Research Update

Effects of Organic Extract on Physiological Fitness and Quality of Creeping Bentgrass under Salt Stress Conditions

Authors: Xunzhang Zhang, Ph.D., Mike Goatley, Ph.D., Isabel Brown, Kelly Kosiarski, and Rose Harvey School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA

Salt stress is a major limiting factor in turfgrass management in many areas. Organic extract EarthMax contains not only humic acids, but also beneficial microorganisms including Bacillus Subtillis . Previous study showed that EarthMax improved turfgrass quality and physiological fitness under summer stress. The objective of this study was to investigate if foliar application of Bacillus Subtillis -containing EarthMax at three different rates affects physiological fitness and quality of creeping bentgrass under salt stress conditions.

We harvested mature ‘A4’ creeping bentgrass plugs (4" diameter) from field plots and transplanted into 6 inch pots filled with a USGA sand in Jan. 2022. The bentgrass was maintained at 15 mm and fertilized at 0.2 lb/1000 ft2 at transplanting and then 0.15 lb N/1000 ft2 biweekly thereafter. After about five weeks of nonstressed growth with optimum temperature, water, fertilizer, and light, we placed the pots in a controlled environment growth chamber at 72 F day (12 h)/64 F night, light intensity at 450 µmol m-2 s-1, 12 h photoperiod, and 65% RH. EarthMax and salt stress treatments were initiated. There were 5 treatments with 4 replications. A randomized block design was used. The treatments include 1). fertilized control + salt stress; 2). Fertilized control + no salt stress; 3). Earthmax at 1 fl oz/1000 ft2 + salt stress; 4). EarthMax at 2 fl oz/1000 ft2; and 5). EarthMax at 4 fl oz/1000 ft2. The treatments were applied biweekly. The EarthMax solution was applied to the canopy uniformly and the same amount of water was applied to the control treatment #1 and 2). After 12 h of EarthMax treatment, we initiated salt stress treatment. Sodium chloride (NaCl) solution with NaCl concentration gradually increased from 2 ds/m to 8 ds/m concentration in 48 h period. The salt concentration in the growth media was maintained at about 8 ds/m level during the trial.

The results showed that EarthMax application at the three rates improved leaf color ratings (Fig. 1) as measured from day 14 through day 56. EarthMax application at all three rates improved GL as measured at day 28, day 42, and day 56. Application of EarthMax at all three rates increased chlorophyll content at day 42 and 56. EarthMax treatments improved PE as measured from day 14 through day 56, except for low rate at day 28. EarthMax applied at mid and high rates improved antioxidant enzyme SOD activity at measured at day 28, 42, and 56. EarthMax treatments increased root length (Fig. 1) and root viability. The results of this study indicated that foliar application of organic extract can improve physiological fitness and salt stress tolerance of creeping bentgrass.

We would like to thank Harrell’s for the support of this research.

Leaf color response to EarthMax treatment in creeping bentgrass under salt stress.

Root growth response to EarthMax treatment in creeping bentgrass under salt stress.