TY - JOUR AU - Hartz, Tim AU - Smith, Richard AU - Cahn, Mike AU - Bottoms, Thomas AU - Bustamante, Sebastian Castro AU - Tourte, Laura J. AU - Johnson, Kenneth AU - Coletti, Luke TI - Wood chip denitrification bioreactors can reduce nitrate in tile drainage JF - California Agriculture JO - Calif Agr Y1 - 2017/02/17 VL - 71 IS - 1 SP - 41 EP - 47 PB - University of California Agriculture and Nature Resources SN - 0008-0845 UR - http://dx.doi.org/10.3733/ca.2017a0007 L3 - 10.3733/ca.2017a0007 AB - Widespread contamination of surface water with nitrate-nitrogen (NO3-N) has led to increasing regulatory pressure to minimize NO3-N release from agricultural operations. We evaluated the use of wood chip denitrification bioreactors to remove NO3-N from tile drain effluent on two vegetable farms in Monterey County. Across several years of operation, denitrification in the bioreactors reduced NO3-N concentration by an average of 8 to 10 milligrams per liter (mg L-1) per day during the summer and approximately 5 mg L-1 per day in winter. However, due to the high NO3-N concentration in the tile drainage (60 to 190 mg L-1), water discharged from the bioreactors still contained NO3-N far above the regulatory target of < 10 mg L-1. Carbon enrichment (applying soluble carbon to stimulate denitrifying bacteria) using methanol as the carbon source substantially increased denitrification, both in laboratory experiments and in the on-farm bioreactors. Using a carbon enrichment system in which methanol was proportionally injected based on tile drainage NO3-N concentration allowed nearly complete NO3-N removal with minimal adverse environmental effects.