Soils (NF)

Question 1

Why is soil important? (2 marks)

Answer 1

• Provides a habitat for living organisms.
• Supports plant growth.

Question 2

What does soil fertility mean? (1 mark)

Answer 2

• The ability of the soil to support plant growth.

Question 3

What are the five components of soil? (5 marks)

Answer 3

• Minerals - quantity determines soil texture (sand, silt, clay). Comes from breakdown and weathering and rocks.

• Water - keeps soil stuck together and carries essential nutrients for plants.

• Air - for aerobic respiration.

• Soil biota (living organisms) - e.g. worms, invertebrates and earwigs. Bacteria (part of the nitrogen cycle).

• Dead organic matter (remains of living things) - soil with lots of dead organic matter will be dark and sticky.

Question 4

What is humus? (2 mark)

Answer 4

• Humus is dark, organic material that forms in soil when plant and animal matter decays.

• It makes soil porous, increasing its air and water holding capacity. It is rich in nutrients (e.g., minerals) that promote plant growth.

Question 5

How does water effect the fertility and productivity of soil? (2 marks)

Answer 5

• Plants can only take up nutrients in a soluble form (when dissolved in water).

• Too much water can cause anoxic conditions (waterlogging).

Question 6

How do soluble materials such as micro and macro nutrients and metal ions effect the fertility and productivity of soil? (2 marks)

Answer 6

• A plant needs lots of nitrogen which is a macronutrient. Macronutrients is what plants need a lot of, for example phosphate and potassium.

• Iron, magnesium and copper are examples of micronutrients.

Question 7

How does air content effect the fertility and productivity of soil? (3 marks)

Answer 7

• Important for aerobic bacteria and aerobic respiration.

• Nitrifying bacteria - aerobic conditions preferred.

• Denitrifying bacteria - anaerobic conditions preferred.

Question 8

How does dead organic matter effect the fertility and productivity of soil? (2 mark)

Answer 8

• The breakdown of dead organic matter releases nutrients.

• Humus - increases soil fertility.

Question 9

How does pH effect the fertility and productivity of soil? (3 mark)

Answer 9

• Most soils are slightly acidic (5.5-7) because rain is slightly acidic. Carbon dioxide in the atmosphere mixes with water, creating carbonic acid.

• This means metals can go into solution that wouldn’t otherwise.

• If soils become too alkali then phosphates are less readily soluble.

Question 10

How does soil biota effect the fertility and productivity of soil? (4 mark)

Answer 10

• Nitrogen fixing bacteria - gaseous nitogren to ammonium ions.

• Nitrifying bacteria - oxidises ammonium ions to nitrite ions then to nitrate ions.

• Decomposers including bacteria and fungi, break down dead organic matter. They secrete digestive enzymes and rely on detritivores to physically break up the dead organic matter and increase its surface area.

• Detritivors such as beetle larvae and slugs break up dead organic matter and release nutrients into soil. Worms also increase soil drainage and aeration by creating tunnels in the soil.

Question 11

How does soil texture effect the fertility and productivity of soil? (2 mark)

Answer 11

• The measure of the proportion of sand, silt and clay determines soil texture and type.

• Texture effects how well water and nutrients are retained in the soil.

Question 12

How does soil structure effect the fertility and productivity of soil? (3 mark)

Answer 12

• Soil is made of peds (agrogates of soil particles).

• Some peds are more spherical and some are flat and platey.

• This can effect how water drains through soil.

Question 13

How does soil depth effect the fertility and productivity of soil? (1 mark)

Answer 13

• Increased depth means increased plant size nutrient availability.

Question 14

How does particle size and type affect drainage? (3 marks)

Answer 14

• Sand - quicker drainage (allow for faster movement of water).

• Clay - slower drainage (hard for water to go through).

• Silt - in-between

Question 15

How does particle size and type affect water content and capillary action?

Answer 15

Higher water content in clay soils due to smaller, flatter particles.
Lower water content in sand soils due to larger, spherical particles.

Question 16

How does particle size and type affect aeration?

Answer 16

Sandy soils have a greater aeration due to larger, spherical particles.
Clay soils have a greater aeration due to smaller, flatter particles.

Question 17

How does particle size and type affect nutrient levels?

Answer 17

Nutrients absorb easily into clay particles but not easily into sand particles.

Question 18

How does particle size and type affect thermal capacity?

Answer 18

Water has high specific heat capacity, so water content mostly determines thermal capacity.
Clay soils have highest water content.

Question 19

What is thermal capacity?

Answer 19

Ability to hold onto heat energy.

Question 20

How does particle size and type affect root penetration?

Answer 20

Easy in sand and hard in clay soils

Question 21

How does particle size and type affect ease of cultivation?

Answer 21

Sand soils are easier to cultivate and clay is harder.

Question 22

Soil Analysis Method: Soil Texture

Answer 22

Sedimentation Method:

• Place a large handful of soil in your sample tray
• Rub the soil sample through finger tips to separate particles
• remove obvious pieces of organic matter and any particles over 2 mm
• transfer the sample to the cylinder (half fill the cylinder)
• fill the cylinder with water and bung
• invert repeatedly to mix and suspend sample
• leave for at leave two weeks for all of the particles to settle
• using graduations on the cylinder to work out the percentage of sand, silt and clay in your sample an use the soil triangle to determine your soil type

Question 23

Draw and Label The Soil Triangle

Answer 23

Question 24

How long does it take sand, silt and clay to settle out of still water?

Answer 24

Sand - 2 minutes
Silt - 2 hours
Sand - 2 days

Question 25

Describe an alternative method of separating sand, silt and clay to determine soil type.

Answer 25

Sieve Method

• Dry sample out
• break up soil sample
• stack up sieves
• soil at the top and shake
• big at the bottom
• then measure whats in the sieves
• if holes in the sieve are greater than 2 mm it traps twigs and pebbles
• between 0.02 mm and 2 mm it traps sand
• between 0.002 mm and 0.02 mm it traps silt
• in the ban bottom there will be clay

Question 26

Soil Analysis Method: Water content

Answer 26

• weigh the crucible
• add half a handful of soil to the crucible and reweigh
• place the crucible in the oven at 100 C for 24 hours
• weigh the crucible and dry soil sample
• determine the mass of evaporated water
• work out the percentage mass or water in your original sample

Question 27

Water content: The soil sample may have dried out completely in less than 24 hours, how could you tell if all the water had evaporated?

Answer 27

The weight of the soil/mass of soil is constant.

Question 28

Describe an alternative method of determining water content of a soil sample that could be used if you did not have access to an oven.

Answer 28

Leave the soil out for a longer period of time in the sun. Weigh the mass until its constant to determine that all water has left the soil sample.

Question 29

why should the soil sample be kept in a sealed container or box?

Answer 29

To prevent water loss

Question 30

Soil Analysis Method: Air content

Answer 30

• add 200 ml of soil to a 500 ml beaker
• add 200 ml of water and stir
• record the new volume, you may need to use a measuring cylinder for this

Question 31

Soil Analysis Method: Organic Matter

Answer 31

• weigh an empty crucible
• add some dry soil and reweigh
• determine the mass of the soil
• place in the oven at 450 C and leave overnight
• weigh the crucible and soil sample again
• determine the loss of mass (organic matter)
• work out the percentage organic matter in your dry soil sample

Question 32

When determining organic matter content in soil, why should the oven temperature be kept below 550 C?

Answer 32

To prevent the burning of other things

Question 33

Explain 3 ways in which you can measure soil pH.

Answer 33

Universal indicator -
use colour chart to compare the colour of the paper

Universal indicator solution -
Add 2.5 cm^3 soil to a test tube
Add 1 cm^3 barium sulphate (settles sediment fast)
Add 3.5 cm^3 water
Add 10 drops universal indicator
Bung it then shake it
Compare to a colour chart

Electronic pH probe -
Often need re-calibrating using a pH probe

Question 34

What is the optimum soil pH range for most plants?

Answer 34

5.5-6.5, slightly acidic

Question 35

What methods could you use to sample or measure soil organisms/biota?

Answer 35

• Soil flooding
  Suitable for worms
  Set out an area and flood it
  An irritant such as mustard can be used
  Done a few times
  Then calculate proportion for the whole field
• Soil pit extraction (hand sorting)
  Suitable for worms
  Mark out an area and hand sort the soil (after digging out)
  Small worms may be missed

Question 36

How may human activities affect soil fertility?

Answer 36

• Planting/remaining legumes (have nitrogen fixing bacteria on nodular)
• Acid rain may alter pH
  (sulfur released from combustion/burning coal may produce)
• Addition of fertilisers (fish meal, manure, inorganic)
• Calcium carbonate/limestone powder to reduce soil acidity
• Reduced aeration due to heavy farm machinery compacting soil
• Increased aeration due to ploughing
• Creation of further habitats for biota such as beetle banks
• finish