Synthetic fertilizers are used in intensive agriculture because they rapidly replace mineral nutrients removed through repeated harvesting, allowing farmers to maintain high crop productivity. However, this can reduce long-term environmental sustainability.
Level: SL and HL: Subtopic 5.2 Agriculture and food
The Mechanism
Intensive agriculture seeks a high yield per unit area using inputs such as machinery, irrigation, pesticides and fertilizers. Crops absorb mineral nutrients, especially nitrogen, phosphorus and potassium, from soil. When harvested, these nutrients leave the agricultural system in biomass rather than returning through decomposition.
Without replacement, soil nutrient storage declines and nutrient availability becomes a limiting factor. Synthetic fertilizers provide concentrated, readily soluble mineral nutrients that roots can absorb quickly. Their composition and application rate are also easier to control than those of many organic fertilizers.
| Reason for use | Benefit to intensive agriculture | Possible sustainability cost |
|---|---|---|
| Rapid nutrient replacement | Supports fast growth and high yields | Excess nutrients may be lost through leaching or run-off |
| Predictable nutrient content | Allows application to match crop requirements | Production and application generate greenhouse gas emissions |
| Continuous cultivation | Reduces the need for long fallow periods | Dependence may discourage organic matter recycling |
| Greater output per hectare | Improves food supply and may reduce land conversion | Nutrient pollution can cause eutrophication |
The Green Revolution in India illustrates this trade-off: high-yielding varieties combined with irrigation and synthetic fertilizers increased harvests and food security. Yet poorer farmers could struggle to afford inputs, while nutrient pollution imposed costs on downstream communities. This links agricultural productivity to environmental justice.
Exam Technique
For an IB ESS explain question, link harvesting to nutrient removal, declining soil fertility, fertilizer addition and increased productivity. Avoid the misconception that synthetic fertilizers simply “make soil fertile”: they replace specific nutrients but do not automatically maintain soil structure, organic matter or long-term sustainability.