Long-term study of Sitka spruce (Picea sitchensis (Bong.) Carr.) on blanket peat. 2. Water-table depth, peat depth and nutrient mineralisation studies.

Abstract

Depth to water table was monitored during two growing seasons, peat depth changes over a 15 year period measured and nitrogen and phosphorus mineralisation studies conducted in a fertiliser and lime experiment on a pole stage crop of Sitka Spruce (Picea sitchensis (Bong.) Carr) on oligotrophic blanket peat. The original fertiliser experiment, a nitrogen and phosphorus factorial was established in 1967 and in 1977 it was subdivided, one part receiving no further treatment (Experiment 1) with lime and further applications of nitrogenous and phosphatic fertilisers being made to the other (Experiment 2). When the two experiments were treated as one, mean depth to water table was linearly related to growth parameters. The best relationship was obtained with basal area. However, there were marked differences between experiments and significant differences in water table depth were recorded between treatments in Experiment 2, where fertiliser induced growth differences were also measured. but not in Experiment 1 where the 1967 treatments were no longer producing growth increment differences. Peat subsidence has occurred in the experimental plots at an average rate of 1.2cm per year. In shallow peat situations experimentation on peat-soil mixing should be initiated to test long-term effects. Levels of mineral nitrogen were depressed in forest floor samples from limed, fertilised plots. Neither total nitrogen concentrations nor mineral nitrogen levels showed any evidence of a residual effect of fertilisation. Plots treated with phosphate in 1977, by contrast had markedly higher extractable phosphorus concentrations than material from Experiment 1.