Nutritional Requirements of Azadirachta Excelsa (Jack) Jacobs Stand at Labis, Johore
The growth of forest is a long-term process. Studying the cycling of nutrients is important in order to understand the ecological functioning of a forest. The use of fertilizers in forest management has a profound effect on nutrient cycling processes at the plant-soil interphase. The transfer of...
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| Format: | Thesis |
| Language: | English |
| Published: |
2004
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/324/1/549568_T_FH_2004_9.pdf |
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| Summary: | The growth of forest is a long-term process. Studying the cycling of nutrients is
important in order to understand the ecological functioning of a forest. The use of
fertilizers in forest management has a profound effect on nutrient cycling processes at the
plant-soil interphase. The transfer of nutrients among the various compartments or pools
is a continuous process and the aim of the present study is to quantify the flow of
nutrients between these pools and to identify some of the factors involved in influencing
this process. A field experiment in Sungai Karas, Johore, Malaysia was initiated with the
objective of evaluating growth responses and distribution of nutrients within tree
compartments in Azadirachta excelsa (Jack) Jacobs under different fertilizer regimes.
The findings should provide plantation managers with some baseline data on nutrition
management in A. excelsa plantations. The treatments involved a factorial combination
of three rates of urea N (50, 100 and 150 kg ha-1), three rates of triple superphosphate P
(50, 75 and 100 kg ha-1) and two rates of dolomite lime (0 or 53.25 kg Ca and 30 kg Mg ha-1) applied in split (three times; 26, 30, and 34 months after planting) in a 2-year-old
stand established on a degraded soil.
Slope, in association with soil depth, had the greatest influence on stand growth
two years after planting. The growth parameters were negatively correlated with slope
and soil exchangeable K. Soil nutrient status remained unchanged despite receiving
regular fertilizer application, suggesting that higher requirement and uptake by the plants
or leaching had taken place. Thus, proper site selection and fertilizer application rate are
important factors to be considered when establishing A. excelsa stands.
Thirty-six trees were randomly selected from different treatments and harvested
for biomass assessment. Based on the harvested samples, the effect of fertilizers and
dolomite lime were insignificant on biomass production. This may be caused by
competition from the undergrowth and low levels of fertilizer used. The aboveground
biomass ranged from 3.4 to 28.4 t ha-1, of which 6.6% was foliage. Equations for
predicting stem volume were also developed in the present study using the data from
felled trees. The equations were selected from three commonly used models and
validated using data from 36 tree samples from the 4-year-old plantation. The least
biased and most precise estimates of stem volume were obtained using the logarithmic
equation. Regression equation using diameter at breast height as the variable was a good
predictor of aboveground biomass among the prediction variables tried. Concentrations
of nutrient were highest in foliage with the exception of Ca. The total nutrient contents in
the aboveground biomass (in kg ha-1) were 45.15 for N, 6.66 for P, 39.67 for K, 5.97 for Mg and 11.43 for Ca. Current harvesting method of timber coupled with burning activity
during site preparation would result in the removal of substantial amounts of nutrients,
and may lead to degradation of site quality.
Mean increments of tree volumes (estimated using regression) in two years of
observation or 51 months after planting ranged from 25.95 to 54.67 m3 ha-1. Growth of
A. excelsa was strongly influenced by the addition of N. Foliar P concentration was
increased by additions of N and P at 39 months but this was not found at 51 months.
Consequently strong correlation between P foliar nutrient concentrations and growth was
found at 39 months. The best growth was associated with foliar concentrations at 39
months of about 2.57% N and 0.27% P. The rather substantial decrease in growth in
second half of the experiment indicates the need to continually repeat fertilizer
application to sustain growth rates.
Additions of dolomite lime and fertilizers increased soil pH, and concentrations of
Mg and Ca in the soil two years after the commencement of the present study. Liming
led to a reduction of soil total N suggesting higher N mineralization may have taken
place. Application of N and P increased soil total N and P availability in the soil.
Mean annual litterfall ranged from 4.95 to 6.60 t ha-1 yr-1. The addition of
fertilizer and dolomite lime did not result in any changes in the mass of litterfall. Leaf
litter accounted for more than 88% of total litter production. The mean standing crop of
leaf litter ranged from 1.26 to 3.76 t ha-1. Nitrogen application increased the mass of leaf litter accumulated on the forest floor but not the nutrient concentration of the leaf litter.
Differences among the treatments were found only at the early stages of decomposition
for both the decomposition rates and weight losses. Release of the nutrients at the end of
the experiment was positively correlated with their initial concentration.
The results highlight the importance of understanding nutrient fluxes before
recommending a fertilization regime aimed at increasing productivity of A. excelsa
plantations. General fertilizer prescriptions and management practices of A. excelsa
plantation are presented. However, detailed assessments of fertilizer requirements are
required if soil types other than those described here are used. |
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