Glyphosate, 1,1’- dimethyl-4,4’-bipyridinium dichloride and Atrazine induces changes in Soil organic carbon, bacterial and fungal communities in a tropical alfisol

Abstract

The increasing use of agrochemicals for weed control has raised concerns about theirecotoxicological effects on soil micro-biota communities and soil functions which serveas indicators of soil quality. Thus, this study was conducted to evaluate the effects ofcontinuous field applied herbicides glyphosate, paraquat, atrazine and their combinedforms over a period of five years on soil organic carbon, bacterial and fungal populationin Akure, Ondo State Nigeria. Soil samples from farmer’s field which have been exposedto continuous herbicide application were collected and analysed for physio-chemicalproperties, organic carbon, total bacterial and fungal population. Simultaneously, soilsamples designated as control were collected from adjacent fields with no history ofherbicide application and analysed. Results showed a significant (P=0.05) 86% and128% increase in bacterial population from glyphosate and atrazine treated fieldsrespectively and 42% decrease in paraquat and Glyphosate + paraquat fields whencompared with the untreated field. A significant 35% decrease in fungal population wasobserved in fields applied with atrazine and a further 10% decrease in fungalpopulations in all herbicide treated fields irrespective of herbicide type andcombinations when compared with the untreated field. These changes also correlateswith the abundance of beneficial microbes such as Pseudomonas aeruginosa,Pseudomonas fluorescens, Proteus mirabilis, Aspergillus flavius with a probable influenceon plant growth promotion and potentials for biodegradation of persistent herbicides.SOC, SOM and pH was significantly (P=0.05) increased in atrazine and atrazine +paraquat treated fields when compared with the untreated fields and other herbicidetreatments.