SUBSURFACE DRAINAGE WATER-QUALITY FROM STRUCTURED SOIL

The often rapid arrival of pesticides at the ground water has been exp lained by the concept of preferential movement of water and solutes th rough the soil. To facilitate understanding of these transport process es, a drainage study was conducted by applying a nonadsorbed tracer to plots drained by subsurface drains. Three management practices were e mployed: no-till, conventional-till, and conventional-till with incorp oration of the tracer. The plots were irrigated with 71-203 mm of wate r. Drainage line outflow and tracer concentration in the outflow were monitored for up to 52 hr. The resulting soil profiles were analyzed f or tracer concentration. The main effect of plowing and incorporating the tracer was a more uniform concentration in the resulting profile. A simple mixing-layer model was used to predict the rate at which the tracer was transported out of the root zone into the layers below. The model was found to be in reasonable agreement with drainage outflow p atterns, especially from the incorporated plots. These results may be helpful for future development of best-management practices for contro lling the effects of agriculture on environmental pollution.