field experiment was conducted at the College of Horticulture, Bagalkot, to evaluate the combined effects of seven fertigation levels (F1–F7, based on 125:75:125 kg NPK/ha) and two levels of foliar Nano DAP (2 mL and 4 mL at 30 and 60 DAP) on the growth, yield, quality and economics of onion cv. Bhima Super during the kharif season, using a Factorial Randomized Block Design with 14 treatment combinations. The treatment combination F4N2—80% RDF applied through fertigation combined with a foliar spray of 4 mL Nano DAP—significantly outperformed the other treatments, recording the highest bulb yield (34.0 t/ha), the highest proportion of A-grade bulbs and TSS, high dry matter content, improved nutrient uptake and fertiliser-use efficiency, and the highest interaction-level benefit:cost ratio (4.61), while using 20% less recommended fertiliser than the full-RDF treatments. These findings indicate that water-smart fertigation integrated with foliar nano-nutrient application can reduce fertiliser inputs without compromising productivity, offering a resource-efficient and economically viable nutrient-management strategy for onion cultivation under the conditions of the northern dry zone of Karnataka.