Knowledge about herbicide behavior in the environment, especially in soil, allows predicting possible impacts caused by its use in agricultural systems. An experiment using Sorghum bicolor as a bio-indicator was carried out to evaluate imazapyr sorption in soil. Sorption was evaluated in washed sand and in soils of 3 different textures: very clayed, sandy clayed loam and sandy loam, respectively from Sete Lagoas, João Pinheiro and Rio Casca - Minas Gerais. The value of I50, which inhibits 50% of dry biomass accumulation of the test-plant, and sorption relation (SR = I50 soil - I50 sand/I50 sand) were determined. I50 values observed were 29.41, 10.20 and 7.33 mg kg-1 and SR values were 9.77, 2.73 and 1.68, respectively for very clayed, sandy clayed loam and sandy loam soils. The order of substrate sorption presented by imazapyr was very clayed > sandy clay loam > sandy loam > washed sand. In sandy soil and soil with low organic matter content, low imazapyr sorption predisposes the product to leaching, and it may contaminate the underground water.
leaching potential; bioassay; herbicide
