The influence of vegetation, microbial inoculation, and aging of pesticide residues on the degradation of atrazine and metolachlor in soils

Abstract

The abilities of native prairie grasses, big bluestem (Andropogon gerardii), Indian grass (Sorghastrum nutans L.), and switch grass (Panicum virgatum L.) and two soil bacteria, Agrobacterium radiobacter J14a and Pseudomonasfluorescens UA5-40, to degrade the herbicides atrazine and metoiachlor were evaluated in soils taken from two pesticidecontaminated sites in Iowa (Alpha and Bravo). J 14a and vegetation significantly decreased the concentration of atrazine in Alpha soil when the initial concentration of atrazine was 93.3 |ig g*1. However, they had no effect on the degradation of atrazine when the initial concentration of atrazine was 4.9 ng g1. The effect of Jl4a on the degradation of atrazine was not enhanced by the presence of the plants. Inoculation with J 14a and addition of the plants did not increase the atrazine degradation in the Bravo soil. The degradation of atrazine by J 14a and the indigenous atrazine-degrading microbial population in Bravo soil was not affected by the presence of exogenous nitrogen. Vegetation significantly increased the number of atrazine-mineralizing microorganisms in J14a-inoculated Bravo soil, and exogenous N significantly increased the number of the atrazine-mineralizing microorganisms. In the Bravo soil without vegetation and N amendment, atrazinemineralizing microorganisms were significantly more numerous in the uninoculated soil than in the J14a-inoculated soil. Inoculation of UA5-40 did not enhance the transformation of metoiachlor in either soil. The native prairie grasses significantly decreased the metoiachlor residues in both soils. Aging metolachlor-treated soils did not influence the degrading capability of the plants. Our results indicate that the degradative ability of J 14a and the native prairie grasses on atrazine is affected by the bioavailability of the compound and the presence of indigenous atrazine-mineralizing microorganisms. KeywordsAgrobacterium radiobacter J14a Pseudomonas fluorescens UA5-40 Atrazine Metoiachlor Bioavailability Vegetation N Amendment