Replenishment of nutrients in the soil

• Plants utilize the mineral nutrients, especially nitrogen present in the soil, for their growth.
• As a result there is a depletion of nitrogen in the soil over a period of time.
• So, the farmers use manure and they spread it in their fields.
• Manure contains a lot of nitrogen apart from potassium and phosphorus.

Why replenishment of soil is necessary?

• The ideal soil has sand, silt, clay and organic matter in about equal amounts.
• It is also uniformly mixed to at least twelve inches deep.
• The subsoil then allows the excess water to drain away.
• So, basically no soil is ideal but soil can be improved with soil amendments and drainage.

Example:

• Symbiotic association of Rhizobium and leguminous plants such as pea is a natural way of replenishing the soil with nitrogen.

Methods of Replenishment:

• Repeated growing of crops in the same soil, year after year results in the depletion of the various nutrients in the soil.
• As a result, soil loses its fertility and requires replenishment which can be done by:
• Keeping land fallow – Keeping the field free for a season to make up the lost nutrients.
• Crop rotation – Leguminous plants are grown alternately with other crops to replenish the nitrogen which had been used up by the crops.

Interesting facts/Brass tacks:

• It takes more than 500 years to form 2cms of topsoil.
• Soil stores around 10% of the emissions of carbon dioxide.
• One gram of soil contains 5000 to 7000 different species of bacteria.
• 75% of the earth's crust is composed of silica and oxygen.
• According to the system of classification of organisms, fungi is no longer considered in plant kingdom. It is placed in a separate kingdom—Kingdom Fungi.