Gilmore City DWRF

corn and soybean drainage research plots
Nutrient Management

Title:  Gilmore City DWRF

Location:  Gilmore City

Time Period:  1989-present

Research Team:  Matt Helmers, Carl Pederson, Emily Waring, and Chelsea Clifford

Project Description:  Research focused on the effects of nitrogen (N) management on crop production and tile drainage water quality has been conducted in north-central Iowa near Gilmore City since 1989. The research site ag drainage well (ADW) includes 72 individually drained plots that are 50 feet wide and 125 feet long. Tile lines were installed at a depth of 3.5 feet spaced 25 feet apart. The center tile line from each plot is pump monitored continuously for drainage volume with a flow meter and a flow-proportional sample is passively collected for nitrate-nitrogen (nitrate-N) and dissolved phosphorus (P) analysis. Drainage flow is recorded and water samples are collected for analysis weekly. Soil types at ADW include Nicollet, Webster and Canisteo, all of which are clay loams. The 30-year average annual rainfall for ADW is 33.5 inches.  At ADW, multiple management practices have been examined for their impact on N and P loss and crop yield.

Crops: Corn-soybean, continuous corn, perennial forage.

Management Practices: Cover crops, tillage, land use, N-fertilizer source/rate/timing.

Treatments were changed in the fall of 2015 and current is studying the impacts of: Cereal rye winter cover crop vs. no rye (with and without tillage), conventional tillage (fall chisel plow with spring cultivation) vs. no-till (with and without rye), timing of N-application and use of nitrification inhibitor.

Publications:  Qi, Z., M.J. Helmers, R.D. Christianson, and C.H. Pederson. 2011. Nitrate-nitrogen losses through subsurface drainage under various agricultural land covers. Journal of Environmental Quality 40: 1578-1585.

Lawlor, P. A., M.J. Helmers, J. L. Baker, S. W. Melvin, and D. W. Lemke. 2008. Nitrogen application rate effects on nitrate-nitrogen concentrations and losses in subsurface drainage. Trans. ASABE 51(1): 83-94.

Funders:  Primary funder since 1989 has been the Iowa Department of Agriculture and Land Stewardship, in part, through funds authorized by the Iowa Groundwater Protection Act. Research from 2011-2015 was part of a regional collaborative project supported by USDA-National Institute of Food and Agriculture, award number 2011-68002-30190, “Cropping Systems Coordinated Agricultural Project: Climate Change, Mitigation, and Adaptation in Corn-based Cropping Systems,” project website: Have also had support from Koch Agronomic Services from 2016-2019.

Disclaimer:  This is an active research site, please contact Matt Helmers ( prior to planning any site visits.