13 Fertilisers

  • Created by: lee8444
  • Created on: 23-02-20 14:45

The need for fertilisers

  • All plants need mineral ions, especially nitrates from the soil
  • Intensive food production depletes the stores of ions
  • Mineral ions are removed and not replaced as the crops are sold or eaten and the livestock is sold
  • No decomposition returning the nutrients to the soil
  • Without replenishing the nutrients, nutrients will become the limiting factor
  • Natural (organic) fertiliser - dead and decaying organisms as well as animal waste e.g. manure
  • Artificial (inorganic) fertiliser - minerals are mined from rocks and are blended and converted into a blend with the appropriate balance of minerals needed
  • Fertilisers contain nitrogen, phosphorus & potassium
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How fertilisers increase productivity

  • Plants require minerals for growth
  • e.g. nitrogen is needed for amino acids, ATP and nucleotides
  • Therefore, places with more nitrate ions tend to have plants that grow quicker than normal and with bigger leaves and taller plants, more photosynthesis can happen increasing productivity
  • This makes food cheaper as more food can be produced
  • Use of fertilisers has doubled UK food production since 1995
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Effects of nitrogen-containing fertilisers

  • Reduced species diversity
    • Nitrogen-rich soils favour the growth of grasses, nettles and other rapidly growing species
    • They, therefore, outcompete other species which results in their death
    • Species-rich hay meadows only survive when nitrogen concentrations are low enough to allow other species to compete with grass
  • Leaching - can lead to pollution of watercourses
    • Leaching is the process where nutrients are removed from the soil
    • Rainwater can dissolve soluble nutrients such as nitrate ions
    • This takes the ions deep into the soil or into watercourses such as streams and rivers
    • Here, they can have a harmful effect on humans if the water is for drinking as it prevents efficient oxygen transportation in babies and can cause stomach cancer
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  • Most lakes and rivers have a naturally low concentration of nitrate and so nitrate ions are the limiting factors for the growth of algae
  • As the nitrate ion concentration increases due to leaching, it is no longer the limiting factor
  • Algae grow rapidly on the surface - an algal bloom
  • The dense surface layer prevents light from going through
  • LIght is the limiting factor for plants beneath and the plants can't photosynthesise and die
  • Saprobiontic bacteria populations grow using the dead organisms as food
  • Saprobiontic bacteria require oxygen for respiration increasing the demand for oxygen
  • The concentration of oxygen decreases and nitrates are released from the dead organisms
  • There is no longer enough oxygen for fish to breathe so they die as the oxygen is used up
  • Without aerobic organisms, anaerobic organisms can thrive so their populations rise
  • They release toxic wastes such as hydrogen sulphide which makes the water putrid
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