Soil nutrition

Plants require a large range of nutrients to survive, the majority of which they source from the soil. These are sorted into major and minor nutrients – they are all equally important to plants, but they generally require greater quantities of the major nutrients.

The major nutrients are nitrogen, phosphorous, potassium (these three are often represented by the abbreviation ‘NPK’), potassium, magnesium, calcium and sulphur. The minor nutrients include iron, manganese, zinc and boron.

Nutrients in the soil come from two sources; either the mineral particles weathered from the parent rock or the organic matter in the soil (living or dead).

The nutrient levels within the soil depend on many factors:

  • The amount of organic matter residues in the soil (nutrients such as nitrogen are released from organic matter as it decomposes and is broken down into humus).
  • The amount of clay and humus in the soil – these very small particles hold on to nutrients (so they are not leached from the soil by rainwater) and make them available to plants.
  • The pH level of the soil can reduce the availability of some nutrients.
  • The type of parent rock.
  • Any fertilisers added to the soil.

The other nutrients required by plants (namely carbon, hydrogen and oxygen) are obtained predominantly from water and atmospheric sources.