CRESCIMENTO DE PLANTAS JOVENS DE EUCALYPTUS UROPHYLLA EM MEIO HIDROPÔNICO COM DIFERENTES PROPORÇÕES DE NITRATO E AMÔNIO

GUIMARÃES, M. M. C. Growth of Eucalyptus urophylla young plants in hydroponic medium containing different nitrate and ammonium ratios. Vitória da Conquista – BA: UESB, 2012. 65p. (Dissertation – Master’s in Agronomy: Phytotechny Concentration Area) * . The ammonium and nitrate ions are the main ionic forms of nitrogen uptake by plants in soils. Different proportions of these ions in nitrogen fertilization can cause physiological changes to the plant, reflected on their growth and development. This experiment was carried out in a greenhouse, and it was aimed to evaluate physiological responses and characteristics associated to the growth of Eucalyptus urophylla clone AEC0144 seedlings, under different proportions of nitrate and ammonium in hydroponic solutions. It was adopted the completely randomized design, in which treatments were five nitrate/ammonium ratio in nitrogen fertilization (0/100, 25/75, 50/50, 75/25 and 100/0), with four repetitions. For adaptation to the hydroponic medium, the seedlings were transferred from little tubes of original cultivation to Clark hydroponic solution, previously prepared by 33%, 50% and 100% of ionic strength, where they remained for 21 days, seven days at each level of ionic strength. After this period, the plants were grown for 70 days in pots containing the nitrate/ammonium ratios. The hydroponic solutions were renewed every 10 days. The results were submitted to statistical analysis and Tukey test 5%. The nitrate/ammonium ratios caused the following effects on the initial growth: changing in the biomass accumulation, Dickson quality index, nitrate reductase activity, chlorophyll content (SPAD index) and leaf macronutrient content. Based on the expansion of tissues and organs and biomass accumulation, the plant growth was particularly favored the 75/25 nitrate/ammonium ratio. However, the nitrate/ammonium ratios didn’t cause significance changing in some physiological aspects, like net photosynthesis, water status and nitrogen assimilation. The plant nutritional status was affected by the nitrate/ammonium ratios, but there weren’t visible symptoms of macronutrients deficiency or excess in leaves. The pH of hydroponic solutions was also changed for the nitrate/ammonium ratios, particularly in solutions containing only one N source.