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Tile Water Monitoring 2018, Part 1: Results by Landform

Article cover photo
More than 4,000 tile water samples were collected and analyzed in 2018 through the Iowa Soybean Association's tile water monitoring program. (Photo: Joseph L. Murphy/Iowa Soybean Association)

This is the first installment of a four-part series on the Iowa Soybean Association’s tile water monitoring program and aggregated results from 2018.

By Tony Seeman, ISA environmental research coordinator

Iowa landform regions are remnants of the state’s geologic history. Each landform region has unique topography, soils, drainage patterns and more. Often these characteristics define how the landscape is used and managed. In addition to land use, rainfall and water usage responds differently within each land region.

Studying water quality differences between landforms presents an opportunity to focus improvement efforts. Using appropriate conservation farming practices in areas of greatest nutrient loss can generate a greater water quality benefit per dollar invested in conservation practices. 

The Iowa Soybean Association’s (ISA) tile water monitoring program explores water content on several scales. Last summer, the Environmental Programs and Services (EPS) team worked with farmers and other partner organizations to collect more than 4,000 samples from Iowa streams, drainage tiles and edge-of-field practice locations for analysis in ISA’s certified water lab.

These samples were analyzed for nitrate-nitrogen, phosphate-phosphorus and other parameters which impact nutrient loss and transport. The EPS team examines the data on the field scale, watershed scale and between the Iowa landforms.

Figure 1: Average nitrate-N concentrations and average amount of nitrate-N lost per day by Iowa landform regions for 2018. *Asterisks note significant differences between groups.

At the most basic level, the water monitoring results show that each landform region has distinct differences in nitrate-N loss. The ISA water monitoring program had significant sampling locations in Iowa’s three largest landform regions: the Des Moines Lobe (DML), Iowan Surface (IS) and the Southern Iowa Drift Plain (SIDP) (see Figure 1). In 2018, a few sampling sites were added in the Northwest Iowa Plain (NIP) and the Paleozoic Plateau (PP).

The water samples revealed differences in the average nitrate-N concentration. The concentrations in the Des Moines Lobe and the Northwest Iowa Plain were higher than in the Southern Iowa Drift Plain and Iowan Surface, when compared using statistical analysis.

The Des Moines Lobe had the highest nitrate loss while the other three areas were not statistically different from each other. The nitrogen loss in the Des Moines Lobe of 0.17 lbs/acre per day represents nearly 31 lbs. of nitrogen between April 1 and Sept. 30. Similar spatial trends have been observed since ISA began widespread tile monitoring in 2014.

Water sampling details

The individual tile site water samples were combined with management information including: previous and current crop, tillage method, applied nitrogen rates, inhibitor use, conservation practices implemented and other cropping system details. By knowing what was happening on the land helps the researchers with data interpretation of nutrients found in the water samples.

The EPS team sends each farmer participant monthly and year-end reports, informing them of their fields’ performance and showing conservation practices at work. Although individual farm results are confidential, the ISA research team aggregated the data and shared local results at the ISA Farmer Research Tour in February.

For those interested in participating in the ISA tile water sampling program, contact the EPS team at

Contact Anthony Seeman at

For media inquiries, please contact Katie James, ISA Public Relations Manager at or Aaron Putze, ISA Communications Director at

For permission to republish articles or to request high-res photos contact Aaron Putze at Iowa Soybean Association | 1255 SW Prairie Trail Pkwy | Ankeny | IA | 50023 | US

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