Soils & Human Activity (AQA A Level Geography)

Revision Note

Tropical Red Latosol

Zonal soil characteristics

  • Soils form the layer between the bedrock and the surface of the ground

  • They consist of weathered bedrock and decomposed organic matter from plants

  • Climate is a key factor in how quickly bedrock weathers and organic matter decomposes

  • Zonal soils form over long periods of time, typically taking 100 years for every inch of soil

  • Cross profiles of soils show distinct layers, known as soil horizons

  • Two examples of zonal soils are tropical red latosols and taiga podsols

Tropical Red Latosol

  • Located in tropical rainforest biome

  • Weathering of bedrock and decomposition of plant matter rapid due to warm and humid climate, forming deep soils 30-40 metres thick

m-merged-latsol
Cross Profile of Tropical Red Latosol Soil with Layer Characteristics and Impact on Human Activities

Taiga Podsol

Taiga Podsol

  • Podsol (or Podzol) soils form under coniferous woodland or heather moorland in taiga biomes (also known as boreal forest in North America)

    • Occupies a large belt of land just south of the tundra biome of the Arctic Circle in North America, Northern Europe and Northern Russia

  • Weathering of bedrock and decomposition of plant matter slow due to a cold winters and cool summers, so soils are shallow (rarely exceeds one metre thick)

m-merged-podsol
Cross Profile of Taiga Podsol with Layer Characteristics and Impact on Human Activities

Examiner Tip

Watch out for questions asking you to compare two different soil types. Make sure you can say how the characteristics of each are determined by various physical factors, and think about the similarities and differences between their impacts on agriculture and other human activities.

Agriculture, Soil Problems & Management

Soil Erosion, Waterlogging, Salinisation, Structural Deterioration

Soil Problems and their Management


Soil Problem 


Causes 


Impact On Agriculture


Management Options


Soil Erosion

Wearing away of fertile topsoil by wind and water


Deforestation and overgrazing exposes soil


Farming practices such as ploughing downslope can lead to rilling


Relief as soil more likely to be washed away on steep slopes


Climate as water erosion more likely after heavy rainfall and wind erosion more likely in very dry conditions


Soil becomes less fertile as nutrients are removed 


Soil’s ability to retain water reduced


Can cause rills and gullies that make the cultivation of paddocks impossible


Results in lower yields and higher production costs


Around 10 million hectares of land abandoned each year due to lack of crop productivity 


Afforestation to allow roots to stabilise soil and return leaf litter nutrients 


Fertilisers added to soils to improve nutrient content


Rotate crops to allow soil to recover before planting again


Planting natural windbreaks, such as hedges


Ploughing across, rather than down, slopes


Terracing on steep slopes


Waterlogging


When pores between soil particles fill with stagnant water


impermeable soils that have few pores, such as clay


Heavy rainfall in areas where rates exceed evapotranspiration


Over-irrigation


Hard-pans can stop percolation and create an impermeable layer


Gleying leads to soil infertility


Rotting of plant roots


Weeds outgrow crops as can survive waterlogged conditions better


Reduced soil temperature leading to slower crop growth


Improving field drainage


Sustainable irrigation systems


Adding sand to clay soils to increase pore spaces


Salinisation


Accumulation of salt within soil


Natural causes

  • High temperatures and low precipitation lead to high rates of evaporation so that salts left on ground surface

  • Sea-level rise can draw salt up into soil in coastal areas

Human causes

  • Over-abstraction of groundwater for irrigation leads to saltwater intrusion

  • Over-irrigation of water containing dissolved salts

  • Fertilisers containing salts left in soil


3000-6000 ppm of salt can be toxic to plants


Decreases osmotic potential of soil so plants can’t get required water


Pea and bean crops particularly vulnerable


Salinisation in San Joaquin Valley, California, projected to cost the state $1-1.5 billion


Drip-irrigation and soil moisture monitoring


Selection of deep-rooted crops to increase water retention


Soil flushing with water (although this moves problem elsewhere)


Using fertilisers with low salt content


Strategies to avoid waterlogging (as above)


Structural Deterioration


Pore spaces are lost as the structure of the soil is squeezed or collapses


Removal of vegetation so that roots no longer there to support the soil


Soil compaction from heavy farm machinery or livestock trampling


Salt in soil causes clumping together of clay particles



Lack of space in soil for infiltration of water to occur so crops dry out quickly


Plant roots unable to grow through compacted soil as they need air pockets to survive


Farmers unable to till and plough the soil if it is too compacted


Avoiding use of heavy machinery


Move livestock around to avoid compaction


Introducing more organic matter into the soil to encourage the soil to aggregate together to increase number of pore spaces


Strategies to avoid salinisation (as above)

 

Examiner Tip

You could be questioned on any one of these soil problems, so make sure for each you are able to explain the factors that cause them and how best to manage the issue. Try and link your knowledge of these problems to the two zonal soil examples learnt in the previous section. For example, leaching is an issue in both tropical red latasols and in taiga podsols, but hard-pans only occur in Taiga podsols.

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