Effects of paper mill sludge on tree growth and competition in young red pine plantations

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Virginia Tech


The disposal of pulp and paper industry sludge has become a significant problem in recent years. Increasing costs and regulatory constraints associated with landfilling and incineration have caused the industry to look for viable alternatives for the disposal of their wastes. In September of 1988, a nutrient-enriched, combined (primary/secondary) paper mill sludge was surface applied to a 4-year-old and a 6-year-old red pine (Pinus resinosa Ait.) plantation in central Wisconsin at rates of 10, 20 and 40 dry Mg ha⁻¹. Red pines measured 10 and 22 months following sludge application did not show a significant volume growth response to increasing sludge rates. Nonetheless, some biologically significant trends did occur following the first growing season, namely, diameter growth in the younger plantation decreased by 27%, 36% and 39% with increasing rates of sludge application. Reductions in height, crown width and volume growth were seen as well. Increased absorption of moisture among the heavier application rates coupled with already dry conditions is believed to be the cause of the growth reduction. Tree growth in the older plantation was more variable, possibly reflecting the greater degree of establishment and reduced susceptibility to moisture deficits. By the end of the second growing season, there was some indication that the trees were responding to sludge application in both plantations, with the greatest growth occurring among the 40 Mg ha TM treatment plots for all growth parameters. Red pine fascicles examined 12 months following sludge application showed significant increases in foliar concentrations of N, P, Ca, Mg and S with increasing rate of sludge application. This corresponded with a significant increase in fascicle biomass relative to application rate in the younger plantation. Fascicle biomass was not affected by sludge application in the older plantation. Analysis of nutrient response, in general, indicated luxury consumption taking place among all nutrients with the exception of boron, which decreased in foliar concentration, to low or deficient levels, and content in sludge amended plots in both plantations. Analysis for nutrient concentrations and dry matter production of Carex spp. (sedge), the predominant herbaceous understory component, showed increasing foliar N levels with sludge application 21 months following treatment in above-ground tissue, with a corresponding increase in above-ground biomass relative to controls of 22%, 33% and 85% among the 10, 20 and 40 Mg/ha treatments, respectively. An assessment of woody vegetation using a competing vegetation assessment system (CVAS) showed essentially no response by hardwood competition to sludge application for either study site. Total weed control, consisting of 0.140 kg ha⁻¹ a.i. of Oust™ and 1.3 kg ha⁻¹ a.i. of Garlon™ was performed in August of 1989 and resulted in significantly reduced coverage of herbaceous and woody competing vegetation in both plantations the following growing season. Analysis of red pine volume growth between weed control treatments did not show a significant response relative to sludge application for either plantation one year following herbicide application. Additionally, there was evidence of reduced weed control efficacy with increasing sludge application rate in the younger plantation. This suggests that weed control efficacy may be greater if weed control is performed prior to sludge application; however, given the apparent sequestering ability of the herbaceous vegetation, removal of this component may contribute to elevated levels of undesirable leachates in soilwater and groundwater.