IB Environmental systems and societies 5.2C Synthetic Fertilizers Notes

Why Intensive Farming Becomes Dependent on Synthetic Fertilizers

How the Dependency Builds

1. Intensive agricultural systems rely heavily on synthetic fertilizers because fast-growing crop varieties rapidly deplete soil nutrients.
2. Large monocultures demand continuous nutrient inputs, removing nitrogen, phosphorus, and potassium faster than natural processes can replace them.
3. Synthetic fertilizers provide an immediate, concentrated nutrient supply that enables high yields for commercial farming.
4. Most synthetic fertilizers are made using fossil fuels, especially natural gas, so production is energy-intensive and adds to climate change.
5. This dependence becomes unsustainable over time, because soils degrade biologically and farmers must apply ever-larger amounts to hold yields steady.

Synthetic Fertilizers Create Serious Environmental Problems

Water Pollution and Eutrophication

1. Most applied fertilizer does not stay in the soil because rainfall dissolves it and washes nutrients into streams, rivers, and lakes.
2. Leached nitrates contaminate groundwater and pose health risks such as blue baby syndrome.
3. Runoff into surface waters causes eutrophication, triggering algal blooms, oxygen depletion, and loss of aquatic biodiversity.

Soil Biological and Chemical Degradation

1. Synthetic fertilizers disrupt soil microbial communities, especially the organisms that drive the nitrogen cycle.
2. Nitrogen-fixing bacteria decline, reducing the soil's natural ability to replenish nitrogen.
3. Nitrifying and denitrifying bacteria increase, speeding the conversion of nitrogen into gaseous forms that are lost from the soil.
4. This shift weakens natural soil fertility and deepens the farm's dependence on synthetic inputs.

Nitrous Oxide Emissions from Soil

1. Nitrogenous fertilizers raise microbial production of nitrous oxide, a greenhouse gas nearly 300 times more powerful than carbon dioxide.
2. Enhanced nitrification and denitrification cause greater nitrogen losses from soil, lowering fertilizer efficiency and raising emissions.

Feedback Loops Trap Farms in a Cycle of Rising Fertilizer Use

1. Negative feedback stabilises the system when added nitrogen boosts denitrifying bacteria.
   1. These bacteria convert nitrates back into atmospheric nitrogen, counteracting the added nutrients.
2. Positive feedback amplifies the problem when repeated fertilizer use kills off nitrogen-fixing bacteria.
   1. Soils become less fertile, so farmers apply even more fertilizer.
   2. This vicious cycle makes soil degradation and fertilizer dependence worse year after year.