Qualidade da fibra, crescimento e produtividade do algodoeiro herbáceo sob irrigação.

Abstract

Cotton has a great potential to grow in the semiarid region, due to favorable climatic conditions. However, some technological steps must be improved such as water management in plants. This work aimed to evaluate the effect of five irrigation depth on growth, yield and fiber quality of two cultivars of upland cotton. The experiment was conducted at the Experimental Station of Embrapa Cotton, in Barbalha, CE, in the period of July to December 2010. Treatments consisted of a factorial combination of two cultivars of upland cotton (BRS Aroeira, BRS Araripe ) and five irrigation depth (260.93, 418.93, 514.21, 711.81 and 894.68 mm). The experiment was carried out on a split plot experimental design, with ten treatments and four replicates, totaling 40 experimental units. The amount of water replacement (WR) for each treatment and irrigation event was calculated according to the reference evapotranspiration (ET0), determined by the Penman-Monteith method, multiplied by the crop coefficient (Kc) (WR = ET0 * Kc in mm). At harvest it was measured and evaluated, on 10 plants per plot, the stem diameter, plant height and leaf area. Were harvested and weighed the two central lines of each plot and collected 20 cotton bolls in the middle third of the plant, determining production per plot and its respective seed cotton yield per hectare and the fiber quality. The fiber quality variables analyzed were: length, uniformity, short fibers, strength, elongation, micronaire, maturity, degree of yellowing and reflectance index. The means for each treatment were compared by Tukey test at 5% probability for the qualitative factor (cultivars) and regression analysis for the quantitative factors (water depth), using the SISVAR statistical program. It was observed that irrigation affected significant the stem diameter, plant height, leaf area, yield and mean boll weight, while the cultivars affected significantly leaf area, yield and mean weight of bolls. It was also found interaction between cultivars and irrigation for the same variables affected by cultivars. With respect to fiber quality, irrigation significantly increased the length, short fiber index, strength, micronaire, maturity and reflectance of the fiber. Cultivars influenced significantly the percentage, length and color of the fiber. The highest productivity and better fiber quality was obtained with the BRS Araripe cultivar irrigated with 514.21 mm. All fiber quality components analyzed were well suited to the standards required by the modern textile industry.