Drainage Control to Diminish Nitrate Loss from Agricultural Fields

Abstract

Abstract In an attempt to reduce NO 3 − ‐N movement to drainage waters, flashboard riser‐type water level control structures were installed in tile mains or outlet ditches at two locations to raise the water table to increase denitrification during the winter. A large reduction in NO 3 − ‐N movement through tile lines occurred (from 25–40 to 1–7 kg/ha) in moderately well‐drained soils because of reduction in effluent volume. In the moderately well‐drained soils, there was no indication of increased denitrification in the field. In poorly drained soils, drainage control had no influence upon soil profile oxidation‐reduction potentials but resulted in approximately.a 50% reduction in NO 3 − movement through drainage ditches. This reduction was due to increased water movement into and through deeper soil horizons (below 1 m). The NO 3 − ‐N concentrations and low Eh values in all profiles below 1 m indicate that the NO 3 − which moved to this depth underwent denitrification.