Qualidade microbiológica da água da cultura do arroz irrigado, no sul do Brasil

Total and fecal coliforms are bio-indicators of the environmental impact caused by anthropic action and are considered indicators of the microbiological quality of the water. In the cultivation of rice by irrigation much water is used and care in water management is required in order to increase the volume and quality of production while reducing the environmental impact. The objective of this research is to evaluate the quality of the irrigation water used in five rice-growing regions of the State of Rio Grande do Sul during the vegetative and reproductive phases. The results demonstrate that the indices of total and fecal coliforms in the rice field plots of the fields in all the rice producing regions of Rio Grande do Sul evaluated in this study were lower in the reproductive than in the vegetative phases. The irrigation channel presented low indices of fecal coliforms but a higher incidence of total coliforms. The data demonstrated that irrigated rice cultivation can alter the microbiological quality of the water in the plots by its potential capacity of circulating the nutrients with the result that the drainage water presents a smaller quantity of contaminating microbial agents. Key words: water, irrigation, fecal coliforms, rice fields.