2017 ASHS Annual Conference

Turfgrass managers often apply large doses of potassium to turfgrass (>300 kg/ha) to golf course turfgrass. The conventional wisdom is that high levels of potassium confer various stress tolerances to the plant. However, potassium applications have been associated with increased winter diseases in northern climates. The objective of this long term research project was to evaluate putting green quality, growth, and disease incidence over a wide range of soil test and tissue potassium levels. This project was initiated in 2011 on a USGA putting green with ‘A4’ creeping bentgrass (Agrostis stolonifera L.). The experiment was a randomized complete block design with four replications. The treatments included five different levels of biweekly liquid potassium sulfate at rates ranging from zero to 30 kg/ha of K. Paired soil and plant tissue samples were collected monthly along with measurements of clipping yield. Turfgrass color and visual quality was evaluated biweekly. Disease incidence was quantified using visual estimation, counting infection centers, and by the grid intersection method. Few, if any, differences in turf color, quality, or growth rate among the treatments were observed during the first four years of the study. In the fifth year, significantly lower turf quality was observed on the two no K treatments. However, these low K treatments had significantly less microdochium patch than the treatments receiving K applications during the past three winters. Interestingly, the turf quality of these two 'low K' treatments improved in 2016, and were found to be statistically similar or better than the treatments recieving regular doeses of K. Plant tissue K content appeared to be a more reliable indicator of potential for microdochium patch with low potential when tissue K fell below 1.5%. Mehlich-3 soil K was ranged from 20-50 mg/kg, but changes in soil K did not reflect the amount of K being removed from the soil by the grass by mowing suggesting that the bentgrass was extracting a substantial amount of K from non-exchangeable pools of K and traditional soil testing methods may not be appropriate for evaluating plant available potassium. No significant differences in dollar spot or brown patch diseases were observed during the study. Results suggest that potassium fertilization can be manipulated to affect microdochium patch on bentgrass.