VARIABILITY IN SOIL STRUCTURAL PROPERTIES AND ORGANIC CARBON STORAGE IN ULTISOLS UNDER DIFFERENT LANDUSE TYPES IN SOUTH EASTERN NIGERIA

ABSTRACT

A study was conducted at Umuahia North LGA, Abia State to ascertain the variability of structural properties and carbon storage of Ultisols under selected landuse types. Four agricultural landuse types (continuously cultivated land (CC), forest land (FL), grassland (GL) and oil palm plantation (OP)) were selected for the study. Two sets of samples were collected for the study. The first set was collected by delineating each landuse into three portions of approximately equal dimensions. Soil samples were randomly collected from the top soil of each portion and bulked. Thus, three bulked samples were obtained from the top soils of each landuse representing three replicates, and used for the characterization of each landuse under investigation. This set of samples gave a total of twelve (12) observational units (4 landuses x 3 replicates) and the layout was a randomized complete block design (RCBD). Another set of soil samples were collected from each of the landuse types for specific parameters (aggregate stability indices, bulk density, water retention characteristics, water conductivity properties and organic carbon storage). This was achieved by digging nine (9) replicates of 100cm depth mini-pits in each landuse type. Soils were sampled at every 20cm intervals of each pit. This was laid out as split plot experiment in RCBD with landuse type and depth as factors. Landuse type was the main plot factor while depth was the sub-plot factor. The four (4) levels of landuse type and five (5) levels of depth gave a total of twenty (20) treatment combinations. Hence, there were a total of one hundred and eighty (180) observational units. Similarly, core samples of soil were collected from the pits in each landuse type. The samples were prepared and sent for laboratory analyses. The data obtained was subjected to statistical analyses using appropriate statistical packages. The results obtained from the first set of samples showed that landuse types varied significantly (P ≤ 0.05) in the soil physico-chemical properties with forest land (FL) and OP having good qualities for all the parameters measured. Thus, FL had the best rating for pH (5.60), TN (0.18g/kg), avail. P (45.07mg/kg), Mg (2.87cmol/kg), K (0.22cmol/kg) and CEC (7.91cmol/kg) while OP showed the best quality in OC (2.11g/kg), Ca (3.73cmol/kg), EA (0.75cmol/kg), and % BS (89.90%). The highest sand fraction and low clay content were observed in FL and GL while CC and OP had relatively high clay content. The CC had the lowest quality of all the parameters measured except for BD which was observed to be highest under GL. The results of the specific parameters obtained from the second set of samples revealed that there was significant interaction (P ≤ 0.05) of landuse type and depth in influencing soil structural properties and OC storage. At 0 – 20cm depth, the highest values of DR (29.48%) and CDI (42.33%) were obtained under FL and GL, respectively, while the lowest value of DR (19.41%) and CDI (25.00%) were under CC. The highest values of ASC (19.98%) and CFI (75.00%) were obtained under CC while the lowest values of ASC (10.11%) and CFI (57.67%) were obtained under FL and GL, respectively. The highest value of MWD (1.33mm) at 0 - 20cm depth was obtained under OP while the lowest (0.86mm) was under GL. Organic carbon was highest (51.92ton/ha) under OP but lowest (22.98ton/ha) under CC.  The highest values of Ksat, PT and PM across the depth of 0-80cm were observed in CC, followed by FL while GL had the lowest values. The highest BD was observed in GL while the lowest was in CC. The best microaggregate stability was observed at CC followed by OP while FL showed the lowest stability of microaggregates to water. The OP had the highest values of MWD followed by GL, while CC had the lowest values across the depths. The order of OC storage was OP > FL > GL > CC. The results further revealed that the specific parameters varied significantly (P ≤ 0.05) with depths. There was significant decrease in OC storage, MWD, and water conductivity properties with depth in all the landuse types while clay content, microaggregate stability indices, BD, and water retention characteristics significantly increased with depth in all the landuse types. The results of the regression analysis showed that the rate of change in Ksat and BD for any unit change in OC was highest under CC (b = 0.21 and 0.02, respectively) and lowest under OP for Ksat (b = 0.06) and FL for BD (b = - 0.005). it also revealed that the influence of OC on microaggregate stability was highest under FL (b = 0.44, – 0.12 and – 0.45 for CDI, DR and CFI, respectively) and lowest under CC (b = 0.24 and – 0.23 for CDI and CFI, respectively) and OP (b = 0.02 for DR). Whereas there was a negative linear relationship between OC and DR under CC, other landuse types showed positive linear relationship. The highest influence of OC on MWD was observed under CC (b = 0.016) and the lowest was observed under GL (b = 0.002). The influence of OC on water retention characteristics was highest under CC (b = - 0.62, - 0.22 and -0.40 for FC, AWC and PWP, respectively) while the lowest influence was observed under OP (b = - 0.16, -0.06 and – 0.10 for FC, AWC and PWP, respectively). The results of the correlation analysis revealed that there was significant (P ≤ 0.05) positive relationship among OC, MWD, Ksat, PT and PM while there was a significant negative relationship between OC and BD, clay content,CFI, ASC and water retention characteristics in all the landuse types. There was significant (P ≤ 0.05) positive relationship between clay content and microaggregate stability indices, clay content and BD as well as clay content and water retention properties in all the landuse types. Results of the spatial analysis showed that there was spatial variability in soil structural properties and organic carbon storage across the various landuse types. Areas with high concentration of OC were dominant in OP while areas with low concentration of OC were dominant under CC.  The highest spatial variability in Ksat and PT was observed under GL and OP while the highest variability in CFI was observed under FL. Areas with relatively high CDI dominated the soils under FL and OP while areas with relatively low CDI dominated soils under CC and GL. Soils under FL and OP were dominated by areas with relatively high DR compared to CC and GL. Soils under FL showed high variability in ASC compared to the other landuse types, and had a high dominance of areas with relatively low ASC. There was less spatial variability in MWD under FL and CC but much under OP and GL. Areas with high MWD dominated the soil under FL. Generally, landuse significantly influenced soil structural properties and SOC. There was also a significant interaction of landuse and depth in influencing soil structural properties and SOC. There was also a remarkable spatial variability in soil structural properties and SOC within each landuse type. Oil palm plantation (OP) improved OC storage at the top soil followed by FL while CC significantly reduced OC storage. Soils with high OC content are likely to have low clay content, and this will reduce the BD. Organic carbon storage helped in improving macroaggregate stability while clay helped in improving microaggregate stability. High OC content greatly improved water conductivity properties while high clay content greatly improved water retention characteristics. However, in a sandy soil, high OC can help in improving water retention characteristics. Pulverization of soils by tillage using simple farm tools reduced BD and improved water conductivity properties at the pulverized zones of the soil whereas the use of heavy machineries in tillage operation induced high soil BD as observed under GL. The dispersion of microaggregates may be aggravated with increase in OC, and this may have grave implication on sandy soils. Intrinsic properties of soils such as texture greatly influenced soil structural and aggregate stability indices.

TABLE OF CONTENTS

Title page ……………………………………………………………………………… i

Declaration ……………………………………….…………………………………… ii

Certification …………………………………………………………………………….iii

Dedication ……………………………………………………………………………… iv

Acknowledgement ……………………………………………………………………… v

Table of contents …………………………………………………………………………vi - vii

List of tables …………………………………………………………………………….. viii

List of figures …………………………………………………………………………… ix - x

Abstract …………………………………………………………………………………. xi - xii

CHAPTER 1: INTRODUCTION

1.1 Background information …………………………………………………………….. 1 - 3

1.2 Justification of the study …………………………………………………………….. 3 - 4

1.3 Objectives of the study ………………………………………………………………. 5

CHAPTER 2: LITERATURE REVIEW

2.1 Implication of landuse change on soil Quality ……………………………….……… 6 – 7

2.2 Soil structural properties under some landuse types …………………………………. 8 - 9

2.3 Soil carbon sequestration and its effect on soil aggregate ………………………….... 9 – 11

2.4 Strategies of soil carbon storage and its effect on soil structural stability ……………. 11 – 13

2.5 Agricultural landuse practices and soil carbon storage ………………………………. 13 – 18

2.6 Soil management for carbon storage …………………………………………………. 18 – 20

2.7 Relevance of soil aggregate stability in soil productivity and erosion control ………. 20 – 21

2.8 Factors affecting soil structural stability ……………………………………………… 21 - 22

2.9 Binding and dispersing actions of soil organic matter ………………………………... 22 – 23

CHAPTER 3: MATERIALS AND METHODS

3.1 Location and description of study area ………………………………………………… 24

3.2 landuse types …………………………………………………………………………..24 – 27

3.3 Fieldwork ………………………………………………………………………………28 – 30

3.4 Laboratory analysis …………………………………………………………………….30 – 35

3.5 Experiment design and statistical analysis ……………………………………………..35 – 37

CHAPTER 4: RESULTS AND DECISION

4.1 Variability in some characteristics of soils studied …………………………….……... 38 – 46

4.2 Variation in soil physical properties and OC storage due to landuse types ...………… 47 – 52

4.3 Variation in some soil physical properties and OC storage due to depths ……………. 53 – 57

4.4 Interaction of landuse types and depths on soil physical properties and OC storage…..58 – 77

4.5 Simple linear regression analysis between OC and some physical properties of soils... 77 – 91

4.6 Simple linear correlation analysis of some soil physical properties and SOC ……….92 – 102

4.7 Spatial variability of soil structural properties and OC under the landuse types ……103 – 121

CHAPTER 5: CONCLUSION AND RECOMMENDATION

5.1 Conclusion ………………………………………………………………………… 122 – 123

5.2 Recommendation ………………………………………………………………….. 123 – 124

References ………………………………………………………………………………125 – 135

Appendices …………………………………………………………………………….. 136 – 141

LIST OF TABLES

Table 3.1: Geographical position of the sampling units (pits) in the various landuse types …... 29

Table 4.1.1: Variability in some physical properties of soils studied ………………………….39

Table 4.1.2: Variability in pH, total nitrogen, organic carbon and avail. P. of soils studied …...41

Table 4.1.3: Variability exchangeable bases and base saturation of soils studied …………...…46

Table 4.2.1: Variability in aggregate stability indices across the various landuse types ………..48

Table 4.2.2: Variability in clay content, bulk density, hydraulic conductivity, total and macro porosities across the various landuse types ……………………………………………………..50

Table 4.2.3: Variability in water retention characteristics and organic carbon storage across the various landuse types……………………………………………………………………………52

Table 4.3.1: Variability in aggregate stability indices across the depths ……………………….54

Table 4.3.2: Variability in clay content, bulk density, saturated hydraulic conductivity, total and macro porosities across the depths ……………………………………………………………..56

Table 4.3.3: Variability in water retention characteristics and organic carbon storage across the depths ………………………………………………………………………………………….57 

Table 4.6.1: Simple linear correlation analysis of some soil physical properties and organic carbon in forest land (FL) ……………………………………………………………………… 94

Table 4.6.2: Simple linear correlation analysis of some soil physical properties and organic carbon in continuously cultivated land (CC) …………………………………………………... 97

Table 4.6.3: Simple linear correlation analysis of some soil physical properties and organic carbon in grassland (GL) ………………………………………………………………………. 99

Table 4.6.4: Simple linear correlation analysis of some soil physical properties and organic carbon in oil palm plantation (OP) ……………………………………………………………. 102

LIST OF FIGURES

Fig. 3.1: Photograph of forest land …………………………………………………............... 26

Fig. 3.2: Photograph of grassland …………………………………………………………….. 26

Fig. 3.3: Photograph of continuously cultivated land …………………………………………. 27

Fig. 3.4: Photograph of oil palm plantation …………………………………………………… 27

fig. 4.4.1a: Interactive effect of landude types and depths on Dispersion ratio (DR) ………….58

fig. 4.4.1b: Interactive effect of landuse types and depths on clay dispersion index (CDI) ……60

fig. 4.4.2: Interactive effect of landuse types and depths on aggregated silt + clay (ASC) …… 62

fig. 4.4.3: Interactive effect of landuse types and depths on clay flocculation index (CFI) …… 63

fig. 4.4.4: Interactive effect of landuse types and depths on bulk density (BD) ……………….. 65

fig. 4.4.5a: Interactive effect of landuse types and depths on saturated hydraulic conductivity ..67

fig. 4.4.5b: Interactive effect of landuse types and depths on total porosity (PT) ……………... 68

fig. 4.4.5c: Interactive effect of landuse types and depths on macroporosity (PM) …………… 69

fig. 4.4.6: Interactive effect of landuse types and depths on mean weight diameter (MWD) … 71

fig. 4.4.7: Interactive effect of landuse types and depths on percentage clay ………………… 72

fig. 4.4.8a: Interactive effect of landuse types and depths on field capacity (FC) ……………. 74

fig. 4.4.8b: Interactive effect of landuse types and depths on available water capacity (AWC) 74

fig. 4.4.8c: Interactive effect of landuse types and depths on permanent wilting point (PWP).. 74

fig. 4.4.9: Interactive effect of landuse types and depths on organic carbon (OC) storage …… 76

Figure 4.5.1: Simple linear regression analysis between independent variable (OC) and dependent variables (BD and K_sat) in each landuse type ………………………………………. 78

Fig. 4.5.2: Simple linear regression analysis between independent variable (OC) and dependent variables (DR and CDI) in each landuse type ………………………………………………….. 80

Fig. 4.5.3: Simple linear regression analysis between independent variable (OC) and dependent variables (CFI and ASC) in each landuse type ………………………………………………….82

Fig. 4.5.4: Simple linear regression analysis between independent variable (OC) and dependent variables (PT and PM) in each landuse type …………………………………………………… 84

Fig. 4.5.5: Simple linear regression analysis between independent variable (OC) and dependent variables (FC, AWC and PWP) in each landuse type …………………………………………...86

Fig. 4.5.6: Simple linear regression analysis between independent variable (OC) and dependent variable (CLAY) in each landuse type …………………………………………………………. 88

Fig. 4.5.7: Simple linear regression analysis between independent variable (OC) and dependent variable (MWD) in each landuse type …………………………………………………………..89

Fig. 4.7.1: Spatial variability of soil organic carbon in the various landuse types ………..….. 105

Fig. 4.7.2: Spatial variability of bulk density in the various landuse types …………………... 108

Fig. 4.7.3: Spatial variability of saturated hydraulic conductivity in the various landuse types.110

Fig. 4.7.4: Spatial variability of total porosity (%) in the various landuse types ………………112

Fig. 4.7.5: Spatial variability of clay flocculation index (%) in the various landuse types ……114

Fig. 4.7.6: Spatial variability of clay dispersion index (%) in the various landuse types …….. 115

Fig. 4.7.7: Spatial variability of dispersion ratio (%) in the various landuse types ……………117

Fig. 4.7.8: Spatial variability of aggregated silt + clay (%) in the various landuse types ……..118

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND INFORMATION

Aggregate stability and bulk density of soils influence their total porosity, thereby affecting water infiltration and retention, access to water and nutrients by plants. These soil properties also affect seedling emergence, root penetration, plant growth and soil erodibility (Nathalie, 2014). However, these properties are greatly influenced by human activities through landuse and management such that their variability, both laterally and vertically, across soils follow systematic changes as a function of these influences (Amusan et al., 2006; Mbagwu and Auerswald, 1999). Hence, understanding the relationship between landuse and soil structural properties is paramount for effective soil management and landuse allocation.

Inappropriate landuse can aggravate the rate of soil degradation thereby affecting soil biological, physical and chemical qualities (Saikl, et al., 1998). In Nigeria, bush burning, intensive cultivation (Senjobi et al; 2007), tillage related practices (Lal, 1998; Khurshid et al., 2006), low input agriculture, accelerated erosion (Fahnestopck et al.,1995) and construction work are major causes of land degradation resulting to soil structural instability. Soil physical properties deteriorate with changes in landuse especially from forest to arable. Cropping usually results in losses of soil organic matter and soil aggregates, increased bulk density and compaction (Chisci and Zanchi, 1981). Soil structure is greatly affected by intensity of landuse which has influence on the distribution of microbial biomass as well as microbial processes that lead to soil aggregation and structural stability (Gupta and Germida, 1988). Landuse significantly influenced soil physical properties especially structural parameters. Oguike and Mbagwu (2009) reported that changes in landuse, such as conversion of natural forest to cropland, contributed to land degradation that manifested in losses of soil organic matter and reduced stability of soil aggregates. Landuse greatly influences stability of soil aggregates more than intrinsic soil properties while percolation stability of soils increases with increase in organic matter content (Mbagwu and Auerswald, 1999). Soils under conventional tillage practices become poorly structured and are easily eroded (Chisci and Zanchi, 1981). Kutilek (2005) reported that intensive cropping leads to disaggregation in surface soils because of decline in organic matter content due to repeated machinery movement. He further stated that long use of machinery during tillage operation causes an irreversible soil compaction to a depth of about 60 – 70cm.

Continuous cultivation results in increase in sand fraction and bulk density, reduced aggregation and water retention capacity as against bush fallow landuse (Malgwi and Abu, 2011). Therefore, landuse affects the structural parameters of the soil. However, more studies are required to reveal the extent to which these landuse types affect these parameters down the soil profile (residing depths) and the trend of the variation with specified depths. The degradation of soils due to unsustainable landuses has released billions of tons of carbon into the atmosphere (Schwartz, 2014). The world cultivated soils have lost 50 – 70% of their original carbon stock (Schwartz, 2014). Holland (2004), showed how effective land restoration through bush fallow and conservation tillage could be in sequestering CO₂ and slowing down climate change. In order to mitigate the effects of rapid increase of atmospheric CO₂, soil carbon losses and carbon sequestration have become important issues in research.

Intensive soil tillage increases soil aeration and changes the climate (temperature and moisture) of topsoil and thus, often accelerates soil organic matter decomposition rates (Balesdent et al., 2000). Conservation tillage is therefore considered as a measure to sequester carbon in soils as it has proven to be effective in conserving soil organic matter at the top soil (Holland, 2004). On the other hand, there is experimental evidence that no-till does not quantitatively change the total soil carbon stock, but only changes its distribution with depth (Powlson and Jenkinson, 1981; Angers et al., 1997). Soil sampling, deeper than 30cm, is necessary to understand the effect of landuse types on soil carbon beneath this depth (Baker et al., 2007). Blaire et al. (2006) revealed, in a comparative study on grassland and cropland, that there was a significant difference in the amount of carbon stored in grassland than that in cropland under similar site conditions such as climate and topography. The study further revealed that more favorable conditions for soil biota under grassland enhanced the soil structural stability and thus, improved the physical protection of soil organic matter than manured cropland.

1.2  JUSTIFICATION OF THE STUDY

Over many years, man has engaged in exploiting the soil beyond its capacity through irrational land utilization, thereby altering the ecological balance in nature. The awareness of land utilization and its implication on the general wellbeing of man and the ecosystem at large is still below the level needed to stimulate behavioral change. This may be due to the limited level of information on this subject matter. Though some researchers have made conscious efforts in generating information on this matter, much is still needed to be done, especially in the area of how the landuse types affect soil structural properties and carbon storage at lower depths. This therefore aims at mitigating soil structural degradation often manifested in soil loss via surface and subsurface (piping) erosion, crusting and slaking. Also, the findings from this research will help boost the bank of information that will foster practices that will engender soil carbon restoration with a view of combating the increased loss of carbon to the atmosphere often manifested in global warming and climate change while promoting productive agriculture and environmental quality.

Considering the need to have a broader view on the effect of landuse types on soil structural properties and carbon storage, some researchers have in there recommendations, suggested the sampling of soils below the depth of 30cm. Hence, in this study, soils were sampled at every 20cm interval up to the depth of 100cm aimed at quantifying the amount of organic carbon sequestered at each depth under the various landuse types for appropriate comparison. This will also help in capturing the pattern of vertical variation in soil structural properties in relation to the amount of organic carbon sequestered at each depth. Therefore, with these, appropriate land utilization policies can be established for the soils under the various landuse systems studied.

Moreover, in order to ensure high precision agriculture and site specific soil management, the need to ascertain the spatial variability of the soil parameters under investigation becomes significant. This therefore formed part of this research interest. Hence, the spatial variability of soil structural properties and organic carbon storage in each site under study was ascertained. This helped in generating qualitative information that will help to engender rational application of organic amendments, appropriate tillage practices, irrigation scheduling and application, mulching and erosion control measures at varying locations in each of the sites.  

1.3 OBJECTIVES OF THE STUDY

The main objective of this study was to evaluate the variability of some soil structural properties and organic carbon storage under different landuse types. The specific objectives are to:

1.     evaluate the effect of landuse types and soil depths on soil organic carbon storage and microaggregate stability indices, mean weight diameter (MWD), bulk density (BD), hydraulic conductivity (Ksat), total and macro porosity (PT and PM), field capacity (FC), permanent wilting point (PWP) and available water capacity (AWC).

2.     ascertain the spatial variability of soil organic carbon, microaggregate stability indices, MWD, BD, Ksat, PT and PM under each landuse type.

3.     assess the relationship between soil organic carbon storage, microaggregate stability indices, MWD, BD, Ksat, PT and PM under each landuse types.

Buyers has the right to create dispute within seven (7) days of purchase for 100% refund request when you experience issue with the file received. 

Dispute can only be created when you receive a corrupt file, a wrong file or irregularities in the table of contents and content of the file you received. 

ProjectShelve.com shall either provide the appropriate file within 48hrs or send refund excluding your bank transaction charges. Term and Conditions are applied.

Buyers are expected to confirm that the material you are paying for is available on our website ProjectShelve.com and you have selected the right material, you have also gone through the preliminary pages and it interests you before payment. DO NOT MAKE BANK PAYMENT IF YOUR TOPIC IS NOT ON THE WEBSITE.

In case of payment for a material not available on ProjectShelve.com, the management of ProjectShelve.com has the right to keep your money until you send a topic that is available on our website within 48 hours.

You cannot change topic after receiving material of the topic you ordered and paid for.