Tag: Environment,Integrated Science,Soil Studies

Erosion may mean the wearing or washing away of something. Some of the forces which make soil can also erode the soil so that it is lost to the farmer.

Therefore, soil erosion is the removal oftop soilby agents of soil erosion, such as rain, wind and flowing water. Soil conservation can be defined as the science and art of looking after the land in such a way that soil is retained in one place and not carried away by agents such as water, wind, and animals, including man.

Erosioninvolves the transport of weathered material. Wind, glaciers, rivers and seas all play a part in moving rocky debris and soil. They are called carriers. The material being transported can also cause further erosion by abrasion (rubbing).

Eventually the eroded material is deposited as pebbles, sand or mud. This happens as a result of gravity when the carrier slows down. As the wind drops, for instance, the dust settles. Rock debris will be eroded, transported or deposited by a river depending on the different speeds at which the river is flowing. For example, coarse sand will be eroded by a fast-flowing river. It will be transported by a slow-flowing river, and deposited by a very sluggish river. Rivers deposit sand and gravel when they lose speed:

• on the inside curves of rivers, and
• when a river flows into a lake or the sea.

Types of Erosion

There are different types of soil erosion, namely: water erosion, sheet erosion, rill erosion,gulley, sedimentation, and wind erosion. Now let us look at what is involved on each one of them.

Water Erosion:This is usually caused by‘run offwater which carries top soil away.

Sheet Erosion:This is where water removes a thin layer or‘sheet’of soil, from sloping land. It is also called‘splash erosion’because heavy rain drops first loosen the bare soil and then soil is transported by running water down the hill.

Rill Erosion:A rill is a tiny channel in the soil made by running water. Rills remove the valuable top soil. If not stopped, they can soon become deeper and remove sub soil as well.

Gulley Erosion:A gulley is a deep channel made by running water. Gullies can develop from small hills with heavy rains on the steep slopes.

Sedimentation:Sediment is made of soil particles which are picked up by moving water, Sedimentation occurs when these soil particles are deposited on the lower land as the water stops moving. The sediment may be enough to cover crops growing in lower areas, and may fill reservoirs and ditches. It may also spoil low land soil by covering it with poor sediment sand.

Erosion by Wind and Sun:When soil is left bare, it is quickly dried up by the sun. The sun also destroys the humus which holds soil together. After this, the wind blows away the soil.

Causes of soil erosion

Soil erosion is caused by any of the following:

(a)Overgrazing-This is the result of overstocking or keeping a few animals on a piece of land for a very long time.

(b)Over cropping (over cultivation)– The same crop is repeatedly grown on a piece of land without rest. The organic matter content and soil fertility run down and, as a result, crops grown cannot form a dense cover. When it rains water erodes a lot of soil.

(c)Removal of vegetation– Careless removal of vegetation such as cutting down forests (deforestation) and burning bushland can lead to erosion. The vegetation which acts as a barrier against soil erosion is lost.

(d)Improper farming methods, such as:

(i) ploughing along the slope, i.e. ploughing up and down sloping land

(ii) planting crops along the slope

(iii) planting annual crops on very steep slopes

Methods of controlling soil erosion

There are many ways of controlling erosion so that soil can be conserved. Some of the ways are by following good methods of farming.

Erosion controlis the practice of preventing or controlling wind or water erosion in agriculture, land development, coastal areas, river banks and construction. Effective erosion controls handle surface runoff and are important techniques in preventing water pollution, soil loss, wildlife habitat loss and human property loss. The ways by which soil may be conserved, are:re-forestation, late burning, correct stocking, crop rotation, using cover crops, inter-planting, mulching, winter ploughing, contour farming and terracing (Bench terracing).

1.Construction Erosion Control

A major component of construction is the clearing and grading of land, which exposes, disturbs, and moves the soil. This inevitably increases an area’s susceptibility to erosion. Since in these situations it is not feasible to eliminate all erosion risk factors and, thus, all erosion, the goal of implementing erosion control measures is primarily to minimise erosion.

The benefits of implementing effective erosion control measures include the reduction of soil washed off-site and reduced clogging of streets and drainage systems, as well as reduced damage to adjacent properties. There are several best management practices that can be implemented to reduce erosion in construction sites and minimise movement of sediment into drainage systems.

When soils have been disturbed, erosion can be minimised with one or more of the following treatments.

2.Vegetative Cover

Vegetative cover is efficient in reducing erosion and is a relatively inexpensive erosion control measure. Vegetative cover provides a canopy that covers the soil from the impacts of wind and water energy and a rooting system that holds soil particles together. Dense and short vegetative covers like grass are often more effective than tall and sparse vegetation for control of water erosion. Dense vegetation covers the soil surface and reduces the impact of energy of falling rain. On the other hand, dense and tall vegetative covers are more effective than short vegetation for control of wind erosion. This is because tall vegetation, depending on the wind speed, reduces the wind velocity, therefore, reducing its erosive energy.

(a)Maintaining or Preserving Vegetation:

Existing vegetation is the best antidote for erosion. Trees, shrubs, and grasses that do not interfere with the construction process should be left undisturbed or maintained to minimise damage. The more vegetation area that is preserved the less area exposed to erosion.

(b)Planting New Vegetation:

In areas of housing development, it is important to establish permanent vegetation to minimise soil exposure to water and wind erosion. Vegetation/plants that have fibrous root system with fast establishment of roots and ground cover are good options (see suggested list of shrubs).

Temporary Seedingis the planting of grasses or plant materials that will quickly germinate and grow into protective cover for the soil until a permanent planting is established. Temporary seeding is recommended during the land grading and construction processes. Rapidly growing plants such as annual grasses, small grains, or legumes are appropriate temporary seeding options. Temporary seeding protects the soil and reduces mud and dust produced during construction. Thus, it is a short-term erosion control measure (Less than 1 year).

Permanent Seedingis the establishment of the appropriate grasses or plants in the construction sites. Unlike temporary seeding, permanent seeding requires that the construction phase be complete. Only then more appropriate and/or desired plants are established. Thus, permanent seeding is for long-term control of soil erosion. If the season is not appropriate for permanent seeding, temporary seeding options are often considered to minimise bare soil exposure until permanent seeding can be done. Either temporary or permanent seeding can be done through hand seeding and/or hydroseeding. Hydroseeding is done if the land is especially steep and irregular for hand seeding.

(c)Mulching

Similar to seeding, mulching is a method of applying plant or non-plant materials to cover bare soil surface. The main goal of mulching is to protect the surface of the soil from the impact of erosive forces. In construction sites, mulch can be placed to minimise wind and water erosion. However, the type of mulching selection depends on the land (i.e., slope). Heavy and large sized mulch would be more appropriate for a steep slope. In steep or gentle slopes, matting can be done to hold the mulch in place and reduce its movement by wind or water.

Aside from protecting the soil from erosion, mulching conserves water and reduces soil temperature fluctuations. If the mulch is plant-based or organic, it also increases the soil tilth. For a table of the advantages and disadvantages of various mulch types, click the button below.

(d)Silt Fencing

Silt fencing is a temporary barrier placed along the perimeter of a construction site. Silt fence does not serve to prevent erosion; rather, it traps soil or sediment from leaving the perimeter of the construction site. To be effective, silt fence must be constructed carefully and be in place before construction begins. Silt fences are primarily intended for trapping sediment from water erosion. They are less effective for wind erosion because they are not tall enough barriers.

(e)Impoundments

Impoundments are man-made ponds or lakes constructed to control storm run-off and/or trap sediments. Before soil or sediment reach the drainage system, detention ponds can be placed to trap and settle sediments. This in effect is NOT an erosion preventive measure but a measure to minimise the already detached or eroded soil from entering waterways. It is a sediment control measure.

There are two kinds of impoundments: permanent ones called retention ponds and temporary ones called detention ponds.

A good example of a retention pond is Holmes Lake, which receives storm sewer water and runoff from the City of Lincoln. Holmes Lake serves to retain sediments before the water drains into Antelope Creek, Salt Creek, and eventually into the Platte River.

Detention ponds are small in area because they drain a relatively smaller area. Because construction changes the topography, or lay of the land, drainage characteristics of the land change. Detention ponds are often constructed during road or building construction because the removal of topsoil and compaction reduces water infiltration into the soil and increases the risk of runoff. In addition, paved roads and streets are impervious to water and often become a conduit for runoff and sediment to move into drainage systems.

(f)Wetlands

Wetlands are areas that are frequently saturated by surface water or groundwater, staying wet at least part of the year (i.e., swamps, bogs, fens, marshes, and estuaries). Wetlands are often natural but can also be constructed. Wetlands are effective at controlling sediment and filtering nutrients and other chemical pollutants because they are a biologically active system.

Soil fertilityis defined as the ability of the soil to produce and sustain high crop yields indefinitely. In other words, fertility is a measure of the available nutrients in the soil and the proportion in which they occur. The soil is able to do this only if it can adequately supply the nutritional requirement of the crop plants in question.

A.Factors contributing towards soil fertility

Some of the factors are as listed below:

1. Soil depth- deep soils afford plant roots greater volume to exploit.
2. Good drainage to avoid water logging.
3. Good aeration to promote healthy root development and functioning.
4. High water-holding capacity
5. High level of nutrients
6. Soil pH.
7. Freedom from pests and diseases

In farming soil fertility may be lost in many ways. The common ways include the following:

1. Soil erosion by either water or wind
2. Soil capping: formation of an impervious layer of soil on the surface of the soil which obstructs rain infiltration leading to run off.
3. Development of hard pans short distance below the surface of the soil which impedes water percolation as well as root penetration. Hard pans may be caused by repeatedly ploughing at the same depth.
4. Loss of organic matter through rapid oxidation by soil micro-organisms due to unduly too frequent cultivations.
5. Leaching, especially serious with such nutrients as nitrogen which are highly soluble in water.
6. Loss of nutrients through sale of farm produce off the land without replenishing the nutrients removed in the produce.
7. Weeds. These compete for nutrients and moisture.
8. Alteration ofsoil pH, such as through misuse of certain fertilisers.
9. Build-up of soil pests and diseases by practicing certain systems of farming such as monoculture.

B.Plant Nutrients

In plant nutrients, you may discover that certain elements are essential for plant growth. Those being required in the largest quantity are known as major or macro elements while those needed in small amounts are known as minor or micro elements, and those needed in very minute quantities are known as trace.

The elements needed in large amounts are carbon, hydrogen and oxygen, obtained mainly from air and water. Nitrogen, Phosphorus, potassium, calcium, magnesium, sulphur and iron are obtained from the soil dissolved in water, or from application offoliar sprays. Essential trace elements are copper, manganese, zinc,molybdenum,boronand chlorine which can be made available to plants either through their roots or their leaves.

The table below summarises the importance of major and minor nutrients to the plants, deficiency symptoms and their sources.

Table 3.3

C.Inorganic fertilisers

As for Inorganic Fertilisers, these are artificially made fertilisers which are manufactured to supply the chemical nutrient needs of plants. The proportions of the main contents are stated on the container. Fertilisers which supply one main element such as nitrogen, phosphorus and potassium are known as straight fertilisers. Those containing mixtures in definite proportions are known as compound fertilisers.

The table below shows examples of straight fertilisers:

(a)Nitrogen

Phosphorus

(c).Potassium

It is necessary to note that top dressing fertiliser is sometimes applied with fertilisers of nitrogen. Plants, which are adequately supplied with potassium, are better able to withstand drought conditions than those suffering from a shortage.

On the other hand, Compound fertilisers are fertilisers containing more than two major elements along with minor elements. They are mostly applied as basal dressing fertilisers.

The table below shows the percentage constituents of Nitrogen, Phosphorus and potassium present in the different compound fertilisers

D.Organic Fertilisers

As for organics, these are the waste and residues of plants and animals. These organics can be in many forms such as poultry manure, cow dung/animal manures, farm yard manure, green manure and compost. They are natural manures and their decomposition is achieved by bacteria to form humus. Organic manures have bad and good effects on the soil.

There are four main components of soil, which are: those resulting from the breakdown of rocks, organic matter, water and air. In addition, soil contains microbes or micro-organisms.

Soil is made up of inorganic particles of different sizes such as stones, sand, silt and clay. Each of these is surrounded by microscopic film of moisture in which nutrients are dissolved. These particles aggregate together to form larger lumps of soil crumbs about l-5cm diameter. The presence of organic matter facilitates the formation of soil crumbs. The presence of these crumb structures indicates the ideal soil structure for cultivation and planting. If thesoil textureis too friable, then the roots will not be held firmly and crops will fall over, be blown or knocked out of the soil.

Water and Air

Water comes down from the soil surface trickling between the soil particles and the soil crumbs. Some water will be held but there are some spaces filled with air (soil contains water and air). Roots of crops penetrate the soil always by growing downwards (the direction of gravity). The roots touch the nutrient solution; roots take in water and they take the nutrient solution as food. Scattered about the soil are the soil organisms and dead plant and animal remains.

Air is not solid or liquid, but a combination of gaseous elements that are found naturally in Earth’s atmosphere. In soil, air pockets allow water to pass through the soil and into the plants growing above and below the soil line. Water in soil usually contains dissolved salts and other chemicals. Water is an essential part of components of soil; plants cannot survive without it. Some soils, like clay, retain water much better than others. When water lingers in soil instead of passing through it easily, the soil becomes more densely packed. Some plants cannot grow in heavy, moisture-rich clay soils.

Minerals

All soil is composed of sand, silt and clay, though some types of soil have heavier concentrations of these minerals than others. Rocks and minerals make up the largest chunk of soil’s composition. The rocks and minerals found in soil come from non-living, inorganic materials. Sand comes from small fragments of quartz and other minerals, and by itself is not rich in the nutrients that plants need.

Sand is the largest and coarsest of soil particles; water passes through sand more easily than other soil types. Silt is a combination of quartz and other rocks. Silt particles are smaller than sand but larger than clay. Clay is the richest of soil minerals, containing nutrients like iron, potassium and calcium. The smallest soil particles come from clay, which can become very dense and hard to work.

Organic

Decayed plants and animals provide the organic materials found in soil. Through decomposition, organic materials are broken down and turned into nutrients that plants can use. Mineralisation also occurs through decomposition, and through this process organic materials become inorganic.

Biological Materials

The fifth of components of soil, which is not always recognised, is the living world that exists under the ground i.e., the biological component. Bacteria and fungi are microscopic organisms; those living in the soil decompose and are beneficial (but there are many others which cause diseases).

The biological world, provides these important organic elements that are so essential. Plants and animals, when they die, become part of the ground once more, and so the cycle continues. Soil gives life; life gives itself back to the soil.

All parts of soil are essential to plant development, and each is necessary for plants to survive. The composition of the components of soil varies to create different soil types. Soil that is classified as clay, for example, contains more water than light, sandy soils.

Experiment:

Carry out experiments to show that the components of soil include organic matter, air, water, and rock particles.

You may find the following materials useful in your experiment. These are:

Samples of garden soil, scale, water, clear plastic or glass bottle, cans, Bunsen burner/charcoal brazier, cotton wool, funnels, stirring rod, etc.

After carrying out theexperiment, now answer the question below:

Describe the importance of the following components of soil to a growing plant: –

(i) Rock particles

(ii) Soil water

(iii) Soil air