Efeito do potássio em plantas jovens de Bambusa vulgaris Schared ex Wendland cultivadas em sistema hidropônico

Abstract

Bamboo is a quite promising crop in Brazil. It is employed for diverse purposes, from simple craftwork to high-resistance paper and energy production. However, literature in Brazil on fertilizing this crop is scarce. Among the essential elements for the plant, potassium is responsible for the activation of more than 60 enzymes. A lack of potassium causes a substantial imbalance in vegetal development. The aim of the present study was to assess the responses of bamboo to different levels of potassium and obtain data for estimating a recommendation formula for the rational fertilization of bamboo crops. The experiment was conducted in a greenhouse at the Chemistry Department of the Universidade Federal Rural de Pernambuco (Brazil) in a randomized block design, with six replications and six doses of potassium: zero, 0.5, 1.0, 2.0, 5.0 and 10.0 mmol.L-1. Bamboo plants were cultivated for 90 days in pots, employing a hydroponic system with static aeration. Growth variables and organic solute contents were assessed. The addition of potassium led to an increase in plant height, tiller and sprouts, and shoots biomass and the allocation of biomass in the roots; a reduction in both fresh and dry biomass of the leaves, stalk and roots, the allocation of biomass in the leaves and stalk, and in growth rates comparing to the treatments with 0.0 and 10.0 mmol.L-1 of potassium. Regarding to solute content, bamboo plants had different answer to potassium treatments. Chlorophyll a, b and total chlorophyll, there was a reduction proportionate to the increase in potassium content in the nutritive solution. The chlorophyll a/chlorophyll b ratio changed from 0.98 to 1.42. The increase in organic solutes was proportional to the potassium content in the nutrient solution. The 5.0 and 10.0 mmol.L-1 potassium treatments provided the highest increases in total soluble carbohydrates, reducing sugars, nonreducing sugars, total free amino acids, soluble proteins and free proline. The best potassium content in the nutritive medium for hydroponic cultivation is between 0.5and 1.0 mmol.L-1, where as 10.0 mmol.L-1 is considered a stressing dose.