Fertilisers Flashcards
What is intensive food production
Food production concentrated on specific areas of land that are used repeatedly to achieve maximum yield from the crops and animals grown on them.
Why does intensive food production make large demands on the soil
Mineral ions are continually taken up by the crops or animals grown in it.
What are the two types of fertilisers
1) Natural (organic) fertilisers: these consist of dead and decaying remains of plants and animals as well as animal wastes such as manure, slurry and bone meal.
2) Artifical (inorganic) fertilisers: These are mined from rocks and deposits and then converted into different forms and blended together to give the appropriate balance of minerals for a particular crop. Compounds containing the nitrogen phosphorus and potassium are always present.
List some of the detrimental effects that nitrogen-containing fertilisers have had
1) Reduced species diversity
2) Leaching
3) Eutrophication
Describe how nitrogen containing fertilisers have reduced species diversity
- Nitrogen rich soils favour the growth of grasses, nettles and other rapidly growing species.
- These out-compete many other species, which die as a result.
What is leaching and describe how it happens
- Leaching is the process by which nutrients are removed from the soil.
- Rainwater will dissolve any soluble nutrients, such as nitrate ions, and carry them deep into the soil where they are beyond the reach of plants roots.
- The leached nitrate ions find their way into watercourses, such as streams and rivers, that in turn may drain into freshwater lakes.
- Here it may have a harmful effect on humans if the river or lake is a source of drinking water.
Give a few ways in which leached nitrate ions are harmful to the environment
- Very high nitrate ion concentrations in drinking water can prevent efficient oxygen transport in babies and link to stomach cancer in humans.
- Leached nitrate ions can cause eutrophication.
Summarise simply what eutrophication is
The process in which nutrient concentrations increase in bodies of water
Describe eutrophication
1) In most lakes and rivers there is naturally very low concentration of nitrate and so nitrate ions are a limiting factor for plant and algal growth.
2) As the nitrate ion concentration increases as a result of leaching, it ceases to be a limiting factor for the growth of plants and algae whose populations both grow.
3) As algae mostly grow at the surface, the upper layers of water become densely populated with algae. This is called an ‘algal bloom’.
4) This dense surface layer of algae absorbs light and prevents it from penetrating to lower depths.
5) Light then becomes the limiting factor for the growth of plants and algae at lower depths and so they eventually die.
6) The lack of dead plants and algae is no longer a limiting factor for the growth of saprobiontic bacteria and so these populations grow,using the dead organisms as food.
7) The saprobiontic bacteria require oxygen for their respiration, creating an increased demand for oxygen.
8) The concentration of oxygen in the water is reduced and nitrates are released from the decaying organisms.
9) Oxygen then becomes the limiting factor for the population of aerobic organisms. These organisms ultimately die as all the oxygen is used up altogether.
10) Without aerobic organisms there is less competition for the anaerobic organisms whose populations now rise.
11) The anaerobic organisms further decompose dead material, releasing more nitrates and some toxic wastes, such as hydrogen sulphide, which make the water putrid.
What causes eutrophication
Organic manures, animal slurry, human sewage, ploughing old grassland and natural leaching all cause eutrophication, but leaching if artificial fertilisers is the main cause.
