Chapter 17 Conservation of Soil and Land

NIOS Class 12 Environmental Science Chapter 17

INTEXT QUESTIONS 17.1

1. Define soil.

Ans: Soil is the uppermost layer of the earth’s crust, which can be dug or ploughed, and in which plants grow.

2. Name two natural agencies which cause soil erosion.

Ans: Water and wind.

3. What is coastal erosion?

Ans: Coastal erosion is caused by the wave action of the sea and the inward movement of the sea into the land.

4. What is surface creep?

Ans: Surface creep refers to the transport of soil at ground level by high velocity winds.

5. How does wind erosion damage roads and agricultural fields?

Ans: Wind erosion damages roads and fertile agricultural fields by depositing large quantities of air-blown soil particles.

INTEXT QUESTIONS 17.2

1. Name any three human activities which cause soil erosion.

Ans: Certain human activities accelerate soil erosion.

• Deforestation
• Farming
• Mining
• Developmental work, human settlements and transport.

2. What is monoculture?

Ans: Monoculture refers to the practice of planting the same variety of crop in the field.

3. Why monoculture may lead to soil erosion? State one reason.

Ans: Monoculture practices can lead to soil erosion in three ways.

• (i) A monoculture crop is harvested all at one time, which leaves the entire field bare, exposing it to both water and wind.
• (ii) Without vegetation, natural rainfall is not retained by the soil and flows rapidly over the surface rather than into the ground. It also carries away the topsoil which results in soil erosion and degradation.
• (iii) In the event any disease or pest invades the field, the entire crop is usually wiped out, leaving the bare soil susceptible to water and wind.

3. How does building construction soil erosion?

Ans: Building construction also promotes soil erosion because accelerated soil erosion takes place during the construction of houses, roads, rail tracks, etc. The construction of such facilities causes massive disturbance to the land, resulting in soil erosion and disruption of the natural drainage system.

INTEXT QUESTIONS 17.3

Give one to three words for the following:

1. The loosening and displacement of topsoil particles from land.

Ans: Soil erosion

2. The deterioration in the quality of land results in a reduction of crop productivity.

Ans: Land degradation

3. The first phase of soil formation, which is a physico-chemical process that leads to the breakdown of rocks into their mineral constituents.

Ans: Weathering

4. The erosion of soil from the banks of rivers due to flowing water. Stream bank erosion. 

Ans: Sheet/ wash off erosion

5. Man-made varieties of agricultural plants, fodder plants, forest trees, livestock and fish that have been raised and modified by us by means of various breeding techniques in order to increase productivity.

Ans: High-yielding varieties/ HYV

6. Toxic chemicals are used to kill organisms that are pests.

Ans: Biocides

7. The progressively increased concentration of chemicals in organisms through the food chain.

Ans: Biomagnification

INTEXT QUESTIONS 17.4

1. How does polyvarietal cultivation prevent soil erosion?

Ans: Polyvarietal cultivation also helps in controlling soil erosion. In this method, the field is planted with several varieties of the same crop. As the harvest time varies for different varieties of crops, they are selectively harvested at different times. As the entire field is not harvested at one time and so it is not bare or exposed all at once, and the land remains protected from erosion.

2. Out of the ladybird beetle and the cottony cushion scale (Icerya purcahsi), which is the pest and which the predator?

Ans: 

• Pest: (Icerya purcashi)
• Predator: Ladybird beetle

3. How do microbes resist soil erosion?

Ans: Microbes in the soil decompose the organic matter and produce polysaccharides, which are sticky and act in glueing in the soil particles together and thus help the soil to resist erosion.

TERMINAL EXERCISE

1. Define soil erosion.

Ans: Soil erosion is the loosening and displacement of topsoil particles from the land. Soil erosion is a natural process that occurs on all lands.

2. State the difference between geological and accelerated erosion with respect to (i) rate and (ii) cause.

Ans: 

• Geological erosion is a slow process caused by natural physicochemical factors such as wind and water. 
• Accelerated soil erosion is a faster process caused by human activities or natural causes like floods. 

3. What are the various ways in which water erosion takes place? Give details of any one of the three.

Ans: Soil erosion by water occurs by means of raindrops, waves or ice. Soil erosion by water is termed differently according to the intensity and nature of erosion. 

• (i) Raindrop erosion: Raindrops falling on the land surface cause the detachment of the soil particles. The loose soil particles are washed away by flowing water. Raindrops thus initiate water erosion.
• (ii) Sheet erosion: The detachment and transportation of soil particles by flowing rainwater is called sheet or wash-off erosion. This is a very slow process and often remains unnoticed.
• (iii) Rill erosion: In rill erosion, finger-like rills appear on the cultivated land after it has undergone sheet erosion. These rills are usually smoothed out every year while forming. Each year, the rills slowly increase in number, become wider and deeper. When rills increase in size, they are called gullies
• (iv) Stream bank erosion: The erosion of soil from the banks (shores) of the streams or rivers due to the flowing water is called bank erosion. In certain areas where the river changes its course, the river banks get eroded at a rapid rate. Stream bank erosion damages the adjoining agricultural lands, highways and bridges.
• (v) Erosion due to landslides: Sudden mass movement of soil is called a landslide. Landslides occur due to instability or loss of balance of land mass with respect to gravity. Loss in balance occurred mainly due to excessive water or moisture in the earth mass. Gravity acts on such an unstable landmass and causes the large chunks of surface materials, such as soil and rocks slide down rapidly.
• (vi) Coastal erosion: Coastal erosion of soil occurs along sea shores. It is caused by the wave action of the sea and the inward movement of the sea into the land.

4. How can soil erosion by water be prevented?

Ans: Prevention of soil erosion by water

• It is essential to retain vegetation cover so that the soil is not exposed to rain. Vegetation cover is important because the roots of plants hold soil particles together. Plants intercept rainfall and protect the soil from the direct impact of raindrops.
• Cattle grazing should be controlled.
• Crop rotation and keeping the land fallow (not planting anything in the soil for some time) should be adopted.
• Vegetation and soil management should be improved to increase soil organic matter.
• To prevent stream bank erosion, runoff water should be stored in the catchment for as possible by maintaining vegetation cover and by constructing dams for storing water.
• For the prevention or reduction of coastal erosion, protective vegetation along the beaches should be re-established. The best method of controlling coastal dune erosion is not to disturb the dunes and the coastal system. Further, construction of buildings and other development should be located behind the dune system.

5. What are the consequences of soil erosion due to wind?

Ans: Consequences of wind erosion

• Wind erosion removes the finer soil material, including organic matter, clay and silt, in a suspension (colloidal) form and leaving behind coarser, less fertile material. 
• Productive capacity of the soil is lost as most of the plant nutrients which remain attached smaller colloidal soil fraction are lost.
• Wind erosion also damages roads and fertile agricultural fields by depositing large quantities of air-blown soil particles.

6. Describe the several causes of soil erosion due to human activities.

Ans: Certain human activities accelerate soil erosion.

• Deforestation: Deforestation includes cutting and felling of trees, removal of forest litter.  Browsing and trampling by livestock, forest fires, also lead to deforestation, etc. Deforestation leads to erosion. Deforestation further leads to land degradation, nutrient and the disruption of the delicate soil plant relationship.
• Farming: Agriculture causes soil erosion through exposing the land to various processes, along with wind and rain.  It causes wash-off or sheet erosion. Moreover, the creeping effect of desertification sets in and the fertility of the land is lost progressively.
• Mining: Mining for minerals destabilises the soil, leading to soil erosion. 
• Developmental work, human settlements and transport: Soil erosion may also occur because of various developmental activities such as housing, transport, communication, recreation, etc. Building construction also promotes soil erosion because accelerated soil erosion takes place during the construction of houses, roads, rail tracks, etc. The construction of such facilities causes massive disturbance to the land, resulting in soil erosion and disruption of the natural drainage system.

7. In what way does land get degraded by the use of agrochemicals?

Ans: Agrochemicals are applied to the soil for two main reasons, namely to:

(i) replenish or replace soil nutrients by using chemical fertilisers.

(ii) destroy plant pests by using toxic chemicals called pesticides.

However, excess use of chemical fertilisers and pesticides leads to the following problems:

• Widespread imbalance in the soil nutrients: Most of the chemical fertilisers used in modern agriculture contain macronutrients like nitrogen, phosphorus and potassium (NPK). Excessive addition of NPK to the soil, however, causes the plants to absorb more micronutrients from the soil. As a result, soil becomes deficient in micronutrients like zinc, iron, copper, etc, and the soil productivity decreases.
• Eutrophication of water bodies: Fertiliser, which is not used by plants, is washed down with rainwater and carried into water bodies, resulting in eutrophication or algal bloom, leading to the death of aquatic life.
• Health problems: About one-fourth of the applied fertiliser is not used by the crop plants and is leached down into the soil and the underground water aquifer. The chemical which usually leaches down is nitrate, whose increased concentration in the drinking water may cause serious health problems. Excess nitrates in water are harmful, especially in bottle-fed infants in which can cause the disease, methaemoglobinaemia.

8. What are HYV? How do they degrade land?

Ans: HYV refers to High-Yielding Varieties. High-Yielding Varieties (HYV) have helped to increase food production, but at the same time, they have greatly impacted the environment. They are man-made varieties of agricultural plants, fodder plants, forest trees, livestock and fish. This means that the HYV have been raised and modified by us by means of various breeding techniques in order to increase productivity. The HYVs require adequate irrigation and extensive use of fertilisers, pesticides to be successful.

9. How can soil erosion and land degradation be prevented?

Ans: Soil erosion and land degradation can be prevented by these methods. 

 (a) Tree planting: To prevent wind erosion, trees should be planted in such a way that they break the

force of the wind. The trees not only cover soil from the sun, wind and water, they also help to hold the soil particles.

(b) Cultivation and farming techniques: Certain cultivation and farming techniques also reduce soil erosion. These include:

• (i) Cultivation of land at the right angles to the direction of wind helps to reduce soil erosion by wind.
• (ii) Ploughing style: The ploughing style substantially reduces the amount of erosion. Tilling the field at right angles to the slope, called counter ploughing in soil of the land, helps prevent or reduce soil erosion.
• (iii) Strip Farming: This is another method of soil erosion. This involves planting the main crops in widely spaced rows and filling in the spaces with another crop to ensure complete ground cover.
• (iv) Terracing: It is another method of reducing or preventing soil erosion on mountain slopes. In this method, terraces are created on the steep slopes. This is another way of preparing the fields for planting and preventing soil erosion. 
• (v) The time or season at which a field is tilled can also have a major effect on the amount of erosion that takes place during the year. If a field is ploughed in the fall, erosion can take place all winter long; however, if the ground cover remains until spring, there is not as much time for the erosion to take place.
• (vi) No-till cultivation is also used as a preventive method for soil erosion. Specialised machinery is available that can loosen the soil, plant seeds and take care of weed control all at once with minimum disturbance to the soil.
• (vii)Polyvarietal cultivation also helps in controlling soil erosion.
• (viii)Addition of organic matter to the soil is also an important method for reducing soil erosion.

10. Give an account of innovative agricultural techniques which prevent land degradation.

Ans: Conservation of cultivable land can be achieved not only through preventive and remedial measures in order to control land erosion and degradation, but also by using innovative agricultural technologies which involve the use of:

• (i) Organic farming or green manures: Instead of applying chemical fertiliser to supplement the nitrogen content of soil, we can use the natural process that involves the use of nitrogen-fixing bacteria in the legume root nodules. In addition to this, the use of organic forms of fertilisers, such as cow dung, agricultural wastes, also improves the nutrient status of soils. This may also help to reduce the excessive and prolonged use of chemical fertilisers and thus minimise their toxic effects.
• (ii) Biofertilisers: Micro-organisms are important constituents of fertile soils. They participate in the development of soil structure, add to the available nutritional elements and improve the physical conditions of soil. A large variety of microorganisms are being used as biofertilisers for improving the nutritional status of crop fields.

(iii) Biological pest control: The natural predators and parasites of pests play a significant role in controlling plant pests and pathogens. They are nowadays used by farmers to control or eliminate plant pests. The biological control agents of pests do not enter the food chain or poison animals and so are not likely to harm mankind. Biological control of pests is an ecologically sound alternative to chemical pest control.

Additional Study Materials

• Chapter 14 Global Environmental Issues
• Chapter 15 Biodiversity Conservation
• Chapter 16 Conservation of Other Natural Resources