1. Why is phosphorus not available in free form in nature?
Elemental phosphorus is highly reactive and when exposed to air it goes through a chemical reaction with oxygen. That is why in nature phosphorus is found a phosphate (PO4-3). Phosphates contain one phosphorus atom that is bound to four oxygen atoms, and all oxygen atoms are bound to each other. The general form of phosphate that we see in nature is HPO4-2.
The phosphate anion bonds with carbon, nitrogen, and hydrogen to form ATP, for example. Also with calcium (and occasionally hydrogen), it forms calcium phosphate which is a component of bones.
2. What is Eutrophication?
Eutrophication can be defined as a process of enrichment of water by nutrient salts that causes structural changes to the aquatic ecosystem. Examples of these changes are increased growth of algae and aquatic plants, general deterioration of the quality of water, depletion of fish species etc.
Eutrophication is harmful to the aquatic ecosystem as some algae produce toxic compounds and when they die, they are decomposed by microbes. During decomposition, a large amount of oxygen is used to break down algal bodies. The spike in oxygen usage lowers the levels of oxygen in water bodies which can lead to the death of many aquatic organisms by hypoxia (lack of oxygen). It can be controlled by reducing the usage of artificial fertilisers.
3. Why is most phosphorous not available to plants?
Most of the available P in soil is not available to plants. There are many reasons.
Bacteria convert the available phosphate into organic which cannot be taken up by plants.
Inorganic phosphorus available in the soil can be chemically bound to soil particles, which makes it unavailable for plants.
Also, inorganic phosphorus compounds need to be soluble so they can be taken up by plants. If the soil’s pH is less than 4 or more than 8, the available phosphorus becomes tied up with other compounds which cannot be utilised by plants.