Fertilisers

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  • FERTILISERS
    • farming breaks the nitrogen cycle because nitrogen is taken from the soil by crops and is not returned
    • NPK
      • nitrogen need for making amino acids- proteins- enzymes
      • potassium needed for making ATP
    • organic=  derived from living matter (free)
    • inorganic= not derived from living matter (costly)
    • eutrophication
      • fertilisers leached into clean water
        • adds more nutrients into the water
          • algal bloom, rapid cell division, creates a layer of algae on the top of the water
            • there is then competition for light (algae blocks the sunlight) between the algae and other plants in the water
              • other plants die as they can't get light for the light dependent stage of photosynthesis
                • detruis
                  • a rapid increase in decomposers e.g. saprobionts
                    • the decomposers use up more oxygen for aerobic respiration
                      • animals in the water die from a lack of oxygen e.g. fish
                        • dead animals add to the detritus
            • consumers can't consume the algae fast enough
              • algae die
                • detruis
                  • a rapid increase in decomposers e.g. saprobionts
                    • the decomposers use up more oxygen for aerobic respiration
                      • animals in the water die from a lack of oxygen e.g. fish
                        • dead animals add to the detritus
      • sewage leached into clean water
        • adds more nutrients into the water
          • algal bloom, rapid cell division, creates a layer of algae on the top of the water
            • there is then competition for light (algae blocks the sunlight) between the algae and other plants in the water
              • other plants die as they can't get light for the light dependent stage of photosynthesis
              • consumers can't consume the algae fast enough
                • algae die
          • IN BOTH FERTILISERS AND SEWAGE
          • FERTILISERS
          • SEWAGE
        • biochemical oxygen demand (BOD)
          • measures the rate of oxygen consumption by a sample of water
          • 1- take many sample of the water at random
            • 2- measure initial oxygen concentration with a calibrated O2 metre
              • 3- leave for 5 days in the dark at 20°C in the dark
                • want the sewage to break down by bacteria, temperature the same because there is more O2 in cold water. Jar is sealed to ensure no more dissolved O2 in the air gets in
                • 4-  measure final oxygen concentration
                  • BOD = initial O2-final O2
                    • a higher BOD means more the water is polluted
          • problems with this
            • may be few bacteria in the sample as it's taken by random
            • toxins released by bacteria may kill others
            • slow break down of cellulose
          • mg dm-3
        • fertiliser application
          • crop rotation
            • whole crop or sometimes just the roots is ploughed back into the soil.
            • the nitrogen that was fixed by the saprobionts is then made available to crops in the following years
          • artificial fertilisers
            • NPK
            • very easy  to apply and effective and can be tailored to each crop's individual mineral requirements
            • very soluble and can be leached out, causing eutrophication. Also expensive
          • natural fertilisers
            • e.g. animal manure
            • they contain NPK but contained in organic compounds such as urea, proteins and lipids
            • organic compounds can be digested by decomposers then the NPK can be released
            • less soluble so the inorganic material is released more slowly which prevents leaching and means that they last longer
            • cheap, improves soil structure which improves drainage and aeration.
            • bulky and less concentrated in minerals than in inorganic fertilisers so need to be spread on a field. heavy machinery that spreads it damages the soil
            • can contain unwanted substances like weed seeds, fungal spores and heavy metal.

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