Nitrate Reduction in an Organic Soil-Water System1
- K. R. Reddy,
- P. D. Sacco and
- D. A. Graetz2
Flooded organic soil as a treatment system for nitrate-nitrogen (NO3-N) removal from agricultural drainage water was evaluated under controlled conditions. Nitrate-N reduction rates in the flood water (agricultural drainage water) and in the underlying organic soil column were measured as a function of NO3-N concentration (10, 25, and 50 µg NO3-N/ml), energy source, and temperature (8, 18, and 28°C). Labeled NO3-N was used to differentiate between denitrification and NO3-N reduction to ammonium-N (NH4-N) or organic N.
Nitrate-N reduction rates in the soil column incubated at 28°C with no excess flood water were best described by first-order kinetics with an average rate constant (k) of 0.751 day−1. Flood water NO3-N removal rates were also described by first-order kinetics. Nitrate removal rates from low oxygen-demand flood water (expressed as first-order rate constants) with an underlying soil column were 0.038, 0.750 day−1 for an incubation temperature of 8, 18, and 28°C, respec- 28°C, respectively. In soil columns incubated with high oxygen-demand flood water, most of the added NO3-N disappeared before it reached the underlying soil column, with k values of 0.172, 0.292, and 0.790 day−1 for an incubation temperature of 8, 18, and 28°C, respectively. In all treatments, denitrification was the dominant process in the removal of flood water NO3-N. At low temperature (8°C), a greater portion of 15NO3-N was reduced to 15NH4-N and organic N. Most of the immobilized 15NO3-N appeared as soluble organic N. At 8°C, flood water NO3-N diffused deeper into the soil column as compared to the flooded soil columns incubated at 28°C.
The results obtained in this study indicate that flooded organic soil can function as an effective sink for reducing NO3-N levels of agricultural drainage waters.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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