Interactive Effects of Nitrogen Form and Oxygen Concentration on Growth and Nutritional Status of Eggplant in Hydroponics

A greenhouse study was carried out to determine the effect of nitrogen forms and different O2 levels on growth and mineral nutrient concentrations of eggplant. The experimental design was a completely randomized factorial experiment with two factors, namely: (i) Two nitrogen forms (Ca(NO3)2 and (NH4)2SO4) and (ii) Three O2 levels of the nutrient solutions (1±0.3, 2±0.3, 3±0.3, and 4±0.3 mg L^-1 O2). The results showed that ammonium application reduced all measured parameters of vegetative growth, whereas high oxygen levels increased the vegetative growth. Comparing with nitrateN, ammonium application increased the concentrations of NPK and Zn in leaves and Zn and Cu in roots, while it decreased the concentration of Mg, Ca, Cu, Mn, and Na in leaves and Ca, Mg, Mn, and Na in roots. High levels of O2 increased N, Mg, Ca, Cu, and Mn content of leaves, as well as Mn and Na content in roots, while it decreased the concentration of K in leaves and P and Zn in roots. According to the results, the increase in O2 amount of the nutrient solutions partly alleviated ammonium toxicity in eggplant. Therefore, in floating hydroponic cultures, O2 level and its distribution should be controlled and must not be lower than 4 mg L^-1.