MATERIAL AND METHOD 1 Experimental Design
Bogor, 21-22 October 2015
302 the production of P. indicus planting stock are in their infancy and the lack of a nursery grading
system compromised the success of reforestation in the Philippines Gazal et al., 2004. Several attempts have been made to optimise the production of nursery stock Zhou et al., 2006; Yang
et al., 2012 but fertilizer regimes are yet to be defined for optimal growth of containerized seedlings and their survival after out-planting. Whilst screening for effective nitrogen-fixing
symbionts such as root nodule bacteria Lok et al., 2006, we noticed that nursery seedlings often displayed stress symptoms indicative of deficiency or excess of phosphorus P
fertilization. Phosphorus is an essential nutrient for plant growth as it is involved in most metabolic
processes. It comprises of nucleic acid, phosphilpids, phosphoproteins, phosphate esters, dinucleotides and adenosine triphosphate. They are required for the storage and transfer of
energy, photosynthesis, transport of electron process and in the synthesis of sugars and starch. As P is phloem-mobile, any disorders in P will easily result in carbohydrate biochemistry and
transport are affected in deficient plants. For instant, the first symptom is the distinct purple colour appearing in older leaves and later to young leaves Dell et al., 1996; Dell et al, 2001.
Therefore, glasshouse trials were undertaken on P. indicus seedlings with the following objectives: a to define the response and symptoms of P stress, b to determine the P
concentration ranges in foliage for stressed and healthy plants, and c to discuss on its sensitivity to P. The results should be useful for nursery managers and can also serve as a
guide for identifying P constraints in seedlings following out-planting in the field. Although the relationship between foliar nutrients and growth has been broadly studied and successfully
applied to a range of plantations species Dell et al., 2001; Salifu and Jacobs 2006, it has not been widely applied to many tropical hardwood species and this is the first.
2. MATERIAL AND METHOD 2.1 Experimental Design
Two glasshouse trials were carried out using Yalanbee Sandy Loam YB and Yellow Sand YS. A randomized complete block design was used in each trial, each comprising of 10
treatments and four replicate pot. The treatments for YB trial were 0, 5, 10, 20,40, 80, 160, 320, 640 and 1280 mg Pkg soil, designated as P0, P5, P10...and P1280 while YS were 0, 2,
4,8, 16, 32, 64, 128, 256 and 512 mg Pkg sand, designated as P0, P2, P4...P512. Phosphorus was supplied as aerophos, CaH
2
PO
4 2
.H
2
O. Both trials were undertaken with natural light in an evaporatively cooled glasshouse in Perth, Western Australia from October to January in YB
trials and July to October in YS trial. The seeds of the plant were sourced from Forest Research Institute of Malaysia FRIM.
2.2 Soil background The YB soil is a typical lateritic soil obtained from the Darling Range in Western Australia
which are infertile and strongly adsorb phosphate. Soil which had never been fertilized was collected at 0-20 cm depth from the Allandale Research Farm in Wundowie, 63 km east of
Perth. It was then sieved through a 4 x 4 mm stainless steel mesh and mixed. Combined core soil samples of 200g from each treatment were collected and sent to commercial laboratory
for analysis. The soil chemical properties obtained were as shown below Table 1: The soils were steam pasteurized at 90
o
C for one hour, allowed to cool for 24 hours and re- steamed before air-dried for five days. They were then potted in a non-draining pot,
measuring 150 mm diameter x 175 mm height and lined with clear plastic bag.
Bogor, 21-22 October 2015
303 Table 1: Soil chemical properties for both soils
Properties [mgkg] YSL Soil
YS Soil
P Colwell 20
4 Nitrate-N
1 1
Ammonium-N 5
5 K Colwell
60 20
S 8.8
11.8 Organic carbon
2.26 0.06
pH H
2
O 5.7
5.6 pH CaCl
2
6.3 6.2
2.3 Harvesting and plant analysis Ten weeks after transplanting, the shoots were separated from the roots at one cm above the
soil and then partitioned into the youngest fully expanded leaf YFEL and the rest of the shoot. The YFEL was chosen as this leaf cohort is suitable for determining the nutrient status
of many broad leaf plants Bell, 1997; Reuter and Robinson, 1997. All plant parts were oven- dried at 70
o
C to constant weight. The dried YFELs were ground by hand in a porcelain mortar and pestle. Digestion of plant materials was carried out using concentrated nitric acid
70 ww and H
2
O
2
30 ww in an open-vessel microwave oven CEM Mars 5 as described by Huang et al., 2004. A standard reference material, Eucalypt 2000 was included in
the digestion process. Total P was measured by induction coupled plasma spectroscopy. The Cowell P Colwell, 1963 soil samples in each harvested pot were taken after shaken for 16
hours in a bicarbonate solution before the soluble extract was analysed for P 2.4 Data analysis
Data were analysed using SPSS version 11.5. The effects of P treatments on shoot dry weight
were subjected to analysis of variance ANOVA and means were compared using Duncan’s New Multiple Range Test at P
0.05. Data were checked for normality before being analysed to satisfy the homogeneity test using Bartlett test at F
0.01. 3. RESULT AND DISCUSSION
3.1 Effect of phosphorus treatment on growth Shoot growth response significantly to P fertilizer P
There was a steep increase in growth at low P rates, a narrow optimum range and the shoot growth was
depressed at high P rates in both soil types Figure 1. a, c. Interestingly, however both shared a similar soil Colwell P concentrations at 118 mg Pkg soil with maximum yield even though
the YB soil had a greater buffering capacity at higher fertilizer rates with less severe toxicity symptoms Figure 1. b, d. Soil analysis showed that Colwell P was lower in YS than YB at low
fertilizer rates Table 1. This was in contrast to the general principle relationship between nutrient concentration and plant yield whereby a gradual increase in shoot growth with
increasing P fertilizer treatments are normally obtained Ulrich and Hills, 1967; Mead, 1984 and Shedley, 1995. The maximum seedling growth was obtained at lower rates of P for YS at
P128: 0.56
0.04g as compared to YB for P320: 3.60 0.13g. There was a strong growth response by Pterocarpus indicus to fertilizer phosphorus for both soil
types. These soil types were selected because they had low concentrations of available P and differ in P adsorption capacity. In normal practices, acute P deficiency occurs at site where it
is first cleared for agriculture or forest plantation. Usually, when P fertilizers are applied the
Bogor, 21-22 October 2015
304 water-soluble P component reacts rapidly with the surfaces of soil constituents by adsorption
to iron and aluminium oxides and with cations in soil solution such as by precipitation with ions of calcium, iron and aluminium Barrow, 1980 restricting P available for adsorption by
plant roots or mycorrhizal fungi. As fertilizer P increased, there is an increase in Colwell P Colwell, 1963 and plant growth. This sodium bicarbonate soil test is widely used in Western
Australia and has been applied to prescribe fertilizer P requirements. Soil test however, give crude estimates in predicting plant yields as compare to plant P for the diagnosis of P
deficiency where this study was carried out.
Figure 1: Effects of P fertilizer on shoot dry weight of Pterocarpus indicus and soil available P Colwell in Yalanbee soil for YB a,b and YS c,d respectively. Data are means of 4
replicates with standard error bars. However, growth response for shoot dry weight, root biomass and total root length was
severely depressed at low P rates in P0-P32 for YS and P0-P40 for YB plants Figure not shown. Compared to the growth response of other woody plants in these soils, there was
surprisingly a narrow response range between P deficiency and toxicity in the species studied. Although anticipated P toxicity usually occurs at high fertilizer rate in the yellow sand due to
low buffering capacity, it was not expected in the Yalanbee Clay loam soil where P adsorption capacity is much higher Barrow, 1997. Thus, this raises the possibility that P is an unusual
100 200
300 400
500 600
P treatment m g Pkg soil
0.0 0.1
0.2 0.3
0.4 0.5
0.6
S h
o o
t d
ry w
e ig
h t
g p
o t
c
100 200
300 400
500
Colwell phosphorus mgkg soil
0.0 0.2
0.4 0.6
0.8
S h
o o
t d
ry w
e ig
h t
g p
o t
d 200
400 600
800 1000 1200 1400
P treatment m g Pkg s oil
1 2
3 4
5
S h
o o
t d
ry w
e ig
h t
g p
o t
a
100 200
300 400
500
Colwell phosphorus m gkg soil
1 2
3 4
5
S h
o o
t d
ry w
e ig
h t
g p
o t
b
Bogor, 21-22 October 2015
305 tree that may be sensitive to fertilizer P supply that would not adversely affect the growth of
other tree legumes with promising growth rates. 3.2 Foliar nutrient concentrations and plant symptoms
Phosphorus, P concentration in the YFEL increased linearly with increase P fertilizer from 0- 1.92 mgg at P0-P512 in the YS plants and 0-5.5 mgg at P0-P1280 in YB plants Figure
2.1. Generally, growth was greater in YB than YS plants as leaves in the YS plants were smaller. There were also early deficiency symptoms at lower P fertilizer treatments in YS P0-
P32 than in YB P0-P80.These seedlings showed depressed shoot dry weight, reduced size of the older leaves, chlorotic foliage and short stems which can be highly branched and rosette-
like appearance Figure 2.
Figure 2: Change in total P concentration in the youngest fully expanded leaf YFEL of Pterocarpus indicus seedlings in response to P fertilizer. Points represent means of four
replicates. Functions with R
2
values are fitted separately to individual replicate data for the YS and YB experiments
Table 2: Symptoms and phosphorus nutrient concentrations in the youngest full expanded leaves YFELs for Pterocarpus indicus.
Element Descriptions
Symptoms Concentration
[mgg
-1
dry weight] P
Deficient Malformed, stunted growth with soft small leaves, early
leaf shedding, stunted stems, short internodes and malformed apical buds