Predicting need for phosphorus fertilizer by soil testing during seeding of cool season grasses

Recent changes in soil testing methodology, the important role of P fertilization in early establishment and soil coverage, and new restrictions on P applications to turf suggest a need for soil test calibration research on Kentucky bluegrass (Poa pratensis L.), tall fescue (Festuca arundinacea Schreb), and perennial ryegrass (Lolium perenne L.). Greenhouse and field studies were conducted for 42 days to examine the relationship between soil test P levels and P needs for rapid grass establishment using 23 NJ soils with a Mehlich-3 extractable P ranging from 6 to 1238 mg·kg^-1. Soil tests (Mehlich-1, Mehlich-3, and Bray-I) for extractable P were performed by inductively coupled plasma atomic emission spectroscopy (ICP). Mehlich-3 extractable P and Al were measured to evaluate the ratio of P to Al as a predictor of need for P fertilizer. Kentucky bluegrass establishment was more sensitive to low soil P availability than tall fescue or perennial ryegrass. Soil test extractants Mehlich-1, Bray-I, or Mehlich-3 were each effective predictors of need for P fertilization. The ratio of P to Al (Mehlich-3 P/AI %) was a better predictor of tall fescue and perennial ryegrass establishment response to P fertilization than soil test P alone. The Mehlich-1, Bray-I, and Mehlich-3 soil test P critical levels for clipping yield response were in the range of 170 to 280 mg·kg^-1, depending on the soil test extractant, for tall fescue and perennial ryegrass. The Mehlich-3 P/AI (%) critical level was 42% for tall fescue and 33% for perennial ryegrass. Soil test critical levels, based on estimates from clipping yield data, could not be determined for Kentucky bluegrass using the soils in this study. Soil testing for P has the potential to aid in protection of water quality by helping to identify sites where P fertilization can accelerate grass establishment and thereby prevent soil erosion, and by identifying sites that do not need P fertilization, thereby preventing further P enrichment of soil and runoff. Because different grass species have varying critical P levels for establishment, both soil test P and the species should be incorporated into the decision-making process regarding P fertilization.