Creeping bentgrass putting green Mehlich-3 soil test phosphorus requirements

The Mehlich-3 soil test is extensively used to determine available soil P; however, calibration studies for sand greens are lacking. The purpose of this field study was to evaluate turfgrass response to different soil test P (STP) levels and application of trinexapac-ethyl (TE) (0.1 kg a.i. ha ^-1 every 200 growing degree days). A creeping bentgrass (Agrostis stolonifera L. 'Penn A4') putting green was constructed at the O.J. Noer Turfgrass Research and Education Facility in Madison, WI, using 30 cm of calcareous sand overlaying pea gravel. A factorial of four STP levels, 0 to 95 mg P kg ^-1, was established with monopotassium phosphate (MKP) with or without TE was arranged in a randomized complete block design with four replicates. Mehlich-3 STP level, clipping yield, tissue P content, and visual turfgrass quality were quantified monthly for two growing seasons. Nonlinear regression analysis was used to calculate STP and tissue P content critical points. Although a wide range of initial STP was established, STP levels in all treatments declined substantially during the two season study, eventually stabilizing to approximately 3 to 5 mg P kg ^-1. Turfgrass quality was the most sensitive to both STP and tissue P content and provided clear critical values with linear plateau regression. The Mehlich-3 STP and tissue P content critical points for visual turfgrass quality ranged from 6 to 11 mg kg ^-1 and 1.5 to 4.4 g kg ^-1, respectively. While TE sometimes statistically altered the STP critical point, the difference was not substantial enough to suggest different STP recommendations for turf maintained with or without TE.