The fate of dissolved organic carbon in tile drained agroecosystems
Abstract
The losses of dissolved organic carbon (DOC) in tile drained soils are an unquantified portion of the terrestrial carbon cycle. Subsurface tile drainage is used to maintain high crop productivity, but can also facilitate the export of soil solutes, such as DOC, to deep subsurface soils or to surface waters. A series of field and laboratory experiments were conducted to quantify the amount of DOC lost via tile drains and to assess the availability of DOC for subsurface denitrification. Losses of DOC via tile drainage were small compared to other organic carbon pools in soils, including soil organic carbon, crop biomass, and applied lagoon effluent. There was no significant difference among a variety of crop management practices on yearly DOC losses or concentrations, including lagoon effluent application and restoration of prairie grass. Application of lagoon effluent increased DOC concentrations when drainage occurred within one month of manure application, but this effect was not consistently seen. The most influential factor in mass DOC loss was drain flow volumes; greater drainage was significantly correlated to greater DOC losses. The DOC concentrations were also affected by drain flow volumes. Over yearly time periods, there was a significant dilution effect of greater drain flow volumes leading to decreased DOC concentrations. However, when determined on a daily basis, a significant flushing effect was determined; greater daily flow led to greater daily DOC concentrations. During discrete drainage events, high DOC concentrations corresponded to high drainage flow rates. The variation in DOC concentration during a drainage event underscores the importance of using a flow-proportional sampling scheme for the determination of long-term losses of solutes in drain water. Denitrification in subsurface soils occurred after the addition of leached DOC, but this effect was not consistently found. At maximum, it was estimated that 12% of leached DOC would be utilized in the subsurface denitrification process. Leached DOC would not reduce nitrate concentration in groundwater beyond 2 mg L-1 after two weeks.
Degree
Ph.D.
Advisors
Brouder, Purdue University.
Subject Area
Agronomy|Soil sciences|Environmental science
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