EVALUATING EFFECTS OF PIGMENT OF HARRELL’S SOURCES
Feature Story
for Improving Bentgrass Putting Green Quality and Root Growth during Summer Stress By Xunzhong Zhang, Ph.D. and Mike Goatley, Ph.D., School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA
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 ft2) every 7 days. 3). P igment at 5.0 fl oz/acre (0.115 fl oz/1000 ft2) every 7 days. 4). P igment at 10 fl oz/acre (0.23 fl oz/1000 ft2) every 7 day.
18 | VIRGINIA TURFGRASS JOURNAL March/April 2020 www.vaturf.org
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.
