Conservation Drainage: Managing Drainage for Yield and Water Quality Benefits.

Subsurface drainage systems have a significant effect on the hydrology and water quality of the watersheds in which they occur. There is a strong correlation between improved drainage and elevated nutrient transport from cropped land. Drainage systems are designed to accelerate the movement of water from the soil profile, and an unintended consequence is the accelerated removal of nutrients, reducing their exposure to attenuating soil processes.

While for most of its history, agricultural drainage has been directed towards improving crop production, in recent years conservation drainage practices, that is, practices that are optimized for both crop production and  water quality, have become the main focus of researchers in the Midwest, and other regions of the United States. One such practice, drainage water management, has gained widespread acceptance and is now cost sharable in many states. In Illinois, we are using paired fields to test the hypothesis that the implementation of this practice will reduce nitrate loads from subsurface drainage systems without adversely affecting yields.  Each pair consists of one field with a conventional drainage system, and one field with a drainage system whose outlet is managed in accordance with the Illinois Practice Standard for drainage water management. Both fields are instrumented to collect crop yield, precipitation, flow, water table elevations and water quality data. Preliminary results are indicative that the practice can result in significant annual nitrate load reductions, even after accounting for water leaving managed fields by pathways other than through the outlets of the drainage systems, without having any adverse effects on yield.