The Discovery Farms programs in Minnesota and Wisconsin conducted a joint study between 2017 and 2020, comparing three approaches to tile drainage monitoring.
The project was funded primarily by a Natural Resource Conservation Service Conservation Innovation Grant and by the Minnesota Corn Research and Promotion Council (MCRPC).
The project analyzed three levels of water quality monitoring: Intensive, intermediate and basic. Intensive sites utilized automated sampling equipment and flow-based sampling. Intermediate sites included continuous flow monitoring and bi-weekly sample collection. Basic sites included bi-weekly flow measurement and water sampling.
The intensive sampling approach is the method used at Discovery Farms core sites for both surface runoff and tile drainage monitoring. This approach provides reliable results but is also much more expensive than the basic approach. The basic approach would allow monitoring and analysis on many more farms at a lower cost but would only be useful if the data can accurately characterize annual nutrient or sediment concentrations.
Data was collected at 48 sites throughout Minnesota and Wisconsin spanning three growing seasons. Previous monitoring has shown that where sediment and phosphorus are of concern, surface runoff monitoring is critical. Conversely, tile drainage monitoring is the key when evaluating nitrate nitrogen losses. In this project, water samples were analyzed for sediment, phosphorus and nitrate nitrogen.
The basic sampling method underestimated sediment and phosphorus losses as compared to the intensive approach, likely because biweekly sampling missed higher flow periods. This suggests that where sediment and phosphorus are of concern, automated sampling methods are needed. However, the basic approach did provide excellent results for nitrate concentrations.
Armed with this information, it is now possible to envision a scenario in which biweekly tile sampling could provide farmers with yet another tool to evaluate nitrogen management practices. Future plans include engaging more farmers with tile-drained fields to grow the dataset so that more context can be provided to compare nitrate numbers.
A few samples collected in isolation may be interesting, but a large number of samples with accompanying agronomic information can begin to shed light on the effectiveness of related practices like cover crops or crop rotation.
Thank you to the NRCS and MCRPC for their funding, and also to Discovery Farms Minnesota coordinator Tim Radatz for coordinating this project.
For more information go to discoveryfarmsmn.org.
Formo is executive director of the Minnesota Agricultural Water Resource Center.