Land application of clean municipal sludge (biosolids) offers potential benefits for some New Hampshire forest soils. These benefits may include: enhanced soil environment for tree growth; reduction in soil erosion especially in heavily disturbed sites; greater water holding and infiltration capacities and reduced overland flow. Sludge is the solid or semi-solid material produced by municipal wastewater treatment plants. It is a source of nitrogen, phosphorous and potassium.
In addition, treatment plants that use the lime stabilization process generate sludge with abundant calcium, an element of low supply in some forest soils. The metal content of sludge varies by municipality. The maximum amounts are regulated by federal law (Clean Water Act, 503 Regulation). The term biosolids is used in this paper for sludges that meet pathogen reduction, vector attraction reduction, and metal pollutant limits for land application.
Application of wood ash from wood-burning energy plants also offers potential benefits for some New Hampshire forest soils. These benefits may include provision of an effective method to neutralize the natural soil acidity and elevate levels of calcium and other plant nutrients in the soils.
Researchers report that the short-term effects of the proper use of municipal sludge and/ or wood ash do not reduce environmental quality. Implicit in proper use is the need for best management practices, site management plans and environmental guidelines. More information is needed on the long-term environmental effects through monitoring activities on carefully managed forest land application sites.
The natural surface horizons occurring in forest soils are distinctive when compared to agricultural soils. Commonly, organic horizons overlie mineral horizons in the forest. On farmed fields all of this has been incorporated into a plow layer or Ap horizon. The role of the forest organic and mineral horizons has been and continues to be a focus for nutrient cycling research activities. Examples of research that studied the impact to the forest ecosystem from applying sludge or wood ash are presented in this booklet published in 1994.