Nutrient Dynamics and Growth Response in a Fertilized Black Spruce Stand1

Abstract

In 1968, a forest fertilization experiment was established in a black spruce (Picea mariana Mill. B.S.P.) stand in central New Brunswick. A factorial combination of three levels of nitrogen (N) in the form of urea and three levels of phosphorus (P) in the form of triple superphosphate were applied to duplicate circular plots. During the 10 years after fertilizer application, various components of the nitrogen cycle, organic matter transformations, and microbial activity were monitored in both field and laboratory using soil samples from the black spruce stand under study. Concurrent stand responses to fertilizer applications were also determined periodically. Application of nitrogen and phosphorus fertilizers increased the foliar N levels in all treated plots. Nitrogen levels in litterfall materials showed similar increases. Concentrations of nitrogen in litter needles from treated and control plots, respectively, averaged 79 and 66 % of those in the crown. The rate of respiration in the organic raw humus materials was higher when incubated with green litter needles from treated plots than when incubated with similar litter from control plots. The stimulatory effect of the litter needles seems to be related to an interaction between dry summers and fertilizer treatments. Nitrate was detected in the soil solution collected from N- and P-treated plots. The data suggest a negligible loss of nitrogen due to leaching of nitrate. Growth rates of trees after fertilizer treatment are related to foliar nutrient levels and to growth rates of trees prior to fertilization.