Levantamento fitossociológico de plantas daninhas em arroz irrigado

Abstract

Phytosociological survey are ecological assessment methods, in order to provide, broadly, the composition and distribution of plant species in a given plant communities. To phytosociological survey of weeds in paddy rice, beyond the identification of weed species, there is also need for quantitative analysis of these species. The application of quantitative phytosociological survey or a given place at a given time allows momentary assessment of vegetation composition. Thus, the phytosociological method is a tool that, if used properly, allows several inferences about the community in question. The aim of this research was to identify and quantify the main weeds present in the early stages growth and pre-harvest in paddy rice through phytosociological survey conducted in the city of Itaqui-RS. The phytosociological survey of weeds in paddy rice was carried out in two different periods: the first collection in the early crop development (between 20 and 25 days after sowing), before the application of herbicides, and the second in pre-harvest. The weed species were identified and quantified by the square inventory method (1.0 x 1.0 m), total of ten random sampling in an area of ½ hectare in each collected areas . The phytosociological surveys were conducted in three farms in Itaqui - RS. The frequency was recorded, relative frequency, density, relative density, abundance, relative abundance, relative importance index and similarity index. In total, were identified 11 weed species, with five distinct families. The Cyperaceae and Poaceae families to be found more frequently, were the main among the five identified. The density of weeds was higher in the early development stage than in the pre-harvest crop in all the sampling sites, in the Granja Oliveiras, Granja Fonte Rica and Granja Angico, the values obtained for 11 this variable in the early development crop was 14.5, 31.5 and 24.6 plants per m², respectively, since the values obtained pre-harvest period was 6.0, 3.1 and 2.8 plants per m². The similarity index early / pre-harvest was 0.88 for the survey in first property and 0.54 to second and 1.0 to the third, therefore, the best index of similarity between species of the weed flora region at Itaqui in Rio Grande do Sul, in in two seasons studied in paddy rice.