Anthropogenic Placic Horizon Formation in Two-Tiered Golf Course Putting Greens.

Placic horizons have been observed at the sand/gravel interface (30 cm depth) in the two-tiered putting greens of a golf course on the Big Island of Hawaii. Results from x-ray diffraction and chemical extractions suggest that the placic horizon is composed of ferrihydrite. Formation of the placic horizon is presumed due to iron chemistry at the textural discontinuity and associated redox conditions, where it has been hypothesized that iron is derived from ferrous sulfate treatment of the turfgrass. Two-tiered putting green soil profiles were constructed in clear acrylic PVC pipes and were seeded with Agrostis stolonifera in the greenhouse. Soil profiles were 80/20 mixtures of sand/sphagnum peat, and consisted of 25 cm of sand overlaying 8 cm of pea gravel. In addition to an untreated control, cores were fertilized with iron in the form of ferrous sulfate at rates of 3, 6, or 30 g m^-2 with an application volume of 25 L m^-2 once every two weeks. Treatments were replicated three times. Turfgrass was irrigated to replace 120% of water lost by evapotranspiration. Iron oxidation was quantified visually with digital image analysis using ImageJ. Air infiltration rate was measured using an air permeameter as a proxy for water infiltration. Data after eight months of experimentation are reported.