Copyright is owned by the Author of the thesis.  Permission is given for 
a copy to be downloaded by an individual for the purpose of research and 
private study only.  The thesis may not be reproduced elsewhere without 
the permission of the Author. 
 
LIME-ALUMINIUM-PHOSPHATE INTERACTIONS 
IN SELECTED ACID SOILS FROM FIJI 
A thesis presented in partial fulfilment of 
the requirements for the degree of 
Doctor of Philosophy in Soil Science 
at Massey University 
Ravendra Naidu 
1985 
ii 
ABSTRACT 
Poor crop production in Fiji has long been associated with Al-toxicity 
and/or P deficiency problems . Although attempts have been made to 
alleviate these problems, the lack of suitable soil-testing procedures and 
a limited understanding of lime-Al-P interac tions are restricting the 
better utilization of these soils . 
Following a preliminary investigation, 4 contrasting Fij ian soils 
(Batiri, Koronivia, Nadroloulou, and Seqaqa) were chosen for a lime-Al-P 
interaction study. The soils, which had pH and M KCl-extractable Al 
values ranging from 3 . 9  to 4 . 9  and 35.6 to 0.3 mmol kg-1,respectively, 
were used to investigate the effect of liming on surface charge, P-sorption 
characteristics, the amounts of P extracted by a number of soil-testing 
procedures, and plant uptake of P .  
A study was conducted to compare M KCl-extraction procedures for 
exchangeable Al and analytical techniques used in the determination of Al . 
For each soil, different extraction procedures and analytical techniques 
measured significantly (P < 0 . 01) different amounts of extractable Al. 
It was recommended that extractable Al in Fijian soils could be best 
determined by the oxine reagent following a 2 x 1-h shaking with M KCl . 
The ion retention method, which is commonly used to measure charge, 
was examined critically with a view to standardising it for the range of 
soils used in the present study. The method involves an initial washing 
of soils with  an electrolyte of high concentration to remove exchangeable 
ions, equilibration of the washed soils with an electrolyte of the desired 
concentration and subsequent  extraction of the equilibrated soils. The 
concentrations of prewash electrolyte (0 . 5M CaCl2, O.lM CaCl2, and 
O.OlM CaCl2) used to remove exchangeable ions prior to equilibration with 
O.OlM CaCl�nd the soil: solution ratio were found to have a marked effect 
on the magnitude of the surface negative charge of unlimed soils. 
However, these differences were largely related to the amount of Al removed 
during the prewash and the equilibration procedures . Thus when the Al 
released in the extracting solution (0.5M KN03) was included in the 
calculation of charge, the differences in the measured negative charge 
obtained either because of varying concentrations of prewash electrolyte or 
for the effect  of soil: solution ratio were reduced. 
Surface charge, determined in O . OlM CaCl2, was always found to be 
higher than that determined in 0 . 03M NaCl and this difference was more 
iii 
pronounced in limed soils at high pH values . Subsequent studies revealed 
that this anomaly was largely due to the inability of Na to exchange 
with Ca at high pH values . The results of these studies, together with 
those involving the prewash electrolytes and the soil: solution ratio, 
suggested that a suitable method of measuring surface charge of limed 
soils would use O . OlM CaC12 as the equilibration electrolyte and include 
in the calculation of charge the amount of Al released in the extracting 
solution . 
Incubation of soils with added lime caused a large increase in 
surface negative charge . However, the magnitude of increase in the 
negative charge varied considerably between soils . For example, the 
negative charge in the Seqaqa soil increased from 8 to over 38 cmol(p)kg-1, 
compared to  only a small increase of 2 to 10 cmol(p)kg-l in the Batiri 
soil over t he same pH range. 
In contrast to liming, P additions resulted in only a small increase 
in negative charge . Interestingly, all soils possessed positive charge 
up to 1 cmol(p)kg-1, even at pH values as high as 7 .  Subsequent studies 
showed that this may have been due to substitution of Ti4+and,hr Mn4+ in the 
iron oxide lattice . 
Extraction of lime- and P-treated soils with Olsen and Mehlich 
reagents showed that liming had a marked effect on the amount of P removed . 
Whereas Olsen P increased on either side of pH values 5 . 5  - 6.0 , Mehlich P 
consistently decreased with increasing soil pH . For example, in the 
high P-sorbing Seqaqa soil, Mehlich P decreased from 0 . 2  mmol kg-l at pH 
4 . 5  to < 0 .01  mmol kg-1  in soils with pH higher than 7 . 0 .  The decrease 
in Mehlich P was shown to be due to the neutralizing effect of lime on the 
extractant. An isotopic-exchange study revealed an increase in exchangeable 
P up to a pH approximating 7, above which there was a sharp decrease, 
possibly indicating the formation of insoluble Ca-P compounds . 
Although liming had only a small effect on the sorption of added P, 
this was sufficient to have a significant effect on equilibrium solution P 
concentration . Generally, liming caused an increase in equilibrium 
solution P concentration up to pH values of 5 . 0 - 6 . 0, above which there 
was a marked decrease . The initial increase in equilibrium solution P 
concentration appeared to result from an interaction between added P, 
surface negative charge and electrostatic potential in the plane of 
sorption. Subsequent sorption studies using Nadroloulou soil incubated 
with either KOH or Ca (OH)2 showed that the decrease in solution P at high 
pH values was probably due to the formation of insoluble Ca-P compounds . 
iv 
The effects of lime and P addition on the growth of the tropical 
legume Leucaena leucocephala were studied in a controlled-climate laboratory . 
With all 4 soils, there was an initial increase in the dry matter yield of 
the plant tops with liming which was followed by a marked decrease . 
This trend was most pronounced in the Seqaqa soil where dry matter yield 
of tops increased by -2000% at the pH at which maximum growth occurred . 
Similar but smaller increases were noted in the other soils. 
The concentration of Al in plant tops increased on either side of 
the pH of maximum growth, but Al uptake by the whole plant (tops + roots) 
declined steadily with increasing pH . Poor growth at low pH values was 
attributed to Al-induced P deficiency within the plant and at high pH 
values largely to a soil P deficiency and to a smaller extent to the 
increased concentration of Al in the plant tops . P deficiency at high 
pH values was attributed to the formation of insoluble Ca-P compounds 
and this was supported by the data obtained from isotopic-exchange and 
P-sorption studies. 
A further plant growth study was conducted on the limed soils, 
previously used for the growth of Leucaena ,leucocephala. Ryegrass (Lolium 
perenne L ) plants were initially grown in sand and then transferred onto 
the soils. Plant growth was again retarded at low and high pH values 
but comparison with control plants grown in a similar manner but not 
transferred onto the soils demonstrated that the poor growth at both high 
and low pH was due in part to a toxicity effect rather than simple P 
deficiency. It is likely that Al was responsible . 
Comparision of the data obtained by resin extraction and plant P 
uptake gave a close 1 : 1  relationship . In contrast, Olsen-, Colwell-, 
Bray (I)-, Bray (II)-, and Mehlich-extractable P were only weakly correlated 
with P uptake. The difficulty in relating plant P uptake data to 
extractable P levels was attributed to the problems associated with 
extracting P from limed soils. 
AC��O��EDGEMENTS 
I would like to express my appreciation to a number of people 
without whose help and guidance this thesis would not have been possible. 
In particular, I would like to thank: 
Professor J. Keith Syers, who with the cooperation of MAFF, Fiji 
and the Fiji Public Service Commission initiated this study. Also for his 
supervision, unending enthusiasm, and encouragement during the study. His 
rigorous standards of scientific thoroughness and presentation , have been 
highly rewarding . 
Mr. Russell Tillman, to whom I am grateful for his patience, 
constructive ideas and continual guidance during the planning and 
execution of this study. 
Dr. J.H. Kirkman for many helpful discussions with several aspects 
of this study. 
V 
Mr. Lance Currie and Dr. I. Warrington of the Department of Soil Science 
and D.S.I.R., respectively, for guidance in the execution of the glasshouse 
trials. 
br. R. Lee, Soil Bureau, Lower Butt, for his advice in the studies 
related to exchangeable Al. 
Past and present Post-doctoral Fellows and students in the Department 
of Soil Science. Especially, Dr. D. Curtin, Dr. N.S. Bolan, Dr. R. Harrison, 
and Miss P. Sorn-srivichai for helpful discussions with certain aspects of 
this study. 
Mr. D.M. Leslie, Soil Bureau, Lower Butt and Professor R.J. Morrison , 
University of the South Pacific, Fiji, for their advice in the collection 
of soil samples. 
Dr. D. Horne, Dr. B. Ponter, and Miss M. Wallace for proof reading 
the thesis. 
Fiji Government for financial support in the form of a scholarship 
and to the University of the South Pacific for granting me study leave. 
The Faculty of Agricultural and Horticultural Science, Massey 
University , for a Johannes August Anderson award. 
Carolyn Hedley for excellent illustration of figures. 
Dianne Syers, for producing an excellent typescript. 
vi 
Finally to my son Roneal for providing a lively atmosphere at home 
and to my wife Shamila who has helped me in many aspects of my work. 
Her patience, help, and encouragement have been a constant inspiration. 
TABLE OF CONTENTS 
ABSTRACT . . . • 
ACKNOWLEDGEMENTS 
TABLE OF CONTENTS 
LIST OF FIGURES 
LIST OF TABLES 
CHAPTER 1 
GENERAL INTRODUCTION 
1. 1 Introduction 
CHAPTER 2 
REVIEW OF LITERATURE . 
2. 1 Introduction 
2.2 Mechanism of Phosphate Retention 
2.3 Effect of Liming on Aluminium and Phosphate 
Chemistry of Acid Soils . • . . . . . • 
2.3.1 
2. 3.2 
2.3.3 
Solution chemistry of pure aluminium 
systems and its implication to soils 
Origin of exchangeable aluminium and its 
interaction with added phosphate 
Lime-aluminium-phosphate interactions 
in acid soils . . . . . . . • 
2.4 Effects of Excess Soil Aluminium and 
Low Phosphate on Plant Growth . . . . 
2.4.1 
2.4.2 
Uptake of aluminium by plants 
Toxicity symptoms 
2.5 Conclusions . • • . . . .  
vii 
Page 
ii 
V 
vii 
xiii 
-- xix 
1 
1 
3 
3 
3 
5 
6 
8 
10 
16  
16 
16 
17 
CHAPTER 3 
GENERAL MATERIALS AND METHODS • . 
3 .  1 Soils • . . • • . • • 
3 . 2  Analytical Procedures 
3 . 3  Selective Chemical Dissolution Techniques 
3 .  3 .  1 
3 . 3 . 2  
Determination of oxalate-extractable 
iron and aluminium • . . . • • • . •  
Determination of citrate-dithionite­
bicarbonate-extractable iron and aluminium 
3 . 4  Preliminary Lime Incubation Study 
3 . 4 . 1  Preparation of soil samples 
3 . 5  Extraction of Aluminium from Soils using M KCl: 
A Comparison of Methods 
3 . 5 . 1 
3 . 5 . 2  
3 . 5 . 3  
3 . 5 . 4 
Introduction • 
Methods • 
3 . 5 . 2 . 1  
3 . 5 . 2 . 2  
3 . 5 . 2 . 3  
3 . 5 . 2 . 4 
Aluminium-release curves • 
Determination of M KCl-extractable 
aluminium: Extraction procedures 
(a) Short-term shaking 
(Pratt and Blair, 1961) 
(b) Long-term shaking 
(c) Long-term standing (Yuan, 1959) 
(d) Leaching (Black, 1965) 
(e) Sequential extraction 
Analytical procedures 
3 . 5 . 2 . 3 . 1  Calorimetric methods 
(a) Oxine • • • • 
(b) Aluminon • • 
3 . 5 . 2 . 3 . 3  Atomic absorption 
spectrophotometry 
Recovery tests • 
Results and discussion 
3 . 5 . 3 . 1  
3 . 5 . 3 . 2 
3 . 5 . 3 . 3  
3 . 5 . 3 . 4  
Aluminium-release curves • 
Comparison of extraction procedures 
Analytical techniques 
Recovery tests • • . • 
Conclusions • • • • • • • • • 
Page 
18 
18 
18 
21 
21 
21 
24 
24 
24 
24 
27 
27 
27 
27 
27 
27 
29 
29 
29 
29 
29 
29 
30 
30 
30 
30 
33 
36 
38 
41 
viii 
CHAPTER 4 
CHARGE CHARACTERISTICS OF ACID SOILS 
AS INFLUENCED BY LIMING • 
4. 1 Introduction . • .  
4.2 Materials and Methods 
4. 2. 1 
4.2.2 
4.2.3 
Preparation of soil samples 
Charge measurement procedures 
4.2.2.1 
4.2.2.2 
4.2.2.3 
Effect of concentration of prewash 
electrolytes on charge subsequently 
determined in O.OlM CaClz solutions 
Effect of soil: solution ratio 
on negative and positive charge 
determined in O.OlM CaClz 
Effect of index cations on the 
determination of negative and 
positive charge . . . . . 
Effect of soil pH and added phosphate 
on negative and positive charge determined 
in 0.01M CaClz 
4.3 Results and Discussion • 
4.3. 1 
4.3.2 
4.3.3 
Charge measurement procedures 
4.3.1.1  
4.3.1.2 
4.3.1.3 
Effect of concentration of 
prewash electrolytes • • • 
Effect of soil: solution ratio 
Effect of index cations 
Effect of soil pH on charge 
characteristics. of soils • . 
Effect of added phosphate on charge 
4.4 Conclusions . • .  
Page 
42 
42 
44 
44 
45 
45 
46 
46 
46 
47 
47 
47 
49 
52 
55 
59 
6 1  
ix 
CHAPTER 5 
EFFECT OF LIMING ON PHOSPHATE EXTRACTED 
BY TWO SOIL-TESTING PROCEDURES . 
5. 1 Introduction . . . . . .  . 
5.2 Materials and Methods . . . .  
5.2. 1 
5.2.2 
Preparation of soil samples . 
Chemical analyses 
5.3 Results and Discussion 
5.4 
5.3.1 
5.3 . 2  
5.3.3 
5.3.4 
Effect of lime and phosphate additions 
on isotopically-exchangeable phosphate 
Effect of lime and phosphate additions 
on Olsen-extractable phosphate 
Effect of lime and phosphate additions 
on Mehlich-extractable phosphate 
Comparison of soil-testing procedures 
Conclusions . . . . . 
CHAPTER 6 
EFFECT OF LIMING ON PHOSPHATE SORPTION BY ACID SOILS 
6. 1 
6.2 
6.3 
6.4 
Introduction . . . . . 
Materials and Methods 
6.2.1 
6.2.2 
6.2.3 
Results 
6. 3.1 
6.3.2 
6.3.3 
Preparation and preliminary 
Incubation of soils with KOH 
Phosphate sorption studies 
and Discussion 
analysis of soils 
Effect of liming on pH, extractable aluminium , 
and Olsen-extractable phosphate • . • 
Effect of pH on phosphate sorption 
Effect of background electrolyte on phosphate 
sorption by Nadroloulou soil incubated with 
calcium or potassium hydroxide 
Conclusions . . 
Page 
63 
63 
64 
64 
64 
65 
65 
68 
71 
73 
75 
78 
78 
79 
79 
79 
79 
82 
82 
83 
89 
94 
X 
CHAPTER 7 
LI�-ALUMINIUM-PHOSPHATE INTERACTIONS AND 
THE GROWTH OF LEUCAENA LEUCOCEPHALA . 
7. 1 Introduction . . . . . 
7.2 Materials and Methods 
7. 2. 1 
7.2.2 
7.2.3 
Soils 
Plant growth study 
Chemical analyses 
7.2.3. 1 
7.2.3.2 
Soils . 
Plants . 
7.3 Results and Discussion . .  
7.3. 1 Effect of liming on EH, extractable 
aluminium, and extractable Ehosphate 
7.3.2 Effect of lime and EhosEhate additions 
on Elant growth . . . . . . . . . . . 
7.3.3 Effect of lime and Ehosphate additions 
on root growth . . . . . . . . . 
7. 3.4 Effect of lime and Ehosphate additions 
on the chemical composition of Leucaena 
7.3.5 Lime-aluminium-Ehosphate interactions 
in soils and plants 
7.4 Conclusions . . . . . . . . . . . 
CHAPTER 8 
ASSESSMENT OF PLANT-AVAILABLE PHOSPHATE 
USING SEVERAL SOIL-TESTING PROCEDURES 
8. 1 Introduction 
8.2 Materials and Methods . 
Soils . . . 
Extractable Phosphate . 
. 
8.2. 1 
8.2.2 
8.2.3 Determination of buffer capacity 
. . . 
. . . . . . . 
. . . . . . 
. . . . . . . 
leucocephala 
. 
. 
. 
Page 
98 
98 
99 
99 
101  
101  
101  
102 
102 
102 
107 
1 10 
1 12 
121  
123 
125 
125 
126 
126 
126 
127 
xi 
8.3 Plant Growth Studies . .  
8.4 Results and Discussion 
8.4.1 
8.4.2 
Plant growth studies 
Relationship between plant uptake 
of phosphate and soil-test results 
8.5 Conclusions 
SUMMARY AND CONCLUSIONS 
APPENDICES . 
BIBLIOGRAPHY 
Page 
128 
128 
128 
129 
137 
139 
144 
150 
xii 
Figure 
2.1 
LIST OF FIGURES 
Solubility of aluminium in water solution 
as affected by pH of solution (McLean , 1976) 
2.2a Influence of pH on the phosphate sorbed by 
goethite at a solution concentration of 
0.2 mmol L-1 together with the proportion 
of phosphate present as the divalent ion 
(Bowden et al. , 1980b) . . . . . .  . 
2.2b Retention of phosphate by hydrolytic reaction 
products of aluminium formed in systems at 
the initial aluminium concentration of 
1.10 mmol L- 1  and OH/Al molar ratio of 3.0 
as a function of  time (Kwong et-al. , 1978) 
2.3 Effect of pH on the amount of phosphate in 
soil solution and on the amount of labile 
phosphate present in an Illinois soil 
studied by Murrmann and Peech (1969) , 
(reproduced from Haynes , 1982) 
3 . 1  Map of  the Fiji Islands showing the location 
of  soils used for the present study 
3.2 Amounts of extractable Al ( • )  released and pH 
( 0 ) of the soil suspension during eight 
sequential extractions _of the unlimed soils 
with M KCl . • . • . . . • • . . . . 
3.3 Amounts of Al extracted from unlimed soils by 
the M KCl extraction procedures , short-term 
shaking , (A); long-term shaking , (B); 
long-term standing ,.(C); 2 X 1 h shaking , (D); 
and 2 h leaching of soils ,(E);relative to the 
cUmulative amount removed during 8 successive 
extractions , (S). LSD (5%) of results for 
comparison between extraction procedure within 
a soil = 0.06 . . • . • • . . . . • . . •  
xiii 
Page 
7 
12 
12 
13 
19 
32 
35 
xiv 
Figure Page 
3.4 Amounts of Al in M KCl extracts of unlimed 
soils estimated by the oxine , (P); 
aluminon , (Q) ; titration , (R) ; and AAS, 
(S); techniques. LSD (5%) of results for 
comparison between analytical techniques 
within a soil = 0.06 
3.5 Effect of increasing the solution 
concentration of K on the intensity 
(absorbance) of colour developed by the 
aluminon reagent 
. . . . . . . . . . . 
4.1 Effect of soil:solution ratio on the distribution 
of (a) total negative .(Ca ads + A1-�KN03), 
(b) negative (Ca ads) , and (c) positive charge 
(Cl ads) in the four soils . . .  
4.2 Effect of soil:solution ratio on the pH 
(in the sixth equilibration) of the soil suspension 
4.3 Effect of soil pH on the distribution of negative 
and positive charge determined in O.OlM CaC12 and 
0.03M NaCl , (a) negative charge determined in 
0 .OlM CaCl2 , (b) total negative charge (Na ads + 
Ca (NH4N03)) determined in 0.03M NaCl , 
(c) negative charge (Na ads) determined in 0.03M 
NaCl , (d) positive charge determined in 0.03M 
NaCl , and (e) positive charge determined in 
O.OlM CaC12 . • . . . . . . 
4.4 Effect of increasing amounts of Ca(OH)2 
on the pH of four contrasting soils 
4. 5 Effect of soil pH and added P on the distribution 
of negative and positive charge in soils. 
(a) negative charge in P-treated (16.1 mmol P kg-1 
soil) soils , (b) negative charge in untreated 
(0 mmol P kg- 1  soil) soils , (c) positive charge 
in P-treated (16.1 mmol P kg-1  soil) soils , and 
(d) positive charge in untreated (0 mmol P kg-1  
37 
39 
50 
51 
53 
56 
soil) soils • • • • • . . • • • • 58 
Figure Page 
5.1 Ef fect of increasing pH on isotopically­
exchangeable P in 4 soils incubated with 
3 rates of added P. ( • = 0; 
5.2 
5.3 
A. = 8. 1; • 16.1 mmol kg-1 soil) . . 
Effect of increasing pH on Olsen P in 4 soils 
incubated with 3 rates of added P. ( • = 0; 
A. • 8.1; e 16.1 mmol kg-1 'soil) .  
Effect of increasing pH on Mehlich P 
and pH of the Mehlich extract ( A ) in 4 soils 
incubated with 3 rates of added P. ( • 0; 
A. = 8.1; • = 16.1 mmol kg-1 soil) 
6.1 Effect of soil pH on the amounts of Al 
extracted from limed soils by M KCl solution 
6.2 Effe ct of soil pH on the amount of P sorbed 
( ) at 2 initial solution P concentrations 
(P1 e and P2 = A. , Table 6.2) and the 
concentration of Ca (- - -)  in the control 
samples ( •) and in the presence of added P 
(P1 = 0 and P2= A ,  Table 6.2) . . . . • • . • .  
6.3 Effect of pH on the amount of P sorbed by 
untreated ( A. ) and P-incubated ( e ) 
Koronivia and Seqaqa soils at initial 
solution P concentrations of 0.69 and 
2.15 mmol L-1 , respectively. 
6.4 Values for pH and Ca and P concentrations from 
the section on the pH-P sorption curve where 
sorption increases, plotted according to the 
method of  Clark and Peech (1955) • . . .  
6.5 Effect of background electrolyte concentration 
on the amount o f  P sorbed by Nadroloulou soils 
incubated with KOH at an initial solution P 
concentration of  1.61 mmol L-1 • . . . • . . .  
66 
69 
72 
84 
86 
88 
90 
92 
XV 
Figure Page 
6.6 Effect of background electrolyte concentration 
on the amount of P sorbed by Nadroloulou soils 
incubated with Ca (OH)2 at an initial solution 
P concentration of 1. 61 mmol L -1. (HzO = • ; 
0.01M KCl 
1M KCl 
A 
. ) 
0 .1M KCl • 
6.7 Effect of electrolyte concentration on pH 
of the sorption medium in the Nadroloulou 
soils incubated with Ca (OH)z 
6.8 Effect of increasing the pH by additions of 
dilute NaOH to soils previously limed to 
pH 6.9 on the amount of P sorbed by 
Nadroloulou soil suspended in M KCl 
7.1 Effect of increasing additions of Ca (OH)2 
on the pH of soils . . . . . • . .  
7.2 Effect of soil pH on the amounts of Al 
extracted by M KCl from soils treated with 
3 rates of added P (Table 7.1). 
( e = P1 , A P2 , and • = P3) 
7.3 Effect of soil pH on the amount of P 
extracted by the Olsen reagent from soils 
treated with 3 rates of added P (Table 7.1). 
( . P1, A = P2 , and a P3) 
7.4 Effect of soil pH on the amount of P extracted 
by anion-exchange resin from soils treated 
with 3 rates of added P (Table 7.1). 
( • = P1 , A P2 , and • = P3) 
7.5 Effect of soil pH and added P (Table 7.1) 
on dry matter top yield. Vertical bars (I) 
represent LSD (pH) at 5 ,  1 ,  and 0.1% level 
of significance. ( • 
e = P3) . . . 
P1 , A P2 , and 
7.6 Effect of soil pH and added P (Table 7.1) on 
dry matter root yield. Vertical bars (I) 
represent LSD (pH) at 5 ,  1 ,  and 0.1% level of 
significance. ( • = P1, A = P2 , and • 
93 
95 
96 
103 
104 
105 
106 
108 
P3) • • . . 111 
xvi 
Figure 
7.7 Effect of soil pH and added P (Table 7 . 1 )  on 
the concentration of P in plant tops. 
Vertical bars (I) represent LSD (pH) at 5, 1, 
and 0. 1%  level of significance. ( • = P 1, 
.& = P2, and • = P3) . . . . 
7.8 Effect of soil pH and added P (Table 7. 1)  on 
the concentration of P in roots. Vertical 
bars (I) represent LSD (pH) at 5, 1,  and 0. 1% 
level of significance. ( • = P1, .& P2 and 
• P3) 
7.9 Effect of soil pH and added P (Table 7.1 )  on 
the concentration of Al in plant tops. 
Vertical bars (I) represent LSD (pH) at 5, 1 
and 0.1%  level of significance. ( a Pl, 
.& = P2, and • = P3) 
7. 10  Relationship between the concentration of Al 
in plant tops and (a) dry matter top yield and 
(b) concentration of P in the tops . . 
7.1 1  Effect of soil pH on the concentration of Al in 
roots of plants grown in soils treated with 
4.84 mmol P kg-1. Vertical bars (I) represent 
LSD (pH) at 5, 1 ,  and 0.1 %  level of significance 
7. 12 Effect of soil pH and added P (Table 7. 1 )  on 
the uptake of Al by plant tops. Vertical 
bars (I) represent LSD (pH) at 5, 1 ,  and 0.1%  
level of significance. ( • = P 1, .& P2, 
and e = P3) . .  
7. 13  Effect of soil pH  and added P (Table 7. 1 )  on 
the uptake of Al by plant roots. Vertical 
bars (I) represent LSD (pH) at 5, 1,  and 0.1%  
level of significance ( • 
and • = P3) . • . . • 
Pl, .& P2, 
xvii 
Page 
1 1 3  
114 
1 15 
1 16 
ll8 
1 19 
1 20 
Figure 
7. 14 Effect of soil pH and added P (Table 7.1) on 
the ratio of P roots to P (roots +tops) 
in plants. Vertical bars (I) represent 
LSD (pH) at 5, 1, and 0.1% level of 
significance. ( • P 1, A = P2, 
and e = P3) 
8.1 Effect of soil pH and added P (4.84 mmol kg- 1) 
on the dry weight of ryegrass tops. 
Vertical bars (I) represent LSD (pH) at 5, 1, 
and 0. 1%  level of significance. 
8.2 Effect of soil pH and added P (4.84 mmol kg- 1) 
on the concentration of (a) Al and (b) P 
in ryegrass tops. Vertical bars (I) 
represent LSD (pH) at 5, 1, and 0.1% level 
of significance . . . 
8.3 Relationship between uptake of P by plants 
(Leucaena leucocephala _-and ryegrass) and 
amounts of isotopically-exchangeable P (a) 
and, Meh1ich- (b), resin- (c), Bray (I)- (d), 
Bray(II)- (e), Olseh- (f), and Colwell-
extractable P (g) 
8.4 Effect of soil pH and added P (4.84 mmol kg-1) 
on the amount of P extracted by the Bray(I) reagent 
xviii 
Page 
122 
130 
131 
132/ 133 
138 
Table 
3.1 
LIST OF TABLES 
USDA and Twyford and Wright ( 1 965)  classification 
of soils used for preliminary analyses . . . . 
3.2 Some chemical parameters used to characterise 
the soil·s . . . ·, . 
3.3 Selective dissolution analyses and mineralogical 
composition of the soils used 
3.4 Amounts of Ca(OH)2 added to the soils during 
the preliminary incubation studies 
3.5 pH of unlimed and limed soils used in the 
standardisation of the M KCl extraction procedure 
3.6 Cumulative amounts of Al removed during 
eight sequential extractions 
3.7 Percentage recovery of Al added to M KCl 
extracts by four analytical techniques . 
4.1 Effect of the concentration of prewash electrolytes 
on the cumulative amount of Al extracted by the 
saturating (CaC12) and extracting (KN03) electrolytes 
and on the negative (Ca ads), total negative 
(Ca ads + Al-KN03) ,  and positive charge (Cl ads) 
determined in O.OlM CaCl2 in a range of unlimed 
and limed soils 
4.2 Correlation and linear regression coefficients 
between negative charge (Na ads) and total negative 
charge (Na ads + Ca(NH4N03)) determined in 0.03M 
NaCl and negative charge (Ca ads) determined in 
0.01M CaCl2 solution . .  
4.3 Ratio of Fe: Ti and Fe:Mn in the citrate-dithionite-
bicarbonate extracts, positive permanent charge 
estimated from Ti(IV) and from Ti(IV)+Mn(IV) substitution 
in iron oxides and that determined by Cl adsorption 
(Cl ads) from 0.01M CaC12 above pH 7 • •  
xix 
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Table 
5.1 Amount of P extracted by the Mehlich reagent 
(pH 1.3) from unlimed and limed and 
subsequently phosphate treated (8 . 1  mmol P kg-l 
soil) Batiri, Koronivia, and Nadroloulou soils . 
5 . 2  Amounts of P extracted by the Mehlich and Olsen 
reagents from unlimed but phosphate treated 
(0, 8 . 1, 16.1 mmol P kg-1 soil) soils 
6.1 pH values of the soils selected to 
investigate the effect of pH on P sorption 
6 . 2  Initial solution P concentration in the 
background electrolyte during the investigation 
of the effect of pH on P sorption 
6.3 Amounts of crystalline free Fe and Al, and short­
range order Fe and A1 extracted by citrate­
dithionite-bicarbonate and acid ammonium 
oxalate reagents, respectively, and the ratio of 
oxalate- to dithionite-extractable A1 and Fe . .  
7.1 Amounts of P added to limed soils prior to 
incubation and growth of Leucaena leucocephala 
8. 1 Proportion of variation in plant P uptake (R2) 
accounted for by extractable P alone and in 
combination with various indices of buffer 
capacity, as determined by multiple regression 
analyses • . 
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8 1 
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