EFFECTS OF CARBON AND LIME ADDITIONS ON MINERALIZATION OF C AND N IN HUMUS FROM CUTOVERS OF WESTERN RED CEDAR - WESTERN HEMLOCK FORESTS ON NORTHERN VANCOUVER-ISLAND

The potential for amendments of simple C compounds or lime to improve N availability in humus from cedar-hemlock cutovers was tested in labo ratory incubations and a greenhouse bioassay. Rates of C and N mineral ization in samples of humus and woody humus during aerobic incubations in the laboratory were not affected by additions of potato starch. Mi neralization of C was stimulated and net N mineralization was reduced after glucose addition. Microorganisms in humus may not be capable of degrading starch, and simpler C sources such as glucose increase immob ilization of N in microbial biomass. The biomass of seedlings of weste rn red cedar (Thuja plicata Donn), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and Sitka spruce (Picea sitchensis (Bong.) Carr.) grow n in pots containing cedar-hemlock humus amended with dolomitic lime w as similar to the biomass of seedlings grown in unamended humus after 18 months. Seedlings grown in humus amended with N and P fertilizers w ere significantly larger than those grown in unamended or lime-amended humus. It is unlikely that applications of C or lime to cedar-hemlock cutovers would increase rates of N mineralization from humus. Additio ns of nutrients appear to be the only practical means of alleviating t he nutrient supply problems on these sites.