The effects of mid- and late-rotation fertiliser application on tree growth and wood quality in softwood saw-timber stands: a critical review

Abstract

The economic benefits of mid- and late-rotation fertiliser application in saw-timber stands are well documented. These benefits are significantly related to a reduction in the length of the compound interest period over which the investment in fertiliser is carried, compared to fertilising at planting, and also to the additional volume produced by fertilisation, which is laid down as clear, high-quality mature wood. Various criteria are used to identify biologically responsive sites and stands that will provide an economic response to fertilisation; these include soil diagnosis and foliar nutrient analysis, site index, initial basal area and stocking levels, and leaf area index (LAI). While it appears that the accuracy of identifying biologically responsive sites is likely to be improved by using a combination of diagnostic criteria, quantifying the difference between a stand's current LAI and its maximum potential LAI have enabled researchers in the USA to estimate response to fertilisation, as well as the appropriate timing, elements and rates of application. Fertilisation needs to be considered in relation to other silvicultural operations such as pruning, thinning, prescribed burning and herbicide application (weed control). The application of fertiliser after thinning may shorten the time taken to achieve pre-thinning LAI and regain maximum volume production.