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Managing nutrients to increase productivity of plantation eucalypts in south China

Xu, Daping (2001) Managing nutrients to increase productivity of plantation eucalypts in south China. PhD thesis, Murdoch University.

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This thesis deals with increasing productivity of plantation eucalypts in south China by use of fertilisers, by harvest residue management and by inoculation with ectomycorrhizal fungi. The soils for eucalypt plantations in south China are generally oxisols and ultisols which are acidic in reaction, highly leached, heavy-textured and deeply weathered. Phosphorus deficiency is very severe and its availability may be reduced to plantation eucalypts because of the limited number of species of eucalyptcompatible ectomycorrhizal fungi in the region. Most of the land available for eucalypts in south China has been degraded over recent centuries with extensive loss of the A horizon. Nitrogen supply is limited because of low organic matter content in topsoil. The low productivity, and small leaf mass of eucalypt plantations in south China, may be caused by limitation in soil nutrient supply, especially P and N. One of the key questions addressed is whether the productivity of plantation eucalypts in south China can be increased to the world average by nutrient management across a rotation. Field trials were established in Guangdong Province (near Gaoyao, Kaiping and Yangxi. one trial at each site) and Yunnan Province (1 trial near Chuxiong) to address this issue (Appendix 1).

Nursery inoculation of eucalypt seedlings with ectomycorrhizal fungi significantly affected tree height and stand volume of the eucalypt plantations, but the effect (positive or negative) was iso late-dependent and related to tree survival rate. A Laccaria isolate (CSIRO E4728) significantly increased stand volume by 27% at Gaoyao and a Scleroderma (MURU LH041) increased growth by 15% at Chuxiong at age three years. All isolates increased tree growth under P-limited soil conditions and only one isolate increased tree growth at marginal soil P. The effect of ectomycorrhizal fungal inoculation was not significant at 4.5 years in Gaoyao.

Application of superphosphate at establishment, in the presence of a basal fertiliser. increased tree growth and survival of E. urophylla in the trial near Gaoyao and of E. globulus in the trial near Chuxiong. It also increased P and N concentrations in the youngest fully expanded leaves (YFEL) at Year 1 and available P in topsoil at Years 2 and 4.5 in the trial near Gaoyao. Application of P increased biomass in all tree components. The addition of 20, 50 and 200 kg P ha'1 increased stand volume by 5, 5 and 7 times of the MAI at P0, respectively. Total tree biomass at P 200 was more than 7 times of the total tree biomass at P0 at Gayao. The more P applied, the higher the percentage of stem-wood and the lower the percentage of root mass. The low P concentrations in leaves and roots in P20 trees at Year 4.5 suggested the withdrawal of P from the biomass, through efficient internal cycling. The addition of P increased N, P, K, Ca and Mg uptake by 2-4, 3-5, 3-5, 3-4 and 3-4 times of the uptake by trees at P0. respectively. However, more than 80% of the nutrient accumulation by trees will be lost by the harvesting practices widely used in China.

In a third trial, located near Kaiping, effect of P fertiliser rate on biomass production. nutrient uptake, partition and use efficiency of a 75 months-old clonal plantation of Eucalyptus grandis x E. urophylla was studied on a hilly site with terraces. Here. P application increased tree growth, biomass and N, P and K uptake. Application of 208 kg P ha-1 was adequate for tree growth. The proportion of stem-wood was increased and the proportion of root biomass was decreased as the quantity of phosphorus applied increased. The N and K use efficiencies for tree biomass and stem-wood production increased with P supply. The P use efficiency was highest in the 13 kg P ha'1 treatment, and decreased at higher rates of P. Phosphorus recovery by tree uptake was between 8- 25% and decreased as the quantity of P applied increased. The study also indicated that N is likely to limit productivity after P due to the high uptake of N by the understorey. Since most eucalypt plantations in south China will shortly pass into their second rotation, effects of P fertilisation in the first rotation, and re-fertilisation (no P) of coppice on nutrient availability, growth and tree nutrient status of Eucalyptus grandis x E. urophylla was investigated in a trial near Kaiping. Phosphorus application in the first rotation increased available P, organic P and total P in terrace topsoil. Both P application in the first rotation and re-fertilisation of coppice increased tree growth, but the coppice response to P was less than the tree response to P in the first rotation. Refertilisation with N. K and B increased stand volume from 35 to 47 m3 across all P treatments. It was concluded that N may be the main nutrient constraining tree growth of coppice after P application.

Effects of harvest residue management, intercropping with N-fixing trees, fertilisation. and regeneration by coppice or replanting on tree growth, nutrient concentration in YFEL, soil properties and soil nutrient availability in the second rotation were studied on a degraded site in Yangxi. A reduction in the amount of residue removed during harvest increased N and P concentrations in the YFEL and tree growth by increasing available nutrient supply and reducing the loss of soil organic C after tree planting. It also increased the amount of litterfall. Tree growth in the treatment where all organic matter was removed and weeds were periodically controlled, was better than in the whole tree harvest plots because of reduced weed competition. Intercropping with N fixing trees enhanced tree growth 2 years after planting and increased litterfall 3 years after planting. Application of N, P and K fertilisers increased N, P and K concentrations in the YFEL and tree growth. The growth increment was much higher than that obtained by harvest residue management on this poor degraded soil. Coppice trees grew better than replanted trees. The difference between coppice and replanted trees was reduced by fertilisation.

From the above trials, it is concluded in this thesis that productivity of plantation eucalypts can be improved to 20 m3 ha-1 yr-1, the average productivity in the world, by nutrient management. The lack of long-term response in tree growth to inoculation may be due to poor fungal persistence. Further work is needed to optimise the selection of eucalypt-compatible fungi that can persist and assist eucalypts especially on infertile and high P-fixing soils. Recommended P fertilisation should be around 50 kg P ha-1 in southwestern China and 50-200 kg P ha-1 in southeastern China, depending on soil fertility and the farmer’s economic capacity. Nitrogen fertilisation in the second rotation is very important and 200-400 kg N ha-1 is recommended over 2-3 applications. Harvest residue retention and coppice regeneration are recommended as operational practices. Future research must address long-term effects of plantation management on soil fertility.

Item Type: Thesis (PhD)
Murdoch Affiliation: Division of Science and Engineering
School of Biological Sciences and Biotechnology
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Dell, Bernard and Malajczuk, Nicholas
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