Agricultural tile drainage can increase crop yields on poorly drained soils, improve the timeliness of field access, and reduce yield variability; however, they can also serve as conduits for nutrient loss, most notably nitrogen in the nitrate form. Because nitrate is negatively charged, it does not bind with negatively charged soil and readily moves with water. Typically nitrate losses are more prevalent in subsurface water like tile drainage, while high phosphorus and sediment losses are associated with surface waters. Although we do have highly accurate ways to measure tile drainage water quality, such as 24/7 automated flow samplers, this approach is typically not economically or logistically feasible for individuals looking to monitor tile drainage on their own farm. 

To help address this limitation, from 2018-2020 Discovery Farms compared the cost-effective approach, annual bi-weekly grab sampling for nitrate-nitrogen concentrations, to the more involved 24/7 automated flow samplers collecting flow-weighted mean concentrations, to see how these two approaches compared in terms of accuracy. Results showed sampling tile water on a bi-weekly basis with no flow calculations can be a useful tool to assess nitrate-nitrogen leaving the field and evaluate how results are related to in-field nitrogen management practices.  

This resource walks you through planning a high-quality tile monitoring strategy including:

1. Recommended planning steps & research justifications 
2. Data interpretation recommendations 
3. Frequently asked sampling questions 
4. Two case studies on how to use annual nitrate-nitrogen concentration data

On-farm tile monitoring is a complex process. This document is not an exhaustive list of all the variables or interpretation considerations that may arise, but rather serves as a guide to get you started. Please contact your local Agriculture Water Quality Outreach Specialist for any help along the way: 

Amber Radatz, Program Manager, amber.radatz@wisc.edu

Chelsea Zegler, Southern Wisconsin, zegler@wisc.edu

Guolong Liang, Central Wisconsin, gliang6@wisc.edu

Laura Paletta, Northeast Wisconsin, paletta@wisc.edu

Kelsey Hyland, Northwest Wisconsin, kelsey.hyland@wisc.edu