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Subsurface Drainage of Valley Bottom Irrigated Rice Schemes in Tropical Savannah

Case Studies of Tiefora and Moussodougou in Burkina Faso

This study was built to investigate the impact of subsurface drainage on iron toxicity in Tropical Savannah irrigated rice valley bottoms. The research leaned upon two complementary approaches: field investigations and designed experiments. Les mer
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This study was built to investigate the impact of subsurface drainage on iron toxicity in Tropical Savannah irrigated rice valley bottoms. The research leaned upon two complementary approaches: field investigations and designed experiments. Important results, covering several fields, where achieved. For example, It appeared that single-season irrigation schemes present higher iron toxicity and acidity risks than double-season ones - 750 up to 1800 mg/l of Fe2+ higher in the single-season scheme of Moussodougou than in the double-season scheme of Tiefora. Furthermore, a statistical analysis of flow time series (ARIMA model) data was performed. It showed that with a simple water level measurement probe installed at the main gate of the scheme, it becomes possible not only to quantify irrigation water consumption, but also to diagnose farmers' irrigation schedule, providing them a means to defuse potential conflicts due to inequity in water distribution. Finally, it was shown that subsurface drainage increases ferrous iron concentration in hematite dominant soils soil - from 935 mg/l to more than 1106 mg/l in the case of the soil of Moussodougou - but also fortunately alleviate soil acidity - from pH 5.6 to 7.3 in Moussodougou. This effect will eventually reduce ferrous iron intake by rice roots, alleviating toxicity.

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Innholdsfortegnelse

1. Introduction
1.1. Background and Objectives
1.1.1. Problem Statement
1.1.2. Research Questions
1.1.3. Research Objectives
1.1.4. Expected Results
1.2. Scope
1.3. Structure of the Thesis
2. Literature Review
2.1. Tropical Savannah in Africa
2.2. Soil Genesis
2.3. The Prominence of Iron and Clay
2.4. Differences between Valley Bottom and Upland Soils
2.5. Iron Toxicity
2.6. Sulphate-Reducing Bacteria in Soils
2.6.1. The Flooded Rice Ecosystem
2.6.2. Iron and Sulphate Reducing Bacteria
2.6.3. The Bacteria Against Nematodes
2.6.4. The Reduction Processes
2.7. Subsurface Drainage
2.8. Concluding Remarks and Knowledge Gaps
3. Material and Methods
3.1. The Two Study Areas
3.2. The Site of Tiefora
3.2.1. Geographic Location
3.2.2. Population
3.2.3. Climate
3.2.4. The Dam
3.2.5. The Valley Bottem Irrigation Scheme
3.2.6. Topography and Valley History
3.2.7. The Pedology and the Reasons of Choosing Plain III
3.2.8. The Problems
3.3. The Site of Moussodougou
3.3.1. Location and Activities
3.3.2. The Problems
3.4. Project Components
3.4.1. First Component
3.4.2. Second Component
4. Irrigation Systems Prediagnoses and Update
4.1. Diagnosing and Mapping Tiefora Valley Bottom
4.2. Lessons from Valley Bottom Irrigated Rice Fields of Valley du Kou
4.3. Diagnosing and Mapping Moussodougou Valley Bottom
5. Clay and Ferrous Iron Stratifications
5.1. Soil Sampling and Measurements
5.2. Statistical Analyses
5.3. Clay Stratification Occurence
5.4. Ferrous Iron Concentration in the Rootzone
5.5. Conclusions
6. Higher Iron Toxicity Risk in Single-Season Irrigation
6.1. Soil Sampling
6.2. Measurements
6.3. Statistical Analysis
6.4. Geochemistry
6.5. Conditions Check for Hypotheses Testing
6.6. Statistical Results
6.7. Geochemical Analysis
6.8. Conclusions
7 . Clay Distribution and Adapted Drainage
7.1. Soil Sampling
7.2. Statistical Analysis
7.3. Soil Texture
7.4. Finding a Regression Model
7.5. Regression Goodness of Fit
7.6. Soil Hydraulics Analysis
7.7. Conclusions
8. Infiltration Rate Increase from Upstream in a Valley
8.1. Boreholes Preparation
8.2. Under Phreatic Infiltration Rate Measurements
8.3. Statistical Analysis
8.4. Selecting a Regression Model
8.5. Regression Goodness of Fit Checks
8.6. Cross Sectional Permeability Comparisons
8.7. Conclusions
9. Water Management Using Autocorrelation
9.1. Water Level Diver Installation
9.2. Assessment of Irrigation Water Use During the Seasons
9.3. Statistical Analysis
9.3.1. Removing Outliers and Stabilizing the Variance
9.3.2. ARIMA Model
9.3.3. Autocorrelation
9.3.4. Partial Autocorrelation PACF