Which of the following soil fertility improvement methods will have the most negative effect on the ecosystem if not controlled?

Analyze the question You are asked which soil fertility improvement method can harm the ecosystem most if it is not controlled.

Concept Some methods work with natural processes. Others add large amounts of foreign chemicals to the soil.

• Crop rotation (D): Growing different crops in turn, including legumes that fix nitrogen, restores nutrients and breaks pest cycles. It is environmentally friendly.
• Mixed farming (C): Crops and livestock are kept together, and animal manure fertilizes the soil. It is a sustainable, balanced system.
• Shifting cultivation (B): Farmers move on to new land and let old plots lie fallow so they recover. It can cause deforestation if the population is high and fallow periods are too short, but it is a traditional method and the damage is usually local and gradual.
• Application of N-P-K fertilizer (A): This is inorganic fertilizer containing nitrogen, phosphorus and potassium. If it is applied excessively or without control, it causes: • Eutrophication: Nutrients leach and run off into streams, rivers and lakes. This causes algal blooms, which use up oxygen and kill fish and other aquatic life. • Soil acidification and a decline in soil microorganisms. • Groundwater contamination, for example by nitrates, which are harmful to health. • Pollution that spreads widely beyond the farm.

Solution Comparing the options, uncontrolled use of chemical fertilizer has the widest and most serious effects on the ecosystem. It affects soil, water and living organisms far from the farm. Shifting cultivation does have some negative effects, but it is mainly a land-use issue, not a pollution issue.

Answer: A. Application of N-P-K fertilizer

Exam tip: When a question says "most negative effect if not controlled," think of chemicals such as fertilizers, pesticides and herbicides. Their overuse is linked to eutrophication and pollution. Organic methods like crop rotation and mixed farming are generally safe.