Subsurface Drainage and Soil Temps

Research Published: 2001

It has commonly been believed that a tile-drained field warms up faster in the spring compared to a surface-drained or undrained field. Researchers from University of Minnesota and NDSU put this to the test in the early 2000’s. They studied two sites in northwest Minnesota to investigate the influence that drainage and lateral spacing has on soil temperature throughout the spring and summer.

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The Takeaway

This study proves that there is an advantage of warmer soils with a subsurface drainage system (about 1.3°F throughout the top 4-ft of soil). However, the greatest difference/advantage is in the subsoil (12-24” deep) and during the early growing season (late May to early July). Dryer soils can warm faster, so the sooner the water table is drawn away from the surface, the sooner it can take advantage of warmer air temperatures.

Lastly, tillage or cropping practices were not accounted for in this study which would likely have a large influence in soil moisture and temperature especially in the top layer of the soil profile.

The Site

  • NW Minnesota – Crookston & Brooks, MN
  • Soils
    • Vallars loam – moderately slow permeability
    • Hegne silty clay loam – poorly-drained, lower permeability
  • Soil temperature measurement depths
    • 79”, 5.9”, 12”, 24”, & 47”
  • Drainage system
    • Spacing: 16’, 40’, 60’, & 80’

The Testing

  • Measured and compared soil temperature and water table level at various depths in soil profile throughout the spring/summer
    • Measurements taken every 2 hours; averaged to get a daily temperature

The Results

  • Tighter spacing resulted in warmer soil (Table 1, red = warmer)
  • Average temperatures throughout soil profile were 3°F higher in drained soils versus undrained.
  • Greater differences were noticed at 12” & 24” depths
    • This is due to drained soils reducing the water past 24” more often