Definition of Soil Erosion
Soil erosion refers to the gradual removal of the topsoil and its nutrients by the agent of denudation such as water, wind, ice, and glacier. Erosion occurs particularly when the soil surface is exposed to rainfall, and the rainfall rate exceeds the absorption or infiltration rate.
Similarly, it is a systematic process of wearing away soil particles, and soil nutrients from the surface of the soil by the various agents of denudation. Soil erosion occurs when the impact of water or wind loosens the soil particles, causes losses of soil fertility, and destroys soil structure.
Human activities such as deforestation, bush burning, and clean clearing make the soil bare and uncovered making it easy for various agents of denudation to remove the soil particles and transport these particles along with these agents to a far distance.
The degree of occurrence of soil erosion varies considerably from one area to another due to geological factors and climatic and soil conditions. Soil deterioration due to erosion and surface runoff has become a severe problem predominantly in the arid region and humid regions, rendering many viable agricultural lands infertile, uncultivated, and abandoned.
These degradations of natural resources have led to a decline in agricultural productivity. The effect of Erosion on agriculture has been a matter of concern, as erosion has a serious negative impact on water quality, eroding topsoil into streams and waterways, eroding crops, and impacting farm animals, aquatic ecosystems, and human activities.
To ameliorate the effect of soil erosion, it is paramount to implement soil management systems that aim to reduce the impact of raindrops, improve soil resistance, and reduce water runoff.
Types of Soil Erosion
There are four types of soil erosion, these are
- Splash soil erosion
- Sheet soil erosion
- Rill soil erosion
- Gully soil erosion
Raindrop/Splash Soil Erosion
This is the first type of erosion caused by rainfall. It involves the destruction of the soil structure by rainfall and it usually occurs in uncultivated or bare land. Splash erosion occurs when raindrops detach or loosen the soil particles and make them susceptible to runoff. Splash erosion is the first stage of erosion leading makes sheet erosion.
Sheet Soil Erosion
Sheet erosion refers to the wearing away of the topsoil in uniform layers by runoff water. The degree of effect on the deterioration of the soil depends on flow velocity, flow volume, and physical and chemical properties of the soil.
Sheet erosion occurs on land where raindrops or splash water have detached or loosened the soil particles making it easy for these particles to be carried through very small definable channels called the inter-rills. These soil particles detached by raindrops are carried through the inter-rill by a very thin layer of the runoff. Sheet erosion usually occurs on land with little or no vegetation cover, when these occur top layer of the soil exposes infertile subsoil to erosion, thus leading to wearing a way of severe loss of plant nutrients.
Rill Soil Erosion
This type of irrigation occurs due to the prolonged occurrence of erosion through a narrow path leading to the formation of furrows. As the water flows through a finger link channel continuously this leads to the widening of the inter rills and formation of a small path which is often known as rills.
Rill erosion becomes wider as runoff transports load and debris over the furrow from the inter-rill area and direct flow through a step channel in the stream leading to the formation of the gully.
Gully Soil Erosion
Gully erosion refers to the creation of deep channels, furrows, and loss of soil due to water-to-surface runoff. The gradual action of rill and sheet erosion in carrying soil layers along a narrow path reaches the advanced stage by creating gullies. The degree of occurrences of gully erosion is influenced by the topography of the soil, the volume of water, and the force of runoff.
Sloppy topography increases the rate of runoff thereby transporting debris and other materials into river systems or downslope. The running water cuts the channels deep into the soil creating downstream problems leading to the destruction of viable agricultural land, roads, and farmsteads, and reduction of water quantity. Gully erosion should become a matter of concern when it is below 30cm from the topsoil
Difference between Sheet Erosion and Gully Erosion
Below are some of the differences between sheet erosion and gully erosion.
| S/no | Sheet Erosion | Gully Erosion |
| 1 | It occurs uniformly on farms by water runoff. | It is caused by heavy rain over a flat surface |
| 2 | It is an advanced stage of splash erosion | It is an advanced stage of sheet erosion |
| 3 | It is caused by heavy rain over a flat surface | It leads to the loosing of the soil, creation of deep channels, and furrows, and loss of soil due water to surface runoff |
| 4 | It occurs in bare, till land, and little vegetation | It occurs in sloppy and insufficient vegetation |
| 5 | It exposes the roots of trees, tuber of crops, and grasses | it occurs unevenly on the farm by water runoff |
| 6 | Wear away the entire soil nutrient | It leads to lost soil, lower soil water holding capacity, and Weak soil nutrients on the channel or furrow. |
Difference Between Splash Erosion and Sheet Erosion
Below are some of the differences between splash erosion and sheet erosion.
| s/no | Splash erosion | Sheet erosion |
| 1 | It occurs uniformly on a farm by water runoff. | It occurs uniformly on farms by water runoff. |
| 2 | It is caused by raindrops or splashed water | It is caused by heavy rain over a flat surface |
| 3 | It leads to the breaking up of the soil structure. | It leads to the detaching, loosening, and wearing away the soil particles |
| 4 | It occurs in bare and till land only | It occurs in bare, till land, and little vegetation |
| 5 | it can easily carried by wind | It is an advanced stage of splash erosion |
Effects of Soil Erosion
- Land degradation: Soil erosion has an overweening effect on the soil by gradually removing or detaching the soil particles leading to the destruction of the soil. Surface runoff wears away soil nutrients, the top layer of the soil, and in most cases creates gullies on the farmland. Soil erosion remains a significant problem worldwide destroying many agricultural lands and rendering land unfit for cultivation or abandoned. The effect of surface runoff in developing countries has led to the decline of agricultural production due to land degradation.
- Destruction of Aquatic Ecosystems: during surface runoff soil particles are transported in large quantities through gullies and drainages into sea, streams, and other waterways. These soil particles that accumulate over a long period will begin to sediment leading to the destruction of the aquatic habitat.
- Water Pollution: erosion can wash toxic chemicals, and erode topsoil, and its nutrients into streams and other waterways therefore rendering it unfit for human and aquatic consumption. Surface runoff transports polythene bags, debris, plastic, and other materials into the sea, stream, or ocean. These materials lead to the pollution of the water. In most cases, polythene can cover the aquatic life in the seas leading to the death of aquatic of aquatic organisms. Erosion reduces water quality, washes soil particles into waterways and sediment-water sources, and reduces water for irrigation purposes.
- Air Pollution (dust): in the arid and semi-arid desert areas where the influence of wind erosion is prevalent. The wind can transport soil particles to a distant area resulting in the formation of dunes and drifts. Wind can soil particles and pollen in the air resulting in breathing difficulty or respiratory disease. Wind can carry soil particles into the roof of a building leading to the destruction of rooftops. Additionally, wind can dust into the walls of a building resulting in the decoration of the building walls and paint
- Leaching of Soil Nutrients: leaching is the downward washing of the soil nutrients below the root zone. Erosion does not only wash away the top soil and its nutrients but also wash the soil nutrients downward below which the root zone of plants can maximized.
- Reduce the Size of Farm Land: The hydrologic processes of rainfall and runoff harm the size of farmland. The rate of surface runoff can create many gullies on the farm land resulting in thereby reducing the side of the farm land. These gullies on the farmland prevent many agronomic, cultural, or structural practices from taking place on the farm.
- Causes reduction in yield of crops: the overall impact of soil erosion is evidence of soil productivity on the yield of crops. The removal of topsoil and subsoil results in poor root growth, soil water availability, and soil fertility. These essential factors are necessary for crop growth and productivity is washed away by surface runoff, plants are left with nothing for productivity. Plant and animal residue that can decay to add organic matter to the soil erosion are washed away by surface runoff reducing the quantity of soil nutrient
- Destruction of economic properties: The hydrologic processes of rainfall and runoff create gullies on the land which led to the destruction of economic properties such as bridges, access roads, farm buildings, and fences. Since erosion is considered uncertain, its occurrence something remains unknown to the farmers until its effect has occurred
Causes of Soil Erosion
The factors that can speed up or increase the erosion of land are as follows.
- Soil structure and composition
- Vegetation cover
- Topography of the land
- Agricultural practice
- Deforestation
- Road construction and Urbanization
- Climate changes (global warming)
- Bush burning
- Soil Structure and Composition: the structure of the soil has a significant effect on the rate of erosion. Soil with poor soil structure is easily washed away by erosion compared to soil that is erosion-resistant. For example, soil erosion occurrence on sandy soil is higher than that of the loamy and clay soil respectively.
- Vegetation Cover: the rate of vegetation on the soil influences the surface runoff and wind erosion. The rate of runoff on bare soil differs significantly for land with high vegetative covers. The root of grasses and crop cover help to bind soil together making it difficult for wind or water to detach and transport the soil particles to another area. Canopy or ground cover crops or grasses resist soil erosion.
- Topography of the land: the nature of the soil is another factor that speeds up the rate of erosion of the soil. The rate of erosion is higher in Sloppy soil compared to undulating soil. Soil destruction is higher in sloppy soil flat or undulating soil. While sheet erosion is more on flat soil.
- Agricultural Practice: agricultural practices such as clean clearing, slashing, weeding, and deforestation help speed up the rate of runoff on the soil. These agricultural practices lead to excesses remover of vegetative cover leaving the soil empty and prone to water and wind erosion.
- Deforestation: This is the cutting down of mature trees for agriculture and lumbering purposes. Cutting down trees has helped to speed up the rate of soil erosion. Afforested feed resists water runoff making it difficult for surface water and wind to detach and carry away the soil particles. Deforested soil is more prone to erosion than affected soil.
- Road Construction and Urbanization: Road construction and Urbanization involves the use of heavy farm machinery and implements leading to the destruction of soil structure. During road construction vegetation and trees are completely removed and topsoil predisposing the soil to erosion.
- Climate changes (global warming): the negative impact of climate changes speeds up the rate of soil runoff. Variations in the rate of rainfall, temperature, and wind weaken the soil structure and increase the surface runoff.
- Bush Burning: bushing burning leads to the destruction of the vegetation and soil structure. These completed destructions of the soil structure predispose the soil to water and wind erosion.
Control of Soil Erosion
Soil erosion control refers to various approaches or measures taken to reduce the impact of raindrops, increase soil resistance, and reduce runoff on the land. Similarly, these are actions taken to reduce the causative effect of soil erosion. Some of the measures taken to prevent the action of erosion according to the West Africa Examination Council, (WAEC, 2009) on agricultural production are.
Cover Cropping
This involves the growing of crops such as sweet potatoes (root crop), cowpea, (legume crop), grasses such as carpet grass, and legume pastures such as centrosema, tropical kudzu to provide ground cover. These crops, grasses, and pasture serve as spread to form a canopy on the soil surface. The roots of these crops bind the soil together which helps to reduce surface runoff and reduce the force of flowing water and wind. The leaves of these cover crops adequately cover the soil intercepting the adverse effects of rain and water. The practice of planting cover cropping serves as a windbreaker thereby reducing wind from carrying the soil particles away.
Terracing
Terracing is a process of breaking a slope into a series of ridges or steps to reduce the speed of surface runoff, and channel water into a specific outlet. These ridges are constructed along a contour so that each of them is of uniform height, but different from those above it or below it. This is done to reduce the length and gradient of the slope and hence reduce the speed of runoff. Water collected on each gentle slope runs across the field rather than down. Each terrace has a drainage channel that empties into grassed water which leads the water down the slope to a nearby channel. Terracing is an erosion management practice aimed at reducing the effect of surface runoff or control.
Contour Plouging
This involves performing tillage on a contour and planting crops along the contour point. Poughing of the land is usually carried out after the contour has been surveyed and the contour has been located. The contours are constructed to run along the slope of the land. The crops are along the slope but not across the slope as many people perceived it to be. The contour ridges are constructed in a pattern, which runs across the slop to intercept water in between these contours, thus reducing the rate of surface runoff and promoting soil conservation.
Strip Cropping
Strip cropping involves the growing of two or more crops in alternate strips across the slope to check off erosion. It involves planting crops in rows along the contour interspersed by rows of uncultivated areas or follow, to serve as a vegetative barrier to the runoff or erosion. Strip cropping is carried out in combination with contour cultivation and crop rotation to achieve good results. The two alternate strips of cropping are erosion-resisting crop and erosion-permitting crops growing together in the same row on the same slope, perpendicular to the wind or water flow such that when the soil is detached from the row crops by the force of wind or water, the dense soil resisting crops will intercept the soil particles, therefore, preventing reduce runoff.
Mulching
Mulching involves the use of materials such as dry grasses, crop residue, polythene sheets, and sawdust to cover the surface of the soil to reduce the speed of surface runoff. These materials spread evenly onto the ground help to absorb and reduce the impact of raindrops on the soil surface. Mulching materials when decay helps to improve soil structure and prevent soil erosion. Soil that is adequately covered helps to reduce temperature and cool the soil making it impossible for wind erosion to impact the soil surface. The overall benefit of the mulching reduce the impact of splash and sheet erosion which are starting points of rill and gully erosion..
Construction of Drainages.
This involves the construction of drainages at the boundaries of the farm to remove or divert excess water from the field. Drainages are constructed to prevent water runoff from wearing away the top soil and its nutrients. There are many types of drainages that can be constructed on the farm. These include open channels or underground channels, and the laying of Pipes along the slope to carry the water straight down into the reservoir.
Afforestation
Afforestation is the cultivation of trees in places where forests have not been established before. In arid and humid regions. Afforestation is considered a practice of controlling wind and water erosion. Afforestation helps to reduce the rate of wind erosion thereby serving as a windbreaker. The leaves and litter from the forest decayed improving the soil structure. The roots of trees also help to bind soil particles together which helps to reduce soil erosion.
Intercropping
This is another measure aimed at controlling soil erosion. Intercropping will help reduce the impact of soil erosion, for example, the cultivation of legumes and other crops on the soil will reduce the impact of wind and water erosion on the soil. For example, the cultivation of legumes and their crops on the field will serve as canopy cover, bind the soil together, and reduce the effect of surface runoff.
Mixed cropping
Mixed cropping ensures adequate utilization of the soil. The planting of different types of crops on the soil ensures adequate ground cover preventing erosion of the soil. These different types of crops have helped to bind the soil particles together and reduce the overall effect of erosion. Crops such as legumes in the field help to reduce the overall impact of wind and water erosion.
Tillage Practices
Tillage practice which involves the manipulation of the soil into fine tilt such that it is adequate to receive seed if properly executed can help reduce surface runoff. Tillage practices help to improve infiltrations and reduce soil erosion. Different types of tillage tillage exist in agriculture for the control of surface runoff.