Pot Culture Experiment  to  Determine  Desirable  Leaf  Nutrient  Levels

 

for

 

Maximized  Growth   of   Acacia  mangium

 

by

 

Amitabha  Guha

Agricultural  Research  &  Advisory  Bureau   [ARAB]

1988

 

 

 

ABSTRACT  

 

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.

 

 

INTRODUCTION   

 

 

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 cm drainage hole covered with a thin weft of glass wool. The holes were stoppered with a single hole rubber bung through which a short glass tube was inserted to facilitate the inflow / outflow of the nutrient solution from / to 2 liter bottles.

 

Prior to transplanting of the A. mangium seedlings from polybags (filled with well fertilized soil), the sand in the pots was treated with acid and subsequently flushed with deminneralized water to remove any nutrients from within the pots. The roots of the 6 month old seedlings were then cleaned gently of polybag soil with running deminneralized water and transplanted into the pots.

 

At the start of the experiment (during Phase 0), all 50 pots were treated daily for 1 month with deminneralized water only, until the plants all appeared stunted, sickly and chlorotic.

 

Complete Nutrient Solution was then applied daily (during Phase 1) to all the 50 pots for 2 months to bring the nutrient levels in the plants to optimum or above optimum levels.  A modified Bolle-Jones nutrient solution was used, some changes being   made to adjust the pH to about 6.

 

It was then that actual nutrient solution treatments were begun (Phase2) where every lot of 5 pots underwent a different treatment such that 5 pots continued to be treated with Complete Nutrient Solution (as a control), another 5 pots being treated with all nutrients except N (-N  Nutrient Solution), another 5 pots being treated with all nutrients except P (-P Nutrient Solution), and so on for K, Ca, Mg, S, Fe, Mn, and B. Thus a total of 10 treatments (including the Control) was effected without replicates.

 

 

The composition of the various Nutrient Solutions and their pH values are presented in Tables 1 & 2. It should however be noted that due to selective nutrient uptake by the plants at various times within the   pots, these compositions were continually altering, thus also affecting the pH values.

 

To limit such variations in the composition of the nutrient solution   within the pots, the pots were weekly flushed with deminneralized water and refilled with nutrient solution to restore the desired nutrient concentrations. Throughout the duration of the experiment, the concentration of the nutrient solution within the pots was not allowed to vary more than 10% of the concentration applied for a particular nutrient.

 

 

 

 

Establishment  of   Foliar Sampling Technique

 

In order to identify the particular type of leaf tissue (or more accurately, the phyllode) to be sampled for analysis, the effects of leaf age, the leaf's exposure to various micro-environments, the age of the tree and the position of the leaf within the tree structure, were considered.

 

This had to be done because the analytical values of the leaf for the various plant nutrients have to represent, as accurately as possible, the nutrient status of the whole tree. Thus, the variation in the nutrient content (due to the above mentioned factors) of various leaves within a tree had to be studied to find a leaf that shows minimal variation in nutrient content. Such a leaf would best reflect on the nutrient status of the tree, and should thus be sampled.

 

 

For this purpose, leaf samples were taken from forest areas of Acacia mangium, where the Acacia mangium trees were divided into 3 age groups:-

 

1. Young Plantings, below one year in age, with no branching and fully sun-exposed.

 

2. Young Plantings, approximately between one and two years of age, with first and/or second series branching, but all fully sun-exposed.

 

3. a>  Plantings approximately more than two years old in the field with a developed canopy that does not converge in the tree row / interrow.

 

   b>  Plantings approximately more than two years old in the field with a developed canopy that does converge in the tree row / inter row.

 

 

Foliar samples were collected from different positions on the trees   under the various age groups. They were then analyzed to study the variation in nutrient content on the following basis:

 

       - the position of the leaf within a stem / branch.

 

       - the position of the branch.

 

       - the effect of sunlight / shade.

 

 

  All leaf types (the bud + leaf upto the 15th leaf) were sampled individually.  

 

  The foliar samples were then analyzed for five macro - nutrients   i.e. N, P, K, Ca, Mg.

 

The levels for each of the above macro-nutrients in the various plant   parts were then graphed and used to identify a leaf that shows the most stable nutrient levels for these macro-nutrients.  From these plots it appears that generally, the 6th leaf lies in a position of most stability for the various macro-nutrients on a   particular branch.  As such, the 6th leaf of the second series branching in the lower canopy was chosen as a standard for sampling purposes.

 

 

The 6th leaf nutrient levels were thus tracked for these pots during Phase 1 & 2 of the experiment as it was this leaf that showed relatively stable macro-nutrient levels from one plant part to another within a particular plant in samples collected from the field. This was especially true for all the primary macro-nutrients (N,P,K) and for Mg. Levels of Ca were comparatively less stable, the former probably reflecting age variation of the sampled 6th leaf.

 

 

 

Monitoring Nutritional Status of Treatment Plants

 

During Phase 1, 6th leaf sampling was carried out on a weekly basis from all 50 plants to make 1 composite sample.

 

During Phase 2, 6th leaf sampling was carried out on a weekly basis for 2 months and then later, on a fortnightly basis.

 

Sampling was carried out on each treatment lot of 5 pots to make10 composite samples.

           

Growth measurements (Height and Girth) were taken from all 50 pots during Phase 1; and from each treatment lot of 5 pots during Phase 2.

 

Girth was measured 20 cm from the base (sand level) while Height was measured up to the bud-tip from the base.

 

In the process of daily maintaining the sand medium with its water holding capacity, the evapotranspiration rate was measured. This value was found to be approximately 0.1 cm3 water/cm2 leaf surface area in 24 hours on a 'hot' day.

 

 

 

 

Chemical Methods  used  for   Foliar Analysis

 

Standard laboratory methods were used to analyze nutrient contents in plant tissue samples collected.  N and P levels in foliar tissue was measured by an Autoanalyzer, while the cation nutrients, K, Ca, Mg, Fe and Mn were determined by atomic absorption.

 

The determination of N is based on a colorimetric method in which an emerald-green colour formed by the reaction of ammonia, sodium salicylate, sodium nitroprusside and sodium hypochlorite (chlorine source) in a buffered alkaline medium at a pH of 12.8 - 13.0. The ammonia salicylate complex is read at 660 nm. The classical Kjeldahl digestion of leaf dry ash was used before passing the samples through the Autoanalyzer.

 

The determination of P is based on the colorimetric method in which a blue colour is formed by the reaction of ortho phosphate, molybdate ion and antimony ion followed by reduction with ascorbic acid at an acidic pH. The phosphomolybdenum complex is read at 660 nm.

 

S was determined with Barium Chloride after dry ashing and read by a photoelectric colorimeter set as 425 mu.

 

B levels were measured by colorimetric determination based on the quantitative reaction of B with carmine solution in concentrated sulphuric acid which results in a blue carmine - boron complex being formed. (The interference from nitrates was removed by the addition of hydrochloric acid).

 

 

 

 

RESULTS             

 

Fig. 1a.– i. illustrates the nutrient levels in the 6th leaf of Acacia mangium during Phase 1 & 2 for the Complete nutrient solution treatments. Fig. 2a.– i.  does the same for the various Complete and Minus nutrient solutions during Phase 2.

 

Fig. 3a illustrate the Growth pattern of Acacia mangium as indexed by Height and Girth during Phase 1 & 2 for the various nutrient treatments. Fig. 3b illustrate the calculated Volume Growth Index pattern (which is a function of both Height and Girth).

 

 

Findings on the respective leaf nutrient levels and their deficiency symptoms are as follows:

 

 

Phase 1   - All pots treated with Complete Nutrient Solution

                   (after being starved nutritionally).

 

N - Leaf N levels increased at a relatively fast rate in a near linear manner without slowing down (curving out). However, the curve dipped temporarily at the 3.0% and the 3.1% level when new leaf flushes appeared, caused by a possible temporary dilution effect.    

 

N deficiency symptoms, as evidenced by general chlorosis of the whole plant, seem to be evident at levels below 2.4% N.

 

P - Leaf P levels decreased for the most part from a high of 0.30%, but leveled off at 0.20% and then rose towards the end of this phase.

 

This indicates that leaf P levels had decreased to the critical level when it leveled off. As this occurred at the 0.20% level, the critical level is likely to be thereabout.

 

 

K - Leaf K kevels rose during the first half of this phase to 1.80% but leveled off and fell gradually during the second half. It again rose at 1.60% towards the end of this phase.

 

This indicates that the critical level may be at the minimum point of the drop i.e. at 1.60%.

 

Ca- Leaf Ca levels were very variable and followed no distinguishable pattern, perhaps partly reflecting a variation in the age of the sampled 6th leaf.

 

 

Mg- Leaf Mg levels rose quite sharply during the middle portion of this phase, fell suddenly, and then rose again at the 0.20% mark, thus indicating this to be the critical level for optimum growth. Excessive Mg levels could be about 0.23% as this was the point at which Mg levels began to drop.

 

Mg deficiency symptoms were observed to manifest itself as sharp interveinal leaf chlorosis at levels below 0.15%.

 

S - Leaf S levels rose but fell sharply during the third quarter of  this phase. As no leveling off was observed, it is difficult to identify a critical level for this nutrient.

 

S deficiency appeared similar to N deficiency symptom (general chlorosis/paling of the whole plant).

 

 

Fe- Leaf Fe levels rose sharply for the most part of this phase, but also fell sharply towards the end without leveling off. Thus, a critical level could also not be identified for this nutrient.

 

Mn- Leaf Mn levels fell rather slowly and then sharply during this phase. However, it leveled off at the 140 ppm mark which could well be the critical level.

 

 

B - Leaf B levels rose sharply and fell sharply towards the last quarter of this phase. However, as no leveling off was observed, it was difficult to specify a critical level during this phase.

 

 

For almost all nutrient levels tracked (i.e. N, P, K, Ca, Mg, Mn, but not S, Fe and B), the drop and rise effect occurred towards the end of this phase when nutrient levels were more than adequate for maximum growth and when new leaf flushes were forming. The short term drop in nutrient levels is likely to be due to the dilution effect that occurs when new leaves form and when nutrients are translocated from older leaves to younger ones.

 

 

From the 50 plants measured for Growth, a rather linear height and girth growth rate was noted during this phase. This resulted in an exponential Relative Volume growth rate.

       

 

 

 

Phase 2   - Pots treated with Complete and various Minus Nutrient Solutions.

 

 

N - Leaf N levels fluctuated within the 3.0% - 3.4% range for the Complete Nutrient Solution treatment (the control). But as the canopy developed and after the start of the dry season, this range was lowered to 2.6 - 3.0%.

 

However, for the various Minus Nutrient Solution treatments (except the -N treatment), the lower limit of the fluctuation was 2.7%, and later, this dropped to 2.4%.

 

For the -N treatment, leaf N levels dropped below 2.4% - when N deficiency symptoms (general plant chlorosis) was exhibited - to as low as 2.0%. However, this level rose to become comparable to treatments where Nitrogen was applied during the last 60 days of the experiment. Also, the colouration of the leaves turned greener. This is due to good nodule development during this time. The nodules, when sliced open, were brownish-pink in colour, thus indicating that leghemoglobin, which is found in active nitrogen fixing nodules, was present.

 

Nodulation occurred in all treatments to various degrees except in the -S treatment. Nodulation in the -N, -K and -B treatment plants were quite good. In the -Fe treatment plants, nodulation was poor and the reddish-pink colouration of leghemoglobin was absent. Nodulation was also poor in the -Mn treatment.

 

 

P - Leaf P levels fluctuated between the 0.20% and 0.32% range for the Complete Nutrient Solution treatment although this was largely concentrated between 0.20 and 0.23%.

 

However, for the various Minus Nutrient Solution treatments (except the -P treatment), the upper limit generally reached was 0.28%. But for the -Ca treatment, the upper limit reached was 0.38%, thus suggesting some interaction between Ca and P uptake. Milder interaction effects in such manner were also noted with the -K and -N treatments.

 

For the -P treatment, leaf P levels fluctuated between 0.10% -0.19%. The plants all appeared as dark bluish-green. In some leaves, lamina scorching was noted. There was also some retardation in the development of roots. However, the aerial portions of the plants showed good growth and had a good canopy.      

 

      

K - Leaf K levels fluctuated between the 2.0% - 2.5% range for the Complete Nutrient Solution treatment. But like nitrogen, as the canopy developed and the dry season set in, this range was lowered gradually to 1.5 - 2.0%. However, for the various Minus Nutrient Solution treatments (except the -K treatment), the lower limit generally reaches 1.5%. This was later lowered to 1.0%.

 

For the -K treatment, leaf K dropped to below 1.5% (when temporary general chlorosis of the plant was observed), to as low as 0.5%. As the plants grew older, only the tips and margins of leaves turned yellow, then necrotic, as other parts of the leaf showed a healthy colouration. Later, yellow spottings with enlarging necrotic centres were observed.     

 

 

Ca- Leaf Ca levels mainly fluctuated between the 0.35% - 0.55% range for the Complete Nutrient Solution treatment.

 

However, for the various Minus Nutrient Solution treatments (except the -Ca treatment), the range was wider: 0.22% - 0.62%.

 

For the -Ca treatment, leaf Ca levels dropped to 0.20% and the leaves of these pots were initially large and wide as well as 'papery' in feel at levels below 0.30%. The leaves of these pots were also more susceptible to insect damage.

     


 

Mg- Leaf Mg levels fluctuated between the 0.17% - 0.22% range for the Complete Nutrient Solution treatment.

 

However, for the various Minus Nutrient Solution treatments (except the -Mg treatment), Mg levels in the -Mn, -S and -Fe treatments were found to be below the lower limit of 0.17% while the other treatments had Mg levels above the upper limit of 0.22% (especially the -Ca treatment).

 

For the -Mg treatment, the Mg level fell to below 0.15% (where very marked interveinal chlorosis of individual lower leaves were noted), to 0.08%. The leaves of the plants undergoing this treatment were quite small and narrow. Root development seemed to be somewhat retarded in plants undergoing this treatment.

 

 

S - Leaf S levels generally fluctuated between the 0.20% - 0.35% range for the Complete Nutrient Solution treatment.

 

However, for the various Minus Nutrient Solution treatments (except the -S treatment), S levels in the Mg, Fe, and Mn treatments fell below the lower limit of0.20%, while the other treatments fell above the upper limit of 0.35% (especially the -Ca treatment).

 

For the -S treatment, S levels fell to 0.05% giving these plants a pale colouration (general chlorosis). Root development was also retarded in plants not provided with S.

 

 

Fe- Leaf Fe levels mainly fluctuated between the 45 - 75 ppm range for the Complete Nutrient Solution treatment.

 

However, for the various Minus Nutrient Solution treatments (except the -Fe treatment), the fluctuation was very variable.

 

For the -Fe treatment, Fe levels in the lower canopy were not much lower or higher than that of the Complete Nutrient Solution treatment (the control) at any time. However, their leaves in the upper canopy showed diffused interveinal chlorosis.

 

 

Mn- Leaf Mn levels fluctuated between the 140 - 190 ppm range for the Complete Nutrient Solution treatment.

 

However, the Mn level in all the Minus Nutrient Solution treatments (other than the -Mn treatment), generally fell within the above range of 140 - 190 ppm, except in the -K treatment where Mn levels exceeded the 300 ppm mark.

 

For the -Mn treatment, Mn levels in the lower canopy fell to as low  as 63 ppm although at various times their levels were similar to that of the Complete Nutrient Solution treatment (the control).   Like the -Fe treatment plants, their leaves in the upper canopy showed diffused interveinal chlorosis. However, these leaves later scorched, starting from the tip and moving down the margins (usually more on one side).

 

 

B - Leaf B levels fluctuated between the 30 - 70 ppm range for the Complete Nutrient Solution treatment but as the canopy developed  this range dropped to 10 - 30 ppm.

 

The B levels of the various Minus Nutrient Solutions (except the -B treatment), also fluctuated in a similar manner as the above control treatment.

 

For the -B treatment, B levels fell to below 10 ppm to as low as 3ppm to exhibit very marked deficiency symptoms: dying off of the  leader shoots and the appearance of crinkled/blackened new leaf buds  that were closely spaced with other leaves. The severe defoliation that resulted contrasted very sharply with the dense canopy that the  plants of this treatment showed earlier.

 

 

With respect to the Growth of the plants undergoing various treatments during this phase, no treatment showed a linear growth rate in both height and girth. However, the Relative Volume growth pattern was linear for the Complete Nutrient Solution treatment - the control, while that of the other treatments deviated from this slightly at various times, particularly that  of the -K, -Ca, and -Mn treatments. The plants of the -B treatments however, stopped growing as soon as their deficiency symptoms appeared.

 

 

 

 

Statistical Analysis of  Leaf Nutrient Levels

 

Table 3 provides Summary Statistics of Nutrient Concentrations in   plants undergoing Complete Nutrient Solution Treatment during Phase 2  i.e. when the plants had achieved a balanced nutrient status.

 

 

 

Nutrient  Removal

 

Leaf samples of old senescing leaves just about to drop indicate that the following approximate amounts of plant nutrients are exported in leaf litter:

 

 Nutrient  Removal

 through  Leaf  Litter

 by Acacia mangium

Plant

Nutrient

 

 Levels in Leaf Litter

Macronutrient:

 

 

 N

%

1.60 - 1.80

 P

%

0.28 - 0.38

 K

%

0.85 - 0.90

 Ca

%

0.50 - 0.55

 Mg

%

0.25

 S

%

0.48

Micronutrient:

 

 

 Fe

ppm

85

 Mn

ppm

353

 B

ppm

70 - 90

 

 

The nutrient amounts removed through fruit drop was not determined a