The Role of Amino Acids, Potassium and Selenium in Improving Growth of Eucalyptus citriodora Hook Plants and their Tolerance to Forest دور الأحماض الأمينية، البوتاسيوم والسيلينيوم في تحسين نمو نباتات الکافور الليموني (Eucalyptus citriodora Hook) وزيادة تحملها للبرودة أو الصقيع

This study was undertaken in the open field at the nursery of Hort. Res. Inst., ARC, Giza, Egypt during the winter of 2016/2017 and 2017/2018 seasons to find out the effect of some fertilization treatments, which were: foliar spraying with aqueous solution of amino acids mixture at the rate of 1 g/l (T1), T1 + soil drenching with potassium sulphate (K₂SO₄) at 2 g/plant (T2), T1 + sodium selenate (Na₂SeO₄) as foliar spray at 1 g/l (T3), T2 + Na₂SeO₄ as foliar spray at 1 g/l (T4) and foliar spray with tap water only (as control) on growth, chemical composition and tolerance of one-year-old seedlings of Eucalyptus citriodora Hook. grown in 25-cm-diameter plastic pots filled with about 4 kg of sand + clay soil mixture (1:1, by volume) to winter months. The treatments were applied 2 times every month in a complete randomized design. The obtained results showed that means of the different growth parameters; expressed as: plant height, stem diameter, No. leaves/plant, root length, as well as fresh and dry weights of stem, leaves and roots were significantly increased as a result of applying the various treatments mentioned above relative to control means in the two seasons. However, the dominance was for the sole treatment of amino acids (T1) that gave the highest values over the combined treatments in both seasons. A similar trend was also obtained regarding the leaf content of chlorophyll a, b, carotenoids, total soluble sugars and total carbohydrates, as T1 treatment attained the highest records of such constituents, with few exceptions. However, the opposite was the right concerning the leaf content of N, P and K, where N % slightly decreased by T1 treatment, but increased to maximum by T2 one. As for P and K % recorded the highest by T4 treatment.  Hence, it is enough to spray the foliage of E. citriodora plants cultivated in 25-cm-diameter plastic pots with the aqueous solution of amino acids mixture at the rate of 1 g/l, once every 15 days in winter months for keeping well growth and better quality plants.