EFFECT OF NITRATE/AMMONIUM RATIOS ON GROWTH, ROOT MORPHOLOGY AND NUTRIENT ELEMENTS UPTAKE OF WATERMELON (CITRULLUS LANATUS) SEEDLINGS

Nitrogen is taken up by most plant species in the form of nitrate and ammonium. The objective of this study was to investigate the effect of different nitrogen forms on the growth of watermelon seedlings. Plants were grown in hydroponic culture with five nitrate (NO3-)/ammonium (NH4+) ratios (100/0, 75/25, 50/50, 25/75, 0/100). When the proportion of NH4+ was increased, the leaf number, leaf area, shoot height, net photosynthesis, biomass, and root growth were significantly decreased. Higher concentrations of nitrogen (N) and phosphorus (P) were observed when plants were supplied with mixed NO3- and NH4+ compared to NO3- or NH4+ alone, whereas the concentrations of potassium (K), calcium (Ca), and magnesium (Mg) were decreased with increasing NH4+. The microelements concentrations were generally increased with more NH4+ added. In addition, plants fed with higher NO3-/NH4+ ratios resulted in more minerals accumulation.