Determining Sludge Fertilization Rates for Forests from Nitrate-N in Leachate and Groundwater’

hfunlclpal and papermill wastewater sludges were ipplled to conifer and hardwood forests growing on sand soils (Entic Haplorthods, Spodic Udipsamments, and Alfic Haplorthods), In northwestern Lower Michigan where annual preclpltatio~~ averaged 765 mm/y, to Investigate the Impact of sludge on nitrate-N concentntlons In soil water and groundwater. During the first growing season after treatment, all forms of N in groundwater and soil water remained near background levels excep( under aspen (Populusgrondldcnrora Mlchx.) plots treated with 46 dry Mg munldpal sludge/ha. Following the flnt spring snowmelt period after sludge was applied (spring 1977), nltrateN concentrations exceeded the 10 mg/L potable water standard In groundwater under plots treated with 16 or more dry Mg/ha andigested papermill sludge. Soil leachate exceeded 10 mg/L under pine pladtations receiving 19.3 dry Mg/ha and aspen sprout stands IVceivlng 2.3 dry Mg/ha or more anaerobically digested munldpal