Crescimento e produção do algodoeiro colorido marrom escuro CNPA 2002/26 sob estresse salino.

Abstract

Upland cotton (Gossypium hirsutum L. r. latifolium Hutch) under irrigation is one of the main agricultural alternatives for the semi-arid the Brazilian Northeast. Considered as tolerant to salinity, it makes possible the use of salt affected soils and of the waters considered inadequate for sensitive crops, as well as, the possibility to produce colored fibers, a product " environmental correct". This in absence of need for artificial coloration does not pollute the environment. The objective of present research was to study the effects of different salinity levels and composition of the irrigation water on the germination, growth and yield of the upland cotton (Gossypium hirsutum L. r. latifolium Hutch) - line CNPA 2002/26 - Dark Brown Cluster. For this, an experiment was conducted under greenhouse conditions at Embrapa - Cotton, Campina Grande - PB, using as substrate a Neossolo regossol of sandy loam texture, initially classified as non saline. The experiment was conducted during the period of April to September of 2003 in a 6 x 2 factorial scheme using completely randomized design with three replications. The effects of 6 of water salinity levels -ECw (2.0, 3.5, 5.0, 6.5, 8.0 and 9.5 dSm"1) and 2 irrigation water compositions with Na/Ca ratios (9.5/0.5 and 6.0/4.0) in chloride forms, were studied. The variables analyzed were germination and growth (plant height, number of leaves, leaf area, dry weight of the aerial part total plant and root weight), physiological indexes (absolute and relative growth and ratio of leaf area) and production variables (number of capsule and it's mean weight). The obtained results showed no abrupt alterations of the soil pH with the treatments and in spite of leaching; there was increase of the electrical conductivity of soil (EC) at the end of experiment and reduction of the water consumption by the plant, indicating that the plants suffered water stress induced by the high saline levels. The results also showed that the growth variables were more sensitive than the production variables and, in a general way, the salinity levels were more xxx to plants than the composition the irrigation water. Although the significant effects of the salinity levels were observed on most of the variables analyzed, the results showed an appreciable yield decrease for salinity levels higher than 6.5 dSm"1. The average yield obtained with the level of ECw 8.0 dS m"1 was 37.81 % of that obtained with the level of 2.0 dSnf1. Thus, preliminarily, the cotton line used in the present study is tolerant to the salinity.