Adsorption and desorption of Imazethapyr in Indian soils in relation to soil properties and temperature

The understanding of adsorption desorption of herbicides in soil is important to predict their environmental fate. The effect of properties of soils, temperature and ionic state of imazethapyr on its sorption was assessed using batch equilibration method. Freundlich adsorption coefficient ranged from 0.596 to 10.495 mu g(1-n)g(-1)mL(n) and was significantly influenced by organic matter, pH, clay content and mineralogy of soils. As solution pH was increased from 1.5 to 8.0, adsorption increased in acidic soil while it decreased in alkaline soils. The variability in adsorption with pH of solution was due to existence of imazethapyr predominately in cationic form at low solution pH and in anionic form at high solution pH. Delta H degrees ranged from - 29.11 to - 16.19 kJ mol(-1) suggesting adsorption was a spontaneous exothermic process. Desorption was slow and more hysteretic in alkaline soils indicating irreversible binding of imazethapyr to these soils which can cause a phytotoxic effect on succeeding crops. Principal component analysis suggested that imazethapyr has moderate mobility in studied soils and can contaminate surface and groundwater. The amendment of soils with farmyard manure was an effective management practice to reduce leaching of imazethapyr.