The Effect of $NO_{3}^{-}$-N and $NH_{4}^{+}$-N Ratio in the Nutrient Solution on Growth and Quality of Sweet Basil

Sweet basil (Ocimum basilicum L.) was grown in a closed system to investigate the effects of NO_3^--N and NH_4^+-N ratio in nutrient solution on growth, yield, and quality. Sweet basil plants were grown in NFT supplied with SCU nutrient solution (NO_3^--N 11.6, NH_4^+-N 1.2, P 3.6, K 5.8, Ca 5.8, Mg 3.0 me․L^-^1) treated with five different ratio of NO_3^--N : NH_4^+-N (100:0, 85:15, 70:30, 50:50, and 30:70). In the case of the nutrient solution without controlling pH and concentration, pH was increased in 100:0 treatment, but rapidly decreased in the higher ratio of NH_4^+-N. EC in nutrient solution was decreased in all treatments. Shoot and root fresh weights of sweet basil were increased by higher NO_3^--N ratio, 100:0, 85:15, 70:30, in the nutrient solution and the addition of NH_4^+-N resulted in decreased fresh and dry weight. There were no significant differences in growth of plants grown in 100:0, 85:15, and 70:30. Mineral contents in the leaf tissue increased in plants grown in higher NO_3^--N ratio. The highest nitrate contents in leaves were observed in NO_3^--N single treatment (100:0). Photosynthesis of sweet basil was higher in 85:15 treatment, but did not show any significant differences among other treatments. Based on these results, optimum NO_3^--N to NH_4^+-N ratio in nutrient solution was found to be 85:15 (NO_3^--N 10.9 : NH_4^+-N 1.9 me․L^-^1).