Effects of Sludge Applications on Soil Water Solution and Vegetation in a Northern Hardwood Stand

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Abstract
Dewatered and limed sludge from a primary treatment plant was applied at two rates, 25 and 125 wet metric tons/ha (5.8 and 28.0 dry metric tons/ha), on sandy loam soils in a northern hardwood forest in central New England. Changes in soil water solution were assessed from water samples collected with suction lysimeters at 20‐ and 45‐cm depths below the mineral surface. The light application of 25 metric/ha had little effect, but the heavy application of 125 metric tons/ha caused an increase in the concentration of most ions in soil water. At 20 cm, or just below the B21h horizon, Cl reached a mean maximum of 27.5 mg/liter after heavy application compared to control values of 3 indicated maximum increases in concentration that averaged two‐ to threefold greater than control values of 4 and TOTAL‐P were unchanged. At 45 cm or in the B23 horizon just above a fragipan, the increases in ionic concentrations following the heavy application were less than one‐half the increases that occurred at 20 cm. The concentrations of most ions returned to background levels within 1 year after sludge application. From the time sludge was applied in June 1975 until the end of the growing season in October 1976, leaching losses for calcium were estimated as 18 kg/ha for the control plots, compared to 39 kg/ha from plots receiving the heavy application. Comparable estimates for SO4 were 35 kg/ha for the control plots and 64 kg/ha for plots receiving the heavy sludge application.There were no significant differences in basal‐area growth among control and treated plots for the first two growing seasons after sludge application. In the herb and shrub layer only 3 of the 31 commonly occurring species showed statistically significant changes in frequency. All three changes were on plots receiving the heavy application. Sugar maple (Acer saccharum F.) seedlings declined from an average of 22/m2 before application to 17/m2 in the second summer after application. The shrub Viburnum alnifolium Marsh, increased from an average of 5/m2 before application to 11/m2 after and the herb Viola pallens Brainerd increased from 15/m2 before to 21/m2 after.