Optimizing Nutrient Solution Strength and Root-Zone Oxygen Management for Improving Productivity and Water-Use Efficiency of Mustard (Brassica juncea L.) in NFT Hydroponics

Nutrient availability and root-zone oxygen are essential to consider when enhancing productivity and water-use efficiency in soilless crop production. This study examined the effects of three different strengths of Hoagland nutrient solution (50, 75, and 100%) and two different aeration levels for the root zones of plants growing in a nutrient film technique (NFT) system on the independent and interactive effects of the two factors on mustard (Brassica juncea L.). The experiment used a 3 × 2 factorial design. The results showed that plant growth, root development, biomass production, chlorophyll content, nutrient uptake, yield, and water-use efficiency increased with higher Hoagland concentrations, and that increasing root-zone aeration further improved plant performance. The 100% Hoagland + aeration treatment (T3) produced the highest values for key productivity traits, including 208 ± 6 siliquae plant−1, 26.5 ± 0.7 seeds siliqua−1, 5.28 ± 0.12 g 1000-seed weight, 5512 ± 126 grains plant−1, and 29.11 ± 0.71 g grain yield plant−1, corresponding to 9.70 ± 0.24 t ha−1. It also produced the greatest total fresh biomass (250.30 ± 1.29 g plant−1) and water-use efficiency (1.69 ± 0.04 g L−1). The dissolved oxygen concentration was raised to 7.8–8.6 mg L−1 under root-zone aeration, which was higher than the 4.2–4.8 mg L−1 measured under non-aerated conditions. Grain yield, water-use efficiency, root length, and root volume were strongly correlated. Overall, the 100% Hoagland plus root-zone aeration (T3) treatment was the most successful, highlighting the need for integrated nutrient and oxygen management in mustard production in NFT systems.