Soil pH controls nutrient availability and biological activity in the soil. In acidic soils extensive nutrient lockup occurs and in alkaline soils phosphorus fixation and trace element lock-up becomes a limiting factor. Maximum nutrient availability occurs in the pH (WATER) range 6.0- 7-0.

Most of Australian soils are well outside this range. When soils are strongly acidic approximately only 1/3rd of nutrients are available for any crop. In alkaline soils the reduced phosphorus and trace element availability becomes a concern especially for cereals.

Why is pH so important!

The solubility of nutrients is sensitive to pH

Many nutrients have very low solubility or restricted solubility in acidic soils. This makes these nutrients inaccessible to crops thereby reducing growth rates, quality and yield.

Nutrient Availability Chart

ELEMENT pH4 pH5 pH6 pH7 pH8 pH9 Nitrogen Low Low High High High Marginal Phosphorus Low Low Good Good Low Medium Potassium Low Low Good Good Good Medium Calcium Low Low Good Good Good Good Magnesium Low Low Good Good Good Good Sulphur Low Fair Good Good Good Good Aluminium High High Low Low Low Low Zinc High High Good Low Low Low Iron High High Good Low Low Low Boron High High Good Low Low High Copper High High Good Low Low Low Magnesium High High Good Low Low Low Molybdenum Low Low Good Good Good Good Bacteria Activity Very Low Very Low Good Good Good Good

Soil pH (Soil Reation)

Soil pH is a measure or indication of soil acidity, it reflects the degree of soil acidity or alkalinity. The pH scale is a numerical scale from 0-14.

Values less than 7 are acidic, values over 7 are alkaline and 7 being neutral.

Each pH unit change represents a 10 fold change in degree of acidity or alkalinity, ie logarithmic - pH 4 is 10 times more acidic than pH 5 and ph 4 is 100 times more acidic than pH 6

Why is pH so important?

The solubility of nutrients is sensitive to pH. Many nutrients have very low solubility or restricted solubility in acidic soils. This makes these nutrients inaccessible to crops thereby reducing growth rates, quality and yield.
See Nutrient Availability Chart

Soil Balance

CATIONS: Positive charged nutrients in soil.

Most common cations are:

• Calcium  (Ca2+ )
• Magnesium  (Mg2 +)
• Potassium (K+)
• Sodium (Na+)
• Hydrogen (H+) and
• Aluminum(AI3+)

Their balance to each other, is very vital because is that these cations have different combining power and very different pulling and holding capacity.

The sodium and aluminium for example have much stronger  pulling capacity than calcium. Thus any imbalance will have a marked antagonistic effect on the efficiency and uniformity of nutrient uptake.

Proper CEC balance with a healthy “soil life” which is, (adequate humus and microbial life)  helps allow for adequate release of all nutrients in proper amounts to grow crops.

Nutrients in least supply regulate growth and health, NOT how much nitrogen, phosphorus and potassium you may add. (See Leibig’s liability)

Soil management must concern itself with

• Nutrient balance
• Humus (Organic Carbon)
• Microbial life

Read on to the final and last key...

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