Determination of Desirable Leaf Nutrient Levels
Maximized Growth of Acacia mangium
Agricultural Research & Advisory Bureau [ARABIS]
Acacia mangium plants were grown in a pot culture medium of fine sand supplied with Complete and Minus Nutrient Solutions to study the nutrient status of the plants and their effect on growth under different nutrient treatments.
The nutrient status of the plants were determined by analyzing the 6th leaf from the bud-tip of secondary branches in the lower canopy which was found to show relatively stable macro-nutrient levels from one plant part to another within a particular plant.
The result obtained from this experiment indicates that the optimum 6th leaf nutrient levels for the various plant nutrients are: P: 0.20-0.23 %; Mg: 0.17-0.22 %; Mn: 140-190 ppm.
N and K levels fluctuated at two distinct ranges at different times, but were always above 2.60 % N and 1.00 % K in plants where these nutrients were provided.
Ca, S, Fe and B results are such that no inferences could be made with a reasonable degree of certainty. However, Ca levels mainly fluctuated between 0.35-0.55 %, S between 0.20-0.35 %, and Fe between 40-80 ppm.
The Minus Boron treatment resulted in the leader shoots of the plant dying off and caused the deformation of new leaf buds to seriously affect growth. This may occur at levels less than 10 ppm but will definitely occur at levels below 5 ppm. In treatments where Boron was provided, their levels generally fluctuated between 20-70 ppm.
A linear growth rate pattern, as shown by Relative Volume calculation from height and girth measurements, were observed for those plants treated with Complete Nutrient Solution (the Control) once optimum nutrient status had been reached. Before reaching this nutritionally optimal status, the Relative Volume showed an exponential growth pattern. The growth pattern of the various Minus Nutrient Solution treatments was similar to the control, although in some cases, a slight deviation was observed for a short period, indicating a change in the growth rate.
Acacia mangium is a legume tree species native to the marshy areas of tropical Australia. It is naturally hardy and fast growing (even on poor soils), and is therefore being grown in logged over areas to combat deforestation and erosion in addition to providing a future source of timber and pulp.
It is important to identify nutrient deficiencies of this species as it is being planted on such a large scale requiring high amounts of capital inputs. Thus nutrient deficiencies affecting its growth (and thus its benefits) need to be identified, quantified and subsequently corrected through manuring as economically as possible.
For the purpose of manuring the species economically, the nutrient status of the plant needs to be identified by both visual and foliar analysis, and its nutrient status related to the growth and yield of the species.
This paper describes and discusses the results obtained from a pot culture experiment set up at Agricultural Research and Advisory Bureau to determine optimum foliar nutrient levels for maximized growth of A. mangium. Nutrient deficiency symptoms observed while carrying out the experiment were also recorded.
It is envisaged that fertilization of A. mangium in the field will be targeted to achieve such nutrient levels if the economics of doing so prove viable.
MATERIALS & METHODS
Establishment of Pot Culture
Acacia mangium was grown in 50 twenty-five liter clay pots with glazed inner and outer surfaces and filled with fine sand. A sand particle size of 0.6 - 1.6 mm was used to provide free drainage as well as suitable water holding capacity (12.2%). The pots had a basal outlet in the form of a 2...
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