Fertilização potássica no crescimento de mudas de Eucalyptus camaldulensis Dehnh. sob limitação hídrica

Abstract

The objective of this study was to evaluate the effect of potassium fertilization on the growth of Eucalyptus camaldulensis Dehnh seedlings under water limitation. The sowing was done with improved seeds of E. camaldulensis Dehnh in 80 tubes of 55 cm³ each. The seedlings were grown in full sunlight, and topdressing fertilization with macro and micronutrients, along with different doses of potassium (K), using potassium chloride (KCl) as a source, was applied. After the potassium fertilization was completed, measurements of height (H) and collar diameter (CD) were taken to standardize the seedlings according to each treatment (K dose), and they were transplanted into 5 dm³ capacity pots filled with a substrate composed of 70 % subsurface soil and 30 % commercial substrate. The treatments consisted of a factorial of two irrigation regimes (with and without suspension) by five levels of topdressing fertilization with K (0, 75, 150, 225, and 300 mg dm - ³), arranged in a completely randomized design with 4 repetitions, each pot composing a sample unit. After 15 days of transplantation, irrigation was suspended in half of the pots for 21 days, and the number of leaves (NL) was counted, along with recording visual symptoms of water stress during this period. At the end of the experiment, new measurements of height (H), collar diameter (CD), shoot dry matter (NL) were taken, growth increments were calculated, and stomatal density, chlorophyll index, relative water content, and dry matter were determined. Using the data of height (H), collar diameter (CD), shoot dry matter (SDM), root (RDM), and total (TDM), seedling quality ratios were calculated: SDM/RDM, H/CD, and Dickson Quality Index (DQI). The data were analyzed using analysis of variance (p<0.05), and those indicating significant interaction were subjected to regression analysis within the qualitative factor. Analyzing the statistical data, it was observed that potassium fertilization positively influenced the initial growth of the seedlings in all treatments, with the estimated optimum dose being 286 Kg dm -3 of K. The result of the variables with the factors of K doses and irrigation of Eucalyptus camaldulensis Dehnh seedlings showed a significant difference of 5% only for irrigation.