Effects of Drainage Water Management On Phosphorus Loss From a Tile-Drained Field in Northern New York.

Tile drainage is a common agronomic practice in the Northeast because it can dramatically improve crop yields on poorly drained soils. In certain soils, the transport of phosphorus (P) to tile drainage water can pose water quality concerns.  Drainage water management (DWM) is a technique that uses in-line water control structures to control water table elevation and drainage rate and can reduce nutrient fluxes compared to freely drained conditions.  While studies show that DWM can reduce nitrogen losses by up to 80%, the effect on P transport is less clear. The main objective of our study was to compare P losses between free-drained (n = 4) and tiles under DWM (n = 4).  The site is located in Northern NY at the William H. Miner Agricultural Research Institute in Chazy, NY.  In addition to the field study, laboratory experiments were conducted to assess P loss under oxidized and reducing conditions.  Runoff events analyzed during 2012 indicated a 47% decrease in total P loss for DWM tiles.  Total P ranged from below detection limits to 0.1 mg/L under low flow and from 0.02 to 3.0 mg/L for peak flow events.  Soluble reactive phosphorus (SRP) contributed a large fraction of the total P in drainage water (range from 40 to 80%).  Although differences in P concentration were observed among tiles, an overall reduction in flow appeared to reduce total P loss from DWM treatments.  Leachate P concentrations between freely-drained soil columns and columns saturated for 21 days were not significantly different prior to manure application, but DWM treatments had significantly lower TP and SRP concentrations after receiving approximately 13,000 gal/ac of liquid dairy manure.  Results suggest that DWM may be a viable option to help reduce P loss from tile-drained fields.