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Humic Acid-Based Biostimulant Improves Salt Stress Tolerance of Creeping Bentgrass By Xunzhong Zhang, Ph.D., Mike Goatley, Ph.D., Rose Harvey, Isabel Brown, and Kelly Kosiarski School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA
T
urfgrass is perhaps one of the most important vegetative ground covers in the world as it provides functional, recreational, and ornamental purposes to our landscapes, particularly in urban communities. Salt stress is considered to be one of the major limiting factors in turfgrass management in many regions. Salt stress causes ion imbalance, excess reactive oxygen species-induced oxidative injury, inhibition of root and shoot growth. To improve turfgrass quality and stress tolerance, turfgrass practitioners have used various cultural practices and chemical products, including biostimulants. Plant biostimulants have been used to improve stress tolerance and quality of turfgrasses. Humic acid-based biostimulants have been used to improve turfgrass tolerance to abiotic stresses including salt stress. However, the mechanisms of humic acid-based biostimulant’s impact on salt stress tolerance have not been well understood. This study was to investigate the responses of turf quality, shoot and root growth, chlorophyll, photochemical efficiency, antioxidant metabolism and leaf nutrient content to exogenous application of humic acid-based biostimulant under salt stress conditions. Mature “A4” creeping bentgrass was transplanted from field plots to 15-cm pots. After growing in the non-stressed, optimum temperature, water, fertilizer, and light for five weeks, humic
acid-based biostimulant ‘EarthMax’ (5.6% humic acid, Harrell’s, Lakeland, FL) and salt stress treatments were initiated. There were five treatments including
1. Salt stress control 2. non-salt control 3. ‘EarthMax’ at 1 fl oz/1000 ft2 + salt stress 4. ‘EarthMax’ at 2 fl oz/1000 ft2+salt stress 5. ‘EarthMax’ at 4 fl oz/1000 ft2+salt stress The ‘EarthMax’ solution was applied to the canopy biweekly, and the same amount of water was applied to the controls (treatment #1 and 2). After 12 h of ‘EarthMax’ treatments, the salt stress was initiated. Sodium chloride (NaCl) solution was added into the soil with the concentrations gradually increasing from 2 ds/m to 8 ds/m within 48 h after initiation of salt stress treatment. The salt concentration in the growth media was maintained at about 8 ds/m level during eight-week period of the trial by monitoring the salt concentration with portable TDR-300 meter. Leaf color, green leaf percentage (GL), clipping yield, chlorophyll content, photochemical efficiency (PE), antioxidant superoxide dismutase (SOD) activity, leaf inorganic ions, and root growth characteristics and viability were measured. A randomized block design was used with four replications. The data were analyzed with an analysis of variance and mean separations were performed with Fisher’s protected LSD at P = 0.05. Salt stress reduced leaf color ratings, clipping yield, chlorophyll content, photochemical efficiency, and reduced potassium (K+) and magnesium (Mg++), and increased sodium (Na+) content. The green leaf percentage (GL) declined in response to salt stress. The humic acid-based biostimulant applied at all three rates improved leaf color (Fig. 1), clipping production, GL, photosynthetic pigments, PE, antioxidant SOD activity, and root viability. The biostimulant treatments at the three rates reduced Na+ uptake and increased K+ and Mg++ nutrients uptake relative to the salt control. The results of this study indicated foliar application of the biostimulant, especially at the high rate (4 fl oz/1000 ft2) improved physiological fitness, leaf color, root viability, and salt stress tolerance of creeping bentgrass.
We’d like to thank Harrell’s for the support of this study.
Figure 1. Effects of foliar application of ‘EarthMax’ on leaf color of creeping bentgrass under salt stress.
14 | VIRGINIA TURFGRASS JOURNAL January/February 2024 www.vaturf.org
