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Welcome to The Turf Zone podcast. This episode covers how potassium acetate improves shade tolerance associated with carbohydrate metabolism in creeping bentgrass. Written by Taylor Flanary, Mike Goatley, and Xunzhong Zhang – School of Plant and Environmental Sciences – Virginia Tech – Blacksburg, VA

Introduction and Objectives

Potassium is one of the major essential nutrients in turfgrass management. Potassium acetate is a unique form of potassium available to plants because the acetate may provide a direct carbon source for plant metabolism, especially under stressful environments such as low light or shade. This study evaluated effects of potassium acetate on shade tolerance of creeping bentgrass as measured by plant growth, visual quality, biomass production, non-structural carbohydrates (TNC), and root growth.

Materials and methods

Greenhouse pot trial. We harvested mature ‘A4’ creeping bentgrass plugs (4″ diameter) from field plots and transplanted into 6 inch pots filled with fine sand and 10% calcined clay on February 15, 2023. The bentgrass was maintained at 0.6 inch and fertilized at 0.2 lb/1000 ft² at transplanting and then 0.15 lb N/1000 ft² biweekly thereafter. After about 8 weeks of non-stressed growth with optimum temperature, water, fertilizer, and light in greenhouse conditions. We initiated treatments as listed below, with all other management variables kept identical for the treatments. The product “Stress Relefe” containing 25% potassium derived from potassium acetate obtained from Harrell’s in April 2023 was used for this trial. We tested 4 treatments with 4 replications. The treatment solutions (listed below) were applied to the canopy with the same amount of water applied to the control (treatment #1). Immediately after treatment, the grass was subjected to artificial shade conditions. A frame was installed on the bench of the greenhouse and covered with black knit high-density polyethylene shade cloth, placed on the top of the frame and the cloth was placed about 20 inches above the grass canopy. This allowed 70% photosynthetic active radiation (PAR) to reach the canopy. The grass was kept well irrigated and light intensity, air temperature, and relative humidity were monitored hourly in the greenhouse.

Treatments (applied biweekly):

1. Fertilized control biweekly (0.10 lb N/1000 ft² from fertilizer 28-8-18 biweekly)
2. K acetate 3 fl oz/1000 ft²/week + fertilized control biweekly
3. K Acetate 3 fl oz/1000 ft²/biweekly + fertilized control
4. K Acetate 6 fl oz/1000 ft²/biweekly + fertilized control

The stress period of the trial lasted for 8 weeks and a total of 4 treatment applications were made to the plugs. Turf quality, physiological responses, clipping production, leaf protein content, and non-structural carbohydrates were measured biweekly. At the end of the trial, root biomass was measured.

Results and Discussion

Turf quality

Foliar application of the potassium acetate product at 3 and 6 fl oz/1000 ft² biweekly improved turf quality relative to the control as measured on Day 14 and day 28, and all three potassium acetate rates improved turf quality relative to the control as measured at Day 42 and 56). The best turf quality was achieved when potassium acetate was applied at 3 fl oz/1000 ft² biweekly as measured at the end of the trial.

Photochemical efficiency

The potassium acetate at all rates improved PE relative to the control as measured from day 14 through day 56.

Leaf chlorophyll content

The potassium acetate at all rates improved chlorophyll content relative to the control as measured from day 14 through day 56. Among the treatments, potassium acetate at 3 fl oz/1000 ft² every 14 days tended to have better effects on chlorophyll content.

Clipping production.

There was no significant difference in clipping production among the treatments. Clipping weight tended to increase as the potassium acetate rate increased.

Total soluble protein content.

We found the protein measurement is more stable relative to amino acid content, so we measured leaf total soluble protein content in replacement of amino acid content. The potassium acetate significantly increased protein content in the leaf tissues as measured from day 28 through day 56. The total soluble content tended to increase as the potassium acetate rate increased.

Leaf non-structural carbohydrate content

The potassium acetate at 3 fl oz/1000 ft² weekly improved leaf glucose content when compared to the control as measured at day 56.

The potassium acetate at all rates improved leaf fructose content as measured at day 14. The potassium acetate at 3 fl oz/1000 ft² biweekly improved fructose content as measured at day 28 and 42. At the end of the trial, potassium acetate at 6 fl oz/1000 ft² biweekly improved fructose content relative to the control.

The potassium acetate at all rates improved leaf sucrose content when compared to the control as measured at day 56, with the treatment at 3 fl oz/1000 ft² weekly having better effects. The potassium acetate at 3 fl oz/1000 ft² weekly also improved sucrose content when compared to the control as measured at day 14 and 42.

The potassium acetate at all rates improved leaf total nonstructural carbohydrate (TNC, glucose + Fructose + sucrose) content when compared to the control as measured at day 56, with the treatment at 3 fl oz/1000 ft² weekly having better effects. The potassium acetate at 3 fl oz/1000 ft² weekly also improved TNC content when compared to the control as measured at day 14 and 42.
Root biomass

Foliar application of the potassium acetate product at 3 fl oz/1000 ft² weekly or biweekly and 6 fl oz/1000 ft² biweekly improved root biomass relative to the control. The greatest root biomass was found in the grass treated with potassium acetate at 3 fl oz/1000 ft² biweekly.

Summary. Foliar application of potassium acetate improved turf quality, photochemical efficiency, leaf chlorophyll content, leaf protein and nonstructural carbohydrate content when compared to a non-treated control in creeping bentgrass managed under shade stress conditions. The potassium acetate treatments also improved root biomass relative to the control. No consistent differences in turf quality and physiological responses among the three potassium acetate treatments were found in this study. The potassium acetate applied at 3 fl oz/1000 ft² weekly tended to have larger effects on leaf sucrose and TNC. The results of this study suggest that foliar application of potassium acetate may improve creeping bentgrass performance under shade environments.

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