The 2012 ASHS Annual Conference

Nitrate-N losses in surface drainage and runoff water from ornamental plant production areas can be significant. In nitrogen-limited watersheds discharge of nitrogen from production areas can have significant, negative impacts on non-target aquatic systems. These studies monitored nitrate-N concentrations in production area drainage water originating from a foliage plant production area.  Concentrations were monitored during a transition from 100% reliance on fertigation using urea and nitrate-based soluble formulations (SF) to a nitrate-based controlled release formulation (CRF).  In addition, this project also evaluated the potential use of microbial-based (denitrification), flow-through bioreactors for their nitrate-remediation ability. Duplicate bioreactor systems were constructed at a local foliage plant nursery.  Each bioreactor system consisted of four 242-L tanks with connections alternating between bottom and top. The tanks were filled with Kaldnes^® media to provide surface area for attachment of native microflora.  Molasses was supplied as a carbon source for denitrification and water flow rates through the systems ranged from 5 to 18 L/min. during tests.  During the SF use period, NO₃-N concentrations ranged from 0.5–322.0 mg•L^-1, with a median concentration of 31.2 mg•L^-1.  Conversely, NO₃-N concentrations during the slow-release fertilization program ranged from 0–147.9 mg•L^-1 with a median concentration of 0.9 mg•L^-1.  Nitrate-N concentrations in drainage water during the CRF program were reduced by 94–97% at the 10^th through 95^th centiles relative to the SF fertilization program.  Results indicate consistent removal of 80–100% of the nitrate flowing into the systems using the bioreactors. Accumulation of ammoniacal and nitrite nitrogen did not occur, indicating that the nitrate-nitrogen was removed from the water, and not simply transformed into another water-soluble species.  Occasions where removal rates were less than 80% were usually traced to faulty delivery of the carbon source.  Results indicate that CRF fertilizer formulations and the modular microbial-based bioremediation systems may be a useful tool for helping water managers meet stringent nitrogen water quality regulations, especially at nurseries with limited space for expansion of water retention facilities.