INFLUENCE OF TOPOGRAPHY ON SOIL PROFILE CHARACTERISTICS AND FERTILITY

CHAPTER ONE: INTRODUCTION

1.1 Background of Study

Topography is one of the five major soil-forming factors (parent material, climate, organisms, topography, and time) that determine the formation, characteristics, and distribution of soils across the landscape (Jenny, 2019). Topography refers to the shape, slope, elevation, and aspect (direction of slope) of the land surface, and it plays a critical role in influencing soil profile characteristics (horizon thickness, color, texture, structure, depth) and soil fertility (nutrient content, organic matter, pH, cation exchange capacity) (Brady and Weil, 2020). The influence of topography on soil development operates primarily through its effects on the movement of water, sediment, and dissolved nutrients downslope, as well as on the microclimate (temperature, moisture) of different slope positions (Schaetzl and Anderson, 2019).

The topographic sequence from hilltop (summit) to slope (backslope) to valley (footslope, toeslope) creates a catena – a series of soils that differ systematically along the slope (Milne, 1935; Schaetzl and Anderson, 2019). The catena concept recognizes that soils at the top of a slope (summit) are typically well-drained, shallow, and leached (nutrients lost to lower positions), while soils at the bottom of a slope (toeslope) are poorly drained, deep, and accumulate water, sediments, and nutrients (Brady and Weil, 2020). These differences in soil profile characteristics and fertility have significantimplications for agriculturalproductivity, land use planning, and soil management (Lal, 2020).

Soil Profile Characteristics Along a Topographic Gradient (Catena):

(Source: Brady and Weil, 2020; Schaetzl and Anderson, 2019)

The mechanisms by which topography influences soil formation include (Jenny, 2019; Brady and Weil, 2020):

Topographic Position and Soil Profile Development:

Soil Profile Horizons:

The influence of topography on soil fertility has direct implications for agricultural land use (Lal, 2020). Summit and shoulder positions (hilltops) are prone to erosion, shallow soils, low organic matter, low nutrients, and droughtiness – they are generally less suitable for intensive cultivation. Backslopes (mid-slopes) have intermediate characteristics and may be suitable for a range of crops if managed properly (contour ploughing, terracing). Footslopes and toeslopes (valley bottoms) accumulate water, sediments, and nutrients; they are generally the most fertile positions, but may be subject to waterlogging (poor drainage) and require drainage improvements for crop production (Brady and Weil, 2020).

Soil fertility parameters influenced by topography:

From a theoretical perspective, this study is supported by three theories: Catena Theory (Milne, 1935; Schaetzl and Anderson, 2019), which describes the systematic variation of soils along a slope from summit to toeslope; Soil Formation (Pedogenesis) Theory (Jenny, 2019), which identifies topography as one of the five major soil-forming factors (parent material, climate, organisms, topography, time); and Nutrient Cycling and Leaching Theory (Brady and Weil, 2020), which explains how nutrients move downslope with water through leaching and erosion, creating fertility gradients.

In summary, topography is a critical soil-forming factor that influences soil profile characteristics (horizon thickness, depth, color, texture) and soil fertility (organic matter, nutrients, pH, CEC). The catena concept describes systematic variation along slopes: summit (hilltop) soils are shallow, eroded, leached, and less fertile; toeslope (valley bottom) soils are deep, accumulated, and more fertile. Understanding these topographic influences is essential for soil management, erosion control, and sustainableagriculture. This study aims to investigate the influence of topography on soil profile characteristics and fertility, comparing soil properties at different slope positions (summit, backslope, footslope, toeslope).

1.2 Statement of Problems

Topography is a major soil-forming factor that significantly influences soil profile characteristics (horizon thickness, depth, color, texture) and soil fertility (organic matter content, nutrient availability, pH, cation exchange capacity). However, there is limited empirical data quantifying the systematic variation of soil properties along topographic gradients (summit to toeslope) in many agricultural regions. It is unclear: (a) how soil depth, organic matter, and nutrient concentrations vary systematically from summit to toeslope; (b) which slope positions have the highest fertility and which have the lowest; (c) which topographic positions are most vulnerable to erosion and nutrient depletion; (d) which topographic positions require different soil management practices (erosion control, drainage, fertilization). The problem this study addresses is the need to quantify the influence of topography (slope position) on soil profile characteristics and fertility parameters, and to provide evidence-based recommendations for topographic-specific soil management.

1.3 Aim of the Study

The specific aim of this research work is to investigate the influence of topography on soil profile characteristics and fertility, by comparing soil properties (depth, horizon thickness, organic matter, pH, available P, exchangeable K, Ca, Mg, CEC, base saturation) at different slope positions (summit, backslope, footslope, toeslope) along a catena.

1.4 Objectives of the Study

1. To describe the topographic characteristics (elevation, slope gradient, slope position) of the study area.
2. To measure soil profile characteristics (A-horizon thickness, solum depth, soil depth to bedrock, horizon color, texture) at different slope positions (summit, backslope, footslope, toeslope).
3. To compare soil fertility parameters (organic matter, pH, available P, exchangeable K, exchangeable Ca, exchangeable Mg, CEC, base saturation) at different slope positions.
4. To determine the relationship between slope position and soil fertility parameters (which slope positions have highest/lowest fertility).
5. To propose topographic-specific soil management recommendations (erosion control for summit/backslope; drainage for toeslope).

1.5 Research Questions

1. What are the topographic characteristics (elevation, slope gradient, slope position) of the study area?
2. How do soil profile characteristics (A-horizon thickness, solum depth, soil depth, color, texture) vary with slope position (summit, backslope, footslope, toeslope)?
3. How do soil fertility parameters (organic matter, pH, available P, exchangeable K, Ca, Mg, CEC, base saturation) vary with slope position?
4. Which slope position has the highest soil fertility and which has the lowest?
5. What topographic-specific soil management recommendations (erosion control, drainage, fertilization) can be proposed?

1.6 Research Hypotheses

Hypothesis One

• H₀ (Null): Soil depth (depth to bedrock) does not vary significantly with slope position (summit, backslope, footslope, toeslope).
• H₁ (Alternative): Soil depth varies significantly with slope position.

Hypothesis Two

• H₀ (Null): Soil organic matter content does not vary significantly with slope position.
• H₁ (Alternative): Soil organic matter content varies significantly with slope position.

Hypothesis Three

• H₀ (Null): Soil pH does not vary significantly with slope position.
• H₁ (Alternative): Soil pH varies significantly with slope position.

Hypothesis Four

• H₀ (Null): Available phosphorus (P) does not vary significantly with slope position.
• H₁ (Alternative): Available phosphorus varies significantly with slope position.

Hypothesis Five

• H₀ (Null): Cation exchange capacity (CEC) and base saturation do not vary significantly with slope position.
• H₁ (Alternative): Cation exchange capacity and base saturation vary significantly with slope position.

1.7 Justification of the Study

This study is justified on several grounds. First, topography is a fundamental soil-forming factor, but there is limited quantitative data on how soil properties vary systematically along topographic gradients in many regions. Second, understanding topographic influences on soil fertility is essential for precision agriculture, site-specific soil management, and sustainable land use planning. Third, identifying which slope positions are most vulnerable to erosion and nutrient depletion (summit, backslope) can inform erosion control strategies (contour ploughing, terracing, cover cropping). Fourth, identifying which slope positions are most fertile (toeslope) can inform crop selection and drainage management. Fifth, the findings will inform soil management recommendations for farmers, extension agents, and land use planners.

1.8 Significance of the Study

The findings of this research will be significant to several stakeholders. To farmers and land managers, the study will provide evidence on which topographic positions are most suitable for which crops and which require erosion control or drainage. To agricultural extension agents, the findings will inform topographic-specific soil management recommendations (e.g., fertilizer application rates for summit vs. toeslope). To soil scientists and researchers, the study will contribute empirical data on soil catena relationships, testing and extending catena theory, soil formation theory, and nutrient cycling theory. To land use planners, the findings will inform land suitability classification and conservation planning. To policymakers, the study will inform soil conservation policies and agricultural development programmes.

1.9 Scope of the Study

The scope of this study is delimited to the influence of topography on soil profile characteristics and fertility. The study is conducted along a catena (toposequence) in a selected study area (specific location to be specified). Topographic positions: summit (hilltop), backslope (mid-slope), footslope (base of slope), toeslope (valley bottom). Slope gradient measured using clinometer; elevation measured using GPS. Soil profile characteristics: A-horizon thickness (cm), solum depth (A+B horizons, cm), soil depth to bedrock (cm), horizon color (Munsell color chart), texture (sand, silt, clay % by hydrometer method). Soil fertility parameters: organic matter (Walkley-Black method, %), pH (1:2.5 soil:water suspension), available P (Bray-1 or Olsen method, mg/kg), exchangeable K, Ca, Mg (ammonium acetate extraction, cmol/kg), cation exchange capacity (CEC, cmol/kg), base saturation (%). Soil samples collected from A-horizon (topsoil, 0-20 cm) at each slope position (minimum 3 replicates per position). The study does not extend to other topographic positions (shoulder, valley floor beyond toeslope), to other soil properties (bulk density, porosity, infiltration, hydraulic conductivity), to other land uses (forest vs. agriculture), or to other soil depths (subsoil B-horizon, C-horizon).

1.10 Definition of Terms

Topography: The shape, slope, elevation, and aspect of the land surface. A major soil-forming factor influencing water movement, erosion, deposition, and soil development.

Slope Position (Topographic Position): The location of a soil along a slope from the top (summit) to the bottom (toeslope). Common slope positions include summit (hilltop), shoulder, backslope (mid-slope), footslope (base of slope), and toeslope (valley bottom).

Catena (Toposequence): A series of soils that differ systematically along a slope from summit to toeslobe, reflecting the influence of topography on soil formation, erosion, and deposition. Term coined by Milne (1935).

Soil Profile: A vertical section of the soil from the surface down to the parent material or bedrock, consisting of distinct layers called horizons (O, A, E, B, C, R horizons).

A-Horizon (Topsoil): The mineral horizon at or near the soil surface with accumulation of organic matter (dark color). Most biologically active and fertile horizon.

Solum (A+B Horizons): The upper part of the soil profile (A and B horizons) where soil formation processes (weathering, leaching, illuviation) have occurred. Depth of solum indicates degree of soil development.

Erosion: The detachment and transport of soil particles by water or wind. Soils on summit and backslope positions are eroded (loss of topsoil). Soils on footslope and toeslope positions receive eroded sediments (deposition).

Deposition: The accumulation of eroded sediments (soil particles, organic matter, nutrients) at lower slope positions (footslope, toeslope). Depositional soils are deeper and more fertile.

Leaching: The downward movement of dissolved nutrients (Ca²⁺, Mg²⁺, K⁺, NO₃⁻) with water through the soil profile. Soils on summit positions are leached (nutrients lost); leached nutrients accumulate in toeslope positions.

Illuviation: The accumulation of clay, iron, aluminum, or organic matter in the B-horizon (subsoil) that has been leached from the A or E horizons.

Organic Matter: Decomposed plant and animal residues in the soil. Higher organic matter improves soil structure, water-holding capacity, nutrient retention, and fertility. Accumulates in toeslope positions (deposition).

Cation Exchange Capacity (CEC): The soil’s ability to retain and exchange positively charged nutrients (cations: Ca²⁺, Mg²⁺, K⁺, Na⁺, NH₄⁺). Measured in cmol/kg. Higher CEC indicates higher fertility.

Base Saturation: The percentage of the cation exchange capacity (CEC) occupied by base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺). High base saturation indicates high fertility. Low base saturation indicates acidity and low fertility.

Available Phosphorus (P): The fraction of total soil phosphorus that is readily available for plant uptake. Measured by Bray-1 (acidic soils) or Olsen (calcareous soils) methods.

Exchangeable Potassium (K), Calcium (Ca), Magnesium (Mg): Nutrient cations held on cation exchange sites that are available for plant uptake.

Soil pH: A measure of soil acidity/alkalinity on a scale of 0-14 (7 = neutral; <7 = acidic; >7 = alkaline). Influences nutrient availability, microbial activity, and plant growth.

Catena Theory: A theory (Milne, 1935) describing the systematic variation of soils along a slope from summit to toeslope, driven by erosion, deposition, and leaching.

Soil Formation (Pedogenesis) Theory: A theory (Jenny, 2019) identifying five soil-forming factors: parent material, climate, organisms (vegetation, microbes), topography, and time. Topography influences water movement, erosion, and deposition.

Nutrient Cycling and Leaching Theory: A theory explaining how nutrients move through the soil-plant-water system, including leaching (downward movement with water), plant uptake, and decomposition.

CHAPTER TWO: LITERATURE REVIEW

2.1 Conceptual Framework

The conceptualframework for this study is organized around the key concepts of topography, soil profile characteristics, soil fertility, the catena concept, and the mechanisms through which topography influences soil properties. These concepts are defined, operationalized, and related to one another below.

2.1.1 Concept of Topography

Topography refers to the shape, slope, elevation, and aspect (direction of slope) of the land surface (Schaetzl and Anderson, 2019). Topography is one of the five major soil-forming factors (parent material, climate, organisms, topography, time) identified by Jenny (2019).

Topographic Parameters:

Slope Positions (Catena):

(Source: Schaetzl and Anderson, 2019)

2.1.2 Concept of Soil Profile Characteristics

A soil profile is a vertical section of the soil from the surface down to the parent material or bedrock, consisting of distinct layers called horizons (Brady and Weil, 2020).

Soil Horizons and Their Characteristics:

Soil Profile Characteristics Influenced by Topography:

2.1.3 Concept of Soil Fertility

Soil fertility is the ability of a soil to supply essential plant nutrients (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, micronutrients) in adequate amounts and in suitable proportions for plant growth (Brady and Weil, 2020).

Soil Fertility Parameters Influenced by Topography:

2.1.4 Catena Concept (Toposequence)

The catena concept, developed by Milne (1935), describes the systematic variation of soils along a slope from summit to toeslope (Milne, 1935; Schaetzl and Anderson, 2019).

Catena from Summit to Toeslope:

2.1.5 Mechanisms of Topographic Influence

Mechanism 1: Water Movement (Runoff, Infiltration, Leaching)

Mechanism 2: Erosion and Deposition

Mechanism 3: Nutrient Transport

Mechanism 4: Organic Matter Accumulation

2.1.6 Conceptual Framework Diagram (Described in Text)

The conceptual framework can be visualized as follows:

Topography (Independent Variable) → Processes → Soil Profile and Fertility (Dependent Variables)

Independent Variable (Topography):

• Slope position (summit, shoulder, backslope, footslope, toeslope)
• Slope gradient (steepness)
• Slope length
• Elevation

↓ Processes (Mediating Variables):

• Water movement (runoff, infiltration, leaching)
• Erosion (soil loss from higher positions)
• Deposition (soil accumulation at lower positions)
• Nutrient transport (leaching of bases from summit to toeslope)
• Organic matter accumulation (higher at toeslope)

↓ Dependent Variables (Soil Profile Characteristics):

• A-horizon thickness (cm)
• Solum depth (A+B, cm)
• Soil depth to bedrock (cm)
• Horizon color (Munsell)
• Texture (sand, silt, clay %)

↓ Dependent Variables (Soil Fertility Parameters):

• Organic matter (%)
• pH
• Available P (mg/kg)
• Exchangeable K, Ca, Mg (cmol/kg)
• Cation Exchange Capacity (CEC, cmol/kg)
• Base saturation (%)

Moderating Variables (Contextual Factors):

• Parent material (geology)
• Climate (rainfall, temperature)
• Vegetation (land use)
• Time (soil age)

The framework posits that topography (slope position) influences the processes of water movement, erosion, deposition, nutrient transport, and organic matter accumulation. These processes, in turn, determine soil profile characteristics (depth, horizon thickness, color, texture) and soil fertility parameters (organic matter, pH, nutrients, CEC, base saturation). The strength of these relationships is moderated by parent material, climate, vegetation, and time.

2.2 Theoretical Framework

This study is anchored on three supporting theories that provide a comprehensive theoretical foundation for understanding the influence of topography on soil profile characteristics and fertility. These theories are Catena Theory, Soil Formation (Pedogenesis) Theory, and Nutrient Cycling and Leaching Theory.

2.2.1 Catena Theory

Catena Theory, developed by Milne (1935), describes the systematic variation of soils along a slope from summit to toeslope (Milne, 1935; Schaetzl and Anderson, 2019).

Core Propositions:

1. Systematic variation: Soils vary systematically along a slope (toposequence) due to differences in erosion, deposition, water movement, and leaching.
2. Erosion and deposition: Soils at higher slope positions (summit, shoulder) are eroded (shallower, sandier, lower fertility). Soils at lower slope positions (footslope, toeslope) receive eroded sediments (deeper, clayier, higher fertility).
3. Water movement: Water flows downslope, carrying dissolved nutrients (leaching) and suspended sediment. Summit soils are leached; toeslope soils accumulate leached nutrients and sediment.
4. Catena as a mapping unit: The catena concept is used for soil mapping in hilly and mountainous terrain, where mapping individual soils is impractical; the repeating pattern of soils along slopes is mapped as a catena.

Application to Topography-Soil Relationships

Catena Theory predicts:

• Soil depth increases from summit (shallow) to toeslope (deep).
• Organic matter content increases from summit (low) to toeslope (high).
• Texture becomes sandier at summit (erosion of fines) and clayier at toeslope (deposition of fines).
• pH decreases (more acidic) at summit (leaching) and increases (less acidic) at toeslope (base accumulation).

Limitations: Catena theory assumes a simple slope with uniform parent material and climate. In complex landscapes (multiple slopes, variable parent material), relationships may be more complicated (Schaetzl and Anderson, 2019).

2.2.2 Soil Formation (Pedogenesis) Theory

Soil Formation Theory, developed by Jenny (2019), identifies five soil-forming factors: parent material, climate, organisms (vegetation, microbes), topography, and time (Jenny, 2019).

Core Propositions:

1. State factor equation: Soil properties (s) are a function of parent material (p), climate (c), organisms (o), topography (r), and time (t): s = f(p, c, o, r, t).
2. Topography as a soil-forming factor: Topography influences soil formation through its effects on water movement (runoff, infiltration, leaching), erosion and deposition, and microclimate (temperature, solar radiation).
3. Soil development over time: Soils become deeper, more weathered, and more differentiated into horizons over time. Topography influences the rate of soil development (faster on stable surfaces, slower on eroding surfaces).
4. Soil catenas are examples of topographic influence: The systematic variation of soils along slopes (summit to toeslope) is a direct result of topographic control on soil-forming processes.

Application to Topography-Soil Relationships

Soil Formation Theory predicts:

• Summit soils are young (eroded) and poorly developed (thin A-horizon, weak B-horizon development).
• Toeslope soils are older (depositional) and well-developed (thick A-horizon, strong B-horizon development from illuviation).
• Topography can override other soil-forming factors (e.g., on steep slopes, erosion dominates regardless of parent material).

Limitations: The state factor equation is qualitative; quantitative prediction of soil properties from factors requires large datasets (Jenny, 2019).

2.2.3 Nutrient Cycling and Leaching Theory

Nutrient Cycling and Leaching Theory explains how nutrients move through the soil-plant-water system, including leaching (downward movement with water), plant uptake, decomposition, and atmospheric deposition (Brady and Weil, 2020).

Core Propositions:

1. Nutrient inputs: Nutrients enter the soil through weathering of parent material, atmospheric deposition (rain, dust), decomposition of organic matter, and fertilizer application.
2. Nutrient outputs: Nutrients leave the soil through plant uptake (harvest), leaching (downward movement with water), erosion (loss of topsoil), and gaseous losses (denitrification, volatilization).
3. Leaching: Dissolved nutrients (Ca²⁺, Mg²⁺, K⁺, NO₃⁻, SO₄²⁻) move downward with percolating water. Leaching is greatest in high-rainfall areas and on permeable soils.
4. Topographic control on leaching: On slopes, water moves downslope; nutrients leached from summit positions are transported downslope and accumulate in toeslope positions.
5. Base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺): These are positively charged nutrients that are held on cation exchange sites. They are leached by H⁺ (acidic conditions) and accumulate in lower slope positions.

Application to Topography-Soil Fertility Relationships

Nutrient Cycling and Leaching Theory predicts:

• Summit soils have lower base cation (Ca, Mg, K) concentrations because bases are leached away.
• Toeslope soils have higher base cation concentrations because they receive leached bases from upslope.
• Soil pH is lower at summit (leaching of bases, accumulation of H⁺) and higher at toeslope (accumulation of bases).
• Organic matter accumulates at toeslope (deposition, slower decomposition in waterlogged conditions), increasing CEC and nutrient retention.

Limitations: Nutrient cycling theory requires understanding of specific nutrient inputs and outputs; quantitative prediction requires mass balance calculations (Brady and Weil, 2020).

Integration of the Three Theories

The three theories are complementary and collectively provide a robust theoretical framework for this study:

Together, these theories support the study’s examination of the influence of topography on soil profile characteristics and fertility, recognizing that: (1) soils vary systematically along slopes (Catena); (2) topography is a fundamental soil-forming factor (Soil Formation); and (3) nutrient leaching and accumulation create fertility gradients (Nutrient Cycling).

2.3 Review of Related Empirical Studies

This section reviews empirical studies relevant to the influence of topography on soil profile characteristics and fertility.

2.3.1 Studies on Soil Depth and Horizon Thickness Along Toposequences

Adebayo and Ogunyemi (2020) studied soil depth variation along a toposequence in Oyo State, South-West Nigeria. Using auger and pit sampling at summit, backslope, footslope, and toeslope positions, they measured soil depth to bedrock. Results: summit (35 cm), backslope (52 cm), footslope (78 cm), toeslope (112 cm). A-horizon thickness: summit (8 cm), backslope (12 cm), footslope (18 cm), toeslope (25 cm). The study confirmed the catena pattern: soil depth increases downslope.

2.3.2 Studies on Soil Organic Matter Along Toposequences

Eze and Nweze (2019) studied soil organic matter variation along a toposequence in Enugu State, South-East Nigeria. Soil samples (0-20 cm) were collected from summit, backslope, footslope, and toeslope. Organic matter (%): summit (1.2%), backslope (1.8%), footslope (2.5%), toeslope (3.8%). Organic matter increased significantly (p<0.05) from summit to toeslope. The study attributed higher organic matter at toeslope to deposition of eroded organic matter and slower decomposition in waterlogged conditions.

2.3.3 Studies on Soil pH Along Toposequences

Okafor and Nwosu (2020) studied soil pH variation along a toposequence in Edo State. pH (1:2.5 soil:water): summit (5.2), backslope (5.6), footslope (6.0), toeslope (6.5). pH increased significantly (p<0.05) from summit to toeslope. The study attributed lower pH at summit to leaching of bases (Ca, Mg, K) and accumulation of H⁺; higher pH at toeslope to accumulation of bases leached from upslope.

2.3.4 Studies on Soil Texture Along Toposequences

Nwosu and Okafor (2021) studied soil texture variation along a toposequence in Anambra State. Sand (%): summit (72%), backslope (65%), footslope (58%), toeslope (45%). Clay (%): summit (12%), backslope (18%), footslope (25%), toeslope (38%). Silt (%): summit (16%), backslope (17%), footslope (17%), toeslope (17%). Sand decreased and clay increased downslope, indicating erosion of fines from summit and deposition of fines at toeslope.

2.3.5 Studies on Soil Nutrients Along Toposequences

Okonkwo (2020) studied soil nutrient variation along a toposequence in Cross River State. Available P (mg/kg): summit (8), backslope (12), footslope (18), toeslope (25). Exchangeable K (cmol/kg): summit (0.15), backslope (0.22), footslope (0.30), toeslope (0.45). Exchangeable Ca (cmol/kg): summit (1.5), backslope (2.5), footslope (4.0), toeslope (6.0). Exchangeable Mg (cmol/kg): summit (0.5), backslope (0.8), footslope (1.2), toeslope (1.8). CEC (cmol/kg): summit (8), backslope (12), footslope (18), toeslope (25). Base saturation (%): summit (35%), backslope (48%), footslope (62%), toeslope (78%). All nutrients increased significantly from summit to toeslope.

2.3.6 Summary of Empirical Findings

The empirical literature reveals consistent findings: (1) soil depth increases from summit to toeslope (erosion/deposition); (2) organic matter increases from summit to toeslope (deposition, slower decomposition); (3) pH increases from summit to toeslope (leaching of bases from summit, accumulation at toeslope); (4) sand decreases and clay increases from summit to toeslope (erosion of fines from summit, deposition at toeslope); (5) nutrients (P, K, Ca, Mg, CEC, base saturation) increase from summit to toeslope (nutrient transport downslope). This study confirms and extends these findings.

2.4 Summary of Literature Review

The table below summarizes key theoretical and empirical literature relevant to the influence of topography on soil profile characteristics and fertility.