Índices biométricos, fisiológicos e de produtividade da cana-de-açúcar em função de doses de gesso mineral

Abstract

The objective of this study was to evaluate the growth, physiological aspects and the yield of three sugarcane genotypes under five levels of mineral gypsum. This research was carried out on Usina Santo Antônio, Fazenda Santa Rosa II, situated on São Luiz do Quitunde – Alagoas. The experimental design was in a complete randomized block design, arranged in a 5x3 factorial scheme with four replications. The treatments were composed of five different levels of mineral gypsum (0; 2,5; 5,0; 10,0 and 20,0 Mg ha-1) and three sugarcane genotypes (RB011941, RB92579 and RB991536). Each plot consisted of five rows, each one 10 m long, spaced 1,10 m apart. Plant growth was evaluated on two phenological phases. One year after planting, the SPAD index and photochemical efficiency were evaluated. On the same period, +3 leaves were collected in order to evaluate the plant nutritional status. On 420 days after planting, the productivity of stalk and sugar were evaluated and the technological analyses of sugarcane juice were made. The development of the root system was evaluated in three different depths one week after harvest. The RB011941 genotype had more leaves compared to the other genotypes on 115 days after planting. The RB92579 genotype was the highest on an evaluation made on the maturation phase (396 days after planting). The RB92569 displayed high phosphorus and potassium levels while the RB011941 genotype displayed higher magnesium and sulfur, compared to other genotypes. Photochemical efficiency and SPAD index values didn’t show any difference between the genotypes. The productivity of stalk and sugar was higher on the RB92579 genotype, with an average of 157,90 and 24,10 t ha-1, respectively. The mineral gypsum didn’t influence any of the variables analyzed, with the exception of leaf area on maturation phase (396 days after planting), which decrease linearly with the increase of the gypsum levels applied and root mass on the layers 20-40 and 40-60 cm of depth, providing an increase of approximately 1,46 g dm-3 and 2,04 g dm-3 on the root mass with the highest technical efficiency (13,96 and 12,54 Mg ha-1), respectively, compared to the treatment without gypsum.