Soil PH, Fertiliser, Growing Media & Hydroponics Flashcards
What is soil PH?
A term used to express the acidity or alkalinity of a soil solution and ranges from 4-8 for good plant growth.
It is measured on a scale of 1-14.
What is the ideal PH for growing most plants?
6.5
Why do soils become acid over time?
Because they leach calcium.
Sandy soils often more acidic because they leach calcium more readily.
Where is acidic on the PH scale?
Below 7 (between 7-0)
Where is alkaline on the PH Scale?
Above 7 (between 7-14)
Where is neutral on the PH scale?
7
What happens to plants if they are grown in soils outside of the 4-8 range on the PH scale?
Become nutrient deficient or toxic levels of nutrients build up.
How does soil PH affect nutrients to plants?
If the soil solution is too acid or too alkaline the nutrients may not dissolve and therefore won’t be available for plant uptake.
What PH do most nutrients dissolve at?
6.5
Which nutrients are less available below a PH of 6?
Nitrogen, phosphorous and potassium are less available.
Which minor nutrient is affected by alkaline soils?
Trace minerals and minor nutrients such as Iron. Which leads to lime induced chlorosis. Some plants very sensitive to iron deficiency. (Rhododendron).
Which kind of soils are more favourable conditions for disease like club root?
Acidic soils.
Which kind of soils are more favourable conditions for diseases like potato scab?
Alkaline soils.
Does PH affect the amount of nutrients in the soil?
No, the nutrients are still present they are just not readily available to the plant if the PH is at either extreme.
Give 3 examples of sources of acid that affect the soil?
- Carbonic acid in rain. (causes chemical weathering of rocks)
- Fertilisers - bacteria involved in nitrification of ammonia to nitrate produce H+ ions.
- Organic matter - humic acid from microbial decomposition of organic matter.
- Crop removal - calcium stored in the plants are removed each time they are harvested and therefore slowly reduce in the soil each season.
Give 3 examples of how soils can become acid?
- Leaching of calcium from the soil. (particularly in sandy soils)
- Calcium removal from the soil by growing plants.
- Over application of ammonium fertilisers.
What happens if you add Gypsum to clay soils in Autumn?
Free lime on clay soils can lead to better crumb formation by flocculating the clay.
What is the name of the lime product added to clay soil to flocculate the soil and make it form a better structure?
Gypsum (Calcium sulphate)
What 2 other things have an impact on the structure of the soil, that is related to PH?
- Earthworms are generally more active and effective when there is some free lime in the soil. They do not like very acidic conditions.
- Below certain acidity levels soil bacteria stop decomposing organic matter.
Which is more difficult lowering or raising PH?
Lowering PH is expensive and difficult.
Raising PH is easier and cheaper.
How do you lower the PH of soil?
Add an acidifying agent. Often sulphur.
Takes a long time, weeks. Months in winter.
How do you raise the PH of soil?
Add garden lime. (calcium carbonate).
Easy and cheap to do.
What is the main limitation with adding lime?
Over liming may affect availability of nutrients. Eg. lime induced chlorosis due to iron being unavailable.
How do you add lime (calcium carbonate)?
Worked into top soil to 15 cm depth.
Apply in winter.
Has effect for 1-2 years.
What can you add to the soil to lower the PH? Make it more acidic.
Horticultural sulphur
Ammonium sulphur.
How quickly does adding horticultural sulphur work?
Acidification takes weeks, maybe months if cold weather. Need to apply in warm weather.
Sulphur dust is quicker acting than sulphur chips & more expensive.
Can still take years to affect root zone.
What are the limitations when applying horticultural sulphur to lower the PH?
Acidifying soils high in calcium carbonate can be futile.
Health & safety considerations when applying.
What does adding organic material - leaf mould, pine needle leaf, peat, or composted bracken or manure do to the PH?
Usually lowers PH. Acidifies.
Has an increased amount of humic acid.
Peat is the most effective as most acid.
Need to repeat frequently as OM is broken down.
What does calcifuge mean?
Lime hating plants.
also called acid lovers.
What does calcicole mean?
Lime loving plants!
Give 4 examples of Calcifuge plants?
Lime hating plants. Acid lovers. Rhododendron 'Christmas cheer' Arbutus unedo Camellia japonica Acer japonicum
What are lime hating plants like Rhododendron ‘Christmas cheer’ and Camelia japonica most prone to?
Iron becomes less available as PH increases.
These plants are particularly prone to lime induced chlorosis due to lack of iron when on alkaline soils.
3 plant examples for a neutral soil PH?
Vicia faba (broad bean)
Tulipa ‘Queen of the Night’
Narcissus ‘February Gold’
4 plant examples which prefer an alkaline soil?
Clematis montana
Lavandula augustifolia
Erysimum cheiri
Syringa vulgaris (common lilac)
What commonly occurs on Calcicoles grown in acidic soils? For example Clematis montana?
Calcicoles grown on acidic soils often develop the symptoms of aluminium toxicity - necrosis - reddening of the leaves and stunted growth.
Why are sandy soils more prone to becoming acid compared to clay soils?
Calcium will leech downwards when it rains as sandy soils are more porous. Loss of calcium results in an acidic soil.
State 3 harmful effects of very acid soil?
- Decreased bacterial activity and worm activity so organic matter will not be broken down to make nutrients available to the plant.
- Major nutrients become unavailable due to chemical reactions.
- Certain plants such as Brassicas can get club root as the disease prefers acid conditions.
State 2 harmful effects of very alkaline soils?
- Nutrients become unavailable particularly iron which results in PH induced interveinal chlorosis in acid loving plants.
- Potatoes are prone to scab, a fungal disease.