Effect Of Organic Fertilizer On Degradation Of Imazethapyr In Soil

Imazethapyr is a pillar product in China’s highly efficient herbicide field and is widely used for weed control in legume crops such as alfalfa and soybeans.However,the environmental issues that come with it are becoming increasingly prominent as its application area in agricultural production continues to expand.To improve the degradation of imazethapyr in the environment,researchers have taken various measures,but traditional remediation methods face problems such as poor adaptability,high cost,and easy secondary pollution.In recent years,stimulating microbial community growth through organic fertilizer application and returning it to the fields has been considered the most cost-effective and effective bioremediation method for improving the degradation of organic pollutants in soil.Therefore,this study used alfalfa pot experiments to investigate the effects of different proportions（2%,4%,8%）of organic fertilizer（cow manure-corn straw organic fertilizer material）on the degradation of imazethapyr in soil（black soil and saline-alkali soil）,determined the key factors driving its degradation,and elucidated the microbial mechanisms by which organic fertilizer affects the degradation of imazethapyr.The results of the study can provide basic reference data for the rational application of organic fertilizers,the reduction of ecological and environmental risks from imazethapyr,and the construction of a green and healthy grass system.The main conclusions are as follows:（1）The addition of organic fertilizer at the proportions of 2%and 4%had a promoting effect on the degradation of imazethapyr in black soil,with the best effect observed at the 4%addition level,which increased the degradation rate by 12.58%and shortened the half-life by 53.40%.The addition of 8%inhibited the degradation of imazethapyr in black soil.All three levels of organic fertilizer application（2%,4%,8%）inhibited the degradation of imazethapyr in saline-alkali soil,with the strongest inhibitory effect observed at the 8%addition level,which decreased the degradation rate by 16.35%and prolonged the half-life by 40.00%.（2）The addition of 4%organic fertilizer significantly increased the richness and diversity of the bacterial community in black soil,as well as the relative abundance of the major bacterial families Sphingomonadaceae,Vicinamibacteraceae,Gemmatimonadacea,Xanthomonadaceae,and Chitinophagaceae.Pathway analysis results confirmed the metabolic capability of Sphingomonadaceae for imazethapyr.The promoting effect of 4%organic fertilizer on the bacterial community in black soil was long-lasting,and at the end of the experiment（60d）,the richness and diversity of the bacterial community and the relative abundance of the major bacterial families were still higher than those of the blank control.（3）The addition of 4%organic fertilizer had an inhibitory effect on the bacterial community in saline-alkali soil,especially in the early stage after application,where the richness and diversity of the bacterial community and the relative abundance of the dominant bacterial families Sphingomonadaceae,Vicinamibacteraceae,and Gemmatimonadacea were significantly reduced.However,this inhibitory effect gradually decreased over time,and at the end of the experiment（60d）,the bacterial community had recovered to the same level as the blank control.（4）Redundancy analysis（RDA）results showed that total organic carbon（TOC）and alkali-hydrolyzable nitrogen（AN）were the key factors driving the variation of the bacterial community in soil after organic fertilizer application.Pathway analysis showed that organic fertilizer mainly regulated the appropriate carbon-to-nitrogen ratio by inputting carbon and nitrogen elements,stimulated the growth of the bacterial community in black soil,and enhanced the degradation activity of the dominant bacterial families for imazethapyr.（5）Due to the low nutrient content and weak microbial activity in saline-alkali soil,the addition of organic fertilizer led to strong antagonistic effects between bacterial communities competing for nutrients such as TOC,AN,and ammonium nitrogen（NH₄⁺-N）,which reduced the metabolic activity of bacteria for imazethapyr.