Tile-drained Farm Fields Generally Increase Yields but Can They Protect Water Quality Too?

Joshua Faulkner, Don Ross, and Kirsten Workman of the University of Vermont are conducting research to improve understanding of interactions among tile-drained fields, best management practices for agriculture, and phosphorus losses in the subsurface and through surface runoff.  In fall 2019 at the University of Vermont Rubenstein School of Environment and Natural Resources, Joshua Faulkner (JF) gave an informative talk on the status of his research. In follow up, Lake Champlain Sea Grant (LCSG) asked him to answer a few questions and share key messages.

LCSG: Let’s start at the beginning: What are tile drains and why do farmers use them?
JF: Tile drainage is the placement of perforated pipe about 36” below the soil surface in a farm field. Modern tile drainage systems consist of a network of pipes, spaced 25 to 50 feet apart throughout an entire field and all connected to a single outlet pipe or “main” that drains the field. Farmers use tile drain systems to lower the water table below the root zone of the crop, helping avoid negative impacts on the plants due to saturated soils and thus increasing yield. In addition, farmers can more easily manage their tile-drained fields without damaging or compacting wet soil. Importantly, farmers indicate that they can more easily employ conservation practices such as cover crops in tile-drained fields.

LCSG: Are there trade-offs to using tile drains for farmers?  For the environment?  Please describe.
JF: Tradeoffs to tile drainage systems are minimal for farmers, but they do occur in some situations. Current installation costs can be $1,500 per acre, so they represent a significant investment. If farmers do not simultaneously address other factors that limit yield, such as fertility and soil compaction, tile may not be cost-effective. For most farmers, the return on investment is quickly realized, and the payback period for the tile drainage system is fairly short. 

Tradeoffs to tile drainage systems for the environment are possible. Scientists are not yet sure how tile drainage impacts the total amount of phosphorus lost from a field and, therefore, how tile drainage affects water quality. We do know that tile drainage changes the hydrology of the field, decreasing surface phosphorus runoff and increasing subsurface loss of phosphorus. However, we still don’t know whether the net change in total phosphorus lost from the field is positive or negative. Whether there is or isn’t an increase in phosphorus loss, it is still very important to understand how to manage the tile-drained field to minimize the phosphorus loss, given the altered hydrology. That is the question that we are investigating with our Lake Champlain Sea Grant-funded research: How can farmers minimize any environmental tradeoffs (i.e., phosphorus loss) by how they manage soil and manure in tile-drained fields?     

LCSG: What is the area of tile-drained agricultural fields in the Lake Champlain basin?  Is use of tile drainage systems increasing or decreasing?
JF: We don’t know the extent of tile drainage within the Lake Champlain basin, but we do know that installation has increased over the past several years as farmers have begun to be affected more and more by a changing climate. Data indicate that annual precipitation is increasing in Vermont, and this is leading to more periods of saturated soils that can reduce yield in undrained fields.     

LCSG: You’re just getting started so you don’t have research findings yet, but do you have a hypothesis about how farmers can design tile drain systems and use soil best management practices to benefit economically and mitigate negative environmental impacts?
JF: We hypothesize that how manure is applied to fields may minimize phosphorus loss. Specifically, we suspect that manure injection may be a very important tool for two reasons: 1) manure injection avoids placing phosphorus on the soil surface and thus reduces surface runoff of phosphorus, and 2) manure injection forces manure into the soil matrix and breaks up preferential water flow paths (e.g., cracks and root channels) that can be responsible for rapid movement of water downward through the soil to tile drains and thus slows phosphorus runoff. 

LCSG: Going forward, do you have recommendations about how we should approach research on tile drains when considering their impact on Lake Champlain?  What are the next stages of research needed?
JF: We think that research on tile drains is critical to understanding phosphorus loading to Lake Champlain from agricultural lands. The next stages of research should build on the work we are doing to understand the most effective soil, manure, and crop management for minimizing phosphorus loss.  We need to investigate this question in different soil types and for different crops. We are studying corn fields currently, but tile drains are increasingly common in hay fields as well. I also think that research is needed on end-of-pipe treatment solutions for capturing phosphorus, particularly solutions that would reduce the cost and increase the effectiveness and longevity of these systems. 

LCSG: What are your research plans for this Sea Grant-funded project and for related research over the next few years?
JF: We plan to continue monitoring surface and subsurface runoff using a paired watershed approach for at least three more years, using funding from Lake Champlain Sea Grant and the United States Department of Agriculture Natural Resources Conservation Service (USDA NRCS). We are currently in the calibration year at the study site. Next year, we will enter our treatment period, when we will implement what we think are the most promising management practices on the treatment watershed and evaluate their effects. 

USDA-NRCS is also funding us to conduct larger watershed-scale monitoring in the Lake Champlain basin to improve understanding of the effects of conservation practices over the longer term. This project will also test innovative edge-of-field treatment practices in tile-drained fields and evaluate “stacked” conservation practices (i.e., source control, in-field practices, and multiple levels of edge-of-field practices). 

LCSG: Where should readers go to learn more about tile drain systems and their impact on agriculture and the environment?
JF: Learn more about the Lake Champlain Sea Grant project on the UVM Extension’s Drainage and Water Management webpage.