Manejo da irrigação em cultivares de algodoeiro herbáceo no semiárido brasileiro

Abstract

Cotton (Gossypium hirsutum L.) is a tropical climate crop and Cotton (Gossypium hirsutum L.) grown in most warm climate regions, presenting ideal characteristics for the semiarid region of northeastern Brazil. Due to the droughts that occur periodically in this region, it is necessary to use technologies such as irrigation practice to minimize the effect of water deficit on this crop. This study was conducted to evaluate irrigation management, water suppression and water deficit in different phenological phases, in herbaceous cotton cultivars in the Brazilian semiarid, and their effects on yield components, water efficiency, fiber quality and accumulated degree days. For two consecutive years, field experiments were conducted in the Apodi - RN. In 2016, the treatments were constituted during different phenological stages (First Square, First Flower, Peak Bloom and First Open Boll) and four cultivars (BRS 368 RF, BRS 336, BRS 432 B2RF, BRS 430 B2RF). In 2017, the experiment was divided between irrigation management methods (Irrigameter, Crop evapotranspiration and SmartCrop) and periods of water deficit (70% and 50% of the crop evapotranspiration at the beginning of flowering and 70% and 50% of the crop evapotranspiration at the peaky of floewring) and 4 cultivars (BRS 433 FL B2RF, BRS JADE, BRS 416 e BRS 430 B2RF). The experiments consisted in randomized block, arranged in a split-splot design with four replicates. The data were subjected to variance analysis by F test, being the treatment means of the factors compared by Tukey test at 5% probability. Productivity of the cotton seed, lint percent, lint yield, number of open bolls per plant, fiber quality traits determined were evaluated. The analyzed fiber quality variables were: fiber percentage, length, uniformity, short-fiber index, resistance, elongation at rupture, micronaire index, maturity, degree of yellowing, reflectance degree and count strength product (CSP) index. SmartCrop and ETc managements provided the best results of fiber quality and yield components, while Irrigameter resulted in higher water use efficiency. The suppressions in flowering resulted in lower values of crop yield components. Except for the elongation at rupture, in general, there was no significant difference for fiber characteristics between control treatment and applied deficits, because all fiber quality characteristics acceptable for the domestic textile industry. Accumulated degree days also varied according to water stress, with a shortened phenological cycle for treatments with water deficit in comparison to the control without stress.