1. TABLE OF CONTENTS
Abstract i
Acknowledgements v
Table of contents vii
List of tables xii
List of figures xiv
Introduction 1
Background
1
Aims and key questions
4
Chapter 1: Acid-Base properties of soils under
coniferous forests: A literature review.
5
1.1. Introduction
5
1

2. 1.2. Chemical properties of acid soils under coniferous forests
6 1.2.1.
Soil acidity
6
1.2.2. Chemistry of Al in acid soils
7
1.2.3. Al phytotoxicity in acid soils
8
1.3. Effects of silviculture and afforestation on soil on chemical status 9
1.3.1. Nutrient depletion from forest soils
9
1.3.2. Nutrient uptake and
retention by trees 10
1.4. The Ca/Al ratio as an index of growth
stress 12
1.4.1. Other ratios in solution
14
1.5. Acidification and nutrient status in pine forests of Southern Africa 15
1.6. Conclusions 16
Chapter 2: Study areas, sampling and statistical
methods 17
2

3. 2.1 Study area - general description
17
2.1.1. Climate
17
2.1.2. General geological and
mineralogical Background 19
2.2. Rhenosterhoek forest area
22
2.2.1. Topography
22
2.2.2 Geology and soils
22
2.2.3 Sampling sites
23
2.3. Grootfontien forest area
23
2.3.1. Topography
24
2.3.2. Geology and soils
24
2.3.3. Sampling sites
25
2.4. Klipkraal forest
25
3

4. 2.5. Sampling methods
26
2.6. Statistical treatment
27
Capter 3: Soil characterisation and acidity status 28
3.1. Introduction
28
3.2. Materials and methods
28
3.3. Results and discussion
30
3.3.1. Organic carbon (OC)
30
3.3.2. Soil pH
31
3.3.3. Exchangeable
acidity 34
3.3.4. Exchangeable
cations 35
3.4. Summary and conclusions
41
4

5. Chapter 4: Soil solution composition 43
4.1. Introduction
43
4.2. Materials and methods
43
4.3. Results and discussion
44
4.3.1. pH of the saturated paste
44
4.3.2. General composition
of the saturated paste extracts 46
4.3.3. Electrical conductivity (EC) 49
4.3.4. Aluminium (Al) 51
4.3.5. Ca/Al ratio in the soil
solution 57
4.3.6. Ammonium (NH4
+
)
59
4.3.7. Fluoride (F-
)
60
4.3.8. Dissolved organic carbon
(DOC) 62
4.4. Comparing the Ca/Al ratio between the soil solution and the
exchange phase 63
5

6. 4.5. Conclusions
65
Chapter 5: General discussion and conclusions 67
5.1. Soil chemical status under pine plantations in the eastern
highlands of Southern Africa 67
5.2. Practical implications of the current study
69
5.3. Future studies 69
Referneces 71
Appendix A: Site maps I
A.1: Rhenosterhoek plantation I
A.2: Blyfstaanhoogte plantation II
A.3: Grootfontein plantation III
A.4: In Die Diepte plantation IV
A.5: Soil profile description for two selected pits in P. Patula
plantations in the Rhenosterhoek area V
Appendix B: Analytical methods VI
6

7. B.1. Introduction VI
B.2. CuCl2 extractable Al VI
B.3. FAAS - flame atomic absorption spectroscopy VII
B.4. Acid neutralising capacity (ANC) VIII
B.5. Organic carbon VIII
B.6. Monomeric Al VIII
B.7. Cation and anion concentrations IX
B.8. Trace element concentrations X
B.9. Dissolved organic carbon (DOC) determination X
Appendix C: Precision and reproducibility of data XIII
C.1. pH determination XIII
C.2. Electrical conductivity (EC) XVI
C.3. Exchangeable cations by FAAS XVII
C.4. Acid neutralising capacity (ANC) XVII
C.5. Cation and anion concentrations determination by
ion chromatography XVIII
C.6. Trace element determination by ICP-MS XX
C.7. Monomeric Al XXIII
C.8. Silicon XXIV
Appendix D: Pine ecology with respect to the
studied species XXV
D.1. Introduction XXV
D.2. P. patula XXVI
D.3. P. elliottii XXVII
D.4. P. taeda XXVII
7

8. Appendix E: MINTEQA2 modelling output XXVIII
Appendix F: A proposed sampling design plan for
further studies XXXV
F.1. Introduction XXXV
F.2. Setting a hypothesis XXXV
F.3. Setting the sampling area XXXVI
F.4. First sampling set XXXVI
F.5. Second sampling set XXXVII
F.6. Summary XXXVIII
8