Quantitative and qualitative responses of an established Kentucky bluegrass (Poa pratensis L.) turf to N, P, and K additions

Kentucky bluegrass is a common turf species used on golf courses, sports fields, municipal parks, sod farms, road banks, as well as residential and school yards. Our objective was to determine the effects of N, P, K rates on turfgrass quantitative response (clipping yield and underground turf biomass) and qualitative response (shoot density and foliage colour) under a continuous clipping removal. A 3-yr field study was conducted on two sites, a sand that met the specifications of the United States Golf Association (USGA) and a loam. The factorial experiment was arranged in a randomized complete block design with four replicates and different levels of three nutrients, N (0 or 50 to 300 kg ha(-1) yr(-1)), P (0 or 21.8 to 87.3 kg P ha(-1) yr(-1)), and K (0 or 41.7 to 250 kg K ha(-1) yr(-1)). The maximum clipping yield was produced at the rate of 200 kg N ha(-1) yr(-1) in the loam and 300 kg N ha(-1) yr(-1) in the sand. Increasing N rates linearly reduced underground turf biomass. Added P and K had no effect on clipping yield and underground turf biomass. Nitrogen significantly improved shoot density and foliage colour. However, equivalent shoot density and colour ratings required 40 to 80 kg more N ha(-1) yr(-1) in the sand compared to the loam. Phosphor-us and K had no significant effect on shoot density and colour in the loam. Colour response to P and K depended on N rates in the sand. Fertilizer units needed to increase Soil test P averaged 6 kg added P ha(-1) mg(-1) PM-III kg(-1) across soil types. To replenish soil K, 7 kg K ha(-1) per mg KM-III kg(-1) were required in the sand, and 3 kg K ha(-1) per mg KM-III kg(-1) in the loam. Phosphorus and K fertilizer programmes should account for P and K removals to maintain low to medium fertility levels for P, and medium for K when conditions are similar to those in this research.