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 groundwater can occur.
Select the correct answer using the codes given below.
Explanation
With excessive use of nitrogenous fertilizers in agriculture, the necessity for nitrogen-fixing bacteria decreases as soil nitrogen levels increase. The soil becomes more acidic and nitrate leaches into the groundwater when nitrogenous fertilisers are used excessively or inappropriately. Fertilizers in agriculture increase inputs of nutrients to soils affecting their pH value.
Statement 1 is incorrect: Nitrogen-fixing microorganisms, such as Rhizobium (in leguminous plants), Azotobacter, and Cyanobacteria (blue-green algae) fix atmospheric nitrogen into the soil. But excessive nitrogen fertilizers reduce biological nitrogen fixation because plants get sufficient nitrogen from fertilizers and do not depend on these microbes. Thus instead of increasing, nitrogen-fixing bacteria decrease in population due to reduced plant-microbe symbiosis.
Statement 2 and 3 are correct: The conversion of Nitrogen from one form to the other involves the generation or consumption of acidity and the uptake of urea, ammonium or nitrate by plants will also affect the acidity of the soil. Due to the leaching process, these substances accumulate underground.
For S1, If plenty of nitrogen is already being dumped into the soil by fertilizers, will the soil "want" microbes to work harder? No. The natural balance gets disturbed. The plant and soil reduce dependency on nitrogen-fixing organisms. In fact, such microbes decline because their service is no longer "in demand." Hence S1 likely false, Eliminating options A and D.