Soil Fertility

What is soil fertility?

Soil fertility is the ability of soil to supply plants with nutrients, air and water in the right amounts. In the Junior School CBC (KICD), Grade 8 Agriculture builds on soil knowledge so learners can raise healthy crops.

Characteristics of fertile soil

• Contains enough nutrients.
• Has good water-holding and drainage.
• Rich in humus (decayed organic matter).
• Has a suitable pH, roughly 6 to 7 for most crops.
• Contains useful living organisms such as earthworms.

Plant nutrients

Maintaining soil fertility

1. Manure and compost - add organic matter.
2. Crop rotation - for example, maize followed by beans (legumes fix nitrogen).
3. Inorganic fertilisers - such as DAP, CAN and NPK, used in correct amounts.
4. Mulching - covers soil and reduces erosion.
5. Fallowing - resting land.
6. Soil conservation - terraces and cover crops reduce loss of topsoil.

Organic versus inorganic

• Organic: manure, compost, green manure; improves soil structure; releases nutrients slowly.
• Inorganic: factory-made; fast acting; can harm soil if overused.

Worked example

A farmer's maize yields keep falling and leaves turn pale yellow. This suggests nitrogen shortage. He can apply farmyard manure, plant beans next season and use CAN as top dressing.

Safe practice

Wear gloves when handling fertilisers and store them away from children and food.

Try it

• List four signs of infertile soil.
• Make a small compost heap with kitchen waste at home.
• Explain why legumes help soil fertility.
• Name one organic and one inorganic fertiliser.