Effects of nutrient and paper mill biosolids amendments on the growth and nutrient status of hardwood forests

Aboveground net primary productivity (ANPP) and soil and vegetation nutrient concentrations were measured in pole-sized northern hardwood and aspen forests to quantify the potential for various nutrient amendments to increase tree growth, as well as potential deleterious effects on vegetation. Four blocks were installed in each forest type containing the following treatments: control, N+Ca+Mg+K+P+S (complete), wood-fired boiler ash (ash), N+wood-fired boiler ash (N+ash), and two rates of paper mill sludge (sludge and 2× sludge). The northern hardwood forests had three additional treatments: N, Ca+Mg+K (base cations), and N+Ca+Mg+K (N+base cations). Fertilizer treatments were designed to provide N at a rate of 100 kg ha −1. Other nutrients were applied in proportion to N so that N, P, K, S, Mg, and Ca were applied at a ratio of 100:50:33:9:5:4, respectively. Total ANPP was not significantly different among treatments for the maple stands, but plots treated with wood ash were 10% greater than controls. ANPP was greater in 1998 and 1999 for aspen plots receiving N+ash, but results were only statistically significant ( p=0.013) in 1999. Basal area differed by 40–60% among experimental plots within any given block and was positively correlated to wood increment. Wood increment, adjusted for basal area, did not differ significantly among treatments for the aspen stands, but the N+ash treatment was 30% greater than the control. A two-way factorial comparison indicated that ash had a significant ( p=0.024) positive effect on wood increment and N had a significant ( p=0.044) negative effect on wood increment for the maple stands. Tree growth was not correlated to foliar nutrient concentrations, but ratios of K to other elements (K:Ca, K:Mg, K:N, and K:P) were highest, on average, for wood ash plots. These differences were not statistically significant with the exception of K:N for the aspen stands and K:Ca for the maple stands. We did not observe any beneficial effects of paper mill sludge on forest growth, but there was some evidence that wood ash increased annual wood production.