Evaluating Effects of Humic and Fulvic Acid Products for Improving Bentgrass Putting Green Quality and Root Growth during Summer Stress

摘要

Introduction and ObjectiveHumic 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 blue-grass. 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 turfquality and root growth of a creeping bentgrass putting green during summer stress.