Soil inorganic nitrogen under fertilized bermudagrass turf

Managed turfgrass acreage in the southeastern USA is steadily increasing. There is public concern that fertilization of turfgrass systems, particularly additions of N on golf courses, might be adversely affecting groundwater quality due to nitrate leaching. This study was conducted to measure soil nitrate levels in situ under continuously managed bermudagrass (Cynodon spp.) and to evaluate influences from fertilization and mineralization. Two experimental sites were established on 50- and 75-yr-old golf course fairways in the Neuse and Cape Fear River basins in eastern North Carolina. Soil sampling was done seasonally. Results indicate that nitrate-N levels were consistently low (I to 4 mg kg(-1) soil) and similar to adjacent natural areas throughout the 120-cm sampling depths during the 2-yr experiment at both sites. Levels were relatively uniform with depth and across several landscape positions. The soil nitrate levels under fertilized fairways were similar to those in adjacent nonfertilized natural areas, indicating minimal influence from turf management practices. From laboratory mineralization studies and soil temperature data, it was estimated that 60 to 154 kg N ha(-1) would be released from organic N pools during the bermudagrass growing season (May to October). Because of similar temperature responses, it appeared that N release from mineralization would be synchronized with bermudagrass growth. Substantial bermudagrass growth in nonfertilized plots provided direct evidence that mineralization was a significant contributor to turf nutrition. There was no evidence that N fertilization or the ecology of the bermudagrass system posed inherent risks to water quality and the environment.