Case Study:

In a village near Nagpur, a group of farmers noticed that their cotton yield had reduced significantly over the past two years. The local agricultural extension officer advised them to conduct soil pH testing before adding more fertilizers.
Samples were collected from four different farms and tested using a universal indicator. The results were:

1. Farm A: pH 5.2
2. Farm B: pH 6.8
3. Farm C: pH 8.1
4. Farm D: pH 7.0

The officer explained that most crops grow best in slightly acidic to neutral soil (pH 6–7.5). Cotton, which is widely grown in Maharashtra, prefers soil with pH around 6.0–7.0.

Farm A’s soil was too acidic, possibly due to excessive use of ammonium-based fertilizers. Farm C’s soil was alkaline, which can reduce availability of essential nutrients like iron and phosphorus. Farm B and D had nearly ideal soil conditions.

The officer recommended adding slaked lime (Ca(OH)₂) to Farm A to neutralize acidity and adding organic compost to Farm C to improve soil quality. After corrective measures, crop productivity improved the following season.

This case highlights the importance of pH in agriculture, the role of acids and bases in soil chemistry, and how scientific testing helps in decision-making.

Questions

Section A - MCQs

Q1. Which farm requires treatment with a base to improve soil condition?
A. Farm B
B. Farm D
C. Farm A
D. Farm C

Q2. Why is cotton growth poor in Farm C (pH 8.1)?
A. Soil is highly acidic
B. Soil is alkaline affecting nutrient availability
C. Soil is neutral
D. Soil contains too much water

Q3. If slaked lime is added to Farm A, the expected change in pH will be:
A. Decrease further below 5
B. Remain constant
C. Increase towards 7
D. Become highly alkaline above 10

Q4. Which farm has soil most suitable for maximum cotton yield without treatment?
A. Farm A
B. Farm B
C. Farm C
D. Both B and D

Section B - Short Answer Questions

Q1. Explain why acidic soil reduces crop productivity. 

Q2. How does adding slaked lime help in improving acidic soil? Explain with chemical reasoning.

Q3. Suppose a farmer ignores soil testing and keeps adding chemical fertilizers. What long-term effect can it have on soil pH and crop yield?

Section C - Long Answer Question

Q1. A farmer in another village tests his soil and finds the pH to be 4.8.

(a) Identify the nature of the soil.
(b) Suggest two chemical and two agricultural measures to correct it.
(c) What would happen if no corrective action is taken for 3–4 years?
(d) If excessive lime is added accidentally, what new problem may arise?

Answer Key

MCQ Answers:

1. C

2. B

3. C

4. D

Section B Answers

Q1. a) Acidic soil (pH < 6) increases solubility of toxic metals like aluminum.

• b) Essential nutrients become less available.
• c) Root growth is affected, reducing productivity.

Q2. a) Slaked lime is a base (Ca(OH)₂).

• b) It neutralizes excess acid in soil.
• c) Acid + Base --> Salt + Water
• d) pH increases towards neutral range.

Q3. a) Continuous fertilizer use may increase acidity.

• b) Soil becomes unbalanced chemically.
• c) Nutrient deficiency increases.
• d) Crop yield decreases over time.

• Section C Answer

(a) Soil is strongly acidic.

(b) 1) Chemical measures:

i) Add slaked lime (Ca(OH)₂).

ii)Add limestone (CaCO₃).

2) Agricultural measures:

i)Add organic compost.

ii)Practice crop rotation.

(c) 1) Nutrient deficiency increases.

2) Microorganisms die.

3) Crop failure risk rises.

(d) 1) Soil may become alkaline.

2) Micronutrient deficiency (like iron) may occur.

3) Productivity may again decline.