Technical Abstract: Competition for water and nutrients by plants plays a major role in controlling the level of reactive forms of nutrients and their availability for off-site leakage. The processes controlling competition are, however, poorly understood and quantified. The goal of this research is to unravel the mechanisms controlling competition for water among roots of different plants. To that end, this project proposes to use the annuals maize (Zea mays L) and sunflower (Helianthus annuus), as well as the perennials fescue (Festuca) and white clover (Trifolium repens), to study competition in controlled conditions. The project’s ultimate objective is to produce an algorithm for competition that is suitable for comprehensive agricultural systems models. These models are invaluable tools for environmental assessments used to design or evaluate agricultural management practices that aim at improving water quality and controlling air pollutant emissions through sustainable agricultural production.