The aim of this study was to determine the effects of different rates and forms of nitrogen (N) on shoot growth and root morphological and leaf physiological responses of watermelon (cv. Crimson Tide F1) under hydroponic growth condition. The nutrient solution experiment was conducted between January - March in 2018 by using an aerated Deep Water Culture (DWC) technique in a fully automated climate room placed in the Plant Physiology Laboratory of Erciyes University, Faculty of Agriculture, Kayseri in Turkey. Plants were tested under two N-Rates (N1: 1000 and N2: 2000 µM N) and three different N-Forms (Am-N: NH4+, Nit-N: NO3-, 50% mixture of both N-Forms Mix-N: NH4+NO3) by growing in 8 L pots filled continuously aerated nutrient solution (modified Hoagland). The experiment was conducted with a completely randomized block design with four replications. From each pot two plants were harvested 42 days after treatment (DAT) by separating into stem, leaf and root fractions. The results indicated that shoot growth, root morphological and leaf physiological responses were significantly (p<0.001) affected by N-Rate, N-Form and N-Rate x N-Form interaction. The lowest performance under sole Am-N supply was achieved, since it severely reduced shoot and root growth and leaf area development as compared to sole Nit-N and Mix-N treatments. Irrespective of N rates, best growth performance in shoot growth was achieved under Mix-N supply, while root growth significantly improved under sole Nit-N supply. All these clearly indicate that the application of sole ammonium (1000 µM N) is detrimentally toxic for hydroponically grown watermelon plants. On the other hand, a 50% mixed of ammonium with nitrate even at a higher dose (N2: 2000 µM ammonium N) can be more advantageous for the growth and development of watermelon plants grown in the hydroponic system. Furthermore, our study showed that the effects of N-Form (Nit-N and Mix-N) on the improvement of shoot growth, root morphology and leaf physiological development and photosynthesis were significantly higher than the effects of N-Rate. Therefore, the application of nitrogen fertilizers in the form of Mix-N could be a useful N management strategy for growth and yield of watermelon plants under hydroponic conditions.
Nitrogen, Watermelon, N-form, Ammonium toxicity