Indiscriminate use of fertilizers have led to

The answer is D, all of the above. Fertilizers help crop yield, but when they are applied without regard to soil test results, crop need or timing, they spill into soil, water and air.

• Soil pollution: Repeated overuse of urea and other chemical fertilizers causes nutrient imbalance, soil acidification or salinity, and loss of organic matter. Phosphatic fertilizers can also add heavy metals such as cadmium as impurities.
• Water pollution: Excess nitrate leaches into groundwater, and nitrate and phosphate runoff triggers eutrophication in rivers and lakes, which is why algal blooms follow heavy fertilizer use.
• Air pollution: Nitrogen fertilizers release ammonia through volatilisation, and nitrous oxide, a potent greenhouse gas, through denitrification in soil.

The core concept is nutrient use efficiency. Only a fraction of applied nitrogen is taken up by the crop, and the rest moves into the environment. This links to Environment and Agriculture for Prelims, and to Mains questions on sustainable agriculture, the nutrient based subsidy regime and soil health cards.

Trap: Aspirants often pick A or B because they think of only one pathway. When a question says the impact spans soil, water and air, mark D.