2102 - Soil pH

Question 1

Soil pH definition

Answer 1

A scale used to specify the Acidity or Alkalinity (base) of soil.

0 - 14 where 0 is the most Acidic and 14 the most Alkaline.

7 is considered neutral.

Most Plants prefer 6.5 (slightly acid).
Plants in the Uk will tend to grow in 5.5 to 7.5 range.

Measured with a pH meter, or using a litmus paper test.

(Hydrogen ions = acid / Hydroxide ions = Alkaline)

Question 2

Availability of soil minerals and nutrients

Answer 2

High pH (above 8)
- reduced Iron availability

Low pH (below 5.5)

• Potassium, Magnesium, Calcium reduced in soil
• Reduced microbial activity thus reducing nutrient recycling and availability to plant

Extremes of either end, can lead to root damage and scorch

Question 3

Calcifuge Plants (refugee, flee from acid)

Answer 3

Acid loving plants (ericaceous). Hate alkaline soil and must have an acidic soil.

• cannot access nutrients in the soil unless soil is acidic
• will show signs of deficiency if grown in high pH
• Lack of Iron available to the plants (young leaf chlorosis)

Rhododendron, Pieris japonica, Erica, Camelia japonica

Question 4

Calicole Plants

Answer 4

Tolerate Chalk and Alkaline conditions, though can grow on a range of soils.

Rosmarinus officinalis, Clematis spp, Fraxinus excelsior

Question 5

Increasing Soil pH

Answer 5

• making the soil more Alkaline (base)
• apply garden lime (calcium carbonate)
• Calcified Seaweed
• Ground Chalk

Always check soil pH before addition of Lime
Never add Lime at the same time as fertilisers, as it could render nutrients unavailable to plants due to chemical reactions.

Question 6

other uses of Lime

Answer 6

• can improve Crumb structure in clay soils

- reduces Club Root in Brassicas

Question 7

Decreasing Soil pH

Answer 7

• making the soil more Acidic
• apply Pine Needle Mulch, will gradually reduce pH if constant application.
• apply Sulphur Chips or Powder (changes to sulphuric acid)
• Ammonium Sulphate (nitrogen fertiliser)
• Acidic Organic Matter (peat)