Phosphorus forms and related soil chemistry of Podzolic soils on northern Vancouver Island. I. A comparison of two forest types

Abstract

When cedar-hemlock (CH) and hemlock - amabalis fir (HA) forests of northern Vancouver Island are clearcut and replanted, growth of replanted trees is often poor on CH clearcuts but not adjacent HA clearcuts. This poor growth can be overcome with nitrogen (N) and phosphorus (P) fertilization, which suggests differences in nutrient cycling between CH and HA forests. The objective of this study was to investigate soil P in mature, uncut stands of CH and HA forests. The results suggest that there are no inherent differences in soil P concentration between the CH and HA forests. The diversity of P forms as revealed by 31P-NMR spectroscopy was typical of cool, moist acidic forests with high P immobilization. Diester phosphates were found throughout the soil profile, albeit at very low levels in the mineral horizons. Phosphorus forms and cycling were vertically stratified down the profile. Most of the P in the LF horizon was in organic forms typical of litterfall. In the more humified H horizon the P forms were more typical of soil organisms. The high C/N and C/P ratios in the LF and H horizons at the CH site are consistent with microbial immobilization. In the upper Bhf horizon, inorganic P was predominantly nonoccluded. Organic P was present, mainly as orthophosphate monoesters, which were probably adsorbed on soil colloids. In the lower Bhf horizon, most P was occluded in amorphous sesquioxides, with low levels of organic P, mainly as orthophosphate monoesters.