Imazapyr sorption in soils with different textures

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, Joao Pinheiro and Rio Casca - Minas Gerais. The value of I-50. which inhibits 50% of dry biomass accumulation of the test-plant, and sorption relation (SR = I-50 soil - I-50 sand/I-50 sand) were determined. I-50 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.