Forest soil pH is a site factor which has been frequently correlated with tree growth. An investigation was conducted on 22 even- aged spruce-fir stands in eastern Maine to evaluate the acid chemistry, ph variability, and chemical composition of these soils in relation to tree growth and tissue composition. Chemical analysis of each of the major horizons (0, 42, B, and C), analysis of red spruce needle composition, phosphate fractionation and soil solution analysis of the B horizons, and site productivity measures were used to gain insight into the soil acidity-site phenomenon.
The investigation showed these stands were supported by highly acid, podzolic soils formed in glacial till with distinct horizon morphologies and chemistries. Chemical analysis of the major soil horizons showed all of these, materials were highly acidic yet no significant correlations between the ph of any two horizons were detected.
Soil variables most significantly correlated to site productivity measures were 0 horizon ph, total organic matter in the A2 and B horizons and organic phosphorous in the B horizon. Of the elements examined in red spruce needles, it was the calcium composition which most significantly contributed to site productivity.
Aluminum and organic matter content were the most important soil variables associated overall, with variations in pH. Increased pH in the O horizon reflected greater exchangeable calcium and less exchangeable aluminum with better site productivity. Tire most important factor affecting ph variation and site productivity for the A2 horizon was total organic matter content.
The critical relationship in the B horizon for correlations with soil ph and site productivity was related to the formation of an organic natter-aluminum-phosphorus complex. Within the B horizon pH range encountered (pH 4.03 to 5.08), higher ph values favored the formation of a complex between organic matter) aluminum, and phosphorus which reduced aluminum and phosphorus activity in the soil environment. Correlations suggested the formation of this complex was positively related to site productivity which may have resulted from aluminum toxicity, rather than phosphorus deficiency, being limiting to growth.
Variations in C horizon acidity were a function of exchangeable aluminum. The impact of the hydrolysis of exchangeable aluminum on ph variation increased in all horizons examined as organic matter content declined.
Phosphate fractions in the B horizon showed that phosphorus was bound primarily as occluded phosphorus with very little phosphorus in available forms. Analysis of equilibrium B horizon soil solutions, in conjunction with soil analysis, suggested only at higher ph or low organic matter contents would the solubility of inorganic phosphates control phosphorus availability in the B horizon.