Fertilisers for eucalypt planting: Review and recommendations.  R. Borschmann.  September 1999.  15pp. (unpubl.)

SUMMARY

Fertiliser application in native forests is currently undertaken to provide planted seedlings with a competitive advantage over recolonising weeds. The objectives are therefore primarily for survival and moderate growth, rather than the very high growth rates expected from fertiliser application to commercial eucalypt plantations.

The aims of this report were to:

• review recent advances in fertiliser technology for eucalypt plantations in Victoria and elsewhere;
• revise current operational practices in native forest for both reforestation and routine regeneration planting operations, in relation to different species/soil types; and
• identify knowledge gaps and recommend research and development requirements.

Factors examined included: species growth responses in a range of soil types in native forest as compared to plantations; interaction with weed control; form of fertiliser and amount applied; placement in relation to the seedling and timing and costs of application. Prediction of fertiliser requirements from bioassays was also examined.

Conclusions from the review are:

• Species response: The growth response by a particular species varies with the soil type, but is not consistent within soil types and therefore a fertiliser prescription may assist in many instances, but not in all situations. There is generally insufficient knowledge to prescribe specific fertilisers for different species and/or different sites.
• Site response: Growth responses to fertiliser have been recorded for eucalypt establishment in both native forest and plantation situations. However a response in native forests is more likely than in plantations being established on ex-pasture sites.
• Form of fertiliser: The form of fertiliser (granular or tablet) is not important, but a slow release fertiliser can be beneficial if growing conditions are not suitable for some time after fertiliser application. Sachets of soluble fertiliser in the planting hole can be deleterious to growth.
• Placement of fertiliser: There is a degree of tolerance as to where fertiliser should be placed. However it should not be placed adjacent to the seedling, or on the surface uphill from the seedling. In the absence of weed control, the fertiliser should be buried beneath the seedling if prolific growth of annual weeds is expected.
• Timing of application: Fertiliser needs to be available to the seedlings when growth commences in early spring. For winter plantings, fertiliser application at planting to 4 weeks after planting makes no difference to growth response, but application 8 weeks after planting is not as good as application within 4 weeks.
• Cost: Cost of granular fertiliser is cheaper than tablet form, although cost of application of tablets is cheaper than granular. There are likely to be more operational challenges in the application of granules compared to tablets, but in favourable weather conditions, the total cost of granular use would be less than tablets.
• Amount of fertiliser: In some instances a small application of N and/or P produces a growth response. A higher application of fertiliser often gives a better growth response, but not in all situations. Where survival and early height growth are more important than optimum early growth, a small amount is likely to be sufficient to get a satisfactory response.
• Predicting fertiliser requirements: A satisfactory bioassay for predicting fertiliser requirements may be developed through the use of foliar analysis, although this technique would not be suitable for prescriptions for native forest seedlings during their first year of growth. Fertiliser prescriptions could be developed for management units (based on similar growth conditions), by monitoring foliar levels at age one year and then applying the appropriate fertiliser to similar areas planted in the following years.

Recommendations from the review with respect to fertilising eucalypts at planting are:

For native forests:

• maintain the current prescription of a slow release fertiliser placed in the planting hole unless the use of granular fertiliser is found to be cheaper;
• maintain the current prescription of the use of 21 g Agriform tablets, although other brand tablets may be also suitable;
• where higher initial growth rates are a key priority, increase rates of fertiliser to 15-20 g of P and 20-30 g of N per tree using granular fertiliser; and
• establish trials to monitor the response to N, P, K, and trace elements over the range of soil types encountered where there is an ongoing fertiliser program within a forest type. Soil and foliar nutrient levels should be monitored to develop predictive models for fertiliser use.

For grasslands and improved pastures:

• do not apply fertiliser for at least six months after planting, where weeds are not controlled by herbicides or other means, or where survival and establishment are the key priorities; and
• consider increased application rates of fertiliser to 10-15 g of P and 20 g of N per tree using granular fertiliser where higher initial growth rates are a key priority.