Soil Chemistry and Contamination Questions and Answers

Q: Gypsum is :

Gypsum is calcium sulphate dihydrate, CaSO4.2H2O.It is a soft evaporite mineral. Heated to about 150 °C it loses three-quarters of its water and becomes plaster of Paris; it is also used to set cement and as a soil amendment for sodic soils, where its calcium replaces sodium.CaCO3 is calcium carbonate, the mineral calcite or limestone. CaCl2 is calcium chloride, used as a drying agent and a road de-icer. CaF2 is calcium fluoride, the mineral fluorite.

Q: Immobilization of sulphur in soil occurs when the C : S ratio is :

Sulphur is immobilised when the C : S ratio is above 400 : 1.Soil microbes need carbon and sulphur in a balance. When residues added to the soil are rich in carbon and poor in sulphur, the microbes take the sulphate they lack from the soil solution and build it into their own cells, so it is temporarily unavailable to plants: immobilisation. The usual rule is that net immobilisation occurs above a C : S ratio of about 400 : 1, while net mineralisation occurs below about 200 : 1, and between the two neither process dominates.The options 'below 50', 'below 100' and 'below 200' all describe residues rich in sulphur, which release sulphate (mineralisation) rather than lock it up.

Q: Which one of the following is a micronutrient for plants ?

The micronutrient is boron (B).Plant nutrients are divided by the amount needed. Micronutrients are needed in traces, usually less than 100 mg per kg of dry matter: iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel. Boron is needed for cell wall formation and pollen tube growth, and its deficiency causes disorders such as heart rot of sugar beet.Sulphur (S) and calcium (Ca) are secondary macronutrients, and phosphorus (P) is a primary macronutrient alongside nitrogen and potassium. All three are needed in much larger amounts than boron.

Q: Which clay mineral has hydrogen bond ?

The clay mineral with hydrogen bonding is kaolinite.Kaolinite is a 1:1 clay: each layer has one silica tetrahedral sheet and one alumina octahedral sheet. Adjacent layers are held together by hydrogen bonds between the hydroxyl groups of one layer and the oxygens of the next. These bonds are strong enough to stop water entering between the layers, so kaolinite does not swell and has a low cation exchange capacity.Vermiculite, beidellite and montmorillonite (printed 'Beidelite' and 'Montniorillonite') are 2:1 clays whose layers are held by cations and water, which is why they can expand.

Q: The chemical formula of Talc mineral is :

Talc is the magnesium silicate \(\mathrm{MgSi_{4}O_{10}(OH)_{2}}\); its full formula is \(\mathrm{Mg_{3}Si_{4}O_{10}(OH)_{2}}\), and the option as printed omits the subscript 3.Talc is a hydrated magnesium silicate in sheets, the softest mineral on the Mohs scale (hardness 1). The option keyed is the only one containing magnesium, silicon and hydroxyl, the elements of talc.The others are different minerals: \(\mathrm{CaF_{2}}\) is fluorite, \(\mathrm{CaSO_{4}.2H_{2}O}\) is gypsum and \(\mathrm{SiO_{2}}\) is quartz.

Q: Rate of water percolation is the lowest in :

Percolation is slowest in clayey soil.Clay particles are very fine, less than 0.002 mm, so the pores between them are tiny. Although clay can hold a lot of water, the small pores make its permeability very low, so water moves down through it slowly and tends to stand on the surface or run off.Sandy and desert soils are coarse with large pores and drain quickly. Alluvial soils are loamy mixtures whose percolation lies between sand and clay.

Q: Which one of the following is not a nitrogenous fertilizer ?

The fertilizer that is not nitrogenous is superphosphate.Single superphosphate is made by treating rock phosphate with sulphuric acid and supplies phosphorus (about 16 per cent P2O5), along with calcium and sulphur, but no nitrogen.The others supply nitrogen: urea contains about 46 per cent nitrogen, ammonium sulphate about 21 per cent, and diammonium phosphate (DAP) about 18 per cent nitrogen together with 46 per cent P2O5.

Q: The soil is a result of the actions and reciprocal influence of parent rocks, climate, topography, plants, animals and age of the land. It can be represented by the formula where S-soil, g-geology, e-environment, b-biological influence and t-time :

The formula is \(S = (g.e.b)\Delta t\).The stem describes soil as the joint result of the parent rock (geology, g), climate and topography (environment, e) and plants and animals (biological influence, b), acting over the age of the land (time). Writing soil as the product of the three factors together, operating over a span of time \(\Delta t\), captures that idea, in the spirit of Jenny's factors of soil formation.Options A and B put one factor in the denominator, as if more geology or more environmental influence produced less soil, and option C treats time as a factor and the biological influence as the span over which they act, reversing their roles.

Q: Brown soils are generally associated with areas originally covered by :

Brown soils are associated with areas originally under deciduous forest.Brown forest soils (brown earths) develop in temperate regions under broad-leaved deciduous trees such as oak and beech. The annual leaf fall supplies plenty of organic matter that decomposes into mild humus, mixed into the soil by earthworms, giving a fertile, brown, moderately leached profile.Soils formed under ice (tundra soils), under water (gley and marsh soils) and under mangroves (saline, waterlogged soils) have quite different characteristics.

Q: The addition of lime into the soil will :

Adding lime will reduce soil acidity.Agricultural lime, calcium carbonate or calcium hydroxide, neutralises the hydrogen and aluminium ions that make a soil acid, raising its pH towards neutral. This improves the availability of nutrients such as phosphorus and molybdenum and favours soil microbes, which is why liming is the standard treatment for acid soils.Lime does not change soil texture, which is fixed by the proportions of sand, silt and clay. It can improve structure in clay soils, but increasing porosity or decomposing organic matter is not its main effect.

Gypsum is :

A.\(\mathrm{CaCO_{3}}\)
B.\(\mathrm{CaSO_{4}.2H_{2}O}\)
C.\(\mathrm{CaCl_{2}}\)
D.\(\mathrm{CaF_{2}}\)

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

Gypsum is calcium sulphate dihydrate, CaSO₄.2H₂O.

It is a soft evaporite mineral. Heated to about 150 °C it loses three-quarters of its water and becomes plaster of Paris; it is also used to set cement and as a soil amendment for sodic soils, where its calcium replaces sodium.

CaCO₃ is calcium carbonate, the mineral calcite or limestone. CaCl₂ is calcium chloride, used as a drying agent and a road de-icer. CaF₂ is calcium fluoride, the mineral fluorite.

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Immobilization of sulphur in soil occurs when the C : S ratio is :

A.Below 50 : 1
B.Below 100 : 1
C.Below 200 : 1
D.Above 400 : 1

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

Sulphur is immobilised when the C : S ratio is above 400 : 1.

Soil microbes need carbon and sulphur in a balance. When residues added to the soil are rich in carbon and poor in sulphur, the microbes take the sulphate they lack from the soil solution and build it into their own cells, so it is temporarily unavailable to plants: immobilisation. The usual rule is that net immobilisation occurs above a C : S ratio of about 400 : 1, while net mineralisation occurs below about 200 : 1, and between the two neither process dominates.

The options 'below 50', 'below 100' and 'below 200' all describe residues rich in sulphur, which release sulphate (mineralisation) rather than lock it up.

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Which one of the following is a micronutrient for plants ?

A.S
B.B
C.Ca
D.P

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

The micronutrient is boron (B).

Plant nutrients are divided by the amount needed. Micronutrients are needed in traces, usually less than 100 mg per kg of dry matter: iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel. Boron is needed for cell wall formation and pollen tube growth, and its deficiency causes disorders such as heart rot of sugar beet.

Sulphur (S) and calcium (Ca) are secondary macronutrients, and phosphorus (P) is a primary macronutrient alongside nitrogen and potassium. All three are needed in much larger amounts than boron.

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Which clay mineral has hydrogen bond ?

A.Kaolinite
B.Vermiculite
C.Beidelite
D.Montniorillonite

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: A

The clay mineral with hydrogen bonding is kaolinite.

Kaolinite is a 1:1 clay: each layer has one silica tetrahedral sheet and one alumina octahedral sheet. Adjacent layers are held together by hydrogen bonds between the hydroxyl groups of one layer and the oxygens of the next. These bonds are strong enough to stop water entering between the layers, so kaolinite does not swell and has a low cation exchange capacity.

Vermiculite, beidellite and montmorillonite (printed 'Beidelite' and 'Montniorillonite') are 2:1 clays whose layers are held by cations and water, which is why they can expand.

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The chemical formula of Talc mineral is :

A.\(\mathrm{CaF_{2}}\)
B.\(\mathrm{CaSO_{4}.2H_{2}O}\)
C.\(\mathrm{MgSi_{4}O_{10}\ (OH)_{2}}\)
D.\(\mathrm{SiO_{2}}\)

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: C

Talc is the magnesium silicate \(\mathrm{MgSi_{4}O_{10}(OH)_{2}}\); its full formula is \(\mathrm{Mg_{3}Si_{4}O_{10}(OH)_{2}}\), and the option as printed omits the subscript 3.

Talc is a hydrated magnesium silicate in sheets, the softest mineral on the Mohs scale (hardness 1). The option keyed is the only one containing magnesium, silicon and hydroxyl, the elements of talc.

The others are different minerals: \(\mathrm{CaF_{2}}\) is fluorite, \(\mathrm{CaSO_{4}.2H_{2}O}\) is gypsum and \(\mathrm{SiO_{2}}\) is quartz.

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Rate of water percolation is the lowest in :

A.Sandy soil
B.Clayey soil
C.Alluvial soil
D.Desert soil

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: B

Percolation is slowest in clayey soil.

Clay particles are very fine, less than 0.002 mm, so the pores between them are tiny. Although clay can hold a lot of water, the small pores make its permeability very low, so water moves down through it slowly and tends to stand on the surface or run off.

Sandy and desert soils are coarse with large pores and drain quickly. Alluvial soils are loamy mixtures whose percolation lies between sand and clay.

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Which one of the following is not a nitrogenous fertilizer ?

A.Urea
B.DAP
C.Ammonium sulphate
D.Superphosphate

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: D

The fertilizer that is not nitrogenous is superphosphate.

Single superphosphate is made by treating rock phosphate with sulphuric acid and supplies phosphorus (about 16 per cent P2O5), along with calcium and sulphur, but no nitrogen.

The others supply nitrogen: urea contains about 46 per cent nitrogen, ammonium sulphate about 21 per cent, and diammonium phosphate (DAP) about 18 per cent nitrogen together with 46 per cent P2O5.

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The soil is a result of the actions and reciprocal influence of parent rocks, climate, topography, plants, animals and age of the land. It can be represented by the formula where S-soil, g-geology, e-environment, b-biological influence and t-time :

A.\(S = \dfrac{(g.b)}{e}\Delta t\)
B.\(S = \dfrac{(e.b)}{g}\Delta t\)
C.\(S = (g.e.t)\Delta b\)
D.\(S = (g.e.b)\Delta t\)

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: D

The formula is \(S = (g.e.b)\Delta t\).

The stem describes soil as the joint result of the parent rock (geology, g), climate and topography (environment, e) and plants and animals (biological influence, b), acting over the age of the land (time). Writing soil as the product of the three factors together, operating over a span of time \(\Delta t\), captures that idea, in the spirit of Jenny's factors of soil formation.

Options A and B put one factor in the denominator, as if more geology or more environmental influence produced less soil, and option C treats time as a factor and the biological influence as the span over which they act, reversing their roles.

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Brown soils are generally associated with areas originally covered by :

A.Ice
B.Water
C.Deciduous forest
D.Mangrove forest

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: C

Brown soils are associated with areas originally under deciduous forest.

Brown forest soils (brown earths) develop in temperate regions under broad-leaved deciduous trees such as oak and beech. The annual leaf fall supplies plenty of organic matter that decomposes into mild humus, mixed into the soil by earthworms, giving a fertile, brown, moderately leached profile.

Soils formed under ice (tundra soils), under water (gley and marsh soils) and under mangroves (saline, waterlogged soils) have quite different characteristics.

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10.

The addition of lime into the soil will :

A.Increase porosity of soil
B.Change soil texture
C.Reduce soil acidity
D.Cause decomposition of organic material

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: C

Adding lime will reduce soil acidity.

Agricultural lime, calcium carbonate or calcium hydroxide, neutralises the hydrogen and aluminium ions that make a soil acid, raising its pH towards neutral. This improves the availability of nutrients such as phosphorus and molybdenum and favours soil microbes, which is why liming is the standard treatment for acid soils.

Lime does not change soil texture, which is fixed by the proportions of sand, silt and clay. It can improve structure in clay soils, but increasing porosity or decomposing organic matter is not its main effect.

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