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Evaluating Effects of Humic and Fulvic Acid Products 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 and Objective Humic acid (HA) is the fraction of humic substances that is not soluble in water under acidic conditions (pH less than 2), but is soluble at higher pH values. Fulvic acid (FA) is the fraction of humic substances that is soluble in water under all pH conditions. Humic acids have higher molecular weight than fulvic acis. HA and FA may enhance root growth due to auxin-like activity and improved mineral nutrient availability (Schmidt and Zhang, 1999). In our recent growth chamber study, we found that both fulvic acid (FA) and humic acid (HA) improved creeping bentgrass quality under heat and mild drought stress. O’Dennell (1973) noted that HA at 0.05% to 0.1% could mimic auxin to promote root growth under non-stress conditions. Zhang and Schmidt (1999) found that HA at 11.6 g/1000 ft2 (=0.33%) improved drought tolerance in Kentucky bluegrass. Similarly Zhang and Ervin (2004) found that HA at 11.1 g/1000 ft2 (= 0.32%) enhanced drought tolerance of creeping bentgrass. In a putting green field trial in 2017, we observed that HA at 1.78 oz/1000 ft2 (~0.2%) provided a superior drought response to the lower rate (0.78 oz/1000 ft2, ~0.1%). We also found that FA at 1.2 oz/1000 ft2 did not show consistent beneficial effects as it did in the growth chamber trial. We speculate that the optimum FA rate may be higher in field situations relative to that under the controlled environment. The objective of this research was to evaluate two rates of HA and FA under field conditions and examine effects of FA and HA at both rates on turf
quality and root growth of a creeping bentgrass putting green during summer stress.
Research procedures The study was carried out on the bentgrass putting green at the Virginia Tech Turfgrass Research Center, Blacksburg, VA. There were 6 treatments with 4 replications arranged in a randomized complete block design with 6 x 6 ft plots. Regular mowing and irrigation practices for a putting green were performed. The HA and FA products were provided by Harrell’s.
The humic acid product (Diamond Grow-Humi [K] liquid, Humic Growth Solution, FL) contains 12% humic acid based on analysis by A&L Western Ag Lab. The fulvic acid product [Diamond Grow – Ful-Grow Gold liquid concentrate, Humic Growth Solution, FL] contains 9% fulvic acid. Based on our mung bean bioassay research and previous reports from the literature, a 1% solution of each product was applied as the low rate at 3.5 L per 1000 ft2. In this way, the application solution of HA product contained 0.12% HA (0.89 fl oz/1000 ft2). We used 2%
Table 1: Effects of fulvic acid (FA) and humic acid (HA) on turfgrass quality in creeping bentgrass putting green. Treatment
Leaf color (1-9, 9 = best) 19-Jun
2-Jul
16-Jul
30-Jul
13-Aug
27-Aug
Control
7.0a
6.6a
6.3b
6.1b
6.1b
6.1b
FA1.2
7.0a
6.8a
6.9a
6.5ab
6.8a
6.8a
FA2.4
7.1a
6.8a
6.8a
6.9a
6.9a
6.8a
HA0.89
6.9a
6.6a
6.9a
6.8a
6.9a
7.0a
HA1.78
7.0a
6.6a
6.8a
6.8a
6.8a
6.9a
Mean followed by same letters in each column are not significantly different at P = 0.05. Table 2: Effects of fulvic acid (FA) and humic acid (HA) on photochemical efficiency (PE) and chlorophyll content in creeping bentgrass putting green.
Date Treatment
19-Jun
2-Jul
16-Jul
30-Jul
13-Aug
27-Aug
PE (Fv/Fm) Control
0.53ab
0.63b
0.56a
0.46b
0.64b
0.57c
FA1.2
0.60ab
0.72a
0.63a
0.55a
0.64b
0.58bc
FA2.4
0.58ab
0.65b
0.62a
0.56a
0.66ab
0.61ab
HA0.89
0.61a
0.66b
0.57a
0.52ab
0.66ab
0.59abc
HA1.78
0.54ab
0.63b
0.64a
0.55a
0.68a
0.62a
Chlorophyll (mg/g FW) Control
2.09b
1.95a
2.20b
2.21b
1.91b
1.86b
FA1.2
2.21a
2.21a
2.48a
2.50ab
1.98b
1.98b
FA2.4
2.09b
1.98a
2.54a
2.85a
2.17a
2.14a
HA0.89
2.03b
2.07a
2.38ab
2.44b
2.02ab
1.99b
HA1.78
2.09b
2.09a
2.41ab
2.51ab
1.99ab
1.98b
Mean followed by same letters in each column are not significantly different at P = 0.05.
26 | Virginia Turfgrass Journal January/February 2019 www.vaturf.org
