Fertilisers

Question 1

Why are fertilisers needed

Answer 1

Plants obtain mineral ions from the soil, intensive farming uses specific areas of land repeatedly which puts large demands on the soil, as mineral ions are continually absorbed
Crops grown are eaten
Mineral levels decrease in artificial ecosystems so must be replenished

Question 2

Natural organic fertilisers

Answer 2

Contain dead and decaying remains of plants and animals , as well as animal waste it can also include manure, slurry and bone meal

Question 3

Artificial (inorganic) fertilisers

Answer 3

Mined from rocks and deposits

It is converted into different forms and blended together to give different quantities of minerals for specific crops

Question 4

How do fertilisers increase productivity

Answer 4

• Minerals are required for growth in plants
• Nitrogen required for amino acids, atp and nucleotides in dna which are needed for plant growth
• if nitrate ions are in good supply, plants will develop earlier, grow taller and leaves have a greater surface area. This will lead to increased photosynthesis and therefore improves crop productivity

Question 5

Nitrogen containing fertilisers: reduced species diversity

Answer 5

Nitrogen rich soils - favour growth of grasses, nettles and other rapidly growing species
These species then outcompete other species, causing them to die
For an area to be species rich- nitrogen levels need to be sufficiently high, but low enough so that other species can compete

Question 6

Leaching

Answer 6

= process by which nutrients are removed from the soil, which can lead to pollution of watercourses :

• rainwater dissolves soluble nutrients
• these are carried deep into soil beyond the reach of the roots
• they can enter watercourses such as rivers and streams

Question 7

Problems with leaching

Answer 7

• lower concentrations available to plants
• if they enter watercourse that are drinking sources : it has been found that nitrate ions can prevent efficient oxygen transport in babies as well as cause stomach cancer in humans

Question 8

Eutrophication

Answer 8

Process by which nutrient concentrations increase in bodies of water
Occurs mostly in freshwater lakes and lower reaches of rivers

Question 9

Steps of eutrophication

Answer 9

1. Most rivers have low concentrations of nitrates which means often it limits plant and algal growth
2. Nitrate levels can rise due to leaching and therefore it is no longer a limiting factor
3. Algae grow at the surface so upper regions become densely populated
4. The dense layer of algae absorbs light and prevents it reaching the lower depths. So light becomes a limiting factor for plants at lower depths
5. The lack of dead plants was a limiting factor for saprobiontic bacteria, however it is no longer so their populations increase as they feed on dead plants
6. These bacteria require oxygen for respiration so there becomes an increased demand for oxygen
7. Concentrations of oxygen continue to decline as nitrates increase further due to release during decomposition
8. Oxygen becomes a limiting factor for aerobic organisms such as fish, which there die.
9. Without aerobic organisms there is less competition for anaerobic organisms, so their number increase
10. Anaerobic organisms further decompose dead material releasing more nitrates as well as toxic wastes