R2102 3.2 Explain the significance of soil pH to plant growth

Question 1

What are calcifuge plants?

Answer 1

Those adapted to grow on acid soils below pH 5.5

Question 2

What are calcicoles?

Answer 2

Plants adapted to grow on calcareous soils (calcium rich)

Question 3

General pH for horticultural use

Answer 3

4-8 pH

Most plants grow in the range of 5.5-8

Question 3

General pH for horticultural use

Answer 3

4-8 pH

Most plants grow in the range of 5.5-8

Question 4

Ideal pH in UK

Answer 4

6.5 pH

Question 5

Why is 6.5pH the ideal pH in UK soils?

Answer 5

At this point all the essential plant nutrients are available for uptake by the roots of most plants

Question 6

Why is 6.5pH the ideal pH in UK soils?

Answer 6

At this point all the essential plant nutrients are available for uptake by the roots of most plants

Question 7

Neutral soils

Answer 7

Horticulturally a neutral soil is pH6.5 (true neutral is 7). This is the best pH for the greatest numbers of plants

Question 8

Acidic soil

Answer 8

Below 7 pH e.g. rainwater, carbonic acid, fizzy drinks, lemon juice

Question 9

Alkaline soils

Answer 9

Above pH 7 e.g. limewater, caustic soda

Question 10

Alkaline soils

Answer 10

Above pH 7 e.g. limewater, caustic soda

Question 11

Problems in acid soils (2)

Answer 11

1. Magnesium and club root more prevalent
2. Some nutrients (Ca, P, Mn) are less available to plants

Question 12

Problems in alkaline soils (1)

Answer 12

1. Traces element deficiencies are common: Fe, Mg, B

Question 13

Why soils become naturally more acidic (5)

Answer 13

1. Rainfall washes out free lime from the soil
2. Akaline nutrients like Ca are used by the plant and removed with it when crops are harvested
3. Microorganism activity releases acid into the soil, and so does plant respiration which release CO2 into the soil
4. Some fertilisers used on soils are acidic
5. Rainfall tends to be slight acidic

Question 14

Common way to raise soil pH

Answer 14

1. Using lime (ground chalk or limestone). Should be applied as a fine powder
2. Protect eyes and use gloves - prevent irritation and chemical burns
3. Composted green waste
4. Wood ash

Question 15

Liming (3)

Answer 15

1. Usually applied to soil surface as Calcium Carbonate (ground limestone)
2. Can use hydrated or slaked lime which is stronger and works faster but is tricky to use
3. Plays an important role in improving soil structure on clay soils as it can cause particles to flocculate (come together) into crumb structure

Question 16

Advantages of liming (5)

Answer 16

1. Raise soil pH
2. Provides calcium which otherwise might be lost
3. Encourages worm and bacteria populations which dislike acid soils
4. Improves soil structure on heavy clay soils by flocculating the particles
5. Can make other nutirents more available

Question 17

How to lower soil pH?

Answer 17

1. Sulphur chips can be added (more expensive than lime)
2. Mulching with pine needles and adding lots of organic matter and manure - gradual change
3. Ammonium sulphate can lower pH over a number of years on outdoor soils

Question 18

How to lower soil pH?

Answer 18

1. Sulphur chips can be added (more expensive than lime)
2. Mulching with pine needles and adding lots of organic matter and manure - gradual change

Question 19

What does the pH soil affect?

Answer 19

1. Soil life - bacteria become less active and worms dont thrive when pH less than 4.5
2. Soil structure - Clay, more lime to raise pH but effects last longer. Also clay soils flocculated by lime so structure is improved
3. Nutrient availability -pH affects uptake of nutrients. There are antagonisms between nutrients at different soil pH where the surplus of one prevents the uptake of another.
4. Nitrogen can be lost if the manure is added to the soil to soon after it has been limed - lime reacts to release ammonia gas instead of putting nitrogen into the soil
5. Plant can be susceptible to diseases. Brassicas get club root in acid soils, Potatoes get scab into alkaline soils.

Question 20

Name 3 plants that prefer acid soils (calcifuges).

Answer 20

Rhododendron impeditum

Azalea japonica

Dionaea muscipula

Question 21

Name 3 plants for neutral soils.

Answer 21

Malus domestica

Iris germanica

Daucus carota

Question 22

Name 3 plants for alkaline soils (calcicoles).

Answer 22

Clematis montana

Lavandula augustifolia

Fagus sylvatica