Forest Floor, Soil, and Vegetation Responses to Sludge Fertilization in Red and White Pine Plantations

Abstract An undigested, nutrient‐enriched papermill sludge applied to a 40‐year‐old red pine ( Pinus resinosa Ait.) plantation at rates of 4, 8, 16, and 32 Mg/ha resulted in nitrogen application rates of 282, 565, 1130, and 2260 kg/ha. An anaerohically digested municipal sludge applied to a 36‐year‐old red pine and white pine ( Pinus strobus L.) plantation at rates of 4.8, 9.7, and 19.3 Mg/ha resulted in nitrogen applications of 287, 578, and 1160 kg/ha. Both sludges produced significant forest floor increases in total salt, pH, and concentrations of nitrogen and phosphorous. The municipal sludge applications also resulted in increased levels of trace elements and heavy metals. Accelerated humification developed along the interface between the sludge layer and the accumulated forest litter. Movement of nutrients from the forest floor into the soil was generally limited to nitrate, ammonia, and total phosphorus leaching into the upper soil layers. Very small fluctuations in nutrient levels occurred in the soil below 15 cm. Understory nitrogen and phosphorus levels increased in treated plots on both sites while cadmium increased on plots treated with municipal sludge. Understory hiomass increases of up to 132% over controls were measured on sludge‐treated plots. No metal toxicity symptoms were observed and sludge‐treated understory vegetation remained green later into the growing season well after that on untreated plots had begun to discolor and approach dormancy. Overstory foliar nitrogen concentrations increased on sludge‐treated plots, improving the N:P ratio in the pines. Increases in fasicle dry weight and needle length were noted in sludge‐treated red pine, as were increases in radial growth in white pine. Evidence two growing seasons following sludge fertilization indicated an increased canopy weight, thus an enhanced potential for photosynthesis.