Effect of nitrogen source on growth parameters, chlorophyll content and some elemental concentration of basil (Ocimum basilicum L.) in soilless culture conditions

Basil (Ocimum basilicum L.) is an annual, aromatic and herbaceous plant belonging to the Lamiaceae family which is used as fresh vegetable and traditionally used to treatment many diseases. Plant nutrition is one of the important factors that affect quantitative and qualitative characteristics of plants. Nitrogen is one of the most important nutrients for plant growth and development. Plants can absorb nitrogen either as nitrate (NO3-) or ammonium (NH4+), and for optimal uptake and growth each plant species requires a different nitrate to ammonium ratio. This experiment was conducted to investigate the effect of different nitrate to ammonium ratios on morphophysiological characteristics and element concentration of basil. To study the effect of different nitrate to ammonium ratios (100:0, 75:25, 50:50, 25:75 and 0:100) on hydroponically grown basil, a pot experiment was conducted in a completely randomized design with four replications. In order to evaluate the growth parameters (plant height, stem diameter, number of leaves, leaf area, number and length of axillary shoots, fresh and dry weight of leaves, stems and roots), chlorophyll content and nutrients concentration (nitrogen, phosphorus, potassium, iron, copper, manganese and zinc in the leaves and roots), plant sampling was carried out at flowering stage. The results showed that plant growth parameters (such as number of leaves, number and length of axillary shoots, fresh and dry weight of leaves, roots and stems) and chlorophyll index (SPAD) were significantly affected by different nitrate to ammonium ratios. The different nitrate to ammonium ratios had no significant effect on plant height, stem diameter and leaf area. The growth parameters and chlorophyll content decreased with increasing of ammonium in nutrient solution and the 75:25 ratio of nitrate to ammonium was the most suitable treatment for most growth parameters and chlorophyll content. Also nitrogen (N), phosphorus (P) and copper (Cu) concentration in leaves and potassium (K), iron (Fe), manganese (Mn) and zinc (Zn) content in leaves and roots were significantly affected by nitrate to ammonium ratios. As nitrate to ammonium ratio decreased, N, P, Fe and Zn content of leaves increased, while K, Cu and Mn content of leaves and K, Fe and Mn content of roots decreased. The findings of this study showed that basil plant requires lower concentrations of ammonium in nutrient solution for proper growth. Therefore, a solution containing 75:25 of nitrate to ammonium ratio is recommended for basil plant production under hydroponic culture coditions. Key words: Ammonium, Basil, Hydroponic, Micronutrients, Nitrate