Soils & Human Activity (AQA A Level Geography)
Revision Note
Written by: Robin Martin-Jenkins
Reviewed by: Bridgette Barrett
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
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)
Examiner Tips and Tricks
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
Human causes
| 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 Tips and Tricks
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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