UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Phosphorus forms of podzolic soils of northern Vancouver Island and their use by western red cedar Cade, Barbara Jean

Abstract

After clear-cutting and slashburning the hemlock-amabilis fir (HA) forest types of northern Vancouver Island support good growth, but the trees on the cedar-hemlock (CH) forest types suffer a growth check which can be overcome with N and P fertilization. This study focussed on soil phosphorus (P) fractions in CH and HA forests. Extraction methods were evaluated for total, organic and available P. The Parkinson & Allen digest was better than the Saunders & Williams ignition method for total P. Both the Saunders & Williams method and the Bowman & Moir extraction procedure overestimated organic P. The Bray PI and Mehlich 3 procedures were suitable for available P. Extracts of forest floor samples by NaOH, NaOH-EDTA and Chelex in both water and NaOH were analysed by 31P NMR spectroscopy. The NaOH-EDTA extracted the greatest portion of the total P and yielded spectra with a greater diversity of P compounds. However, this extractant also maintained other ions in solution which reduced the quality of the spectra. Evaluation of P status in relation to soil chemistry of mature CH and HA forests revealed that CH forests had higher pH values and C concentrations in the forest floor. The CH forests also exhibited higher loss on ignition, wider C/N and C/P ratios, and increased concentrations of extractable Ca in mineral horizons. The HA forests had higher C concentrations in mineral horizons and higher concentrations of N, extractable Mg, Al and Fe, and more organically complexed Al and Fe. There were no significant differences in P levels between the forest types. P-31 NMR spectroscopy showed a diversity of compounds, and organic forms throughout the profile. The persistence of labile diester phosphates and wide C/N and C/P ratios suggest slow decomposition. Comparison of the P status and soil chemistry of mature CH forests to those after burning revealed increases in pH, available P, inorganic P and extractable N, and decreased organic P postharvest. By 10 years postburn, significant reductions in organic P and organically bound Fe and Al were revealed in mineral horizons. P-31 NMR showed a shift to orthophosphate after burning, but a return to organic forms within 10 years in surface horizons. The results suggest that the burning of organic matter temporarily disrupts illuviation and the P cycle. In a pot study, cedar grown with high (50 mg P/2) or low (10 mg P/1) levels of phytic acid, ATP, glycerophosphate, pyrophosphate or KH2P04 showed adequate growth with all P forms but phytic acid, and grew best with the high rate of the P compounds. The poor growth with phytic acid was attributed to its binding of Ca, Zn and Cu. Utilization of organic P compounds was facilitated by various phosphatases, produced by cedar plants, mycorrhizae and/or rhizosphere microbes. Phosphorus did not appear to play an important role in the growth check problem of CH sites.

Item Media

Item Citations and Data

Rights

For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.