Research Update

What is the Best Way to Satisfy the P Requirements of Creeping Bentgrass?

By Nathaniel Leiby (BS ’18, current MS AGRO candidate) and Max Schlossberg, PhD., Penn State University Center for Turfgrass Science

Relative to current ‘programmatic’ and/or soil test driven ‘responsive’ fertilization approaches, withholding P fertilizer from creeping bentgrass putting greens until emergence of visual P deficiency symptoms may prove both an environmentally responsible and agronomically effective practice. Prompting our research objectives in July 2018, which were to quantify how programmatic or responsive P fertilization regiments support creeping bentgrass vigor and/or root length density relative to withholding P fertilizer. ‘Penn A-1/A-4’ creeping bentgrass ‘programmatic’ plots were initially treated with monopotassium phosphate (MKP, 0-52-35) to supply 2 lbs P₂O₅ / M-year in four split-applications. Random assignment and application of ‘responsive’ P fertilization treatment (approx. 1 lb P₂O₅ / M, as MKP) to previously unfertilized ‘control’ plots was triggered by: (1) Visual deficiency symptoms; i.e., purple coloration of old leaves on ≥7 unfertilized plots, or (2) leaf clipping P levels ≤0.42% in four or more unfertilized plots. Canopy vegetative and color indices were collected semi-weekly over the 2018, 2019, and 2020 seasons. A deep root sampling event (4–11" depth) preempted the responsive P fertilization treatment. Likewise, emergence of visual deficiency symptoms was followed by clipping yield collection and leaf tissue analysis. A second, deep root sampling event was collected from all plots one year following ‘responsive’ treatment initiation. While sufficient leaf P levels and a canopy free of deficiency symptoms were supported by the programmatic P fertilization regime, improved vigor and/or canopy density weren’t. Final root analyses are underway, thus please check back for conclusions soon!