Discovery Farms to test equilibrium tension lysimters (ETLs)

By Ryan Heiderman, UW-Madison Division of Extension Discovery Farms Program

Hello Peninsula Pride,

My name is Ryan Heiderman, and I was recently hired as the new Nitrogen Projects Coordinator with UW Discovery Farms. I am a UW-Madison alum with a degree in soil science. My interests are in applied agronomic and ecological research, which can provide producers and land managers with the knowledge and tools to make informed, profitable and environmentally-sound management decisions. I am excited to be a part of the Discovery Farms program and to begin working with farmers across Wisconsin.

Since 2015, Discovery Farms has collaborated with farmers across the state to conduct on-farm nitrogen (N) assessments to better understand nitrogen use efficiency (NUE). Benchmarks from data collected on more than 300 fields have been established for different NUE categories ranging from low to high efficiency. These benchmarks allow producers to assess and compare the efficiency of their current N management plans with those on other farms in the state.
In general, these NUE calculations are ratios of outputs to inputs with the simplest calculations of NUE being yield, or N content of harvested yield, divided by the amount of N applied. A more detailed determination of NUE utilizes zero-N test strips, which allows for a better understanding of the soil’s ability to supply N absent additional fertilizer or manure inputs. Comparisons between NUE calculations under cur-rent management with that of the zero-N test strip can show the true economic value of the gain in yield from N application. Discovery Farms encourages producers to participate in this relatively simple NUE monitoring effort and can provide on-farm support for field trial installation. Calculating NUE in your fields can allow you to understand potential economic and environment impacts of shifts in your N management.

Kevin Masarik of UW-Stevens Point Center for Watershed Science and Education shared this photo of himself installing an equilibrium tension lysimter.

While NUE is a powerful tool which can provide a simple assessment of N use by crops, it does not explicitly quantify N leaching losses, which may negatively impact groundwater. In particular, there is concern of groundwater contamination of nitrate from agricultural and other non-point sources.

Nitrate contamination happens when this highly soluble, negatively charged form of N leaches beyond the crop root zone and enters local aquifers. To better understand nitrate leaching under different farm management practices, Discovery Farms will soon be installing research trials to measure in-field drainage and nitrate leaching below the root zone with the use of equilibrium tension lysimeters (ETLs). An ETL is basically a ‘bucket’, equipped with drainage flow measurement and sampling instruments, which is buried below the root zone of an undisturbed soil profile. ETLs maintain the natural flow paths of water by matching the matric potential, or the adhesive attraction of water to the soil matrix, of the surrounding soil by utilizing a vacuum pump. An ETL can continuously measure year-round drainage, as well as collect soil water samples, at specified intervals, to be measured in the lab for nitrate concentration.

Discovery Farms will install ETLs this fall in a Pepin County field to better understand the impacts these practices have on nitrate leaching. Findings from this work and additional future monitoring sites will be used by groundwater scientists and regulatory personnel, farmers, farm advisers, local government personnel and community stakeholders interested in ground-water, public health and agriculture.

For more information about Discovery Farms and the nitrogen related projects visit

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