Persistence of the herbicide butachlor in soil after repeated applications and its effects on soil microbial functional diversity

Abstract

Effects of repeated applications of the herbicide butachlor (N-(butoxymethyl)-2-chloro -N-2′,6′-dimethyl acetanilide) in soil on its persistence and soil microbial functional diversity were investigated under laboratory conditions. The degradation half-lives of butachlor at the recommended dosage in soil were calculated to be 12.5, 4.5, and 3.2 days for the first, second, and third applications, respectively. Throughout this study, no significant inhibition of the Shannon-Wiener index H′ was observed. However, the Simpson index 1/D and McIntosh index U were significantly reduced (P ≤ 0.05) during the initial 3 days after the first application of butachlor, and thereafter gradually recovered to a similar level to that of the control soil. A similar variation but faster recovery in 1/D and U was observed after the second and third Butachlor applications. Therefore, repeated applications of butachlor led to more rapid degradation of the herbicide, and more rapid recovery of soil microorganisms. It is concluded that repeated butachlor applications in soil had a temporary or short-term inhibitory effect on soil microbial communities.

Keywords:

• Biolog
• butachlor
• herbicide
• microbial diversity
• soil

Acknowledgments

This work was jointly supported by grants from the National High Technology Research and Development Program of China (Nos. 2006AA06Z386 and 2007AA06Z306), the China Postdoctoral Science Foundation (No. 20070421174), the National Natural Science Foundation of China (No. 30771254), the Zhejiang Provincial Natural Science Foundation (No. Z306260), and the National Key Technology R & D Program of China (No. 2006BAI09B03).

Notes

^a Values are means of three replicates.

^b RSD: relative standard deviation.

^a Degradation of butachlor in soil followed a first-order function (C = C₀∗e^{− k∗ t} ). Degradation half-lives of butachlor (DT₅₀) in soil were obtained by the function DT₅₀ = ln2/k. Each value is a mean of three replicates. DT₅₀ values followed by different letters within a column are significantly different (P ≤ 0.05).