Phosphorus and Nitrogen Leaching From a Mature Turfgrass.

Nitrogen fate research was initially conducted at Michigan State University in 1991.  The initial research conducted from 1991 through 1993 indicated that there was minimal risk of nitrate-nitrogen leaching from turfgrass.  Subsequent years of research on the same lysimeters indicate the risk of nitrogen leaching changes as the turf ages.  Since the summer of 1998 percolate samples have been collected from the same monolith lysimeters and analyzed for nitrate-nitrogen.  As of 2011, the turfgrass area has now been under continual fertilization practices for 21 years with percolate collection for the last 13 years consecutively.  In addition to concerns about nitrate contamination of ground water sources, phosphorus pollution of ground and surface water from fertilizers applied to turf continues to be a subject of great debate.  Throughout the Great Lakes region governments have passed fertilizer ordinances that restrict phosphorus fertilizer applications to turfgrass. Phosphorus has low water solubility and limited leaching potential in turf systems, with the exception being sand based rootzones. Data on phosphorus leaching from mature turf growing in native soils is lacking.  Starting in 2003, phosphorus applications were made to the monolith lysimeters at MSU to determine phosphorus leaching from this mature turfgrass site.  Phosphorus from triple superphosphate (20% P) was applied at two rates, 49 and 98 kg P ha^-1 split over two applications (24.5 and 49 kg N ha^-1 per application).  The phosphorus application dates coincided with the nitrogen application dates on May 1 and September 1.  Results from 2003 through 2010 indicate low concentrations of phosphorus in leachate.  The mean concentration of phosphorus detected in leachate since initiating phosphorus treatments in 2003 has been less than 0.02 mg L^-1, regardless of phosphorus application rate.