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Soil Science, Soil Chemistry & Fertility (Agriculture & Crop Sciences) Solved Questions & Notes (2026) - Apex Rankers

Agricultural & Veterinary Sciences > Agriculture & Crop Sciences > Soil Science, Soil Chemistry & Fertility

100 Total Questions
~150 mins Read Time
1 Subject Areas
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Q. 1 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
A soil having ECe > 4.0 dS/m, ESP < 15%, and pH < 8.5 is classified as:
A
Acidic soil
B
Saline soil
✓ Correct
C
Sodic soil
D
Saline-sodic soil
💡 Step-by-Step Explanation & Concept Rationale
Saline soils contain excess neutral soluble salts (chlorides, sulfates) with low exchangeable sodium.
Q. 2 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
What chemical amendment is standardly applied to reclaim sodic (alkali) soils?
A
Urea
B
Gypsum (Calcium sulfate, CaSO4·2H2O)
✓ Correct
C
Sodium chloride
D
Potassium nitrate
💡 Step-by-Step Explanation & Concept Rationale
Calcium ions from gypsum displace exchangeable sodium on clay particles, which is then leached.
Q. 3 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
Urea fertilizer has a nitrogen (N) content of approximately:
A
46% N
✓ Correct
B
21% N
C
18% N
D
33% N
💡 Step-by-Step Explanation & Concept Rationale
Pure urea (CO(NH2)2) contains 46% nitrogen, the highest among dry solid fertilizers.
Q. 4 MULTIPLE_CHOICE
Difficulty: HARD (1 Mark)
In high pH calcareous soils of Pakistan, applied phosphorus is rapidly fixed as:
A
Iron phosphate
B
Insoluble calcium phosphate complexes (e.g. dicalcium and tricalcium phosphate)
✓ Correct
C
Aluminum phosphate
D
Magnesium nitrate
💡 Step-by-Step Explanation & Concept Rationale
Free CaCO3 reacts with soluble monocalcium phosphate, reverting it to insoluble forms.
Q. 5 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
The ideal C:N ratio of organic amendments for rapid soil decomposition without nitrogen tie-up is:
A
5:1 to 10:1
B
200:1 to 300:1
C
100:1 to 150:1
D
20:1 to 30:1
✓ Correct
💡 Step-by-Step Explanation & Concept Rationale
At C:N 20-30:1, soil microorganisms break down organic carbon without immobilizing available mineral N.
Q. 6 MULTIPLE_CHOICE
Difficulty: HARD (1 Mark)
Cation Exchange Capacity (CEC) is highest in which soil clay mineral?
A
Quartz sand
B
Illite
C
Vermiculite and Montmorillonite (Smectite)
✓ Correct
D
Kaolinite
💡 Step-by-Step Explanation & Concept Rationale
2:1 expanding lattice clays possess high specific surface area and negative charge, yielding high CEC.
Q. 7 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
Which micronutrient deficiency commonly causes 'Khaira disease' in lowland rice?
A
Boron (B)
B
Zinc (Zn)
✓ Correct
C
Iron (Fe)
D
Copper (Cu)
💡 Step-by-Step Explanation & Concept Rationale
Zinc deficiency in submerged calcareous paddy soils causes chlorosis and brown leaf pigmentation.
Q. 8 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
Soil bulk density is defined as:
A
Soil mass divided by volume of solids only
B
Dry mass of soil divided by total soil volume (solids + pores)
✓ Correct
C
Water weight divided by dry soil weight
D
Mineral density
💡 Step-by-Step Explanation & Concept Rationale
Bulk density (standard 1.3-1.6 g/cm³) reflects soil compaction and porosity.
Q. 9 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
Which soil microorganism forms symbiotic nitrogen-fixing root nodules in leguminous crops?
A
Azotobacter
B
Bacillus
C
Rhizobium species
✓ Correct
D
Pseudomonas
💡 Step-by-Step Explanation & Concept Rationale
Rhizobia infect legume root hairs, forming nodules where nitrogenase enzyme reduces atmospheric N2 to ammonia.
Q. 10 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
Soil texture is determined by the relative proportions of:
A
Rocks and gravel
B
Nitrogen, Phosphorus, and Potassium
C
Sand, Silt, and Clay particles (<2mm)
✓ Correct
D
Organic matter and water
💡 Step-by-Step Explanation & Concept Rationale
Soil textural classes (loam, clay loam, sandy loam) depend on sand (0.05-2mm), silt (0.002-0.05mm), and clay (<0.002mm).
Q. 11 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
In applied field conditions: A soil having ECe > 4.0 dS/m, ESP < 15%, and pH < 8.5 is classified as:
A
Sodic soil
B
Saline soil
✓ Correct
C
Saline-sodic soil
D
Acidic soil
💡 Step-by-Step Explanation & Concept Rationale
Saline soils contain excess neutral soluble salts (chlorides, sulfates) with low exchangeable sodium.
Q. 12 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
In applied field conditions: What chemical amendment is standardly applied to reclaim sodic (alkali) soils?
A
Sodium chloride
B
Urea
C
Potassium nitrate
D
Gypsum (Calcium sulfate, CaSO4·2H2O)
✓ Correct
💡 Step-by-Step Explanation & Concept Rationale
Calcium ions from gypsum displace exchangeable sodium on clay particles, which is then leached.
Q. 13 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
In applied field conditions: Urea fertilizer has a nitrogen (N) content of approximately:
A
46% N
✓ Correct
B
21% N
C
33% N
D
18% N
💡 Step-by-Step Explanation & Concept Rationale
Pure urea (CO(NH2)2) contains 46% nitrogen, the highest among dry solid fertilizers.
Q. 14 MULTIPLE_CHOICE
Difficulty: HARD (1 Mark)
In applied field conditions: In high pH calcareous soils of Pakistan, applied phosphorus is rapidly fixed as:
A
Magnesium nitrate
B
Iron phosphate
C
Aluminum phosphate
D
Insoluble calcium phosphate complexes (e.g. dicalcium and tricalcium phosphate)
✓ Correct
💡 Step-by-Step Explanation & Concept Rationale
Free CaCO3 reacts with soluble monocalcium phosphate, reverting it to insoluble forms.
Q. 15 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
In applied field conditions: The ideal C:N ratio of organic amendments for rapid soil decomposition without nitrogen tie-up is:
A
5:1 to 10:1
B
100:1 to 150:1
C
20:1 to 30:1
✓ Correct
D
200:1 to 300:1
💡 Step-by-Step Explanation & Concept Rationale
At C:N 20-30:1, soil microorganisms break down organic carbon without immobilizing available mineral N.
Q. 16 MULTIPLE_CHOICE
Difficulty: HARD (1 Mark)
In applied field conditions: Cation Exchange Capacity (CEC) is highest in which soil clay mineral?
A
Vermiculite and Montmorillonite (Smectite)
✓ Correct
B
Illite
C
Kaolinite
D
Quartz sand
💡 Step-by-Step Explanation & Concept Rationale
2:1 expanding lattice clays possess high specific surface area and negative charge, yielding high CEC.
Q. 17 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
In applied field conditions: Which micronutrient deficiency commonly causes 'Khaira disease' in lowland rice?
A
Iron (Fe)
B
Boron (B)
C
Copper (Cu)
D
Zinc (Zn)
✓ Correct
💡 Step-by-Step Explanation & Concept Rationale
Zinc deficiency in submerged calcareous paddy soils causes chlorosis and brown leaf pigmentation.
Q. 18 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
In applied field conditions: Soil bulk density is defined as:
A
Mineral density
B
Dry mass of soil divided by total soil volume (solids + pores)
✓ Correct
C
Soil mass divided by volume of solids only
D
Water weight divided by dry soil weight
💡 Step-by-Step Explanation & Concept Rationale
Bulk density (standard 1.3-1.6 g/cm³) reflects soil compaction and porosity.
Q. 19 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
In applied field conditions: Which soil microorganism forms symbiotic nitrogen-fixing root nodules in leguminous crops?
A
Rhizobium species
✓ Correct
B
Azotobacter
C
Bacillus
D
Pseudomonas
💡 Step-by-Step Explanation & Concept Rationale
Rhizobia infect legume root hairs, forming nodules where nitrogenase enzyme reduces atmospheric N2 to ammonia.
Q. 20 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
In applied field conditions: Soil texture is determined by the relative proportions of:
A
Nitrogen, Phosphorus, and Potassium
B
Rocks and gravel
C
Organic matter and water
D
Sand, Silt, and Clay particles (<2mm)
✓ Correct
💡 Step-by-Step Explanation & Concept Rationale
Soil textural classes (loam, clay loam, sandy loam) depend on sand (0.05-2mm), silt (0.002-0.05mm), and clay (<0.002mm).
Q. 21 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
In agricultural practice: A soil having ECe > 4.0 dS/m, ESP < 15%, and pH < 8.5 is classified as:
A
Sodic soil
B
Acidic soil
C
Saline-sodic soil
D
Saline soil
✓ Correct
💡 Step-by-Step Explanation & Concept Rationale
Saline soils contain excess neutral soluble salts (chlorides, sulfates) with low exchangeable sodium.
Q. 22 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
In agricultural practice: What chemical amendment is standardly applied to reclaim sodic (alkali) soils?
A
Potassium nitrate
B
Urea
C
Sodium chloride
D
Gypsum (Calcium sulfate, CaSO4·2H2O)
✓ Correct
💡 Step-by-Step Explanation & Concept Rationale
Calcium ions from gypsum displace exchangeable sodium on clay particles, which is then leached.
Q. 23 MULTIPLE_CHOICE
Difficulty: EASY (1 Mark)
In agricultural practice: Urea fertilizer has a nitrogen (N) content of approximately:
A
33% N
B
46% N
✓ Correct
C
18% N
D
21% N
💡 Step-by-Step Explanation & Concept Rationale
Pure urea (CO(NH2)2) contains 46% nitrogen, the highest among dry solid fertilizers.
Q. 24 MULTIPLE_CHOICE
Difficulty: HARD (1 Mark)
In agricultural practice: In high pH calcareous soils of Pakistan, applied phosphorus is rapidly fixed as:
A
Magnesium nitrate
B
Aluminum phosphate
C
Insoluble calcium phosphate complexes (e.g. dicalcium and tricalcium phosphate)
✓ Correct
D
Iron phosphate
💡 Step-by-Step Explanation & Concept Rationale
Free CaCO3 reacts with soluble monocalcium phosphate, reverting it to insoluble forms.
Q. 25 MULTIPLE_CHOICE
Difficulty: MEDIUM (1 Mark)
In agricultural practice: The ideal C:N ratio of organic amendments for rapid soil decomposition without nitrogen tie-up is:
A
100:1 to 150:1
B
200:1 to 300:1
C
20:1 to 30:1
✓ Correct
D
5:1 to 10:1
💡 Step-by-Step Explanation & Concept Rationale
At C:N 20-30:1, soil microorganisms break down organic carbon without immobilizing available mineral N.
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