Iron Layering in Two-Tiered Golf Course Putting Green Soils.

Layers of cemented iron/manganese, which meet the criteria of the placic horizon in Soil Taxonomy, have been observed at textural discontinuities in two-tiered golf course putting greens. The layer most commonly forms at the sand/gravel interface (30 cm depth), although layering has been observed higher in the profile. The cemented layer severely impedes subsurface drainage and results in deterioration of turfgrass quality due to persistent wet, anaerobic conditions in the root zone. In this study, putting green profile samples were collected from 30 different golf courses around the U.S., with approximately half of the sites featuring some degree of iron/manganese layering. The profiles were analyzed for pH and iron content by depth, and these factors were compared with climatic data, irrigation water quality, and management practices. Iron/manganese layering was observed across a broad range of climatic regimes and irrigation water sources, suggesting that these factors do not contribute significantly to its formation. The layering was most pronounced at sites with acidic soil pH, and the layering always occurred at textural discontinuities. Mass balance calculations suggest that modest rates of iron fertility can contribute as much as 10 to 100 times the amount of iron required for forming the layer. Processes leading to iron layer formation, as well as implications for management of this issue are discussed.