Phosphorus and Nitrogen Fertilizer Effects On Turfgrass Grown On a Low Phosphorus Sub-Soil.

Phosphorus (P) is an essential nutrient for plant growth.    The majority of soils in Michigan have sufficient levels of soil P to support turfgrass growth but new construction often results in turfgrass planted on sub-soils high in clay content, and low in soil P.  The objective was to determine the effect of nitrogen (N) and P fertilizer applications on Kentucky bluegrass (Poa pratensis L.) sod planted on high clay, low P sub-soil.  Research was initiated in 2004 at the Hancock Turfgrass Research Center, Michigan State University.  The soil in the research area was modified by removing the existing soil to a depth of 30 cm and replacing it with the C horizon from a loam soil to simulate an urban sub-soil.  Initial Olsen soil P level was 7 mg kg^-1.  The nitrogen (N) rate treatments were 98, 156, and 208 kg N ha^-1 yr^-1.  The P treatments were 0, 24, and 48 kg P₂O₅ ha^-1 yr^-1.  The 98 kg N ha^-1 rate treatment had the lowest clipping yields, and color and quality ratings, but maintained acceptable color and quality over the 3-years of research.  The 208 kg N ha^-1 rate had the highest turfgrass color, quality, and clipping yields.  There were no effects from P applications throughout the research.  The mean soil P level from the transplanted sod thatch layer was 58 mg kg^-1.  The sod thatch layer with high soil P level resulted in the lack of turfgrass response to P applications.  For turfgrass established from sod grown on a soil with a high soil P level, our research concludes that even when transplanting the sod to a low P soil, the turfgrass may not respond and P fertilizer applications may be unnecessary.