Evaluating Effects of Pigment of Harrell’s Sources for Improving Bentgrass Putting Green Quality and

Introduction

In our field trial in 2018, we found that the pigment of Harrell’s source at 0.22 fl oz/1000 ft² (10 fl oz/acre) every 14 days improved visual leaf and color and photochemical efficiency of creeping bentgrass putting greens during summer months, but did not impact root growth and chlorophyll. It is possible that the rate may be too high so that the pigment may coat the leaf surface and reduce gas exchange via stomata and carbohydrate production for root and shoot growth. It is important to test different rates of the pigment application to identify optimum rate and frequency of the pigment application for improving turf quality, physiological fitness, and root growth during summer stress

Research Procedures

This study was carried out in the creeping bentgrass putting green at Virginia Tech Turfgrass Research Center, Blacksburg, VA. There were four treatments with four replications. Plot size is 6 x 6 ft. Regular mowing and irrigation were performed. A randomized block design was used with four replications. The pigment product Harrell’s PAR SG (a.i. proprietary copper based pigment) was used in this study.

The four treatments were as follows:

1). Fertilized control (0.15 lb (68.1g) N per 1000 sq ft every 14 days from 28-8-18).

2). Pigment at 2.5 fl oz/acre (0.057 fl oz/1000 ft ² ) every 7 days.

3). Pigment at 5.0 fl oz/acre (0.115 fl oz/1000 ft ² ) every 7 days.

4). Pigment at 10 fl oz/acre (0.23 fl oz/1000 ft ² ) every 7 day.

All treatments received the same amount of fertilizers as treatment #1 (control) during the experiment.

The period of the trial lasted for 14 weeks from early June through mid Sept. On August 8, irrigation was reduced to induce mild drought stress and resumed after August 16. The data was collected before drought stress (August 2) and at the end of drought period.

The following measurements took place every 14 days after initial treatments:

1). Leaf color is rated on a visual scale of 1 – 9 with 9 indicating the dark green color, and 1 indicating brown color.

2). Canopy photochemical efficiency was measured based on the Fvm, which is the ratio of variable chlorophyll fluorescence (Fv) to maximum chlorophyll fluorescence (Fm).

3). Leaf samples were collected and chlorophyll content was determined using spectrophotometer method (Zhang et al., 2005).

4). Root biomass. At the end of the trial, 4 root samples (2 cm diameter and 15 cm deep) were collected from each plot, washed and root dry weight was determined after the samples were dried at 70°C for 72 h.

5). Root characteristics. The root length, root diameter, root surface area, root volume, and root tips were analyzed using WinRhizo technology. Briefly, after fine cleaning of each root sample, the sample from each plot was divided into multiple subsamples. Each sub-sample was scanned using WinRhizo and all root morphological parameters were generated and analyzed.

Results and Discussion

We found that application of the pigment at the three rates improved leaf color in all sampling dates 14 days after initial application except for the low rate (2.5 fl oz) on July 5 and August 30 (Table 1). Pigment applied at mid rate (5 fl oz) and high rate (10 fl oz) had a similar effects on leaf color, and both rates had greater positive effect on leaf color than the low rate.

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Table 1: Leaf color responses to Harrell’s pigment product in creeping bentgrass putting green.

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Treatment: Control

Rate (fl oz/A): 0

Leaf color (1-9, 9 = dark green)

7-Jun: 6.5a

21-Jun: 6.1c

5-Jul: 6.1b

19-Jul: 6.0c

2-Aug: 6.0d

16-Aug: 6.1d

30-Aug: 6.8b

13-Sep: 6.9c

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Treatment: Pigment

Rate (fl oz/A): 2.5

Leaf color (1-9, 9 = dark green)

7-Jun: 6.5a

21-Jun: 6.5b

5-Jul: 6.4b

19-Jul: 6.5b

2-Aug: 6.5c

16-Aug: 6.6c

30-Aug: 7.0b

13-Sep: 7.4b

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Treatment: Pigment

Rate (fl oz/A): 5

Leaf color (1-9, 9 = dark green)

7-Jun: 6.5a

21-Jun: 7.0a

5-Jul: 7.0a

19-Jul: 7.0a

2-Aug: 7.0b

16-Aug: 7.1b

30-Aug: 7.5a

13-Sep: 7.9a

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Treatment: Pigment

Rate (fl oz/A): 10

Leaf color (1-9, 9 = dark green)

7-Jun: 6.5a

21-Jun: 7.0a

5-Jul: 7.0a

19-Jul: 7.0a

2-Aug: 7.4a

16-Aug: 7.4a

30-Aug: 7.8a

13-Sep: 8.0a

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Means followed by same letters with each column are not significantly different at P = 0.05.

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The pigment did not impact leaf chlorophyll content in all sampling dates (Table 2). This suggests that the pigment-induced leaf color improvement may be associated with visual color change due to pigment coverage.

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Table 2: Leaf chlorophyll responses to Harrell’s pigment product in creeping bentgrass putting green.

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Treatment: Control

Rate (fl oz/A): 0

Leaf chlorophyll (mg/g FW)

7-Jun: 2.61a

21-Jun: 2.47a

5-Jul: 2.59ab

19-Jul: 2.83a

2-Aug: 3.02a

16-Aug: 2.96a

30-Aug: 3.38a

13-Sep: 3.25a

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Treatment: Pigment

Rate (fl oz/A): 2.5

Leaf chlorophyll (mg/g FW)

7-Jun: 2.58a

21-Jun: 2.57a

5-Jul: 2.23b

19-Jul: 2.78a

2-Aug: 3.08a

16-Aug: 2.94a

30-Aug: 3.30a

13-Sep: 3.27a

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Treatment: Pigment

Rate (fl oz/A): 5

Leaf chlorophyll (mg/g FW)

7-Jun: 2.42a

21-Jun: 2.53a

5-Jul: 2.98a

19-Jul: 2.84a

2-Aug: .25a

16-Aug: 3.00a

30-Aug: 3.45a

13-Sep: 3.46a

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Treatment: Pigment

Rate (fl oz/A): 10

Leaf chlorophyll (mg/g FW)

7-Jun: 2.42a

21-Jun: 2.49a

5-Jul: 2.66ab

19-Jul: 2.86a

2-Aug: 3.19a

16-Aug: 2.73a

30-Aug: 3.33a

13-Sep: 3.07a

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Means followed by same letters with each column are not significantly different at P = 0.05.

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Virginia Tech creeping bentgrass putting green field plots in June, 2019

The pigment applied at mid and high rates increased photochemical efficiency at the end of drought period (August 16; Table 3). However, the pigment application did not consistently impact PE in other sampling dates.

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Table 3: Canopy photochemical efficiency (PE) responses to Harrell’s pigment product in creeping bentgrass putting green.

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Treatment: Control

Rate (fl oz/A): 0

PE (Fv/Fm):

7-Jun: 0.62a

21-Jun: 0.62a

5-Jul: 0.66a

19-Jul: 0.55ab

2-Aug: 0.57a

16-Aug: 0.55b

30-Aug: 0.63a

13-Sep: 0.63a

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Treatment: Pigment

Rate (fl oz/A): 2.5

PE (Fv/Fm):

7-Jun: 0.56a

21-Jun: 0.67a

5-Jul: 0.69a

19-Jul: 0.50b

2-Aug: 0.59a

16-Aug: 0.61ab

30-Aug: 0.65a

13-Sep: 0.64a

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Treatment: Pigment

Rate (fl oz/A): 5

PE (Fv/Fm):

7-Jun: 0.60a

21-Jun: 0.61a

5-Jul: 0.69a

19-Jul: 0.53ab

2-Aug: 0.62a

16-Aug: 0.62a

30-Aug: 0.63a

13-Sep: 0.68a

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Treatment: Pigment

Rate (fl oz/A): 10

PE (Fv/Fm):

7-Jun: 0.59a

21-Jun: 0.65a

5-Jul: 0.71a

19-Jul: 0.60a

2-Aug: 0.61a

16-Aug: 0.63a

30-Aug: 0.63a

13-Sep: 0.69a

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Means followed by same letters with each column are not significantly different at P = 0.05.

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Table 4: Responses of root length, surface area (SA), root diameter, root volume, root tips, root biomass, and root viability to Harrell’s pigment product in creeping bentgrass putting green.

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Means followed by same letters within each column are not significantly different at P = 0.05.

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Treatment: Control

Rate (fl oz/A): 0

Length (cm/cm³): 45.9b

SA (cm²/cm³): 3.18b

Diam (mm): 0.226a

Volume (cm³/cm³): 41.4a

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Treatment: Pigment

Rate (fl oz/A): 2.5

Length (cm/cm³): 73.6ab

SA (cm²/cm³): 5.05ab

Diam (mm): 0.221a

Volume (cm³/cm³): 43.6a

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Treatment: Pigment

Rate (fl oz/A): 5

Length (cm/cm³): 89.2a

SA (cm²/cm³): 6.14a

Diam (mm): 0.223a

Volume (cm³/cm³): 47.6a

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Treatment: Pigment

Rate (fl oz/A): 10

Length (cm/cm³): 70.5ab

SA (cm²/cm³): 5.15ab

Diam (mm): 0.229a

Volume (cm³/cm³): 47.0a

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Treatment: Control

Rate (fl oz/A): 0

Tips (#/dm³): 474.9b

Mass (mg/dm³): 0.753b

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Treatment: Pigment

Rate (fl oz/A): 2.5

Tips (#/dm³): 652.7ab

Mass (mg/dm³): 1.175ab

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Treatment: Pigment

Rate (fl oz/A): 5

Tips (#/dm³): 839.4a

Mass (mg/dm³): 1.355a

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Treatment: Pigment

Rate (fl oz/A): 10

Tips (#/dm³): 663.8ab

Mass (mg/dm³): 1.220ab

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Left Side: Control. Right Side: Pigment (5 fl oz/acre). Photo taken in August 2019.

In this study, we found that the pigment applied at mid rate (5 fl oz/acre) significantly promoted root length, root surface area, number of root tips, and root biomass relative to the control (Table 4). However, it did not impact root diameter and volume. The pigment applied at 5 fl oz/acre increased root length, surface area, and biomass by 94.3%, 93.1%, and 79.9%, respectively, when compared to the control.

In summary, application of pigment at 5 fl oz/acre and 10 fl oz/acre weekly consistently improved leaf color at all sampling dates, and also photochemical efficiency during drought stress. Application of the pigment at 5 fl oz/acre also improved root length, surface area, number of root tips, and root biomass relative to the control. The results of this suggest the pigment applied at 5 fl oz/ acre weekly can be used to improve turfgrass performance and root growth in creeping bentgrass putting green.

Acknowledgment

We would like to thank Harrell’s for the financial support of this research project and Mr. Jonathan Dickerson for the help.