Effects of Phosphorus Fertilization and Turfgrass Clipping Management On Phosphorus Runoff.

Phosphorus (P) enrichment of surface water and the role of home lawns as a source of P is a concern in many urban watersheds. A study was conducted for 5-yrs on a silt loam soil with a 5% slope and high soil test P (27 mg kg-1 Bray P-1) to evaluate P fertilization and clipping management effects on P runoff from Kentucky bluegrass under both frozen and non-frozen soil conditions.  Four fertilizer treatments were compared: 1) no fertilizer, 2) nitrogen (N) + potassium (K) + 0xP, 3) N + K + 1xP, and 4) N + K + 3xP. Phosphorus rates were 21.3 (1xP) and 63.9 (3xP) kg ha^-1 yr^-1 the first year and 7.1 and 21.3 kg ha^-1 yr^-1 the following four years. Data were collected for total P (TP) and reactive P (RP) concentrations in runoff, runoff depth, turfgrass growth and quality, P concentrations in plant tissue, P uptake, and soil test P levels (Bray P-1) at two soil depths. Flow-weighted TP and RP concentrations in runoff increased linearly with increasing P fertilizer application rate in all five years of the study. In the second year of the study, cumulative annual TP runoff was significantly greater for the no fertilizer treatment than for any of the treatments receiving fertilizer. Annual P runoff from the no fertilizer treatment was comparable to the 1xP treatment in the other four years of the study, even though it received no fertilizer P. These results were associated with consistently reduced growth and turf quality for the no fertilizer treatment and increases in runoff depth compared with the fertilized treatments in three of the five study years. Maintaining a dense, healthy stand of turf through practices such as adequate N and K fertilization can reduce P transport by reducing runoff depth.