Tratamento de sementes, herbicidas, temperatura do ar e seus efeitos em arroz irrigado.

Abstract

The sowing time is a major factor to be considered to obtain high yields in irrigated rice. However, when sowing is performed early, low temperatures can cause stress to culture, reducing its emergence rate and the shelf plants and reduce the selectivity of herbicides applied. Seed treatment can be an alternative to increase rice emergence speed and improve the selectivity to herbicides in the initial phase of development of culture. In view of the above, the objectives of this study were to make a literature review about the seed treatment (Chapter I); evaluate the effect of seed treatment on germination and early establishment of rice seedlings in different sowing times and selectivity to herbicides (Chapter II); characterize the biochemical parameters of oxidative stress in rice subjected to low temperatures and the application of herbicides (Chapter III); and evaluate the initial performance resulting from the application of fertilizers in the herbicide selectivity in irrigated rice. Based on the results obtained it can be concluded that the treatment of seeds with gibberellic acid positive influence on the initial growth of the rice seedlings, the optimum temperature (25 °C) and suboptimal (17 °C) and treatment with the combination of dietholate dietolate + fipronil + carboxin + thiram, adversely affected the germination and vigor at both temperatures, reducing the physiological performance of rice seeds in the laboratory. In the field the seed treatments had no effect on phytotoxicity and selectivity of herbicides, which temperature is the determining factor. The bispyribac-sodium herbicide was more toxic to plants when planting occurred at the beginning of September, since when sown in October the major symptoms of phytotoxicity were presented by plants treated with the herbicide profoxidim. Seed treatment does not influence in plant defense responses and the herbicide treatments induce different responses in rice plants by stimulating the secondary metabolism of the same. Low temperature situations with herbicide application may impair the absorption by the plant. The application of liquid fertilizer in rice does not influence the initial development and the sensitivity of the rice herbicide culture. The application of herbicide profoxidim was the treatment that presented the highest level of phytotoxicity in rice.