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

The bacteria Agrobacterium radiobacter J14a and Pseudomonas sp. strain ADP and the enzyme atrazine chlorohydrolase all had a significant effect on the degradation of atrazine in Alpha soil, a soil with a low indigenous atrazine-mineralizing population. However, inoculation with J14a did not increase the atrazine degradation in Bravo soil, a soil with a high number of indigenous atrazine-mineralizing microorganisms. This suggests that the ability of J14a to enhance the degradation of atrazine is affected by the presence of indigenous atrazine-mineralizing microorganisms. Inoculation of Pseudomonas fluorescens UA5-40 did not enhance the transformation of metolachlor in either soil.; The ability of native prairie grasses, big bluestem (Andropogon gerardii), Indian grass (Sorghastrum nutans L.), and switch grass (Panicum virgatum L.), to degrade atrazine was influenced by the presence of indigenous atrazine-mineralizing microorganisms and the duration of the grasses in soil. Vegetation significantly decreased the concentration of atrazine in Alpha soil, but not in Bravo soil. The significant effect of the plants on atrazine degradation in Alpha soil only occurred 57 days after the transplanting of vegetation, but not 28 days after the transplanting of vegetation. The native prairie grasses had a significant effect on the degradation of metolachor in both soils.; The degradative abilities of J14a, atrazine chlorohydrolase, ADP, and the native prairie grasses were influenced by the bioavailability of atrazine. J14a and vegetation significantly decreased the concentration of atrazine in Alpha soil when the initial concentration of atrazine was 93.3 μg g −1. However, they had no effect on the degradation of atrazine when the initial concentration of atrazine was 4.9 μg g−1 . The influence of aging the atrazine-treated soil on the bioavailability of atrazine depends on the length of aging. The bioavailability of high concentration of atrazine (100 μg g−1) significantly declined after 56 days of aging compared with that without aging. However, the bioavailability of atrazine did not significantly decline when aging time increased from 6 to 68 days. Our results suggest that the bioavailability of atrazine applied at a high concentration declines more slowly than that applied at field application rate.