Does Quantity and Quality of Tile Drainage Water Impact In-stream Eutrophication Potential? Evidence from a Long-term Biofuel Cropping Systems Experiment

Sep 2017


The challenge with farming is balancing crop nutrient needs while minimizing losses. Fertilizer nitrogen (N) and phosphorus (P) are added to agricultural fields to increase yields, but these nutrients in excess can lead to eutrophication. Tile drainage is used extensively across the U.S. Midwest, and these tile drainage lines can directly transport nutrients to streams. The quantity (i.e. load) and quality (i.e. chemical composition of nutrients and carbon) of the tile drainage water likely plays a crucial role in stream water quality, but most tile drainage studies focus only on the quantity of total dissolved and inorganic forms of N and P. This may not provide the whole story of how tile drainage water can affect stream water quality.


This project will measure chemical composition and eutrophication potential of subsurface drainage (tile-flow) from a variety of management practices. The goal is to look at how management practices affect the quality of tile drainage water resulting from soil N and P cycling and losses, and how that quality directly relates to in-stream water eutrophication.


Tile drainage water samples will be collected and analyzed from an ongoing, long-term experiment in central Iowa called the Comparison of Biofuel Cropping Systems (COBS). The COBS experiment consists of five treatments: continuous corn, corn-soybean, corn with cover crop, fertilized prairie, and unfertilized prairie.

Award Number: 

Project Updates

April 2020


Researchers found out that adding tile water from land that drained a winter rye cover crop or restored prairie reduced algal growth by 43% and 46%, respectively, compared to tile water from conventional corn-soybean fields.

With dissolved oxygen, there were unexpected, complicated interactions between prior stream condition (and mixing ratio between tile and stream water) that showed contrasting trends with management practices. This means that the prior quality of the stream and volume of tile-to-stream water affects the drop in dissolved incubation under incubation conditions. More work is needed to further investigate these unexpected, complicated interactions with prior stream quality and mixing ratio. See poster summary. 

Other activities and accomplishments:

- 1 field day, 2 presentations