Soils

A is correct. Alluvial soil is rich in all nutrients, and is renewed periodically due to flooding. It is intensely cultivated.

B is incorrect. The soils are poor in lime and silica due to leaching. Also, humus is eaten away by bacteria, thus the soil lacks organic matter.

C is incorrect. Black soil lacks phosphorus and potash.

D is incorrect. Forest soils are acidic and have low humus content.

Black soil is known as the regur soil, because of regurgigation. The soil ‘overflows’, that is, it swells up when water is poured into the soil.

Other options are incorrect.

Statistically, water erosion is responsible for the loss of topsoil in an adverse manner, due to the high velocity of rivers as they flow down the mountains.

Other options are incorrect.

Salinity from irrigation can occur over time whereverirrigation occurs; since almost all water (even natural rainfall) contains some dissolved salts. When the plants use the water, the salts are left behind in the soil and eventually begin to accumulate.

Other options are incorrect.

Soil is top-most layer of the earth, formed by years of erosion of the parent rock material. It is a mixture of debris and organic material, which sustains life by providing essential nutrients.

Formation of soil is affected by relief, climate, parent rock material, vegetation, duration of weathering and presence or absence of other life forms.

The three horizons of the soil are:

• Horizon A: It is topmost horizon, where organic matter and nutrients are present alongside water, to aid the growth of plants.

• Horizon B: It is the middle layer, with some organic matter, but no substantial mineral accumulation.

• Horizon C: It is the innermost layer composed of weathered parent rock material.

Soil degradation refers to the decline in the quality of soil. This is due to a loss of fertility and depth of soil, owing to disuse and erosion.

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Black Soils: Also known as Regur Soils, they are formed from erosion of volcanic rocks by lava flows. In India, it occurs in the Deccan Plateau, which includes parts of Madhya Pradesh, Gujarat, Maharashtra, Tamil Nadu and Andhra Pradesh.

Characteristics:

• These are clayey soils, and are generally very deep.

• They have the ability to SELF PLOUGH, that is, they are shrunk when dry, but swell up on absorbing water that makes them porous.

• They retain moisture for a very long time.

• They are rich in lime, iron, magnesia and alumina.

• They lack in phosphorus, nitrogen and organic matter.

• The colour ranges from deep black to grey.

Soil Conservation: It refers to the techniques employed to maintain the quality (fertility) of soil, and its depth. It involves prevention of erosion and improving the quality of degraded soil, without disrupting the ecological balance.

Measures to conserve soil:

• Lands with sloped from 15-25% should not be cultivated without construction of terraces.

• Over-grazing of soil should be prevented.

• Shifting cultivation should be discouraged.

• Villagers should be educated about the harms of over-grazing of grasslands.

• Mixed farming and crop rotation should be encouraged to avoid the loss of vital nutrients in the soil.

• Gully erosion should be prevented by building of check dams, gully plugging, terracing and planting cover vegetation.

• Shelter belts and agro-forestry should be constructed in semi-arid areas to prevent the formation of sand dunes.

• Lands which are unsuitable for cultivation should be diverted towards grazing.

Soil fertility refers to the ability of soil to support plant growth. Several factors influence soil fertility. In general, fertile soils are:

• Rich in nitrogen, phosphorus and potassium.

• Contain minerals like boron, chlorine and magnesium

• Presence of ample organic matter to retain moisture

• Presence of microbes and nitrogen fixing bacteria

Soil fertility might be renewed naturally by floods and overflowing of banks or culturally, by the use fertilisers and manure. Periodic replenishment is essential for sustenance and continued productivity of land.