Mobility of soil nitrogen and microbial responses following the sudden death of established turf

The stability of nitrogen within a turf-soil ecosystem is important both fo r efficient turf management and preventing the contamination of ground wate r by nitrate. The objective of this study was to quantify responses of the microbial community and the mobility of soil nitrogen following the sudden death of established turf. Twelve-year-old turf plots comprising four cool- season turfgrass species fertilized with five N sources were maintained on an Enfield silt loam (coarse-silty over sandy or sandy-skeletal, mixed, act ive, mesic Typic Dystrudept) at Kingston, RI. Half of the plots were killed with glyphosate in early September and any regrowth was removed mechanical ly. Measurements of soil physical, chemical, and microbiological properties and nitrate leaching in killed and healthy plots were compared for 12 mo. Turf death did not alter soil moisture, temperature, pH, or extractable amm onium. Nitrate levels were higher in both the root zone and at 60 cm follow ing turf death and this difference persisted for the sampling year. Carbon mineralization and microbial biomass C were not different between soils fro m healthy and killed plots. Killed plots leached three times more nitrate t han healthy plots but this amounted to less than 10% of total soil N presen t. Retention of nitrate in a turf-soil system depends on absorption by livi ng grass roots, although reasonable N stability is also provided by N cycli ng within the soil microbiota. Protecting ground water from nitrate contami nation is optimized by maintaining a vigorous turfgrass cover.