IB ESS SL 5.1 Soil Questions

Practise IB ESS SL 5.1 by mapping soil flows, separating transfers from transformations and using texture and property data to explain productivity.

Exam points

Explain soil as an open ecosystem using storages, flows, biotic and abiotic components, and their interactions.
Build flow diagrams linking soil to the atmosphere, lithosphere and organisms; trace matter through water, carbon or nitrogen cycles.
Distinguish soil inputs/outputs from transfers/transformations using weathering, decomposition, leaching and plant uptake.
Classify soil texture from sand, silt and clay proportions; compare sandy, clay and loam effects on plant productivity.
Use nutrient, organic-matter, pH, texture and organism evidence to explain soil fertility and primary productivity.
Explain how over-irrigation changes fertility through salinization, nutrient loss, waterlogging and reduced nutrient cycling.

Covered syllabus points

5.1.1—Soil as dynamic system 5.1.2—Soil composition 5.1.3—Soil profiles and horizons 5.1.4—Soil system inputs 5.1.5—Soil system outputs 5.1.6—Soil transfers 5.1.7—Soil transformations 5.1.8—Soil flow diagrams 5.1.9—Soil foundation role 5.1.10—Soil and biodiversity 5.1.11—Soil in element recycling 5.1.12—Soil texture 5.1.13—Texture affects productivity 5.1.14—Soil carbon role

[Maximum number: 4]

Outline how soil can be viewed as an ecosystem.

Like an ecosystem, soil is an open system with inputs and outputs;
(inputs of) eg water / $\mathrm{O}_{2}$ (and outputs of) eg $\mathrm{CO}_{2}$ / nitrogen; ...and storages and flows/processes;
(storages of) eg nitrates/water (and flows of) eg leaching/decomposition;
like an ecosystem, soil is a community of living/biotic and abiotic elements;
(biotic) eg bacteria/fungi/earthworms (and abiotic) eg clay/sand/silt/water/heat; ...with the many complex interactions/interrelationships/eg mineral cycling/leguminous plants;
interacts with/supports other systems/eg vegetation growth, animal movement/burrowing/human development;

Award marks as above for identifying relevant common features, and also for giving examples (provided it is clear what is being exemplified).

[Maximum number: 1]

Explain how the production of cash crops (such as pineapples) may have an environmental impact on:

soil

[Maximum number: 9]

Soil quality is important for global food production systems.

(a)

Figure:Soil texture triangle

[ 1 ]

(b)

Describe how the addition of sand to a silty clay loam could alter its characteristics for healthy plant growth.

[ 2 ]

Positive effects:
it will increase drainage / prevent water-logging;
it will increase infiltration/permeability / reduce loss of water through run-off;
it will increase porosity/air spaces/reduce soil compaction providing more $\mathrm{O}_{2}$ to roots;
it would allow for increased flow/availability of nutrients;
it will promote detritivore/decomposer/mycorrhizal/microbial communities;
it will allow for easier root penetration;
Negative effects:
it will reduce water-holding capacity so less water for plants;
it will increase possibility of leaching, reducing minerals for plants;
it will reduce stability of soil giving less anchorage to plants;

Award [1] for each correct answer, up to [2 max].
Although question implies positive effects on soil, credit can be given for negative effects as long as candidates make this clear as in MPs given above.

(c)

Figure:Horizons in a typical soil profile

[ 4 ]

(i)

Draw a flow diagram to show the flows of leaching and decomposition associated with the mineral storage in the "A" horizon in the soil-profile diagram shown above.

[ 2 ]

(ii)

Identify one other input to the mineral storage in the "A" horizon.

[ 1 ]

(iii)

Identify one other output from the mineral storage in the "A" horizon.

[ 1 ]

(d)

Outline why leaving arable farmland fallow (unused) between growing seasons could lead to soil degradation.

[ 2 ]

[Maximum number: 1]

Soil quality is important for global food production systems.

Figure:Horizons in a typical soil profile

Identify one other input to the mineral storage in the "A" horizon.

[Maximum number: 5]

Figure Types and causes of soil degradation globally

Figure Soil profile and the relative proportions of each type of microorganism at increasing depth

(a)

Using Figure 2(a), identify which cause of soil degradation makes up the largest percentage globally.

[ 1 ]

(b)

State one process that could reduce the mineral storage from the A horizon.

[ 1 ]

(c)

Explain how deforestation could impact soil quality.

[ 3 ]

[Maximum number: 4]

Outline two transfer processes and two transformation processes that occur within the soil.

[Maximum number: 4]

(a)

Figure 7(b): Impact of irrigation water salinity on crop yield potential

Figure:Impact of irrigation water salinity on crop yield potential

Figure:Fact file on agriculture in California

Figure 7(a): Fact file on agriculture in California
Over 36000 km2 of agricultural land is irrigated. During severe drought, Central Valley farmers receive no state water for irrigation. Over 50% of irrigated land is impacted by salinity. California produces 81% of the world’s almonds, its most economically valuable agricultural export. The water footprint of one almond is 12 litres. Almond samples have contained up to nine pesticide residues, some toxic to bees.

With reference to Figure 7(b), state the relationship between irrigation water salinity and crop yield potential.

[ 1 ]

(b)

over 36 000 km² of California agricultural land is irrigated; over 50% of irrigated land is affected by salinity. California produces 81% of the world’s almonds, and one almond has a water footprint of about 12 litres.

Explain how irrigation has reduced soil fertility in the Central Valley.

[ 3 ]

a. irrigation water is often pumped up from underground/from wells;
b. groundwater contains (mineral) salts / water used for irrigation may contain salts/be saline;
c. in areas of high evaporation/dry/semi-arid climates, water evaporates from the surface, leaving salts behind;
d. the dissolved sodium ( $\mathrm{Na}^{+}$ ) and chloride ( $\mathrm{Cl}^{-}$ ) ions can displace other mineral nutrients in the soil needed for plant growth, such as potassium (K) and phosphorus (P) / minerals required for plant growth are replaced ;
e. salin(is)ation of soils/over time the salts build up, leading to levels higher than macroinvertebrates/decomposers can tolerate;
f. reduction in macroinvertebrates/decomposers may reduce nutrient cycling;
g. excessive irrigation can lead to leaching of nutrients from the soil (reducing soil fertility) / irrigation can lead to erosion of fertile top soil;
h. excessive irrigation can lead to water-logging/rise in water table and poor aeration of the soil, reducing nutrient cycling;
i. irrigation leads to an increase in plant growth that utilizes/absorbs nutrients from the soil (hence reducing soil fertility over time);

Note: do not accept just "salin(is)ation" or "leaching" as this does not explain why loss of soil fertility occurs.

[Maximum number: 2]

Soil quality is important for global food production systems.

Figure:Horizons in a typical soil profile

Draw a flow diagram to show the flows of leaching and decomposition associated with the mineral storage in the "A" horizon in the soil-profile diagram shown above.

[Maximum number: 7]

Explain the link between soil fertility, primary productivity and human activity.

[Maximum number: 1]

Figure Types and causes of soil degradation globally

Figure Soil profile and the relative proportions of each type of microorganism at increasing depth

State the trend of microorganism biomass with increasing depth in Figure 2(b).

[Maximum number: 1]

Figure Types and causes of soil degradation globally

Figure Soil profile and the relative proportions of each type of microorganism at increasing depth

Outline one role that microorganisms play in soil ecosystems.

[Maximum number: 1]

Soil quality is important for global food production systems.

Figure:Soil texture triangle

[Maximum number: 2]

Soil quality is important for global food production systems.

Describe how the addition of sand to a silty clay loam could alter its characteristics for healthy plant growth.

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Covered syllabus points

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Question (ii)

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Question (d)

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