1) Soil pH
- It affects the growth of plants.
- It also affects the availability of soil nutrients to plants.
- It affects the presence of soil microorganisms.
- It causes toxicity to plants and animals in the soil.
2) Soil Texture
- It determines the type of soil in an area.
- It determines the level of soil fertility.
- It determines the type of crops to be grown.
- It affects the level of leaching and erosion.
3) Soil Structure
- It determines the fertility of the soil.
- It determines the water-retaining capacity of the soil.
- It determines the level of soil organisms.
- It determines the level of soil aeration and percolation.
- Topography refers to the shape of the land in relation to the underlying rocks of the earth’s surface.
- Steep and gentle slopes give rise to soil erosion.
- Steep and gentle slopes may also aid the weathering of rocks.
- Even or flat slopes can lead to accumulation of soil.
- Even or flat slopes can be better sites for intensive farming.
5) Soil Fertility
- Fertile soil aids the production of food and cash crops.
- Fertile soil leads to the production of forage crops and plants for grazing.
- It minimizes the use of fertilizers and manures.
- It leads to multiplication of beneficial soil organisms.
- Fertile soil generally leads to reduction in cost of production.
6) Soil Types
- Soil types include sandy, clay and loamy soil.
- Loamy soil is rich in soil nutrients, hence it is the best soil for agriculture.
- Sandy soil does not contain enough nutrients, hence it cannot support crop growth.
- Sandy soil encourages leaching and prevents soil erosion.
- Clay soil encourages water-logging and erosion but prevents leaching of plant nutrients.
7) Soil Erosion
Soil erosion is defined as the wearing away of soil by means of natural agents such as water, ice or glacier, wind and animals.
Erosion takes place for a long time and it is greatly influenced by the following factors:
- Soil properties.
- Human activities.
Agents of Soil erosion: Agents of soil erosion are mainly water and wind.
- Water: Rainwater tends to run off the surface of the soil in deforested or over-grazed areas, thereby removing the top soil. Run-off is the rainwater which does not sink into the soil but flows away over the surface of the soil into streams, rivers or oceans.
- Wind: Wind is capable of moving large quantity of soil and sand. The faster the wind moves, the more it can carry. Wind-caused erosion occurs in dry areas where the soil is bare and loose.
Types of Soil erosion
There are four major types of erosion. These are:
- Splash erosion: Splash erosion is the removal of top soil from a small area due to the forceful fall of rain. The soil particles scattered by the rain-drops will succeed in blocking soil pore spaces against percolation, resulting in sheet erosion.
- Rill Erosion: Rill erosion occurs when raindrops falling on the soil surface cause the gradual removal of soil particles in suspension along narrow tracks or channels either already existing or caused by the rainwater itself.
- Sheet Erosion: When raindrops cause particles to block soil pores against percolation, floods follow. When the flood water flows uniformly over a piece of land, especially over a gentle slope, the fertile surface soil over the whole piece of land is washed away.
- Gully Erosion: Gully erosion occurs when rain water does not all sink into the soil and part of it runs off over the soil surface, removing soil particles along its way. Gully erosion is worse if the speed of the run-off is high, if the land is sloppy and the soil is loose. This continuous removal of soil particles along a particular course results in the cutting of a narrow ditch which will continue to deepen and widen as water flows along it until deep trenches on the land surface called gullies are formed.
Prevention and Control of Soil Erosion Soil conservation practices that can be used to control erosion on a gentle slope:
- Contour ploughing
- Ridging across the slope.
- Construction of drainage channels.
- Cover cropping/ Afforestation/ High density planting.
- Strip cropping.
How each practice can be used to conserve the soil
- It is a practice in which the slope is broken into series of steps or platforms.
- Each platform or step is constructed along a contour so that each of them is on uniform height, but different from those above or below it.
- It is done to reduce the length and gradient of slope and hence reduce the speed of run-off.
- Water collected on each gentle slope runs across the field rather than down.
- Each terrace has a drainage channel which empties into a grassed waterway which leads the water down the slope to nearby channel.
2) Contour ploughing
- The slope is first surveyed to locate contour points.
- Ploughing is now done along the contours joining all areas along each contour.
- These contours are running across the slope of the land.
- Plants are established along the contours and not across.
- It is an effective way of preventing soil loss and hence promoting soil conservation.
3) Ridging across the slope
- Flood water will normally run down along the slope of a land.
- Ridges constructed should be across the slope to block the run-off water.
- Such ridges will also help to trap the water into small reservoirs which will sink into the soil.
- It can be practised by every farmer without much technical know-how.
4) Construction of drainages
- Drainages are means of getting rid of excess water in the field.
- Many types of drainages are available. They may be open channels or underground channels.
- Pipes are laid along the slope to carry the water straight down into reservoirs below, thus preventing soil erosion or loss.
5) Cover cropping/Afforestation /High density planting
- The principle is not to allow the surface to be exposed to agents of erosion e.g. wind, water.
- The slope is planted with cover crops or other crops to trap or retard any run-off water.
- They also promote the percolation of such water which has been retarded in its flow.
- It involves planting of forest tree/other crop species to also trap and intercept water/dust from wind and thus protect the soil surface, especially in the arid areas.
- Their leaves decay and enhance soil fertility, thereby encouraging more growth of other species.
6) Strip cropping
- Planting of crops in rows along the contour interspersed by rows of uncultivated area or fallow, to retard water run-off across the slope.
- It also entails planting of different crops with different growth characteristics in alternate rows along the contour and across the slope to check run-off.
- Mulching is the act of covering soil surface with such materials as dry grasses, crop residues and polyethylene sheets.
- It reduces the impact of rain drops on soil.
- It reduces the speed of run-off.
- Decayed mulch improves soil structure and so helps check soil erosion.