Nutrient balance in the soil - Soil Essentials: Managing Your Farm's Primary Asset - page 14

Animal nutrition
Animals grazing a diverse range of productive plants grown on healthy soils will
have a better chance to be healthy and grow to their genetic potential.
A healthy soil produces healthy plants that produce healthy animals.
Nutrient ratios
All plant nutrients are important for different reasons, some of which alter the
structure of the soil as well as providing nutrition for plants and soil microbiology.
The cations
This group of soil nutrients includes the elements:
Calcium (Ca)
Magnesium (Mg)
Potassium (K)
Sodium (Na)
Hydrogen (H)
Manganese (Mn)
Aluminium (Al). (Aluminium is not really a plant 'nutrient', but it is a cation.)
A soil analysis will usually show the 'cation exchange capacity' (CEC) of a soil,
that is, the amount of calcium, magnesium, potassium, sodium, hydrogen,
manganese and aluminium available. It has been found that the relative ratios of
soil cations inf luence how well plants grow in the soil.
Calcium (Ca)
Calcium (that is found in limestone) helps counteract soil acidity and makes the
soil friable. It is required in quite high amounts by some plants such as lucerne.
Calcium should be between 65% and 70% of the CEC.
Magnesium (Mg)
Magnesium is required in much lower quantities than calcium. In excess it causes
clay subsoils to become very dense and blocky, thus reducing root and water
movement downwards. Magnesium can also be used to raise pH levels in soil.
Magnesium should be between 15% and 20% of the CEC.