Management of water cabbage (Limnochairs flava (L.) buchenau) in wetland rice ecosystem

Abstract

An investigaton entitled ‘Management of water cabbage (Limnocharis flava (L.) Buchenau) in wetland rice ecosystem’ was carried out in the wetland of the Instructional farm attached to the College of Agriculture, Vellayani from February 2011 to January 2012. The major objectives of the experiment were, to study the biology of water cabbage (Limnocharis flava (L.) Buchenau), to evaluate certain new generation herbicides for managing it and to assess the potential of the weed biomass as an organic source. For the study of weed biology (Part I), a part of the weed infested field was selected for the experiment and prepared thoroughly as in the case of rice cultivation and the sample plants were observed from their emergence onwards. The ontogeny of the weed, its vegetative, and reproductive characters and also their allelopathic influence on germination and early growth of rice were studied. The field experiment on weed management (Part II) was laid out in Randomised Block design with eight treatments replicated thrice. The treatments included azimsulfuron @20 and 30 g a.i. ha-1, bispyribac sodium @20 and 30 g a.i. ha-1), (metsulfuron methyl+ chlorimuron ethyl) @ 4 and 6 g a.i. ha-1 and 2, 4-D @ 1 kg a.i. ha-1 along with a weedy check as control. The potential for utilization of the weed biomass through vermicomposting (Part III) was also assessed during the investigation. The data on weed biology indicated that water cabbage had very efficient reproductive mechanism which explains the invasive nature of the weed. A single plant was found capable of producing more than one lakh seeds and about 90 per cent of them germinated under favourable conditions. The plants exhibited pseudovivipary, through production of ramets which gave an additional advantage for the plant to spread. Germination studies revealed that maximum weed seed germination occurred under direct sunlight in crowded condition in the wetland soil condition. Direct sunlight was found necessary for the seed germination. Allelopathic studies showed that the fresh leachate of water cabbage was found to exert a positive effect on the vigour index of rice seedlings while substantial reductions in seedling growth were observed when treated with decayed plant leachate. The results of the field study on weed control efficiency of the different herbicides indicated that 2, 4-D @1 kg a.i. ha-1 was most effective for controlling water cabbage. Among the new generation herbicides (metsulfuron methyl + chlorimuron ethyl) @ 6 g a.i. ha-1 and bispyribac sodium @ 30 g a.i. ha-1 were equally effective for controlling water cabbage. The results of soil microbial studies indicated that the soil treated with the herbicides had much higher microbial population than the untreated plots except in the case of bispyribac sodium. The cost of managing the weed by using new generation herbicide was found considerably lower than that by manual weeding. The chemical analysis of the vermicompost prepared from the weed biomass recorded favourable nutrient composition. The micronutrients and heavy metals were within the safe limits except for the copper content. More over, the luxuriantly growing weed biomass was promising for bioremediation, to remove pollutants from aquatic ecosystems.