TABLE OF CONTENTS Page
Title page – – – – – – – – – — – – – i
Certification page – – – – – – – – – – – – – – ii
Dedication- — – – – – – – – – – – – – – iii
Acknowledgement- – – – – – – – – – – – iv
Table of Contents – – – – – – – – – – – – – -v
List of Tables – – – – – – – – – – – – – – – – viii
List of figures – – – – – – – – – – – – – – – ix
Abstract – – – – – – – – – – – – – x
CHAPTER ONE: INTRODUCTION – – – – – – – – 1
CHAPTER TWO: LITERATURE REVIEW – – – – – – – 4
2.1 Water-stable Soil Aggregation and Aggregate stability of Soils – -4
2.2 Soil Biota and Aggregate stability – – – – – – – 5
2.3 Clay Mineralogy – – – – – – – – 6
2.4 Soil Organic Matter and Aggregate stability – – – – – 6
2.5 Iron and Aluminium oxides and Aggregation – – – – 7
2.6 Agricultural Importance of well aggregated soils – – 8
CHAPTER THREE: MATERIALS AND METHODS – – – – – – – 9
3.1 Site Description – – – – – 9
3.2 Meteorological Information of the Location of Study – – – 9
3.2.1 Rainfall Characteristics and Relative Humidity – – 9
3.2.2 Maximum and Minimum Temperature – – – – – – 11
3.3 Cultural Practices and Management Treatments- – – – – 13
3.4 Crop Establishment – – – – – – – – – – – – 13
3.5 Measurement of Soil Physical Properties- – – – – – 15
3.6 Laboratory Methods – – – – – – – – – – – – 15
3.7 Separation of Water-stable Aggregates and Water Dispersible Clay 16
3.7.1 Separation of Water-stable Aggregates- – – – – 16
3.7.2 Water Dispersible Clay – – – – – – – – – – 16
3.8 Measurement of Infiltration Characteristics – – – – – – 16
3.9 Statistical Analysis – – – – – – – – – – – – 17
CHAPTER FOUR: RESULTS AND DISCUSSION – – – – – 18
4.1 Selected Soil Properties in 2010 and 2011 – – – – – 18
4.1.1 Soil Texture – – – – – – – – – – — 18
4.1.2 Soil pH — – – – – – – – – – – – – – – 18
4.1.3 Soil Organic Matter Content – – – – – – – 21
4.2 Aggregate Stability, Mean Weight Diameter and other Stability Indices 23
4.2.1 Aggregate stability – – – – – – – – – – – – 23
4.2.2 Mean weight diameter (MWD)- – – – — 24
4.2.3 Indices of stability – – – – – – – – – – – – — 24
4.3 Organic matter content and Some Selected Soil Properties Under Different Sampling period – – – – 27
4.4 Aggregate Size Distribution- – – – – – – – 29
4.5 Pore
size distribution, bulk density (BD) and saturated hydraulic conductivity
(Ksat) 32
4.5.1 Pore size distribution – – – – – – – – – 32
4.5.2 Bulk density – – – – – – – – – – – – – 32
4.5.3 Saturated hydraulic conductivity – – – – 33
4.6 Iron and Aluminium Oxides- – – – – – – – – – — 42
4.7 Correlation of Organic Matter with soil properties and stability indices 45
4.8 Infiltration Rates and Cummulative Infiltration – – – – – 48
CHAPTER FIVE: SUMMARY AND CONCLUSION– – – – 51
5.1 Summary – – – – – – – – – – – – 51
5.2 Conclusion – – – – – – – – – – – – – — 52
References – – – – – – – – – – – – – – – 53
Appendix – – – – 64
LIST OF TABLES Page
Table 1: Soil Properties (0-20 cm) at the start of the experiment in 2010 -19
Table 2: Soil Properties (0-20 cm) at the start of the experiment in 2011 -20
Table 3: Effect of cover management on some selected soil properties–26
Table 4: Effects of sampling period and cover management on some selected soil properties studied – — – – – – – – – – 28
Table 5: Effect of sampling period and cover management practices on aggregate size distribution – – – – – – – – – – – 31
Table 6: Effect of cover management on the pore size distribution, bulk density and hydraulic conductivity – – – – – – – 35
Table 7: Effect of cover management on the pore size distribution, bulk density and hydraulic conductivity under different sampling period 36
Table 8: Effect of cover management practices on
Iron and Aluminium Oxides contents 43
Table 9: Effect of cover management practices and sampling periods On Iron and Aluminium Oxides contents – – – – – – 44
Table 10: Correlation of O.M. and other soil properties – – – 47
LIST OF FIGURES Page
Figure 1a: Monthly rainfall, raindays and relative humidity in 2010 -10
Figure 1b: Monthly rainfall, raindays and relative humidity in 2011 -10
Figure 2a: Maximum and Minimum temperature in 2010 – – -12
Figure 2b: Maximum and Minimum temperature in 2011 – – – 12
Figure 3: Field or experimental layout of the study location – – – 14
Figure 4: Organic matter content at three sampling periods under different cover management – – – – – – – – 22
Figure 5: Aggregate stability at three sampling periods under different cover management – – – – – – – – – – 25
Figure 6:
Aggregate size distribution under different cover management practices – – 30
Figure 7: Total
porosity (TP) at three sampling periods under different cover management 37
Figure 9: Microporosity (MICP) at three sampling periods under different cover management – – – – – – 39
Figure 10: Bulk density (BD) at three sampling periods under different cover management – – – – – – – – – 40
Figure 11: Saturated hydraulic conductivity (Ksat) at three sampling periods under different cover management – – – 41
Figure 12: Graph
of infiltration rate against time under different cover management – – – – – – 49
Figure 13: Graph of cumulative infiltration against time under different cover management – – – – – – – 50
ABSTRACT
A study was
conducted in the runoff plots at the University of Nigeria Nsukka Teaching and
Research Farm, in 2010 and 2011 to monitor the changes in aggregate stability,
and some selected physicochemical properties of Nkpologu sandy loam soil under
different cover and soil management systems. The management systems were bare
fallow (BF), grass fallow (GF), legume (CE), groundnut (GN), sorghum (SM), and
cassava (CA) cultivation. Following the characterization of the soil of the
study site, three samplings were carried out at five- month interval marking
the end of first cropping season, and the start and end of the second cropping
season respectively. There was no change in soil texture due to treatments. The
soil was acidic throughout the period of the study with pH values ranging from
5.1 (under BF) to 5.5 (under GF) in 2010 and from 4.8 (BF) to 6.1 (SM) in 2011.
The aggregate stability (AS), mean weight diameter (MWD), water dispersible
silt (WDSi), bulk density (BD), total porosity (TP), macroporosity (MACP),
aggregate size distributions (> 2 mm, 1- 0.5 mm and < 0.25 mm) and Ksat
showed significant (P =0.05) changes under different cover management
practices. The Ksat varied (CV = 52%) significantly (P< 0.05) under
the different cover management practices over the sampling period. Generally,
the highest values for Ksat, AS and MWD were obtained in the first sampling
period whereas the lowest values were obtained in the last sampling period.
There were significant effects (P<0.05) of cover management systems
on AS, MWD and Ksat. The highest values for AS, MWD and aggregate size fraction
> 2 mm (80.3, 2.22 and 55.6 % respectively) were obtained under GF whereas the
highest Ksat(16.8cm/hr) was obtained under GN. The lowest values for these
parameters throughout the sampling periods were obtained under BF. The
preponderance of aggregates < 0.5 mm under BF showed that raindrop impact
and other agents broke down macroaggregates into microaggregates. The
interaction of cover management and sampling period was not significant (P<0.05) for the structural and
hydraulic parameters determined. The
cover treatments generally increased organic matter (O.M.) content compared
with the BF. Soil pH increases with increasing O.M. content and vice
versa. The Fe and Al oxides were
significantly (P<0.05) affected by the different cover and soil
management systems. The concentration of Fe oxides was high relative to the
concentration of Al oxides. The O.M. had significant (P<0.05)
correlation with two aggregate size ranges; 1-0.5mm (r = – 0.276* at
P<0.05) and 0.5-0.25mm (r = – 0.245*at P <0.05)
and Fe oxides. The cover management systems affected the infiltration
characteristics measured. The highest infiltration rates (1,317 mm h-1)
and cumulative infiltration (72,390 mm) were obtained under the GF and CE
respectively whereas the lowest values; 287 mmh-1 (infiltration
rate) and 14,455 mm (cumulative infiltration) were obtained under the BF.
The study has shown that cover and soil
management systems affected the organic matter content, soil pH, Fe and Al
oxides, infiltration characteristics, aggregate stability and structural
properties of the Nkpologu sandy loam soil differently over time. Continuous
addition of organic manure is encouraged. Legume and other crop fallows which
protect the soil and guarantee regular additions of organic materials are
ecologically sound components of sustainable management of Nkpologu sandy loam
soil for improved agricultural productions.
CHAPTER ONE
1.0
INTRODUCTION
Evaluating the impact of agricultural practices on agroecosystem functions is essential to determining the sustainability of management systems which cover the Productivity (Liebig et al., 2001), and environmental components of land use systems (Smyth and Dumanski, 1995). Soil structure is the physical characteristic most vulnerable to soil management practices. Structure describes the state of aggregation of the solid material in soils and their arrangement into what are called either aggregates, structural units or peds (Doerr, 2007). Soil structure exerts important influences on the functioning of soil, its ability to support plant and animal life, and its control on environmental quality with special emphasis on soil carbon sequestration, nutrient and gas fluxes and water quality. A good soil structure is important for sustaining long-term crop production in agricultural soils because it influences water status, workability, resistance to erosion, nutrient availability and crop growth and development (Piccolo and Mbagwu, 1999). Soil structure is often expressed as the degree of stability of aggregates being a major factor which moderates physical, chemical, and biological processes leading the soil dynamics (Bronick and Lal, 2005). Thus; aggregate stability is a measure of the structural stability of soils (Mbagwu, 2003).
Soil aggregate stability, defined as the
ability of the aggregates to remain intact when subjected to a given stress, is
an important index of structure that affects the movement of and storage of
water, aeration, erosion, biological activity and the growth of crops (Amezketa
et al., 2003).Soil aggregate
stability is an important indicator of soil physical quality (Castro Filho et
al., 2002) and maintenance of high aggregate stability in soils is
desirable for sustainable land use, as it is essential for the preservation of
agricultural production, minimizing soil erosion and degradation and reducing
environmental pollution (Amezketa 1999). This process, dynamic and complex, is
influenced in turn by the interaction of several biotic and abiotic factors (Kovistra
and Tovey, 1994; Topp et al., 1997;
Bronick and Lal, 2005) including environmental components such as soil
temperature and moisture (Chen, et al.,
1998), soil management, plant effects through the activities of plant roots (root
exudates), but largely by soil properties such as soil organic matter, clay
mineralogy, and oxide contents (Oades, 1984). Soil aggregation is the result of
aggregate formation or development and their stabilization (Allison, 1968). The
aggregates are primarily formed by physical processes; but biological and
chemical processes are mainly responsible for their stabilization (Allison,
1968; Lynch and Bragg, 1985). Flocculated clay particles, their complexes with
humus and soil organic matter act as main cementing agents in soil aggregate
development (Kodesova and Rohoskova, 2009). The stabilization of soil
aggregates takes place due to the cementing action of organic and inorganic
materials. Silicate clays, calcium carbonate and sesquioxides (Kooreva, et al., 1983) cement particles together
but their binding effect is much smaller than that of humus. The mechanism
involved in soil aggregation is complex but in general is viewed as
microaggregates are formed from organic molecules tied to clay and polycations,
which in turn are linked with other microaggregates to form macroaggregates.
Briefly, aggregation is the result of rearrangement, flocculation and
cementation of soil particles where soil organic carbon, polycations, clay
minerals and, especially biota play a key role (Fernando et al., 2008).
The contributions of soil organic matter
(SOM) to soil aggregate stability have been studied (Tisdall and Oades, 1982;
Six et.al., 2000; Six et.al., 2004). Generally, the level of aggregation and
stability of aggregates increases with increasing organic matter content,
surface area of clay minerals and cation exchange capacity (Bronick and Lal, 2005).
Mbagwu and Bazzoffi (1989) found that
the mineralogy of the clay fraction was an important factor in
microaggregation, with low activity clays being more stable than high activity
clays. Oades and Waters (1991) remarked that for soils high in 2:1 clay
mineral, soil organic matter is a major binding agent because polyvalent
metal-organic matter complexes form bridges between the negatively charged soil
organic matter and 2:1 clay platelets. However, part of the stability in 1:1
clay mineral dominated soils is induced by the binding capacity of oxides and
1:1 clay minerals.
Most tropical soils are low in soil
organic matter. They are predominated by 1:1 clay minerals and are rich in
oxides and hydroxides of Fe and Al, which, according to Rampazzo et al (1993) are closely related to the
structural status of these soils and contribute to understanding of the
structure and its functionality within a soil profile. Six et al., 2002, noted that the cementing effect of free Fe and Al
oxides was important in soils with low organic matter content. Igwe et al. (2004) noted that the stabilizing
role of various forms of Fe, Al and Mn oxide was as a result of their large surface
area, abundance, and favourable environment for their formation.
Several management systems can improve
soil productivity such as conservation tillage, addition of organic and
inorganic manure e.t.c, and modification of some soil attributes such as soil
structure by root growth can be used to evaluate their impact on soil physical
properties. Plant roots are known to influence soil aggregation. As a result of
variation in biomass production and root systems, crops have different ability
to promote aggregation and stabilization of soil aggregates due to carbon
supply (Wohlenberg, et al., 2004),
mechanical effect (Tisdall and Oades, 1979; Silva and Mieliriczuk, 1997, 1998;
Campos et al., 1999), exudates
production or mycorrhizal association(Tisdall and Oades, 1979;Tisdall, 1991;
Degens, 1997), and can contribute to seasonal variation of aggregate stability
over a growing season (Campos et.al.,1999). Soil aggregate distribution has
been used as a conservation index for clayey Oxisols, cultivated with wheat
(Triticum aestivum), maize (Zea mays) and soybean (Glycine max) in Panama state
(Castro Filho, et al., 2002).
Although a number of studies indicate positive effects of plant roots on
aggregate formation, a reduction in aggregate size and stability of soil by root
growth has also been recorded (Reid and Goss, 1981). It is widely recognized
that cropping with soybean reduces soil aggregate size and stability (Fahad et al., 1982; Bathke and Blake, 1984;
Alberts and Wendt, 1985; Nakamoto and Suzuki, 2001) and consequently increases
a risk of soil erosion.
The susceptibility of soil to erosion, or soil erodibility, is linked to soil aggregate stability, which characterizes resistance to soil breakdown. Aggregates stabilize the soil and maintain productivity while preventing erosion and deterioration. Many studies have shown the effects of organic constituents on the size and stability of soil aggregates. However, few studies have considered the contributions of sesquioxides and different crop management practices on the stability of soil aggregates. The knowledge of how the stability of aggregates of our fragile soil is influenced by not only SOM, but also sesquioxides and cropping systems is especially important in the tropics where high rainfall erosivity, variable biomass production and intensive tillage can accelerate soil’s susceptibility to water erosion on agricultural land.
AGGREGATE STABILITY OF NKPOLOGU SANDY LOAM SOIL UNDER DIFFERENT SOIL AND CROP MANAGEMENT SYSTEMS
