Rapid diagnostic tests for nitrate and phosphate sufficiency were tested and found suitable for use in nursery stock and field plants. Omission trials were used in the glasshouse to determine the most likely nutrient limitations to tree growth in a number of representative soils. Plant deficiency symptoms were also described. Photos were used to illustrate these deficiencies and compiled for publication in three books.
The scientists found that applications of high levels of slow-release fertilisers in the potting mix, which remain with the seedling at out-planting, resulted in more effective fertiliser uptake than with the normal broadcast application. The largest commercial plantation forestry company in Solomon Islands, Kolombangara Forestry Products Ltd, now uses the technique routinely for Tectona grandis and Eucalyptus deglupta. Other potential applications are for new Swietenia plantations in Fiji, and for other plantations in Samoa and north Queensland.
The project studied mid-rotation fertilisation for several species through three trials established in Queensland and Samoa, using foliage analysis as a means of determining nutrient deficiencies.
The scientists used project results to devise a simple, robust framework for identifying the likelihood and severity of occurrence of specific nutrient deficiencies. This framework is applicable to new sites on similar soil types/parent materials through the Asia-Pacific region.
There is little information on nutrient distributions in plantation hardwood species of major importance from anywhere in the humid tropics. The scientists sampled 22 logs from each of three species to assess nutrient distribution along and across logs and between individual trees within and between species. The results provided good estimates of log volumes and nutrient contents for E. deglupta.
The scientists established nutrient site budgets that track the amount of nutrient taken off site by logging and the inputs made during growth, to ensure that over time there is no net nutrient depletion from repeated harvesting of the timber. This process has satisfied forest stewardship authorities sufficiently to enable 'Green label' certification of the timber. This attracts a premium price on European markets.
On Kolombangara Island the researchers developed a potting medium for plantation species, using decomposed coconut shells. This medium was superior to forest soil, and seedlings grew much faster. Producing the medium has created a small industry for village women, who grate up the composted coconuts through a metal screen to produce the final product. The women are also paid to plant up the seedlings in the composted mixture and transplant them to the plantations. Because the coconut medium is much lighter than soil, the women can carry and plant more seedlings in a day, increasing their overall earnings.