Laboratory and greenhouse studies were conducted to assess the allelopathic potential of 12 rice cultivars on barnyard grass. Polyethylene glycol （PEG） was used to determine the influence of osmotic potential on the...Laboratory and greenhouse studies were conducted to assess the allelopathic potential of 12 rice cultivars on barnyard grass. Polyethylene glycol （PEG） was used to determine the influence of osmotic potential on the bioassay materials. Effect of different concentrations of stem, root, and leaf extracts of rice cultivars on seed germination, radicle and primary shoot length of barnyard grass seedlings, and rate of respiration of root pieces were investigated in the laboratory experiments. Shoot height and dry weight of weed stands were studied in the greenhouse, Also total peroxidase activity, chlorophyll pigment and mitotic index were determined. Results indicated that, among rice cultivars, Mehr, Tarom-mahali, G3, Nemat, and Shahpasand caused the most inhibition effects on investigated factors. Amol-3 showed the least negative effects on growth of seedlings and stands of barnyard grass. In laboratory, the Mehr cultivar demonstrated the maximum inhibitory effects by reducing barnyard grass seed germination percentage （88%）, radicle length （100%）, primary shoot length （83%）, and root respiration （85%） Cell division, expressed as mitotic index, was significantly reduced in the presence of rice aqueous extracts. Mehr cultivar had higher inhibitory effect on mitosis compared to Amol-3. In greenhouse, the same cultivar showed the maximum inhibitory effect by reducing barnyard grass height （45%） and dry weight （64%）. With increase in extract concentration, the inhibitory effect increased. Leaf extract from rice plants was more effective compared with the root and stem extracts. Comparison of rice cultivars and PEG indicated that any reduction in germination and growth of barnyard grass using rice extract concentrations of 5% and 10% must have been the result of allelochemicals in the extracts. Lower extract concentrations showed a more pronounced inhibitory effect in the laboratory as compared to the greenhouse studies. These results suggest that rice leaf extracts may be a source of natural herbicide.展开更多
Excessive MSW （municipal solid waste） production is a growing management problem for cities in developing countries, such as South Africa. A major problem in the city of Tshwane is that all the MSW generated in the ...Excessive MSW （municipal solid waste） production is a growing management problem for cities in developing countries, such as South Africa. A major problem in the city of Tshwane is that all the MSW generated in the city is currently being landfilled with very little recycling initiatives. Selective waste collection and sorting waste fractions out of the waste stream have become a popular survival strategy for the economically excluded population in Tshwane. Reclaimers （waste pickers） work under severe and chronic occupational health and injury risk on landfill sites. The middlemen who purchase their recovered materials exploit and marginalize them. Environmental and social awareness is however a growing issue in South Africa. The study was conducted with the aim of investigating and proposing community recycling programs and technologies to be sustainably implemented in the city of Tshwane. Successful established community recycling programs in Brazil was investigated to verify its socioeconomic and environmental impacts in a sustainable waste management perspective. Community recycling initiatives have been increasingly used as a strategy to address both the MSW problem and urban poverty in Brazil. The study focused on the city of Tshwane, but it can be argued that the findings can be implemented in any other South African municipality and in other emerging countries in Africa.展开更多
文摘Laboratory and greenhouse studies were conducted to assess the allelopathic potential of 12 rice cultivars on barnyard grass. Polyethylene glycol （PEG） was used to determine the influence of osmotic potential on the bioassay materials. Effect of different concentrations of stem, root, and leaf extracts of rice cultivars on seed germination, radicle and primary shoot length of barnyard grass seedlings, and rate of respiration of root pieces were investigated in the laboratory experiments. Shoot height and dry weight of weed stands were studied in the greenhouse, Also total peroxidase activity, chlorophyll pigment and mitotic index were determined. Results indicated that, among rice cultivars, Mehr, Tarom-mahali, G3, Nemat, and Shahpasand caused the most inhibition effects on investigated factors. Amol-3 showed the least negative effects on growth of seedlings and stands of barnyard grass. In laboratory, the Mehr cultivar demonstrated the maximum inhibitory effects by reducing barnyard grass seed germination percentage （88%）, radicle length （100%）, primary shoot length （83%）, and root respiration （85%） Cell division, expressed as mitotic index, was significantly reduced in the presence of rice aqueous extracts. Mehr cultivar had higher inhibitory effect on mitosis compared to Amol-3. In greenhouse, the same cultivar showed the maximum inhibitory effect by reducing barnyard grass height （45%） and dry weight （64%）. With increase in extract concentration, the inhibitory effect increased. Leaf extract from rice plants was more effective compared with the root and stem extracts. Comparison of rice cultivars and PEG indicated that any reduction in germination and growth of barnyard grass using rice extract concentrations of 5% and 10% must have been the result of allelochemicals in the extracts. Lower extract concentrations showed a more pronounced inhibitory effect in the laboratory as compared to the greenhouse studies. These results suggest that rice leaf extracts may be a source of natural herbicide.
文摘Excessive MSW （municipal solid waste） production is a growing management problem for cities in developing countries, such as South Africa. A major problem in the city of Tshwane is that all the MSW generated in the city is currently being landfilled with very little recycling initiatives. Selective waste collection and sorting waste fractions out of the waste stream have become a popular survival strategy for the economically excluded population in Tshwane. Reclaimers （waste pickers） work under severe and chronic occupational health and injury risk on landfill sites. The middlemen who purchase their recovered materials exploit and marginalize them. Environmental and social awareness is however a growing issue in South Africa. The study was conducted with the aim of investigating and proposing community recycling programs and technologies to be sustainably implemented in the city of Tshwane. Successful established community recycling programs in Brazil was investigated to verify its socioeconomic and environmental impacts in a sustainable waste management perspective. Community recycling initiatives have been increasingly used as a strategy to address both the MSW problem and urban poverty in Brazil. The study focused on the city of Tshwane, but it can be argued that the findings can be implemented in any other South African municipality and in other emerging countries in Africa.
