Influence of Humic Substances on Irrigation Frequency and Phosphate Absorption of Creeping Bentgrass Putting Greens

Humic substances (HS) reportedly enhance moisture retention of soil. However, no information is available as to the effects of HS on sand-based golf course putting greens. HS have acidic functional groups (COOH) that are reaction sites on the molecule. An greenhouse experiment was conducted to evaluate the effect that the acidic functional groups in humic acid, tannic acid and citric acid have on the volumetric water content of sand, and the phosphorus (P) content of ‘Dominant’ creeping bentgrass (Agrostis palustris L.). Bentgrass plugs were grown in calcareous sand and irrigated with 250 mgL C solutions of each of the organic acid products. Irrigation occurred when the volumetric water content of the soil reached 5%. Soil moisture was measured with a HydroSense® water content sensor for 3 months. Phosphate was added as KH2PO4 at 50 kg·ha 2 months into the experiment. The irrigation interval was longer between watering for humic acid, but rarely differed between the treatments. Daily soil moisture percentage following irrigation with all organic acid treatments was different from the control, with humic acid retaining moisture longer on average. Humic acid, tannic acid, and citric acid increased tissue concentrations of P, with tannic acid having the highest percent increase. Further research is necessary to evaluate the residual effects the organic acids may have on longevity in the soil.