SOIL AND WATER CONSERVATIONsoil erosion - causes, types and agents of soil erosion; water erosion - forms of water erosion, mechanics of erosion; gullies and their classification, stages of gully development; soil loss estimation - universal soil loss equation and modified soil loss equation, determination of their various parameters; erosion control measures - contour cropping, strip cropping, mulching; mechanical measures - terraces – level and graded broad base terraces and their design, bench terraces & their design, layout procedure, terrace planning, bunds - contour bunds, graded bunds and their design; gully and ravine reclamation - principles of gully control - vegetative and temporary structures; wind erosion - factors affecting wind erosion, mechanics of wind erosion, soil loss estimation, wind erosion control measures -
List the ways nutrients are lost in the soil
Enumerate factors that determine the degree of nutrient lossesExplain the meaning of erosion and describe the types of erosion
OUtline the various preventive and control measures of erosion.
Enumerate the ways through which soil water loss can be prevented.
Agriculture, farming, agricultural products and crops classification, cultural practices in agricultural science
Meaning of soil water conservationSoil and water conservation are those activities at the local level which maintain or enhance the productive capacity of the land including soil, water and vegetation in areas prone to degradation through
prevention or reduction of soil erosion, compaction, salinity;
conservation or drainage of water and
maintenance or improvement of soil
Conservation is regarded as planned use of any natural resources In order to avoid exploitation, neglect and destruction.
Soil conservation methodsThis is the use of soil without waste so as to sustain higher crop production yield.
It is aimed at preventing waste of the soil and depletion of its nutrients.
Soil conservation is important because plants depend on nutrients in the soil.
Animals indirectly depend on the soil for their feed. It is the soil that provides the medium for plant growth development and hence the sustenance of life.
1. Ways through which soil nutrients are lost,
Soil nutrients are lost in many ways. The most common ways are
3.Crop removal Burning
4. Oxidation and reduction
This is the removal of nutrients out of the reach of plant roots by percolating water. It is common in areas with heavy rainfall, loose soil particles and sparse vegetation.
Primary nutrients such as nitrogen, phosphorus and potassium are lost under such rainfall condition. They dissolve easily in water.
The burning of vegetation reduces soil fertility. This is because it exposes the surface of the soil to the agents of erosion such as water and wind.
Soil micro-organisms of agricultural importance are killed during burning. There is also break down of volatile nutrients like sulphur and nitrogen.
However, burning during farmland preparation can be used to control weeds. It eases the working condition of new farmland. The soil is sterilized. Soil acidity is reduced due to the presence of ash that contains alkali metals such as potassium, calcium, and magnesium.
Soil erosion causes loss of soil nutrients. When the top soil of farmland is removed by water or wind, the available plant nutrients are lost. Erosion is common in soil that is not covered by vegetation.
(e) Oxidation and reduction:
Oxidation and reduction reactions in the soil lead to loss of soil nutrients. For example ammonium radicals in the soil can be oxidized to give ammonia gas.
Nutrients such as nitrates may be reduced to nitrogen gas or nitrogen dioxide gas. The gases go into atmosphere resulting in loss of fertility.
factors affecting soil water conservation2. Factors that determine the degree of soil nutrient loss These are agents or circumstances that hasten or fasten the loss of nutrients from the soil. The Factors affect the ways the nutrients in the soil can be removed. The factors are:
1. The nature of the land or slope of the land.
2. The nature of soil, and
3. Vegetative cover.
4. Cultivation practices.
(a) Slope of the land:
The slope determines the speed at which water carries away particles. Soil particles contain nutrients which are used by plants. The nutrients arc removed faster in areas with steep slope than those with gentle slope. In most cases, the nutrients are washed to the lowland or valleys.
(b) Nature of soil:
The nature of soil in an area plays a role in the extent of nutrient losses that may occur.
The soil in an area may be sandy, clayey or loamy.
Sandy soil has loose particles and little organic matter and therefore easily leached by rainfall
Erosion is higher where the soil is sandy.
Clay and loamy soils have more organic matter and cohesion. The nutrients in these soil are not easily leached wind and water erosion are less.
using Vegetative cover in soil water conservation:
When the soil is covered by plants, the rate of nutrient loss is less. This is because the vegetation reduces the impart of rain-drops and wind.
The speed of run-off water is reduced thereby preventing the development of gullies.
The roots of plants help to bind soil particles. The temperature of the soil is also regulated as a result of the cover.
Above all, the dead vegetative cover crop adds organic matter to the soil, which is a major source of plant food. Where the soil lacks vegetative cover, it is exposed to wind and water that can carry away soil particles and nutrients.
Micro-organisms in the soil are reduced because of lack of organic matter. The soil is subjected to wide temperature fluctuation.
(d) Cultivation practices:
Continuous cropping leads to exhaustion of soil nutrients while over tillage exposes the soil to easy erosion by water and wind. 3.2 Soil erosion Erosion is the removal or wearing away of the surface soil by different agents.
These agents are: 1. Water 2. Wind 3. Animals 4. Ice 5. Man.
1. Types of soil erosion
There are four types of soil erosion depending on how the erosion occurs. These are:
1. Splash or raindrop erosion.
2. Sheet erosion.
3. Rill erosion.
4. Gully erosion.
(a) Splash or raindrop erosion:
This is the first stage of the erosion caused by rainfall. It is the removal of soil particles by little raindrops. The soil particles scattered by raindrops block the soil pores.
This will make it difficult for the rain water to the soil. The result is that the water will begin to flow gradually on the surface of the soil.
(b) Sheet erosion:
Sheet erosion follows splash. It occurs when raindrops cause soil particles to block soil pores. Rain water then shoves slowly over the soil surface.
The soil particles are then removed or carried away evenly. This can also be caused by wind. The wind blowing over the soil that is exposed can carry away soil particles uniformly and deposit them somewhere else":
(c) Rill erosion:
Sheet erosion develops into rill erosion. This occurs when raindrops on the soil surface cause gradual removal of soil particles in suspension along narrow channels.
The channels may be existing before^They could be caused by the rain water itself.
The size of the "channels, or rills becomes larger because of downward cutting. This eventually leads to gully erosion.
(d) Gully erosion:
Channels that cannot be smoothened out by ordinary cultivation are referred to as gullies. Gully erosion takes place when rain water does not sink into the soil, it therefore runs off over the land. The soil particles being carried by the rain water help to cut deeper and deeper into the soil.
Sudden drop in slope or channel increases the cutting power of the water. Where the land is very sloppy and the soil loose, large gullies are easily formed Prevention and control of erosion Prevention and control of erosion can be achieved through the following practices:
Covering the land with vegetation to conserve it:
Covering the soil with plants prevents the soil from being exposed to agents of erosion such as water and wind. The planting of cover crops is to maintain adequate ground cover. Soil fertility is also increased because of leaf fall. Water infiltration is encourage and run-off is reduced because of the vegetative cover.
the use of Crop rotation to manage soil water conservationA well designed crop rotation ensures that the land is always protected against erosion. Where legumes are included in the rotation, they help to control erosion because they Mirad over the soil surface.
how the Application of organic and inorganic manures helps in soil water conservation:
The addition of compost and farm yard manures make the soil cohesive and absorb water.' They also add plant nutrients to the soil. The addition of lime fertilizers such as calcium triococarbonate
(IV) to the soil causes loose soil particles to be bound together. This improves the structure of the soil and the soil cannot be carried a|way easily whether by water or wind.
AGRICULTURAL SCIENCE AND UNDERSTANDING BASIC AGRICULTURE AND FARMING FOR SCHOOLS
Agriculture, farming, agricultural products and crops classification, cultural practices in agricultural science
the use of Mulching in soil water conservation:
This involves covering the soil with mulch materials such as papers, grasses and stones. It prevents direct conduit tween the soil and raindrops.
Mulching increases water infiltration and reduces sheet erosion.
Where mulching is done with plant materials, organic is added to the soil.
This helps to bind loose soil particles together.
Preventing bush burning helps in soil water conservation:
Setting the bush on fire destroys the finesse of the soil. During bush burning, organic matter and many agriculturally important living organisms are destroyed.
The soil is therefore exposed to agents of erosion. Where bush burning is avoided, the organic matter and micro-organisms present help to improve the soil structure and control erosion.
Preventing overgrazing helps in soil water conservationOvergrazing of pasture or field could occur if animals are allowed to remain for a long time on the same land. Almost every vegetation in such a place is eaten up stud will not have time to grow again.
Such land is exposed to poison agents.
The feet of animals also destroy soil structure and cause the formation of hard layers or hard pans below the soil surface.
This makes infiltration difficult and increases surface run-off. Overgrazing by farm animals should therefore be avoided.
(g) Establishment of wind breaks:
The planting of trees prevents erosion by acting as wind breaks.
This is a good erosion preventive measure especially in the Savannah regions and where the soil is sandy.
(h) Contour strip cropping: This involves the growing of close ginning plants such as grasses and row crops such as maize in alternate strips across the slope of the land.
This ensure adequate cover for the land. It therefore reduces the speed of moving water and its load. DIAGRAM Figure 2.3.1: Contour Strip Cropping
the use of Terracing for soil water conservation:
These are embankments constructed across the slope at regular interval to conduct water from the land in such a way as to keep erosion under control. Terracing
types of terracingGenerally, there are two kind of terraces, that is, planting terraces and conservation terraces. The former is constructed mainly to facilitate harvesting, crop evacuation and maintenance operation apart from conserving soil and water. Planting terraces should slope inwards and there should be a vertical drop of about 50 cm between the lip and the rear of the terrace to trap run-off water. Regular stops along the terraces are also necessary for the same purpose.
The dimensions of terraces depend on the crops, planting density, slopes and whether future mechanisation will be implemented. In general, the terraces for oil palms should be more than three metre wide and the horizontal distance between two adjoining terraces (6.5 to 9.5 metres) will depend on the planting distance along the terrace and planting density. Similarly for rubber except that the terrace width is generally smaller at 2 metres or more. For cocoa, planting terraces are seldom constructed although it is now highly recommended. The terraces should be 2.5 to 3.5 metre wide with about 12 metres horizontal distance between two adjoining terraces. There is one terrace in every 3rd cocoa row; the other cocoa trees are planted on platforms.
They reduce the length of slope that may aid erosion.
Terraces are built in form of steps along the contour of the land or across the slope. DIAGRAM FIGURE 2.3.2:
LEVEL BENCH TERRACE
The construction of ridges during land preparation cross or tied ridges helps to control soil erosion. Ridges enhance water absorption by the soil and this reduces the speed of run-off.
(k) Construction of contour bounds:
The construction of ridges called bounds across the slope prevents soil erosion.
contour bounds prevent water run-off down the slopes.
(l) Erection of barriers:
Barriers can he created at intervals in gullies to reduce the speed of water run-off.
Dams of earth blocks, concrete or stones can be used to fill gullies already created.
These help to trap sediments which eventually fill the gullies. Wire netting can also be stretched across gullies. This helps lo trap grasses, soil and debris which gradually block the gullies.
4. Problems created by soil erosion
(a) Erosion reduces the nutrient content of the soil. As soil particles are detached and earned away by the agents of erosion, the nutrients are dissolved and washed away by water.
This renders the soil infertile, resulting in poor crop yield.
(b) Erosion washes away crops.
Crops planted in farms are at times uprooted and carried away by agents such as water.
This is very common where the farmland is sloppy.
(c) Erosion leads to soil destruction. erosion involves the detachment and transportation of soil particles from one area to another.
The top soil which supports crops is gradually removed. The subsoil left can also be broken into gullies making the land useless.
(d) The soil particles detached by erosion are deposited in rivers, reservoirs and dams. This results in water pollution and shortages. The soil particles can also be deposited on crops.
(e) The farmer spends time, labour and money to control erosion once it has occurred. This increases his cost of production, thus lowering his marginal profit.
(f) The water responsible for the erosion is lost. The water is no longer available for crop use.
4. Loss of soil water
Water is lost in the soil through many ways. These include:
(a) Transpiration: This is the loss of water vapour through the leaves of plants. The water is absorbed by the roots of plants and is then transported through the stem to the leaves. High temperature and wind increase the rale of water loss through inspiration.
This is the process whereby water leaves the soil surface into the atmosphere in form of vapour. As a result of heat. water changes form into vapour. The amount of water loss through evaporation depends on the temperature, wind, humidity and vegetative cover of the environment.
(c) Crop removal:
The roots of crops absorb water from the soil. The water is used by the crops for development and production.
the water taken up by crops from the soil is lost for ever as it is never returned to it again.
(d) Seepage or percolation:
This is the-down-ward movement of water through the soil. Soil water moves by infiltration from one layer to another. The water gradually goes into wells and under¬ground water.
The soil at times finds it difficult to absorb excess water. The excess water is removed from the soil when it flows over the land into streams, rivers and other natural water ways. The water is lost from the soil for ever.
Setting the farmland on fire to remove trashes contributes to soil water loss. Fire dries up moisture-from the dipper layer of the soil as a^result of the heat generated. The 'water cannot return to the soil again. Preventing loss of soil water Soil water loss can be prevented or minimized by carrying out the following practices:
(a) Maintaining vegetative cover.
Covering the land with plants presents excessive drying of the soil. It also prevents direct evaporation of soil water.
(b) Good cultivation methods:
This involves tillage. Tillage encourages the soil to absorb water and prevents run-off Contour ridging or ridging across slopes helps to reduce water movement down the slope and thereby encourages infiltration.
(c) Use of organic manure:
This refers to the addition of farm yard, compost or green manures to the soil. These provide cover for the soil. Organic manures bind soil particles together and enable the soil to hold water.
(d) Controlled burning practice:
The burning of the farm during land preparation should be done when no other way of disposing off farm trashes is available. This should be limited to areas where burning is very necessary.
The use of mulch materials to cover heaps, beds and ridges helps in conserving soil water, evaporation and excessive drying by the sun.
This helps to reduce the length of slopes and decreases run-off. Water infiltration is then encouraged.
(g) Use of wind break”
The planting of trees protects the soil against excessive drying by the sun and strong wind. The trees produce cooling effect on the soil.
(h) Regular weeding:
The removal of weeds from the farm reduces unnecessary transpiration. Enough water is therefore conserved for crop use.
(i) Breeding drought resistant crops: The development of crops that use little water will enable the soil to retain most of its water.
(j) Strip cropping:
This involves the growing in alternate strips of different crops in the same field. It ensures that the entire land area is not empty at the same time.
STUDY QUESTIONS 1. Enumerate five ways by which nutrients can be lost from the soil.
2. What are the factors that determine the extent of soil nutrient losses?
3. (a) What is soil erosion? (b) List the different types of soil erosion.
4. Outline five ways of preventing or controlling erosion in your school farmland.
5. Mention five problems erosion may have created for the farmer.
6. Enumerate five ways water is lost from the soil.
7. Outline six ways of preventing soil water loss.
8. Write short notes on the following: (a) Mulching (b) Leaching
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