Practical aspects of the nutrition of exotic conifer plantations and eucalypt forests in Australia.  D. W. Flinn.  May 1985.  22 pp. (unpubl.)

SUMMARY

Fertiliser practices in exotic conifer plantations and native eucalypt forests in Australia are outlined, and several practical issues in forest nutrition that require changes in fertiliser technology and perspective are identified. Four types of fertilisation are defined: starter fertilisation to provide planted seedlings with a competitive advantage, corrective fertilisation where one or more applications correct or prevent nutrient deficiency, later-age fertilisation involving the application of nitrogen to thinned conifer stands, and replacement fertilisation where nutrients lost during harvesting and regeneration are subsequently replaced.

Corrective fertilisation has so far been the dominant method used in conifer plantations, whereas starter fertilisation is most common in eucalypt plantations. For intensively managed forests, it is argued that replacement fertilisation is only justified on sites where it can be clearly demonstrated that growth will otherwise decline. To minimise the requirements for such fertilisation, forest managers should adopt a policy of nutrient conservation wherever practical.

In contrast with Northern hemisphere countries and New Zealand, the practice of later-age fertilisation with nitrogen is just commencing in Australia. Though there are some field trials here to indicate its potential for producing extra wood, widespread adoption of the practice could be limited because soils are commonly phosphorus-deficient and availability of soil moisture frequently limits growth.

In conifer plantations, more attention should be directed at techniques for increasing the efficiency of fertiliser programs. These include wider use of diagnostic aids such as foliar analysis, and evaluation of alternative fertiliser sources and modes of application. Advantage should also be taken of known interactions between fertilisation and either weed control or site preparation to maximise the response. However, it is vital that excessive use of fertilisers be avoided, as this can lead to nutrient imbalances, unfavourable shoot:root ratios and heavy branch development.

The most important issue in the nutrition of native eucalypt forests is the impact of harvesting on sustained productivity. The distribution of nutrients in the biomass of eucalypt forests has been extensively studied in the past decade, and nutrients thought to be critical to the growth of future rotations have been identified. Although depletion rates of one or more nutrients through harvesting may exceed their replacement from natural processes such as weathering and precipitation, the labile pool of nutrients in soils is an important compensating factor. Of particular importance is the manner by which this pool reacts to a sudden loss of site nutrients. To date, there is no evidence of a decline in growth of eucalypt forests following harvesting, and several case studies suggest that replacement fertilisation is unlikely to be necessary in the foreseeable future.

Also published:

Flinn, D.W. (1984)  Practical aspects of the nutrition of exotic conifer plantations and native eucalypt forests in Australia.  Proc. Conf. Research for Forest Management, Eds. J. J. Landsberg and W. Parsons, C.S.I.R.O. Div. For. Res., Canberra, May 1984, pp. 73-93.