Effect of Bio and Mineral Nitrogen Fertilization on Growth and Yield of Three Onion Cultivars under Aswan Conditions.

This study was conducted at the Experimental Farm of the Faculty of Agriculture and Natural Resources, Aswan University, Egypt, during two successive seasons 2022/2023 and 2023/2024 to evaluate the impact of integrating biofertilizers with mineral nitrogen fertilization on the growth performance, pigment accumulation, and bulb quality of three onion cultivars (Giza 6 Mohassan, Giza Red, and Giza White). The experimental layout followed a randomized complete block design in a factorial arrangement with three replicates, incorporating five bacterial strains and three nitrogen levels (50%, 75%, and 100% does of N). Results demonstrated that onion vegetative growth, chlorophyll and carotenoid content, bulb development, bulbing coefficient, and total yield were significantly influenced by the interaction between cultivar, nitrogen level, and biofertilizer strain. Giza Red cultivar exhibited superior plant height, leaf number, neck thickness, and bulbing index, particularly when integrated with full nitrogen dosage and effective biofertilizer strains. Giza 6 Mohassan cultivar showed the highest total yield under moderate nitrogen (75%) with strain Enterobacter cloacae in 2022/2023 and under low nitrogen (50%) with strain Sphingomonas paucimobilis in 2023/2024. Biofertilizer application significantly enhanced nutrient uptake and photosynthetic pigment concentration, especially when combined with full or moderate nitrogen rates. The study concludes that integrating biofertilizers with reduced nitrogen fertilization can optimize onion productivity while minimizing environmental nitrogen load.