The MANAGE Drain Load database: Review and compilation of more than fifty years of North American drainage nutrient studies

As agriculture in the 21st century is faced with increasing pressure to reduce negative environmental impacts while continuing to efficiently produce food, fiber, and fuel, it becomes ever more important to reflect upon more than half a century of drainage water quality research to identify paths forward. This work provided a quantitative review of the water quality and crop yield impacts of artificially drained agronomic systems across North America by compiling data from drainage nutrient studies in the "Measured Annual Nutrient loads from AGricultural Environments" (MANAGE) database. Of the nearly 400 studies reviewed, 91 individual journal publications and 1279 site-years were included in the new MANAGE Drain Load table with data spanning 1961-2012. Across site-years, the mean and median percent of precipitation occurring as drainage were 25 and 20%, respectively, with wet years resulting in significantly greater drainage discharge and nutrient loads. Water quality and crop yield impacts due to management factors such as cropping system, tillage, and drainage design were investigated. This work provided an important opportunity to evaluate gaps in drainage nutrient research. In addition to the current analyses, the resulting MANAGE drainage database will facilitate further analyses and improved understanding of the agronomic and environmental impacts of artificial drainage.