Part 4b. Methods of increasing food production and improving sustainability

4b. Quality of soil

Doc Brown's Biology exam study revision notes

There are various sections to work through,

after 1 they can be read and studied in any order.

Sub-index of notes on increasing food production

Index of notes on ALL aspects of food production

re-edit 11/05/2023


4(b) Poor soil is improved by application of fertilisers - overuse causes environmental problems (advantages and disadvantages)

Ways of improving soil fertility.

Fertilisers contain important nutrients for plants to grow e.g. nitrates for nitrogen, phosphates for phosphorus, ions of magnesium and sulfate (for sulfur) and compounds of trace elements like copper, zinc and boron.

The idea of using fertilisers is twofold:

(i) bring into use poor quality soil deficient n nutrients,

(ii) replace nutrients used up by the previous crops,

(iii) grow crops with increased yield,

(iv) although (i) to (iii) apply to any fertiliser, naturally produced organic fertilisers produce a much better quality of soil.

Organic farming with compost and cattle muck produces much better quality of soil, whose structure and nutrient and water retaining properties are important.

BUT overuse of synthetic inorganic fertilisers has created eutrophication problems in lakes and rivers and they are not cheap, particularly in the context of a poorer country.

Eutrophication is when an excess of nutrients like nitrates and phosphates causes algal blooms, so water is covered in a thick mass of green slimy algae that reduces oxygen levels in water and kills most aquatic life beneath it.

Manure and compost

Organic fertilisers based on plant and animal waste are more beneficial for soil quality and probably produce food of a higher nutritious quality.

See The manufacture & use of fertilisers

and NPK fertilisers-environmental problems

Infertile soils too acidic for growing crops or raising cattle (pH <7), can be treated with alkaline lime to increase the pH of the soil to a more neutral value (~pH 7).


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