Fertilisers Flashcards
Why are fertilisers needed in agricultural ecosystems ?
Crops are harvested and removed. The urine, faeces and dead remains of animals are also rarely returned to the same area of land. As a result the concentration of nutrients in the soil decreases and crop productivity falls
How do fertilisers increase productivity ?
Nitrogen is an essential component of proteins and DNA-both are needed for plant growth
Plants which can obtain nitrates develop earlier, grow taller and have a greater leaf area
This will increase the rate of photosynthesis and improve crop productivity
What are inorganic fertilisers ?
Artificial fertilisers are made up of inorganic matter in the form of powders or pellets that contain pure chemical compounds (e.g. ammonium nitrate)
As the exact chemical composition is known, it is easier to how much to apply and the effects they will have on crop yields
The nutrients present are concentrated so smaller amounts are needed
This means transport costs are lower
These fertilisers are easy to apply evenly and are clean, making them easy to handle
What are natural fertilisers ?
Natural fertilisers are made up of organic matter in the form of the dead and decomposing remains of organisms and their waste products
This includes manure, composted vegetables, crops residues, bone meal, urea
They can also improve soil structure, which helps in reducing soil erosion and increase the water-holding ability of the soil
Nutrients from natural fertilisers are released over long time periods
The nutrients present are not very concentrated so relatively large amounts are needed
Application of very high concentrations of fertiliser to the soil causes plants to wilt. Explain why
Soil has lower water potential so water moves out of the plants by osmosis.
What are the advantages of nitrogen fertilisers ?
Nitrogen is an essential component of proteins and is needed for growth leading to an increase in leaf area.
Rate of photosynthesis increases and crop productivity improves
Provides us with cheaper food
What are the disadvantages of nitrogen fertilisers ?
reduced species diversity -nitrogen rich soils encourage the growth of grasses which outcompete other species.
Leaching- may lead to pollution of watercourses
Eutrophication- caused by the leaching of fertiliser into watercourses
What is leaching ?
is the process by which nutrients are removed from the soil- rain water washes mineral ions into nearby streams, rivers and lakes
What is Eutrophication ?
The consequence of an increase in nutrients, especially nitrates and phosphate in fresh water lakes and rivers that often leads to a decrease in biodiversity.
Explain the process of eutrophication
Excessive fertiliser use causes phosphates and nitrates to be leached into ponds/lakes
This causes an algal bloom
This blocks sunlight
Plants underwater start to die as they are unable to photosynthesise due to increased competition for light
less oxygen produced via photosynthesis.
Submerged plants die. Algae also die when competition for nutrients becomes too intense
As aquatic plants and algae die in increasing numbers, decomposing bacteria feed on the dead organic matter and also increase in number.
As they respire aerobically, these bacteria use up the dissolved oxygen in the water.
As a result, the amount of dissolved oxygen in the water rapidly decreases, so aquatic organisms such as fish and insects may be unable to survive
Explain how the problem of eutrophication can be reduced while still maintaining soil mineral availability
Using natural fertilisers (rather than artificial fertilisers)
Natural fertilisers are less soluble in water
Explain why natural fertilisers are not required in natural ecosystems but are required in agricultural ecosystems.
In natural ecosystems nutrients from dead/waste matter are recycled/returned to the soil by decomposers/saprobionts
In agriculture crops/livestock use nutrients from their environment and are then removed from the system/harvested (and not left to die and decompose, preventing those nutrients from being recycled/returned to the soil)
