5.1 SoilIB Environmental Systems and Societies SL: Subtopic test

1. 1
   A farmer tests soil from three fields. Sample X contains 70% sand, 20% silt and 10% clay. Sample Y contains 20% sand, 30% silt and 50% clay. Sample Z contains 40% sand, 40% silt and 20% clay and has a high proportion of humus.

   (a)

   Soil texture is determined by:

   [1 mark]

   • AThe colour of the soil
   • BThe depth of the soil profile
   • CThe relative proportions of sand, silt, clay and humus
   • DThe number of earthworms in the soil

   (b)

   Which statement is most likely to be true of Sample X?

   [1 mark]

   • AIt drains quickly and holds little water and few nutrients
   • BIt holds large amounts of water and is often waterlogged
   • CIt has the highest primary productivity of the three samples
   • DIt contains no inorganic components

   (c)

   Outline how the humus in Sample Z can increase primary productivity.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a temperate woodland, leaves fall each autumn and form a layer of dead organic matter on the soil. Rainwater washes dissolved minerals downwards through the soil. Earthworms mix the layers. Bacteria and fungi decompose the dead organic matter and release heat.

   (a)

   Which of the following is an input to the woodland soil system?

   [1 mark]

   • AHeat released by decomposers
   • BCarbon dioxide released by decomposition
   • CMinerals lost from the soil in drainage water
   • DDead organic matter from leaf fall

   (b)

   The movement of dissolved minerals from the upper soil to deeper layers is best described as:

   [1 mark]

   • AA transformation
   • BA transfer between horizons
   • CAn input from outside the system
   • DA storage

   (c)

   State two outputs from the woodland soil system.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A study compared the carbon balance of two sites. Site A is undisturbed grassland: dead organic matter adds 3.0 tonnes of carbon per hectare per year, and decomposition releases 2.6 tonnes of carbon per hectare per year. Site B was grassland that has been ploughed for crops: dead organic matter adds 1.8 tonnes of carbon per hectare per year, and decomposition releases 2.9 tonnes of carbon per hectare per year.

   (a)

   Calculate the net annual change in soil carbon at each site, and state whether each soil is acting as a carbon sink or a carbon source.

   [3 marks]

   (b)

   Explain how the relative rates of input and decomposition determine whether soil acts as a carbon sink, store or source, and suggest why ploughing changed the balance at Site B.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school garden club prepares to grow vegetables on three plots. Plot P is mainly sand and drains freely. Plot Q is mainly clay, stays wet for long periods and is often waterlogged. Plot R is a loam with roughly equal amounts of sand, silt and clay and a high humus content. A club member says: "Soil is just dirt that holds plants up."

   (a)

   Explain why the club member's statement understates the roles of soil in terrestrial ecosystems.

   [6 marks]

   (b)

   Evaluate the suitability of the three plots for growing vegetables.

   [6 marks]

   Total for question 4: 12 marks

End of questions