WEED COMMUNITY COMPOSITION AND RICE HUSBANDRY PRACTICES IN NEW-SOUTH-WALES, AUSTRALIA

The composition of weed communities in rice fields is described in relation to crop husbandry and soil factors in New South Wales. Four species characterized the weed community: Cyperus difformis, Elatine gratioloides, Damasonium minus and Echinochloa crus-galli all occurred at over 70% of sites. Variation in floristic composition was mainly associated with less common species that were present in addition to these four. Intensity of rice cropping appeared to be a major environmental factor influencing community composition. The four character species, together with Diplachne fusca and Chara were positively correlated with intensive rice production. Two groups of plants were found to be associated with less intensive production. A group of semi-aquatic and terrestrial pasture species commonly occurred after sod sowing (direct drilling) of rice and/or pasture rotation. The second group comprised native wetland species which were mainly associated with sites in which rice cropping was more recent and less intensive. The data suggest that the weed communities are not in equilibrium with the comparatively recent practice of rice farming in the region. Continuation or intensification of rice cropping in the study area may reduce the incidence of wetland species and favour the character and pasture species. The range of husbandry practices available to rice growers and their flexible application could also contribute to the maintenance of disequilibrium between the weed populations and their environment, thus preventing the build-up of some species.