Efeitos de deficits hídricos no crescimento, desenvolvimento e produção de cultivares do algodoeiro herbáceo (Gossypium hirsutum L. r. latifolium Hutch).

Abstract

The main objective of this work was to study the effects of different water deficits on the growth, development and production of cultivars (BR - 1; PR4139; SU 0450-8909 and IAC-19) of the herbaceous cotton plant (Gossypium Hirsutum, L. latifolium Hutch). The experiment was conducted at the National Cotton Research Center of the Brazilian Agricultural Research Corporation (CNPA / EMBRAPA) in Campina Grande -PB, under potting conditions, adopting experimental design in randomized blocks, in a 4 x 6 factorial scheme, with 3 replicates, where cultivars and water deficits were considered. The treatments corresponded to 10, 15, 20 and 25 days of deficits, started at 45 days post-planting (floral initiation phase), and two periods of consecutive deficits of 15 days, applied between 15 and 45 days post-planting (pre-flowering phase) together the control (without deficit), for comparison purposes. In all treatments, soil moisture content was maintained at field capacity until the beginning of the water deficit period. After this period, for each treatment, the humidity was raised to the previous level and maintained until the end of the crop cycle. The results showed that the water deficits significantly affected the variables related to the growth and development of the cultivars studied, 4 such as: height of plants, leaf area, weight of shoot dry matter and root, besides the root / shoot ratio. Among the cultivars, SU 0450-8909 revealed, in the most cases, higher height; leaf area; root system and higher root / shoot ratio, the relative water content (TRA) in the plant was proportionally affected by the soil moisture levels, however, the variations due to the cultivars were small. Soil moisture levels during the periods of deficits were equivalent to tensions higher than 15 atm. Water deficits slowed the flowering and opening of the cocoons around 10 to 30 days, and significantly affected the fall of flowers / plant, and there were no significant differences between cultivars. For the production, it was verified that the control exceeded all treatments of deficits, at the level of 1% of probability, which in turn, did not differ among themselves. Except for the cultivar SU 0450-890.9, the water deficits applied in the floral initiation phase, even those of smaller amplitudes, promoted drastic reductions in the yields of the cultivars, mainly IAC-19. For the deficit applied in the pre-flowering phase, the cultivars BR-1 and PR-4139 showed the highest and lowest yields. The study also showed that, once the survival of after periods of water deficits, at least 55-60% of their potential yields may be reached. Considering the growth, development and yield: (relative of cultivars studied, under water deficits, the study revealed SU 0450-8909 as the cultivar that presented better ability to tolerate water scarcity, and IAC-19, as the most unfavorable. However, the small volume of soil used could have masked, in part, the effects of the treatments, therefore, similar studies are suggested in field conditions.