Cyanobacteria, pesticides and rice interaction

Abstract

Cyanobacteria (blue-green algae) are widely distributed in tropical wet land rice fields where they play important role in building soil fertility. Due to their ability to photosynthesize and fixing atmospheric nitrogen, these are used as inoculants in rice fields to obtain additional benefits. The fertilizers and pesticides are being extensively used and therefore, it is necessary to find out effects of agrochemicals particularly pesticides on non target organisms like cyanobacteria. In the present investigation interaction of pesticides and cyanobacteria has been studied at different stages of rice crop. It was observed that application of herbicide butachlor decreased growth and N2-fixation of both native and inoculated cyanobacteria whereas insecticide metacid application was found to increase these attributes. The interaction of algal inoculation and both the biocides application were superior than algal inoculation with the herbicide application on both algae and rice. It is concluded from this study that herbicides application affected adversely cyanobacteria but insecticide application was favorable to them and application of both biocides was better than herbicide alone. Therefore judicious use of these chemicals and cyanobacteria in rice fields are suggested.