Question 1
Figure 2 shows a natural soil profile.
Identify the soil horizon represented by each of W, X, Y and Z.
[4]
Question 2
A soil sample was mixed thoroughly with water and allowed to settle. Figure 1 shows the resulting sedimentation jar.
Calculate the percentage of the mineral soil that is clay. Show your working.
[2]
Identify the mineral fraction with the greatest proportion in the sample.
[1]
Explain how the soil texture shown could affect plant growth during a prolonged period without rainfall.
[3]
Question 3
Draw a systems flow diagram for a soil system. Include two storages, one input, one internal flow and one output.
[4]
Question 4
Distinguish between infiltration and percolation.
[2]
Distinguish between erosion and leaching.
[2]
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Question 5
Explain the roles of detritivores and saprotrophs in recycling mineral nutrients from leaf litter.
[3]
Question 6
A woodland footpath has experienced increased visitor numbers. Soil was sampled beside the path and from a nearby undisturbed area.
Calculate the percentage reduction in cumulative infiltration after 10 minutes in the trampled soil compared with the undisturbed soil.
[2]
Describe two differences between the composition of the undisturbed soil and the trampled soil.
[2]
Explain how trampling could produce the infiltration pattern shown in Figure 1(b).
[3]
Evaluate the use of a fenced boardwalk as a strategy for restoring the soil beside the woodland path.
[5]
Question 7
Three soils used for growing beans were examined using sedimentation tests. Equal dry masses of soil were mixed with equal volumes of water and allowed to settle.
Sedimentation layer thicknesses for three soils.
| Soil | Sand layer / mm | Silt layer / mm | Clay layer / mm |
|---|---|---|---|
| A | 30 | 15 | 5 |
| B | 10 | 15 | 25 |
| C | 20 | 20 | 10 |
Determine the percentage of the mineral layer in soil B that is clay.
[2]
Describe the relationship between clay content and drainage time for soils A, B and C.
[2]
Explain why soil C produced a greater bean biomass than either soil A or soil B.
[3]
Evaluate whether the sedimentation results alone are sufficient to select the best soil for bean production.
[5]
Question 8
Equal dry-mass samples from the B horizons of a cultivated garden and a nearby natural woodland were heated to estimate organic matter by loss on ignition. Table 1 shows the results.
Mass measurements before and after ignition for soil samples from two sites.
| Site | Replicate | Dry mass before ignition / g | Ash mass after ignition / g |
|---|---|---|---|
| Cultivated garden | G1 | 20.0 | 18.0 |
| Cultivated garden | G2 | 20.0 | 17.8 |
| Cultivated garden | G3 | 20.0 | 18.2 |
| Natural woodland | W1 | 20.0 | 14.0 |
| Natural woodland | W2 | 20.0 | 13.6 |
| Natural woodland | W3 | 20.0 | 14.4 |
The percentage loss on ignition is calculated using:
where is dry mass before ignition and is ash mass after ignition.
Calculate the percentage loss on ignition for garden replicate G2. Show your working.
[2]
Compare the mean percentage loss on ignition of the two sites.
[2]
Explain how the difference shown in Table 1 may affect soil fertility at the two sites.
[3]
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Question 9
A dry B-horizon soil sample has a mass of . After it is heated to burn off organic matter, the ash has a mass of .
Calculate the percentage mass lost on ignition. Show your working.
[2]
Outline one reason why the calculated percentage may not equal the percentage of carbon in the soil.
[1]
Question 10
The structures of two soils are shown in Figure 1.
Explain two ways in which the different soil textures shown may affect primary productivity.
[4]
Question 11
Draw an annotated profile diagram of a soil with O, A, B and C horizons. Show one input, one transfer and one transformation that contribute to development of the profile.
[4]
Question 12
Outline three reasons why examination of the whole soil profile is more useful for soil classification than examination of a single surface sample.
[3]
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Question 13
A semi-arid farming district uses groundwater for irrigation. Evaporation is high and some fields have poor drainage.
Soil salinity and wheat yield after irrigation begins.
| Years since irrigation began | Soil salinity / | Wheat yield / |
|---|---|---|
| 0 | 1.2 | 5.2 |
| 5 | 2.8 | 4.9 |
| 10 | 5.4 | 3.8 |
| 15 | 8.1 | 2.3 |
Soil salinity and wheat yield after three years under different irrigation management systems.
| Management system | Soil salinity / | Wheat yield / |
|---|---|---|
| Flood irrigation; no drainage | 8.1 | 2.3 |
| Periodic freshwater flushing | 5.0 | 3.6 |
| Drip irrigation + subsurface drainage | 2.6 | 4.7 |
Determine the percentage decrease in wheat yield between year 0 and year 15.
[2]
Distinguish between the transfer of salts by capillary movement and the transformation of the soil by salinization.
[2]
Explain the relationship between irrigation, soil salinity and wheat yield shown in Figures 4(a) and 4(b).
[3]
Evaluate which management system should be adopted to reduce soil degradation in the district.
[5]
Question 14
Figure 2 compares soil organic carbon storage and relative decomposition rate in four ecosystems.
Identify the ecosystem with the greatest soil organic carbon storage.
[1]
Describe the relationship between decomposition rate and soil organic carbon storage shown in Figure 2.
[2]
Explain the difference in soil organic carbon storage between tropical forest and wetland ecosystems shown in Figure 2.
[4]
Question 15
A rainfall simulator applied of water to equal plots with three different surface conditions. Figure 3 shows the measured infiltration, surface runoff and sediment loss.
Measured responses to 50 mm simulated rainfall; infiltration plus surface runoff equals 50 mm for each surface condition.
| Surface condition | Infiltration / mm | Surface runoff / mm | Sediment loss / g m |
|---|---|---|---|
| Bare soil | 12 | 38 | 240 |
| Compacted soil | 8 | 42 | 310 |
| Organic mulch | 35 | 15 | 45 |
Calculate the percentage reduction in sediment loss when organic mulch is used instead of leaving the soil bare. Show your working.
[2]
Describe two differences between the compacted and mulched plots.
[2]
Explain how organic mulch produces the differences shown in Figure 3.
[3]
Question 16
Explain why tropical forest soils commonly contain relatively little stored carbon.
[2]
Explain why wetland soils may act as carbon sinks.
[2]
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Question 17
Figure 3 shows two soil profiles, P and Q.
Classify profiles P and Q as either brown earth or oxisol.
[2]
Outline one feature of each profile that supports the classifications in (a).
[2]
Question 18
On an intensively cultivated hillside, most of the O and A horizons have been removed by erosion, leaving the B horizon exposed.
Explain two reasons why exposure of the B horizon is likely to reduce primary productivity.
[4]
Question 19
Researchers compared soil carbon storage and decomposition in four terrestrial ecosystems. They also incubated wetland and temperate grassland soils at different temperatures.
Soil organic carbon storage and relative decomposition rate in four terrestrial ecosystems.
| Ecosystem | Soil organic carbon storage / | Relative decomposition rate / index () |
|---|---|---|
| Tropical forest | 45 | 9 |
| Tundra | 170 | 2 |
| Wetland | 220 | 1 |
| Temperate grassland | 140 | 4 |
Calculate how many times greater the wetland soil carbon store is than the tropical forest soil carbon store.
[2]
Describe the effect of incubation temperature on soil respiration.
[2]
Explain the differences in soil carbon storage among tropical forest, wetland and temperate grassland ecosystems.
[4]
Evaluate the claim that climate warming will cause these soils to become major carbon sources.
[5]
Question 20
Two soil profiles were recorded in undisturbed forest ecosystems. Profile X occurs beneath a temperate deciduous forest, while profile Y occurs beneath a tropical rainforest.
Climate and litter decomposition summary for the two forest sites.
| Site | Forest type | Mean annual temperature / | Annual precipitation / mm | Litter decomposition / months |
|---|---|---|---|---|
| X | Temperate deciduous | 11 | 850 | 18 |
| Y | Tropical rainforest | 26 | 2400 | 3 |
Classify profiles X and Y as brown earth or oxisol.
[2]
Compare the O, A and B horizons of the two profiles.
[3]
Explain how climate and soil processes produce the characteristics of profile Y.
[4]
Evaluate the reliability of classifying these soils from the profile and climate evidence provided.
[5]
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Question 21
A natural grassland was converted to intensively cultivated cropland 30 years ago. Researchers compared an uncultivated remnant with the cropland.
Comparison of soil characteristics in natural grassland and intensive cropland.
| Soil characteristic | Natural grassland | Intensive cropland |
|---|---|---|
| Annual erosion / t ha-1 yr-1 | 2 | 28 |
| Infiltration / mm h-1 | 48 | 14 |
| Organic matter / % | 6.4 | 1.2 |
| Available nitrogen / mg kg-1 | 34 | 12 |
Calculate how many times greater the annual erosion rate is in the intensive cropland than in the natural grassland.
[2]
Outline three ecosystem functions lost when the O and A horizons are removed.
[3]
Explain how removal of the upper horizons can produce the differences shown in Figure 6(b).
[4]
Evaluate whether fertilizer application alone could restore the intensive cropland to the functioning of the natural soil.
[5]
Question 22
Figure 4 shows two soil profiles from contrasting forest biomes.
State the thickness of the A horizon in Profile X.
[1]
Classify Profile X and Profile Y as brown earth or oxisol.
[2]
Analyse how the transfers and transformations shown account for the contrasting profiles.
[4]
Question 23
Figures 5(a) and 5(b) compare an intact natural soil with a severely eroded soil under intensive agriculture.
Measured soil properties for intact natural and eroded agricultural soils.
| Measured property | Intact natural soil | Eroded agricultural soil |
|---|---|---|
| Plant-available nitrogen / | 24 | 7 |
| Water retained after drainage / % by mass | 36 | 18 |
| Above-ground primary productivity / | 780 | 310 |
Calculate the percentage decrease in water retained after drainage between the intact and eroded soils. Show your working.
[2]
Identify the two horizons lost from the eroded agricultural soil.
[1]
Explain the lower primary productivity of the eroded agricultural soil using evidence from both figures.
[4]
Question 24
Two adjacent fields in a dry region were irrigated with water containing dissolved salts. Field D had subsurface drainage, while Field P had poor drainage. Figure 6 shows changes over five years.
Changes in soil electrical conductivity and crop yield over five years in two irrigated fields.
| Year | Field D conductivity / | Field P conductivity / | Field D yield / | Field P yield / |
|---|---|---|---|---|
| 0 | 1.0 | 1.0 | 4.8 | 4.8 |
| 1 | 1.2 | 1.8 | 4.9 | 4.6 |
| 2 | 1.3 | 2.9 | 4.8 | 4.1 |
| 3 | 1.4 | 4.1 | 4.7 | 3.5 |
| 4 | 1.5 | 5.3 | 4.7 | 2.9 |
| 5 | 1.6 | 6.4 | 4.6 | 2.4 |
Calculate the percentage decrease in crop yield in Field P from year 0 to year 5. Show your working.
[2]
Describe the change in soil electrical conductivity in the two fields.
[2]
Explain the trends in salinity and crop yield shown in Figure 6.
[3]
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Question 25
Outline four ways in which soil sustains terrestrial ecosystems.
[4]
Explain how detritivores, saprotrophs and plants interact in the recycling of nutrients within a soil ecosystem.
[7]
Using named examples, evaluate the use of organic soil amendments as a strategy for maintaining soil fertility and biodiversity in managed ecosystems.
[9]
Question 26
A farmer replaces annual deep ploughing and bare fallow periods with reduced tillage and a permanent cover crop.
Explain how these changes may help conserve the A horizon.
[4]
Question 27
Students compared the B horizons of a fertilized field and an adjacent natural woodland. Equal-volume samples were collected with their centres positioned 10 cm below the upper boundary of the B horizon at each site. Loss on ignition was used as an operational estimate of organic matter.
Calculate the percentage loss on ignition for the woodland B-horizon sample.
[2]
Compare the properties of the field and woodland B horizons.
[3]
Explain how management and transfers through the profiles may account for these differences.
[4]
Evaluate the validity of concluding that the woodland B horizon contains four times as much soil carbon as the field B horizon.
[5]
Question 28
Three neighbouring farms use conventional annual cultivation, no-till cultivation or agroforestry. Measurements were made after 12 years under each system.
Calculate the percentage of the total soil carbon stock located in the A horizon under agroforestry.
[3]
Describe two differences between the A horizons under conventional cultivation and agroforestry.
[2]
Explain how agroforestry could produce the A-horizon and erosion patterns shown.
[4]
Evaluate whether agroforestry is the most sustainable management system for these farms.
[6]
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Question 29
Figure 7 shows soil profiles recorded along a hillslope transect after many years of cultivation.
Identify the position with the thickest A horizon.
[1]
Describe the variation in the A horizon along the transect.
[2]
Analyse how transfers within the hillslope system could produce the profile pattern shown.
[4]
Question 30
Distinguish between a carbon store, a carbon sink and a carbon source in relation to soil.
[4]
Explain why soil carbon storage differs among tropical forests, tundra, wetlands and temperate grasslands.
[7]
Using named examples, to what extent can soil management contribute to climate-change mitigation?
[9]
Question 31
Outline four properties of soil that influence primary productivity.
[4]
Explain how sand, clay and humus can produce contrasting effects on soil fertility and plant growth.
[7]
Using named examples, discuss the claim that increasing inputs to managed soils is sufficient to maintain long-term primary productivity.
[9]
Question 32
Describe the O, A, B and C horizons of a developed soil profile.
[4]
Explain how transfers and transformations produce contrasting brown earth and oxisol profiles.
[7]
Using named examples, evaluate the usefulness of soil-profile classification and mapping for making land-use decisions.
[9]
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Question 33
Explain three reasons why the A horizon is important to terrestrial ecosystems.
[3]
Analyse how intensive agriculture can generate positive feedback leading to the degradation and loss of the A horizon.
[8]
Using named examples, to what extent can degraded A horizons be restored by changing agricultural management?
[9]
Question 34
Outline four types of evidence from a whole soil profile that may be used to classify the soil.
[4]
Explain how conversion of a natural forest to intensive cropland may alter the soil profile and flows within the soil system.
[7]
Using named examples, discuss whether restoring a complete soil profile is necessary for the successful restoration of a terrestrial ecosystem.
[9]
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