Why are fertilisers needed?
When crops are harvested, they are removed from the field where they are grown-the mineral ions they contain are not returned to the soil by decomposes in the nitrogen or phosphorus cycle.
Phosphates and nitrates are also lost from the system when animals or animal products are removed from the land- they take nutrients from plants then are moved elsewhere for slaughter- the nutrients aren’t replaced through their remains or waste products.
Adding fertilisers replaces lost minerals so more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer
What are artificial fertilisers?
Inorganic- they contain pure chemicals( eg ammonium nitrate) as powders or pellets
What are natural fertilisers?
Organic matter-includes manure, composted vegetables, crop residues ( the parts left over after the harvest) and sewage sludge.
What is leaching?
When more fertiliser is applied than the plants need or are able to use at a particular time. This can lead to the fertilisers leaching into waterways- water soluble compounds in the soil are washed away by rain or irrigation systems. They’re often washed into nearby ponds and rivers. This can lead to eutrophication.
Why is leaching less likely with natural fertilisers?
The nitrogen and phosphorus ae still contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed by plants. This means that their release into the soil for the uptake by plants is more controlled.
Why is the leaching of phosphates less likely than the leaching of nitrates?
Phosphates are less soluble in water than nitrates
What is a risk of using fertilisers?
They can change the balance of nutrients in the soil-too much of a particular nutrient can cause crops and other plants to die
What is the process of eutrophication?
-mineral ions leached from fertilised fields stimulate the rapid growth of algae in ponds and rivers
-large amounts of algae block light from reaching the plants below
-eventually plants die because they are unable to photosynthesise enough
-bacteria feed on the dead plant matter. The increased number of bacteria reduce the oxygen concentration in the water by carrying out aerobic respiration
- fish and other aquatic organisms die because there isn’t enough dissolved oxygen
