R2102 3.2 Explain the significance of soil pH to plant growth Flashcards
What are calcifuge plants?
Those adapted to grow on acid soils below pH 5.5
What are calcicoles?
Plants adapted to grow on calcareous soils (calcium rich)
General pH for horticultural use
4-8 pH
Most plants grow in the range of 5.5-8
General pH for horticultural use
4-8 pH
Most plants grow in the range of 5.5-8
Ideal pH in UK
6.5 pH
Why is 6.5pH the ideal pH in UK soils?
At this point all the essential plant nutrients are available for uptake by the roots of most plants
Why is 6.5pH the ideal pH in UK soils?
At this point all the essential plant nutrients are available for uptake by the roots of most plants
Neutral soils
Horticulturally a neutral soil is pH6.5 (true neutral is 7). This is the best pH for the greatest numbers of plants
Acidic soil
Below 7 pH e.g. rainwater, carbonic acid, fizzy drinks, lemon juice
Alkaline soils
Above pH 7 e.g. limewater, caustic soda
Alkaline soils
Above pH 7 e.g. limewater, caustic soda
Problems in acid soils (2)
- Magnesium and club root more prevalent
- Some nutrients (Ca, P, Mn) are less available to plants
Problems in alkaline soils (1)
- Traces element deficiencies are common: Fe, Mg, B
Why soils become naturally more acidic (5)
- Rainfall washes out free lime from the soil
- Akaline nutrients like Ca are used by the plant and removed with it when crops are harvested
- Microorganism activity releases acid into the soil, and so does plant respiration which release CO2 into the soil
- Some fertilisers used on soils are acidic
- Rainfall tends to be slight acidic
Common way to raise soil pH
- Using lime (ground chalk or limestone). Should be applied as a fine powder
- Protect eyes and use gloves - prevent irritation and chemical burns
- Composted green waste
- Wood ash
Liming (3)
- Usually applied to soil surface as Calcium Carbonate (ground limestone)
- Can use hydrated or slaked lime which is stronger and works faster but is tricky to use
- Plays an important role in improving soil structure on clay soils as it can cause particles to flocculate (come together) into crumb structure
Advantages of liming (5)
- Raise soil pH
- Provides calcium which otherwise might be lost
- Encourages worm and bacteria populations which dislike acid soils
- Improves soil structure on heavy clay soils by flocculating the particles
- Can make other nutirents more available
How to lower soil pH?
- Sulphur chips can be added (more expensive than lime)
- Mulching with pine needles and adding lots of organic matter and manure - gradual change
- Ammonium sulphate can lower pH over a number of years on outdoor soils
How to lower soil pH?
- Sulphur chips can be added (more expensive than lime)
- Mulching with pine needles and adding lots of organic matter and manure - gradual change
What does the pH soil affect?
- Soil life - bacteria become less active and worms dont thrive when pH less than 4.5
- Soil structure - Clay, more lime to raise pH but effects last longer. Also clay soils flocculated by lime so structure is improved
- 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.
- 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
- Plant can be susceptible to diseases. Brassicas get club root in acid soils, Potatoes get scab into alkaline soils.
Name 3 plants that prefer acid soils (calcifuges).
Rhododendron impeditum
Azalea japonica
Dionaea muscipula
Name 3 plants for neutral soils.
Malus domestica
Iris germanica
Daucus carota
Name 3 plants for alkaline soils (calcicoles).
Clematis montana
Lavandula augustifolia
Fagus sylvatica
