A Look at Watershed Districts - Balancing Water Quality & Water Quantity

Drainage Water Management in Southeast Iowa

Research Published: 2012 & 2017

This 5-year study from Iowa State University is a continuation from a previous 4-year study (Helmers 2012) comparing performance and impacts of various drainage systems on poorly drained soils. With year-to-year variabilities in weather (specifically rainfall amount and timing), it may be difficult to get a idea of long-term affects of drainage systems with only a handful of growing season data points. 5 more years of data at this site helps provide a more complete picture benefits and impacts of various drainage practices.

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The Takeaway

Obtaining more years of data on the same site helps account for variable weather (dry years, wet springs, hot summers, etc.) year-to-year. Although the rainfall amounts between this 2017 study and the similar 2012 study were relatively different, the data led to similar conclusions:

Conventional Drainage can be a good tool increase corn and soybean yield, but if you plan to hold back a little water through shallow, tighter laterals or manage a controlled drainage system (each with similar effectiveness), you can still have the yield benefit while reducing the amount of Nitrates leaving the site.

The Site

  • Southeast Iowa – Crowfordsville, IA
  • 3- to 6-acre plots (42 acres total)
  • Soils (poorly drained)
    • North: Kalona silty clay loam
    • South: Taintor silty clay loam
  • Crops
    • Corn/soybean rotation
    • 2012 added continuous corn subplots
  • Drainage Practices (installed 2007)
    • Undrained/Surface Drainage only
    • Conventional Drainage
      • 4’ depth, 60’ spacing
    • Controlled Drainage
      • 4’ depth, 60’ spacing
      • Stoplogs placed during growing season; removed for fieldwork
    • Shallow Drainage
      • 5’ deep, 40’ spacing

The Testing

  • For 5-year period (2011-2015) measurements taken for:
    • Rainfall
    • Drainage flow
    • Water Table depth
    • Nitrate-N concentration
    • Crop yield

The Results

  • Similar drainage outflow from Shallow and Controlled Drainage plots
    • About 60% reduction from Conventional
      • 40% reduction in 2012 study
    • Less flow volume = Less Nitrate loading
      • Concentrations remain similar, but slightly higher with Shallow Drainage
      • About 50-60% reduction from Conventional
        • ~40% reduction in 2012 study
      • Undrained plots had (~6%) lower yields vs. Conventional plots
        • Not always consistent, not always significant (Similar finding in 2012 study)
      • Rainfall timing and amount play large roles year to year, but average out over time
        • Similar findings from 2012 study with different moisture conditions


Schott, L., et al. “Drainage Water Management Effects over Five Years on Water Tables, Drainage, and Yields in Southeast Iowa.” Journal of Soil and Water Conservation, vol. 72, no. 3, 2017, pp. 251–259., doi:10.2489/jswc.72.3.251.