How nutrients are stored in the soil

Soils consist of clay, humus, silt and sand. It is the clay and humus that store the soil’s minerals. They do this by forming tiny particles called colloids that are electrically charged.

Clay and humus are negatively charged, but humus also has some positive charges. Minerals are therefore either negatively or positively charged. Minerals that are positively charged are named cations. The negatively charged minerals are known as anions (no, not onions, anions!).

Cations are attracted to the negatively charged clay colloid and they can also stick to the humus colloid. However, anions can only be stored on the positively charged humus colloid.

This means that if there is no humus in the soil, then anions like nitrogen, sulphur and boron will not be easily stored and will in fact leach readily. Sandy soils contain very little clay or humus so that there is very little storage capacity. That is why sandy soil needs such regular fertilising.

The mineral storage capacity of a soil is vitally important to the nourishment of your garden plants. Such soils require a complete fertiliser and soil conditioner where multiple ingredients have been composted in a high carbon base.