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Importance of micronutrients for productivity of plantation eucalypts in East Asia

Daping, X. and Dell, B. (1998) Importance of micronutrients for productivity of plantation eucalypts in East Asia. In: Overcoming impediments to reforestation : tropical forest rehabilitation in the Asia-Pacific region, proceedings of the 6th International Workshop of Bio-Refor, 2 - 5 December 4997, Brisbane, QLD, Australia pp. 133-138.

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Fast growing species of eucalypts are widely planted for land stabilization and commercial forestry in east Asia. In southern China, in particular, large areas of eucalypt plantations have been established since the 1980's and these now total about 800,000 ha. Knowledge of nutrient requirements is important for maximizing eucalypt establishment and growth on these infertile and eroded forest lands. Here, micronutrient supply is usually low because of the depletion of organic matter and nutrient-rich surface soil as a result of past climate conditions and utilization practices, as well as the lack of micronutrient inputs to forest lands. Heavy applications of N, P and K fertilisers have been adopted for eucalypt plantations and this can further exacerbate the extent of micronutrient disorders. Generally, the importance of micronutrient application for sustained tree growth has not been recognised by forest farmers.

Results of micronutrient application experiments for different locations and soil types are presented. In most experiments, application of micronutrients increased growth and productivity of eucalypt trees. Boron deficiency was a common limiting factor in southern China as well as in the Philippines. On soil over shale in Longchuan, Guangdong Province, mixed micronutrient application increased height growth of Eucalyptus urophylla by 80% and diameter by 17%. The B concentration in the youngest fully expanded leaves (YFEL) of trees fertilized with NPK and micronutrients was much higher than the trees supplied only with NPK. The NPK trees had die-back symptoms in the crown indicative of B deficiency. In a B, Zn, Cu and other micronutrient depletion experiment on the same site, the addition of B + Zn + Mn +Fe+ Mo promoted maximum growth. On soil over granite in Wuhua, Guangdong Province, B application substantially increased the growth and form of E. urophylla. In Chuxiong, Yunnan Province, E. globulus growing in soil derived from sandstone developed apical die-back and a dwarf prostrate habit when B was not applied with NPK fertilizer. The application of about one g of B at planting promoted maximum growth. Multi nutrient deficiencies were observed in E. urophylla planted near Malaybalay, Mindanao, Philippines. In a deletion trial, B deficiency severely reduced tree growth but patches of Zn and Fe deficiency were also encountered.

These field trials clearly indicate that the micronutrient requirements for the growth of eucalypts must be considered when formulating fertilizer strategies for plantation eucalypts in east Asia. Furthermore, since there are large differences in soil characteristics across the region, there is an urgent need to identify the limiting micronutrients for a wide array of site types. Results from field trials, undertaken to delineate the optimal fertilizer composition and rate for the limiting micronutrients, will lead to improved fertilizer recommendations and increased tree performance.

Publication Type: Conference Paper
Murdoch Affiliation: School of Biological and Environmental Sciences
Publisher: BIO-REFOR
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