UPSC Prelims 2015 – Question 11

Q: What can be the impact of excessive/inappropriate use of nitrogenous fertilizers in agriculture?

1. Proliferation of nitrogen-fixing microorganisms in soil can occur.
2. Increase in the acidity of soil can take place.
3. Leaching of nitrate to the ground-water can occur

Select the correct answer using the code given below:

a) 1 and 3 only

b) 2 only

c) 2 and 3 only

d) 1, 2 and 3

The correct answer is 2 and 3 only. 

• More nitrogen in the soil leads to less need for nitrogen-fixing bacteria. 
• Less nitrogen-fixing bacteria are required when there is more nitrogen in the soil. 
• Increasing the amount of nitrogen-based fertilizer does not lead to more micro-organisms in the field. Hence, Statement 1 is not correct. 
• Nitrogen fertilizers break down into nitrates and travel easily through the soil. Because it is water-soluble and can remain in groundwater for decades, the addition of more nitrogen over the years has an accumulative effect. 
• The application of nitrogenous fertilisers excessively or improperly raises the soil’s acidity and causes nitrate to leach into the groundwater. Hence, Statement 2 is correct. 
• Fertilizers are used in agriculture to increase nutrient inputs to soils, which affects the pH level. 
• The uncharged urea molecule ([CO(NH2)2]0), the cation ammonium (NH4+), and the anion nitrate (NO3-) are three different types of nitrogen molecules that alter soil pH. 
• Acidity is produced or consumed during the conversion of nitrogen from one form to another, and plant uptake of urea, ammonium, or nitrate will also have an impact on the soil’s acidity. 
• The leaching process causes these substances to deposit underground. Hence, Statement 3 is correct. 

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