SEEDLING GROWTH OF TREE SPECIES UNDER DOSES OF HYDROGEL AND TWO LEVELS OF LUMINOSITY
ABSTRACT Hydrogels (polyacrylamide compounds) are recommended in agriculture and forestry as soil conditioners because they are able to absorb water and increase its stocks in the soil. The aim of this study was to determine the most suitable dose of hydrogel to establish seedlings of Enterolobium contortisilliquum (Vell.) Morong under two levels of luminosity. Seedlings of Enterolobium contortisilliquum (Vell.) Morong were planted in pots, following a design of subdivided plots, consisting of two levels of luminosity in the plots: full sun and 50% luminosity, and 10 doses of hydrogel in the sub-plots: 0.0, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5 and 6.0 g L-1. Seventy-two days after the seedlings were transplanted to the pots, plant height and diameter were determined, together with the height to diameter ratio, root length and diameter, shoot and root dry weight, and the shoot to root ratio. The lowest ratios between height and stem diameter (8.50 and 8.68) occurred in the seedlings in full sun at the doses of 0 and 2 g hydrogel L-1 respectively. For shaded seedlings the lowest ratio (8.14) occurred at the dose of 3.0 g L-1, but with a lower coefficient of determination (R2 = 0.68). Shoot dry weight increased with the dose of 2 g L-1 in full sun, and 3.5 g L-1 under shaded conditions. The doses of hydrogel giving the best initial development in seedlings under evaluation were 2 g L-1 in full sun and 3.5 g L-1 in the shaded environment. Although a response by the species to the doses of hydrogel was found, the benefits of the polymer were not evident under the conditions of the present study.