RHS Level 2 R2102 pH Flashcards
Plant nutrition and the root environment
Describe What is meant by pH…
pH is the measurement of balance between acidity and alkalinity within growing media.
Below pH7 are classed as acidic
Above pH7 are classed alkaline
Exactly pH7 are neutral.
What’s the pH range of garden soils and what’s the optimum level and why?
pH 4-8 is found in garden soils.
6.5 is the optimum as this is the pH level that most nutrients are available and which most plants have adapted to in the UK.
How does pH affect soil organisms and structure of soil?
Worms prefer neutral to slightly limy.
Bacteria are more plentiful in neutral soils.
Fungi prefer acidic to neutral.
In turn these affect the breakdown of OM and soil structure.
How does pH affect crumb formation?
For heavy soils which have a high pH you can apply gypsum- calcium sulphate which promotes flocculation and inhibits the dispersion of aggregates.
How does pH affect nutrient availability?
Most favourable level is 6.5 for ensuring availability of all nutrients.
Outside this level nutrients will frequently become unavailable and cause deficiencies.
Some will become more available and can become toxic eh. Manganese, aluminium
What factors can reduce soil pH (make more acidic)?
Acid rain.
Organic acids produced in the breakdown of organic matter.
Artificial fertilisers like ammonium nitrate.
Removing crops from a field.
Certain plants can increase acidity (reduce pH) by dropping acid forming leaves.
Agricultural sulphur is converted to sulphuric acid in the soil.
Adding garden compost is the most acceptable in organic system.
What factors can increase soil pH (make more alkaline)?
Adding lime - ground limestone or chalk.
Organic mushroom compost
Wood ash
Green waste compost
When and how should you apply lime to soil?
Clay soil requires more than sandy soil to make a pH change.
Best time is autumn or spring.
As appropriate to the rotation with vegetables.
Never at the same time as manure (loss of nitrogen).
Mix into top layer of soil if applied just prior to planting.
Name three alkaline loving plants, what’s the definition?
Calcicoles, lime loving plants. Tolerant of a high pH Clematis sp. Scabiosa caucasica Syringa vulgaris (lilac)
Name three acid loving plants, what’s the definition?
Calcifuges, lime hating plants. Need pH as low as 5 to thrive. Rhododendron ponticum Camellia japonica Vaccinium corymbosum
Name three plants which like neutral pH.
Helianthus annuus
Iris unguicularis
Calendula officinalis
