Adubação com magnésio, qualidade do caldo e produção de açúcar pelas variedades de cana RB867515 e RB92579

Abstract

There have been questions about the critical level of magnesium in the soil and some authors mention that the sufficiency range should be between 0.4 and 0.5 cmolc dm-³. Thus, the present study evaluated the nutritional status, broth quality and sugar production of sugarcane varieties RB867515 and RB92579, in the cane-plant cycle, as a function of doses of magnesium applied at the bottom of the groove of planting. The study was implemented in a soil with Mg content equal to 0.61 cmolc dm-³ and was conducted in a randomized complete block design with four replicates. The study was a 2x5 factorial: two varieties of sugarcane: RB867515 and RB92579, and five doses of magnesium: zero, 60, 120, 180 and 240kg per hectare, using Mg as the source of magnesium oxide commercial. The plots were constituted of seven furrows of five meters lengths with 1.0 meter of spacing. All plots received phosphate and potassium fertilization at the dose of 100kg of phosphorus and 150kg of potassium per hectare, without nitrogen fertilization. In the maximum growth phase, the nutritional status of sugarcane was evaluated. One year after planting, when the sugar cane as ripe, the cane-plant was harvested for the quality evaluation of the broth and sugar produciton of the varieties. The mean values of nutrient leaf contents as well as those of broth quality and the production of industrializable stalks and sugars were submitted to analysis of variance. There was no effect of magnesium fertilization on any of the analyzed variables. In relation to the nutrient content in leaf +3 nutritional deficiency was observed only potassium, cooper and manganese. There was a varietal effect for the nitrogen, phosphorus, magnesium, sulfur, manganese and zinc leaf contents. The RB867515 had a higher leaf content for the nutrients Mg, S, Mn and Zn, for the others mentioned previously the leaf contents of RB92579 were larger than those of RB867515. There was a difference between the varieties in the production of industrializable stalks and sugars: RB928579 had average yield of industrializable stalks and sugars, respectively, of 96 and 13.7tons per hectare, surpassing RB867515 about 10%. The purity of the broth of RB92579 was 86%, only 1.86% greater than that of RB867515 but with significant effect. The results of this study confirm reports of other researchers reporting Mg contents of the order of 0.50 cmolc dm-³ are sufficient for an adequate nutrition of.