Adsorption and degradation of thiazopyr in compost-amended and non-amendedsoils

Adsorption and degradation of thiazopyr on two unamended soils and a soil a mended annually during 8 years with compost were studies under laboratory c onditions and compared with the results obtained on soils amended with fres h sewage sludge compost. The adsorption isotherms fitted the Freundlich equ ation well and a marked sorption increase was found in amended soils. Degra dation data followed first-order kinetics and thiazopyr had a half-life of about 75 days at 25 degreesC and 60% water-holding capacity of soil. The ad dition of fresh compost markedly decreased the rate of thiazopyr degradatio n, whereas the compost mineralised in the field after annual additions had only a small influence. Incubation studies with sterile sons showed a very significant decrease of the degradation rate, indicating that degradation b y micro-organisms was the main pathway of thiazopyr degradation in the soil s studied. (C) 2001 Society of Chemical Industry.