How Land Use and Slope Shape Soil Health in Afikpo
Imagine the land as a thin, living skin covering the Earth—a fragile membrane that sustains all life. Now picture this skin being gradually worn away, stripping away its ability to support crops, store water, and nurture ecosystems.
This isn't a scene from a dystopian novel; it's the quiet reality unfolding in the Upper Eyiohia River Watershed in Afikpo North, southeastern Nigeria. Here, the intricate relationship between how we use the land, the steepness of slopes, and soil health determines whether communities thrive or face food insecurity.
Soil erosion rates in the watershed have nearly doubled in just two decades, skyrocketing from 79 tons per hectare annually in 1996 to 149 tons per hectare by 2016 3 .
Rapid population growth and increasing demands for agricultural land have triggered dramatic changes in the landscape, converting protective forests into exposed farmlands 3 .
Different ways we use land leave distinctive fingerprints on soil health and stability.
The steepness of land orchestrates the movement of water, nutrients, and soil.
Physical and chemical characteristics that reveal the vital signs of soil health.
Walk through the Upper Eyiohia watershed, and you'll encounter a mosaic of different land uses, each leaving its distinctive fingerprint on the soil:
These pristine ecosystems act as nature's guardians for the soil. The dense canopy of leaves intercepts rainfall before it hits the ground with destructive force, while intricate root networks bind soil particles together like living glue. Fallen leaves and organic matter continuously replenish precious nutrients, creating a resilient system that withstands erosion and maintains fertility 1 .
When forests give way to farmland, the relationship with soil changes fundamentally. Regular plowing and weeding disturb the soil's natural structure, leaving it vulnerable to the pounding energy of tropical rains. Without protective cover, the soil's organic matter—the very component that gives it structure and fertility—breaks down rapidly, diminishing its capacity to support healthy crops 5 .
The most vulnerable of all landscapes, these areas have lost their vegetative armor completely. Whether left fallow or abandoned after intensive use, bare soils bear the full brunt of rainfall impact, resulting in the highest rates of nutrient loss and sediment transport to waterways 3 .
The steepness of land creates an invisible force that orchestrates the movement of water, nutrients, and soil itself:
At the crest of hills, gravity pulls water downward, limiting how much moisture the soil can retain. This constant drainage creates drier conditions and means these areas often experience the most significant erosion 7 .
These transitional zones experience a complex interplay of processes. The intensity of cultivation on these slopes in Afikpo has made them hotspots for degradation, where soil nutrients are depleting at alarming rates 7 .
At the bottom of the topographic sequence, these areas act as collectors of what washes down from above. Water, sediment, and nutrients accumulate here, often creating more fertile conditions but sometimes leading to waterlogging problems 7 .
Just like vital signs reveal human health, specific physical and chemical properties tell us about soil condition:
These include characteristics like texture (the proportion of sand, silt, and clay), bulk density (how compacted the soil is), and water-holding capacity. Healthy soils have good soil structure that allows roots to penetrate deeply and water to infiltrate rather than running off 4 .
This category encompasses soil acidity (pH), organic matter content, nutrient levels, and the soil's ability to retain these nutrients (cation exchange capacity). These factors determine whether plants can access the essential elements they need to grow 1 .
To understand the scale of change in the Upper Eyiohia watershed, researchers employed sophisticated technologies including satellite remote sensing, geographic information systems (GIS), and detailed field measurements. By comparing satellite images from 1996 and 2016, they could quantify exactly how the landscape had been transformed over two critical decades 3 .
The research team applied the Revised Universal Soil Loss Equation (RUSLE)—a powerful model that estimates soil erosion rates by integrating data on rainfall patterns, soil characteristics, topography, land cover, and conservation practices 3 .
Across the varied terrain of the watershed, scientists established carefully selected study sites representing different land uses and slope positions. Using standard soil sampling augers, they collected hundreds of samples from both surface soils (0-15 cm depth) and subsurface layers (15-30 cm depth) to understand how soil properties changed with depth and management 1 .
Back in the laboratory, these samples underwent rigorous analysis to determine texture, organic carbon, and nutrient levels using standardized methods 1 .
| Land Use Type | Change (hectares) | Percent Change | Primary Driver |
|---|---|---|---|
| Forest Land | -8,600 ha | Significant decrease | Conversion to agriculture |
| Cultivated Land | +3,400 ha | Major increase | Food production needs |
| Settlement Areas | +2,300 ha | Substantial increase | Population growth |
| Bare Land | +2,600 ha | Notable increase | Land degradation |
| Grazing Land | +300 ha | Moderate increase | Livestock keeping |
The data reveals a dramatic landscape transformation over the 20-year period, with forests bearing the brunt of this conversion. The loss of 8,600 hectares of forest represents a significant reduction in ecosystem services that naturally protect soils and regulate water cycles 3 .
The findings demonstrate that cultivated land experiences the most severe erosion—more than double the rate found in forested areas. This stark difference underscores the vulnerability of soils when they're exposed without adequate protection 3 .
| Soil Property | Upper Slope | Middle Slope | Lower Slope | Ideal Range for Agriculture |
|---|---|---|---|---|
| Sand Content (%) | 69.7 | 79.6 | 91.5 | Varies by crop needs |
| Clay Content (%) | 17.2 | 12.3 | 4.5 | Varies by crop needs |
| Bulk Density (g/cm³) | 0.95 | 1.08 | 1.24 | 1.1-1.3 |
| Organic Carbon (%) | 4.87 | 1.80 | 1.15 | >1.5% |
| Total Nitrogen (%) | 0.246 | 0.114 | 0.074 | 0.1-0.5% |
| Available Phosphorus (mg/kg) | 11.21 | 5.98 | 4.45 | 10-30 mg/kg |
The data reveals a clear pattern: soils on upper slopes generally maintain better properties than those further down the slope sequence in cultivated areas. The dramatic decline in organic carbon and nitrogen from upper to lower slopes highlights how cultivation practices are depleting the very nutrients that make soils productive 1 7 .
The research reveals a troubling feedback loop playing out across the Afikpo landscape. When forests are cleared for agriculture on sloping land, the protective vegetative cover disappears. Without this natural armor, intense tropical rains strike the soil directly, dislodging particles and destroying the delicate structure that took centuries to form 3 .
This process explains why cultivated soils in the watershed show such dramatic declines in crucial nutrients. The organic carbon levels in cropping plots measured a meager 1.15% compared to 4.87% in forest soils—a staggering reduction of over 75% 1 .
The research points toward several strategies that could reverse these damaging trends:
Understanding soil health requires both field observations and laboratory analyses. Here are the essential tools and methods researchers use to decode the secrets of the soil:
| Tool/Method | Primary Function | Application in Soil Studies |
|---|---|---|
| Soil Auger | Collecting undisturbed soil samples at various depths | Assessing soil profile characteristics and collecting samples for laboratory analysis |
| GPS Receiver | Precise location mapping | Documenting exact sample locations and creating detailed soil maps |
| pH Meter | Measuring soil acidity/alkalinity | Determining lime requirements and predicting nutrient availability |
| Hydrometer | Particle size analysis | Determining soil texture (sand, silt, clay proportions) |
| Atomic Absorption Spectrophotometer | Quantifying metal elements | Measuring essential nutrients (calcium, magnesium, potassium) and detecting contaminants |
| Walkley-Black Apparatus | Organic carbon determination | Assessing soil organic matter content and fertility status |
| Kjeldahl Digestion System | Total nitrogen analysis | Evaluating soil nitrogen supplying capacity |
| Bulk Density Sampler | Measuring soil compaction | Collecting undisturbed cores for bulk density and porosity calculations |
| Remote Sensing & GIS | Landscape-scale analysis | Mapping land use changes, modeling erosion risk, and identifying degradation hotspots |
The story unfolding in Upper Eyiohia River Watershed carries a powerful lesson: the way we use the land must respect the natural limits imposed by topography and soil type.
The findings from Afikpo offer both a warning and a way forward. They warn us that continuing current practices will likely lead to further degradation, threatening food security and environmental health. But they also point toward solutions rooted in working with natural processes rather than against them.
As farmers, policymakers, and researchers collaborate to implement these practices, the hope is that the next decade will tell a different story—one of rebuilding soil health, stabilizing slopes, and creating a landscape that can sustain both people and nature for generations to come.