Do Humic Substances Bolster Water and Nutrient Availability ?

Increasingly, products containing humic substances are appearing in the turf industry market claiming to reduce water and fertilizer use by increasing soil moisture and nutrient availability. Humic acid is the most common humic substance that has been studied, but results have been highly variable (Cooper et al.; 1998).The response of humic acid is difficult to interpret due to confounding effects of nutrients and other ingredients often included in humic substance products (Karnok, 2000). This study tested a pure humic acid along with commercial humic substance products in both a greenhouse and field experiment. The greenhouse portion of the study used a controlled environment to evaluate the effects of the pure product while the field portion evaluated commercial humic substance products under golf course conditions. Our objective was to determine if humic substances 1) can increase water retention in sand putting greens, and 2) improve uptake of phosphorus. The greenhouse experiment consisted of creeping bentgrass [Agrostispalustris L.) sod grown in 24 centimeters x 36 cm x 30 cm tubs with calcareous sand. The tubs had drainage holes in the bottom and were placed in larger tubs on top of 4 cm of gravel. This setup simulated a USGA putting green (Photo 1). Three organic acids were applied to the turf as watering solutions delivered through an irrigation system. The organic acids consisted of a pure leonardite humic acid (SigmaAldrich), a tannic acid (J.T. Baker Chemical Co.) and citric acid (Mallinckrodt Chemicals) applied at normalized carbon rates of 250 milligrams per liter. The amount of material applied is about 100 times higher than rates used in the This greenhouse experiment urith creeping bentgrass sod field. The organics groum in calcareous sand on gravel beds simulates a were evaluated against USGA putting green. Continued on page 52 Velvet bentgrass Researchers explore the low-input potential behind alternative cultivars 54