Soil Fertility

Soil fertility refers to the nutrient content of the soil and its resultant ability of the soil to sustain plant growth.

Soil fertility is a collective expression to describe the status of the soil in terms of:

• Phosphorus (P)
• Potassium (K)
• Calcium (Ca)
• Magnesium (Mg) and to some extent
• Nitrogen (N)

Fertile soil contains these nutrient elements in adequate quantities to sustain plant growth.

If too few plant nutrients are present, it poses less of a problem in commercial agriculture than if too much is present. It is relatively easy and quite cheap to add nutrient elements to the soil, but seldom easy and cheap, if possible at all, to remove excess nutrients.

Plants absorb sunlight, oxygen and carbon dioxide from the air, and water and nutrients from the soil. Soil fertility is the amount of food that the soil contains for the plants.

Plants need seventeen elements for normal growth. They are:

• Carbon, hydrogen and oxygen (they come from air and water).
• Nitrogen is the major essential nutrient element, and a major plant constituent. Although the atmosphere is 78% nitrogen, it is not directly available for plant use from the air. In plant production, the nitrogen is taken up from the soil.
• The other thirteen essential nutrient elements are iron, sodium, calcium, phosphorous, potassium, copper, sulphur, magnesium, manganese, zinc, boron, chloride, and molybdenum. These elements come from the soil.

In normal circumstances, the nutrients naturally available from the soil vary with clay content – the higher the clay content, the higher the soil fertility, but the fewer nutrients are available to the plant.