Effect of Soil Moisture and Phosphorus Level on Degradation Kinetics of Glyphosate Pesticides

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the National Natural Science Foundation of China (41877072) and the Natural Science Foundation of Shaanxi Province (2019JQ-639).

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    【Objective】 In recent years, more attention has been paid to the persistence of glyphosate and its degradation product, ammethylphosphoric acid (AMPA), in soil, as well as their environmental risks. However, with a similar structure as phosphate and with a positive charge, glyphosate may compete with phosphate for adsorption sites on the surface of soil particles, thereby affecting its environmental behavior and the bioavailability of phosphorus in soil. Our aim was to investigate the degradation kinetics of glyphosate pesticide, soil available phosphorus and soil enzyme activity in Loess soil.【Method】 Laboratory experiments were carried out under different phosphate application levels (0, 50, and 100 mg.kg-1) and water conditions (20% field water capacity (20FC) and 60% field water capacity (60FC)).【Result】 The results showed that:1) The degradation rate of glyphosate was fast at the initial stage of spraying and gradually slowed down at the later stage under different levels of phosphate application and soil moisture. Different phosphate levels had no significant effect on glyphosate degradation while different soil moisture did. Also, the content of AMPA increased with the degradation of glyphosate, and there was no significant difference in the content of AMPA under different phosphate levels. However, the peak and variation characteristics of AMPA under different soil moisture significantly differed. The peak was reached on day 14 after spraying for 20FC and on day 7 for 60FC. In addition, the quantitative characteristics of glyphosate residues fitted the first-order kinetic degradation model, with a half-life time of 69.3~77.0 d (20FC) and 10.5~12.8 d (60FC). 2) After spraying glyphosate, the content of available phosphorus decreased first and then increased with the degradation of glyphosate, which was significantly affected by soil moisture. In addition, phosphatase activity was significantly inhibited after glyphosate application, while the activities of N-acetylamino-β-glucosidase, β-glucosidase and leucine aminopeptidase changed dynamically. Phosphate levels showed no significant effects on soil enzymes' activities while soil moisture did.【Conclusion】 The findings indicate that phosphorus level in Loess soil had no significant effect on the degradation characteristics of glyphosate, but soil moisture significantly affected the degradation rate of glyphosate and the residual level of its metabolite. Meanwhile, glyphosate application had a significant effect on the activities of available phosphorus and phosphatase, which may affect soil phosphorus cycling and plant utilization. Therefore, the feed-effects of glyphosate and soil phosphorus components as well as the related enzyme activities should be considered in follow-up studies, especially the relationship between the persistence of glyphosate and its metabolite and soil health indicators under drought conditions. This will provide scientific-based information to guide glyphosate use in Loess soil regions.

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DING Lingling, XUE Sha, YANG Xiaomei. Effect of Soil Moisture and Phosphorus Level on Degradation Kinetics of Glyphosate Pesticides[J]. Acta Pedologica Sinica,2024,61(2):469-483.

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  • Received:May 11,2022
  • Revised:November 15,2022
  • Adopted:February 10,2023
  • Online: April 11,2023
  • Published: March 15,2024