Soil is the upper most layer of the earth’s crust. It is powdery material with different grades of soil particles. Soil supports the growth and survival of the plants and trees and there by the entire animal kingdom as all animals are dependent on plants for their survival in one or other way. Most animals depend on plants for food while few for shelter (like birds, insects and few animals like monkeys) and also for other materials like clothing, furniture, medicines etc by humans. Soil components which contribute to fertility are nutrients, soil water and soil bacteria.
Soil’s property to provide sustenance too plants is due to its fertility.
Soil fertility is the nutritive organic and inorganic component mixture which are suitable for proper nourishment of plants.
This soil fertility includes major nutrients and minor nutrients and also mineral and non-mineral elements.
And these nutrients are available in organic form in greater ratio than inorganic matter form.
♠ Major Nutrients in soil fertility: These are nutrients required in sufficiently large amounts like Nitrogen, Phosphorous, Potassium.
These elements are useful for plant growth as they are part of cell components like proteins, amino acids, adenosine triphosphate (ATP), nucleic acids like DNA, RNA, hormones, enzymes. Further they also regulate plant cell physiology like buffering action, pH maintenance etc.
♠ Secondary Nutrients: These are nutrients required in sufficiently small amounts like Calcium, Magnesium, Sulfur.
These secondary elements participate in functions like buffering, pH maintenance, components of enzymes, some proteins etc.
♠ Micro-nutrients: These are elements required in minute quantities but are absolutely essential for plants. like zinc, Manganese, Iron, Copper, Boron, Molybdenum, Chlorine.
Most of these micro-nutrients form the components of co-enzymes which are supportive to enzymes involved in photosynthesis, metabolism, detoxification etc.
Other nutrients involved in soil fertility:
These are nutrients available to plants in gaseous form in plenty but also to small extent from soil.
Carbon, oxygen and hydrogen these are present in combined form with organic material of soil. but plants don’t require them through soil.
Water: This is the primary factor which is an indicator of soil fertility. Soil’ s capacity to hold water in its pores i.e between the soil particles is advantageous because,
1. Nutrients mentioned above are all dissolved in soil water.
2. Water ad-mixed with all the above nutrients is taken up by plant roots by capillary action. So water acts as a medium to help plants take up nutrients.
3. Water facilitates growth of soil bacteria which decay the organic matter. Hence, the decayed bulk of organic matter leaves behind only the nutrients in form easily available to the plants through the soil.
This is the reason why desert is lack of any fertility due to low water holding capacity.
4. Water from soil facilitates distribution of nutrients to entire plant as there is no circulatory system.
5. Soil water facilitates germination of seeds by breakage of hard seed coat and also activation physiology.
6. Water in the soil also helps retain or hold essential nutrients.
Soil bacteria: This is the another factor contributing to soil fertility.
Bacteria in soil decays organic matter to provide nutrients into the soil.
Some bacteria even absorb nitrogen from atmosphere and fix in the soil making it available to plants in the form of ammonia.
Soil bacteria also remove organic toxic waste by decay. So soil with beneficial bacteria is considered to be fertile.
Air: Gases to some extent are present in soil pores and are available for plants during germination.
Thus fertile soil has water, nutrients, bacteria in sufficient ratio and contributes for plant germination, growth and survival.