Ways through which soil nutrients are lost
Soil nutrients are lost in many ways. The most common ways of soil nutrient loss
1. Leaching 4. Erosion
2. Crop removal Burning 5. Oxidation and reduction
(a) Leaching: This is the removal of nutrients out of the reach of lant roots by percolating water. It is common in areas wilh heavy rainfall, loose soil particles and sparse vegetation.
Primary nutrients such as nitrogen, phosphorus and potassium are lost under hash rainfall condition. they dissolve easily in water. So leaching is a natural way whereby the soil losses it’s nutrient
(b) Crop removal: Soil nutrients are used by crops for growth and development. Farmers harvest the crops as tubers, seeds, fruits and vegetables. These are used by man for food and other purposes. The nutrients taken up by plants are lost completely from the soil. This is because the harvested parts of crops are not returned to the soil through decay. So harvesting crops and not trying to turn the residue of the crops that are harvested into organic manure or compost farmyard manure tends to lose the nutrients of the soil
(c) burning: 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.
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.
(d) Erosion: 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 oxidised 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.
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 tho’se 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 mav 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.
(c) Vegetative cover: 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.
3.2 Soil erosion
Erosion is the removal or wearing away of the surface soil by different agents. These agents are:
1. Water 4. Ice
2. Wind 5. Man.
However, water is the major agent of erosion in Nigeria.
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 hen Hows 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 panicles 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 slopy and the soil loose, large gullies are easily formed.
2. Prevention and control of erosion
Prevention and control of erosion can be achieved through the following practices:
(a) Covering the land with vegetation: 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.
(a) Crop rotation: A 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 Miirad over the soil surface.
(c) Application of organic and inorganic manures: 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.
(d) Mulching: This involves covering the soil with mulch materials such as papers, grasses and stones. It prevents direct contact 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.
(e) Preventing bush burning: Setting the bush on fire destroys the coverings for 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.
(f) Preventing overgrazing: Overgrazing 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 piosion 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 pitision 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.
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