objectives . To quantify the effects from multi-herbicide use on key soil biological processes in soils 2. To quantify the magnitude and duration of the effects from multi-herbicide applications (pre- and post-emergence) during the cotton season on populations and activities of key microbial groups essential for nutrient availability and uptake, crop residue decomposition and plant growth - Experiments conducted both under field conditions (2000/01, 2001/02 and 2002/03) at ACRI and glasshouse conditions at CSIRO L&W in Adelaide. 3. To evaluate the effects of multi-herbicide application on microbial processes in the rhizosphere and near crop residues of genetically modified cotton varieties and determine their impact on cotton growth and the maintenance of soil health. Since the microbiology of the GM cotton residues was found to be significantly different to that of conventional GM cotton residues, experiments were conducted to determine the extent of differences between GM and conventional cotton varieties (as part of collaboration with CLWC) as a foundation to any future experimentation to investigate the herbicide x GM cotton interaction. 4. To provide recommendations to changes in herbicide usage patterns based on potential impacts on key soil processes