Soil

Soil is the result of the soil formation processes as a result of local environmental factors (rain, temperature). Soil types differ from one place on the surface of the earth to the other, as the result of the differences in both environmental factors and the nature of the parent rock material.

Soil Potential

Soil potential refers to the ability of the soil to support plant growth and produce a good quality crop.

Soil potential is important to agriculture. The soil potential determines the type of crop that can be grown in specific soil and the volume and quality of crops that can be produced.

Soil potential is judged by the following criteria:

• Soil fertility
• Availability of soil water (for plant absorption)
• Soil permeability

These criteria are all influenced by the soil characteristics, specifically soil texture. Soil fertility and plant available water are especially affected by the texture of the subsoil and topsoil, while soil permeability is affected mostly by the texture of the topsoil.

Soil Fertility

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

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, come from air and water.
• Nitrogen is the major essential nutrient element, and also a major plant constituent. Although the atmosphere is 78% nitrogen, it is not directly available for plant use from the air. In-plant production, 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 to plants 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.

Soil Water Holding Ability

The water holding capacity determines the amount of water that is available for water, and which can be stored to provide for the water requirement of plants in the periods between rains and irrigation applications.

The soil infiltration rate plays an important role in the amount of water that is available to the plant.

Soil infiltration rate: The rate at which water is able to infiltrate the soil.

There is a considerable variation in the capacity of soils to store water and release it for plant use. In some clay soils, water holding capacity may be as high as 25mm water per 100mm soil, whereas it can be as low as 6mm per 100mm soil in sandy soils.

Although clay soils can store more water than sandy soils, the water may not be available to the plants during periods of fast growth. Sandy soils retain less moisture, but the water is more readily available to plants.

The water absorption capacity of soil must be taken into consideration at all times when preparing land for planting or planning an irrigation system.

Click here to view a video that explains soil water.