Morphological and Physiological Responses of Maize to Varying Nitrogen Sources and Stress Levels in Hydroponic Systems: A Comparative Study

Abstract

A hydroponic experiment was conducted at the Precision and Automated Agriculture Laboratory, Department of Agronomy and Agricultural Extension, University of Rajshahi, from April to August 2023. The objective was to investigate the morphological and physiological responses of maize to varying nitrogen sources and stress levels in hydroponic systems. The experiment comprised three nitrogen treatments: CN (100% chemical nitrogen as 2 mM NH4NO3), ON (100% organic nitrogen as 4 mM glycine), and LN (low nitrogen as 10% of 2 mM NH4NO3 chemical nitrogen solution). The popular maize variety NH7720 (marketed by Syngenta Bangladesh Limited) was used. The experiments followed a completely randomised design with three replications. The CN treatment consistently outperformed the ON and LN treatments in various growth-related parameters, including plant height (72.73 cm), leaf area (295.54 cm²), shoot dry weight (0.65 g/plant), total chlorophyll content (3.11 mg/g), and shoot (11.06%) and root (10.82%) protein content, indicating that adequate nitrogen treatment stimulated strong growth and development in maize plants. Conversely, the LN treatment exhibited a superior shoot-to-root ratio (85.43%), proline accumulation (188.01 µg/g), number of root tips (21.25), root length (31.65 cm), root network area (619.10 cm²), root diameter (5.63 mm), root volume (13944.71 mm³), and root surface area (3705.51 mm²). These results suggest that under nitrogen-deficient conditions, maize plants allocate resources to root development and stress tolerance mechanisms. The organic nitrogen (ON) treatment showed intermediate results, being statistically similar to both the CN and LN treatments across a range of characteristics, suggesting that organic nitrogen or glycine might be less effective than chemical nitrogen or ammonium nitrate in promoting optimal maize growth.