2018 ASHS Annual Conference

Eutrophication of urban surface waters is a significant problem associated with excess nutrient pollution. Historically, regulatory agencies have attributed urban eutrophication to fertilizer use in lawns and golf courses. Scientific evidence suggests nutrient pollution from turfgrasses can be minimal if fertilizer is applied according to best management practices. Specifically, numerous reports have shown that applied fertilizer is quickly taken up by turfgrass roots and made unavailable to environmental losses. Whether N and P content of turfgrass plants influences the nutrient content of runoff is undocumented. The objective of this study was to directly assess the leachability of N and P from turfgrass above-ground tissues in order to simulate the effects of runoff moving through a turfgrass field.

Bermudagrass (Cynodon dactylon) and perennial ryegrass (Lolium perenne) were established in 5 cm diameter pots containing a calcined clay (Turface MVP) rootzone. Treatments consisted of four N (urea) rates (0, 100, 200, 300 kg N ha^-1) and three P (triple superphosphate) rates (0, 10, 100 kg P ha^-1). Other plant essential nutrients were applied to prevent deficiencies using a commercial fertilizer. After six weeks of treatments, above-ground plant tissue was harvested and clipped to a uniform size before being subjected to a water extraction procedure. The extractant was filtered and analyzed for nitrate-N, ammonium-N, and orthophosphate-P concentration. Plant tissue N and P concentration were measured using reserved above-ground tissue. Relationships between application rates, plant tissue nutrient concentration, and extractable nutrient concentration varied between turfgrass species. In bermudagrass, N tissue content increased with increasing N rate while extractable dissolved inorganic N decreased. A similar pattern was seen for P rates in bermudagrass. In ryegrass, P tissue content decreased with increasing P rate suggesting faster growth under higher P rates led to nutrient dilution in plant tissues. These findings suggest healthy turfgrass tissue (lacking in nutrient deficiency) would not likely be a direct source of inorganic nutrients in an urban watershed.