ABSTRACT
One by which plants can organic and forms of (P) in soils is by of low molecular weight organic acids.
Laboratory and field trials were carried out during the 2011 and 2012 cropping seasons to study the effects of additions of organic acids ( citric, oxalic and tartaric acids) on the mobilization of phosphate of soils from Minna and Mokwa, both in Southern Guinea Savanna of Nigeria.
For initial laboratory studies and prior to field cultivation, soil samples were collected from these locations and incubated at 25± 1oC and 40% moisture content for three weeks with citric, tartaric or oxalic acids at 1.0 mmol kg-1 of soil. Soil Olsen P and inorganic P fractions were analyzed.
The experimental design used during the field trial was a split-plot design with organic material sources (orange waste, amaranthus and tamarind pulp) assigned to the main plot while the rates (0, 2.0, 4.0, 6.0 and 8.0 tons ha-1) of application occupied the sub-plots.
Each treatment received three replications in each of the locations. Maize was planted during the two seasons as a test crop. Both agronomic, Olsen – P and soil inorganic P data were determined.
The results indicated that Olsen – P and NH4Cl – P were significantly increased by treating with the three organic acids. Al phosphate (Al – P), Fe phosphate (Fe –P), occluded phosphate (Occl – P) and Ca phosphate (Ca – P) were also mobilized and released in various degrees in each of the locations irrespective of the cropping season.
The relative fractions of inorganic P was in the order Occl – P > Fe – P > Al – P > Ca – P. The effect of organic acid sources on maize plant height at 4 and 7 weeks after planting in the two locations were not significant during the 2011 cropping season, but significant during the 2012 cropping season.
However, the effect of sources of organic acid and their rates of application on maize grain yield was significant in each location and the season.
It was also observed that the results of soil inorganic P after the field trial followed a similar trend with what was obtained from the initial laboratory studies (Occl – P > Fe – P > Al – P > Ca – P), but the effect was much lower.
The order of increased mobilization of phosphate by these organic acids was citric acid > tartaric acid > oxalic acid and orange waste ˃ tamarind pulp ˃ amaranthus leaves respectively for both initial laboratory studies and field trial.
Also, it could be concluded that hydroxyl acids i.e tricarboxylic acids such as citrate form stronger complexes than those containing single COOH groups.
The pattern of P mobilization by the addition of organic acids differed from one location to another.
The comparison suggested that the mobilization of P was highly soil dependent, and the soil P status such as amount and distributions of P fractions may be important for solubilization of P after the addition of organic acids.
These three organic acids, therefore, have the potential to increase the availability of available P. The practical implication of these processes is that organic residues could be used as a strategic tool to reduce the rates of fertilizer P required for optimum crop growth on acidic and P-fixing soils of Nigeria.
TABLE OF CONTENTS
TITLE I
DESIGNATION II
CERTIFICATION III
DEDICATION IV
ACKNOWLEDGEMENTS V
TABLE OF CONTENTS VII
LIST OF FIGURES XIII
LIST OF TABLES XIV
ABSTRACT X VI
CHAPTER ONE
INTRODUCTION 1
CHAPTER TWO LITERATURE REVIEW 5
2.1. Phosphorus (P) dynamics in soil 5
2.1.1. Soil P transformation 5
2.1.2. Chemical fertilizer P in soil 6
2.1.3. Manure P in soil 7
2.2. Phosphorus dynamics in the rhizosphere 8
2.3. Mechanisms of phosphate solubilization 9
2.4. Solubilization of calcium phosphate (Ca-P) 10
2.5. Solubilization of iron phosphate / aluminium phosphate (Fe- P / Al- P) 12
2.6. Soil P fixation 12
2.7. Organic matter and P interaction in the soil 14
2.8. Phosphorus mobilization 16
2.8.1. Phosphorus mobilization by soil microorganisms 17
2.9. Phosphorus and OM incubation 18
2.10. Phosphate Solubilizing Microorganisms (PSMs) 20
2.10.1. Soil microbial biomass phosphorus and contribution to plant nutrition 21
2.11. Organic acids in soils. 21
2.11.1. Composition and concentration 21
2.11.2. Sorption and persistence of organic acids 23
2.11.3. Competitive sorption of Decomposable Organic Carbon (DOC) and P 25
2.11.4. Competition between P and Low Molecular Weight Organic Acids (LMWOAs) 26
2.11.5. Competition between P and High Molecular Weight Organic Acids (HMWOAs) 29
2.12. Mineralization of organic phosphate 30
CHAPTER THREE MATERIALS AND METHODS
3.1 Study location 32
3.1.1 Climate 32
3.1.2 Geology 32
3.1.3 Vegetation 34
3.2 Soil sampling and preparations 34
3.3 Laboratory studies I: Phosphorus sorption studies 35
3.4 Laboratory studies II: Incubation experiments of organic acids 35
3.5 Field studies 38
3.5.1 Experimental design 38
3.5.2 Treatments 38
3.5.3 Field management 38
3.6 Post soil sampling 40
3.7 Laboratory analysis 40
3.7.1 Soil characterization 40
3.7.1.1 Particle size 40
3.7.1.2 pH 40
3.7.1.3 Organic carbon 41
3.7.1.4 Available P 41
3.7.1.5 Total N 41
3.7.1.6 Cation Exchange Capacity (CEC) 41
3.7.1.7 Exchangeable Bases 41
3.7.1.8 Exchangeable Acidity (EA) 41
3.7.2 Fractionation of soil organic phosphorus 41
3.7.2.1 NH4Cl – P 41
3.7.2.2 Aluminium Phosphate (Al – P) 42
3.7.2.3 Iron Phosphate (Fe – P) 42
3.7.2.4 Occluded Phosphate (Occl – P) 42
3.7.2.5 Calcium Phosphate (Ca – P) 43
3.7.2.6 Total Phosphorus (Total – P) 43
3.7.3 Free oxides of iron and aluminium 43
3.7.3.1 Crystalline form of iron oxide 43
3.7.3.2 Crystalline form of aluminium oxide 44
3.7.3.3 Amorphous forms iron and aluminium 44
3.8 Statistical analysis 44
CHAPTER FOUR RESULTS 45
4.1 Physico-chemical properties of the experimental sites 45
4.2 Phosphorus sorption characteristics of the soil 47
4.3 Inorganic P fractions 53
4.3.1 Olsen P 53
4.3.2 NH4Cl – P 53
4.3.3 Occluded P (Occl – P) 53
4.3.4 Aluminium – P (Al – P) 57
4.3.5 Iron – P (Fe – P) 57
4.3.6 Calcium – P (Ca – P) 60
4.3.7 Total –P 60
4.4 Plant height of maize (4WAP) at Minna in 2011 and 2012 seasons 63
4.5 Plant height of maize (4WAP) at Mokwa in 2011 and 2012 seasons 63
4.6 Plant height of maize (7WAP) at Minna in 2011 and 2012 seasons 66
4.7 Plant height of maize (7WAP) at Mokwa in 2011 and 2012 seasons 66
4.8 Maize grain yield (t ha-1) at Minna in 2011 and 2012 seasons 69
4.9 Maize grain yield (t ha-1) at Mokwa in 2011 and 2012 seasons 69
4.10 Soil Olsen – P (mg kg-1) at Minna in 2011 and 2012 seasons 72
4.11 Soil Olsen – P (mg kg-1) at Mokwa in 2011 and 2012 seasons 72
4.12 Soil NH4Cl – P (mg kg-1) at Minna in 2011 and 2012 seasons 75
4.13 Soil NH4Cl – P (mg kg-1) at Mokwa in 2011 and 2012 seasons 75
4.14 Soil Occl – P (mg kg-1) at Minna in 2011 and 2012 seasons 78
4.15 Soil Occl – P (mg kg-1) at Mokwa in 2011 and 2012 seasons 78
4.16 Soil Al – P (mg kg-1) at Minna in 2011 and 2012 seasons 81
4.17 Soil Al – P (mg kg-1) at Mokwa in 2011 and 2012 seasons 81
4.18 Soil Fe – P (mg kg-1) at Minna in 2011 and 2012 seasons 84
4.19 Soil Fe – P (mg kg-1) at Mokwa in 2011 and 2012 seasons 84
4.20 Soil Ca – P (mg kg-1) at Minna in 2011 and 2012 seasons 87
4.21 Soil Ca – P (mg kg-1) at Mokwa in 2011 and 2012 seasons 87
4.22 Comparison of soil Olsen and NH4Cl – P at Minna and Mokwa locations 90
4.23 Comparison of maize grain yield at Minna and Mokwa locations 90
4.24 Distribution of dithionite and oxalate extractable forms of Fe and Al oxides in Minna 93
4.25 Correlation coefficient between soil P and some physicochemical properties 93
CHAPTER FIVE DISCUSSION 96
5.1 Physicochemical properties of the soils 96
5.2 Sorption characteristics of the soils studied 97
5.3 Inorganic phosphate mobilization 98
5.4 Effects of organic acids on maize plant height and grain yield 99
5.5 Post-harvest soil inorganic phosphate mobilization 100
5.6 Distribution of Fe and Al oxides 101
5.7 Correlation analysis 102
CHAPTER SIX CONCLUSION AND RECOMMENDATIONS 103
6.1 Conclusion 103
6.2 Recommendation for future research 104
REFERENCES 106
INTRODUCTION
(P) is an important plant nutrient and the reactions of phosphate with soil components have been extensively studied from the point of view of soil fertility, soil chemistry and environmental concerns (Parfit, 1978; Sanyal and De Datta, 1991; Hue et al., 1994; Wang et al., 2007).
In tropical and subtropical acidic soils, low P availability becomes one of the limiting factors for plant growth; at the other extreme, accumulation of soil available P has negatively affected water quality (Sharpley, 1995).
The misapplication of usually causes eutrophication of water bodies, unbalanced plant nutrition and low P utilization efficiency. When soil phosphate levels are too low, in plants represents a major constraint to agricultural production (Palomo et al., 2006).
One problem is that P fertilizer can largely be fixed by the oxides, hydroxides and of Iron (Fe) and Aluminium (Al) and clay minerals in acidic soils, which makes it less available or effectively unavailable to plants (Fankem et al., 2006).
This is because the availability of both applied and native P is controlled largely by, the sorption and desorption characteristics of the soil.
Variable charge minerals are also the major components of most soils of the tropics that affect P unavailability to plants. Such is the case with soils of Nigeria which is dominated by and low activity clays (Bala, 1992).
The most likely areas appear to be those dominated by Oxisols, and Alfisols. The low amount of total and available P in these soils make an investigation into problems associated with availability imperative.
Already, the widespread occurrence of P deficiency in most arable land in Nigeria has led to the intensive use of P fertilizer. It has been reported that land utilization also influences capacity (Odunze, 2009).
REFERENCES
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Achal, V., Savant, V.V. and Sudhakara Reddy, M. (2007). Phosphate mobilization by wide type strain and UV-induced mutants of Aspergillus tubingenesis. Soil Bio. and Biochem. 39(2): 655 – 659
Adeboye, M. K. A., Osunde, A. O., Ezenwa, M. I. S., Odofin, A. J. and Bala, A. (2009). Evaluation of the fertility status and suitability of some soils of arable cropping in the southern guinea savanna of Nigeria. Nig. J. Soil Sci.19(2): 115 – 120
Afif, E., Barron, V. and Torrent, T. (1994). Organic matter delays but does not prevent phosphate sorption from Brazil. Soil Sci. 159(3): 207 – 211
Agbenin, J. O. 2003. Extractible iron and aluminium effect on phosphate sorption in a savanna Alfisol. Soil Sci. Soc. Am. J. 67: 587 – 595.
Agbenin, J. O and Igbokwe, S. O. 2006. Effect of soil-dung manure incubation on the solubility and retention of applied phosphate by a weathered tropical semi-arid soil. Geoderma 133: 191 –203
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