Nutrição, aspectos fisiológicos e produtividade de cana-de-açúcar sob fertilização potássica

Abstract

The study evaluated the effect of potassium fertilization on nutrition, physiological aspects and productivity of sugarcane. Three experiments were performed, two in field and one in a greenhouse. Field experiments were performed at the Carpina Sugarcane Experimental Station (EECAC) and the Tabu distillery. The effect of six rates of K2O (0, 25, 50, 100, 200 and 250 kg ha-1) on two sugarcane varieties (RB92579 and RB962962) on EECAC and in one variety (RB992506) on Tabu were evaluated. The experimental design was in randomized blocks with four replications. Were evaluated the nutritional status (N, P, K, Ca, Mg, S, Cu, Zn, Mn and Fe), physiological characteristics (stomatal conductance, transpiration, liquid photosynthesis and internal CO2 concentration) in both experimental fields. In Tabu was also evaluated the concentration and critical levels of K in the soil and leaf, the content of total recoverable sugars (TRS) on the cane and physiological characteristics (catalase (CAT), superoxide dismutase (SOD), arcorbate peroxidase (APX) , Proline, protein, soluble sugars, chlorophyll A, B, Total, A/B and carotenoids) in the maturation phase (9 months). In the greenhouse experiment were evaluated the effect of five concentrations of K (0, 0.5, 1.0, 2.0 and 6.0 mmol L-1) in nutrient solution in two sugarcane varieties (RB92579 and RB992506 ). The experiment was carried out in randomized blocks in a factorial scheme (2x5) with four replications. The physiological aspects (CAT, SOD, APX, proline, protein, soluble sugars, chlorophyll A, B, Total, A/B and carotenoids) and dry mass production were evaluated. Analysis of variance and regression, for the quantitative data, were performed for all data. In the field, the rates of K2O applied promoted significant effect only for the experiment performed in the Tabu distillery. It was observed rise of foliar concentration of K, S, stomatal conductance and transpiration and decrease of Mg concentration in sugarcane leafs. It was also observed a quadratic effect of the K2O rates on sugarcane yield, with the increase in productivity observed up to 150 kg ha-1, and a linear increase in total sugars. The maximum agronomic efficiency rate was 150 kg ha-1 of K2O and the productivity of maximum agronomic efficiency was 116 t ha-1. Critical levels in soil and leaf were 0.18 cmolc dm-3 and 9.53 g kg-1, respectively. The application of K2O rates increased the levels of proline and the leaf pigments (chlorophyll a, b, total and carotenoids) up to the rate of 150 kg ha-1 in the maturation stage. In the greenhouse experiment, the rates of K+ applied in nutrient solution caused decrease in SOD and CAT enzyme activity and increase of cane protein content. Greater CAT and APX enzyme activity of was observed in the variety RB92579 than in RB992506. However, leaf pigment contents were higher in RB992506 variety. The K+ rates promoted a quadratic increase in sugarcane dry mass, with higher dry mass production observed in the RB992506 variety.