Top 4 Phosphatic Fertilizers Used in Soil

List of top four phosphatic fertlizers used in soil.:- 1. Single Super Phosphate 2. Bone Meal 3. Triple Superphosphates 4. Basic Slag.

Phosphatic Fertilizer # 1. Single Super Phosphate:

Calculated amount of sulphuric acid is added to finely ground rock phosphate in a pit or den where the following reaction takes place:

The temperature rises to about 100°C when hydrofluoric acid (HF) evaporates. The mixture of gypsum (about 50 per cent), Mono calcium phosphate (about 27 per cent) and di-calcium phosphate (about 3 per cent) is ground to powder and is bagged for marketing as Single Super Phosphate.

Properties:

Single super phosphate is an ash coloured powder containing about 16 per cent water soluble P₂O₅, 20 per cent Ca and 12 per cent S.

It should not be mixed with lime because water soluble mono-calcium phosphate is gradually converted to water insoluble tricalcium phosphate as shown in the following equation:

Reaction of Soil:

Strongly acid soils contain excessive amounts of aluminum and ferric ions and also aluminum and ferric hydrous oxides, which react with mono-calcium phosphate and convert it into insoluble aluminum and ferric hydroxyphosphate when a single super phosphate is added to acidic soils.

This above process of conversion of water soluble phosphate to water in soluble phosphate to known as fixation of phosphorus.

Strongly alkaline soils contain excessive amounts of calcium ions and calcium carbonate, which react with the mono-calcium phosphate and convert it into water insoluble tricalcium phosphate, as shown in the following equations:

The most phosphate is available to crops in soils of pH 6.0 to 7.0.

Phosphatic Fertilizer # 2. Bone Meal:

Bones have been used as manures for time immemorial.

Bone meals are of two kinds i.e:

(i) Raw bone meal and

(ii) Steamed bone meal.

Raw bone meal contains about 25 per cent P₂O₅ and 4 per cent nitrogen, which is in the slow acting organic form. Steamed bone meal contains about 25 to 30 per cent total phosphorus (P₂O₅) and about 1-2 per cent N. It contains about 25 per cent citrate soluble phosphorus (P₂O₅). Steamed bone meal can be readily ground to powder because it is more brittle.

Bone meal is applied to the soil few days before sowing the crop. Bone meal is mainly used on acidic soils. Almost all the phosphorus is converted into a readily available form if bones are charred, although charring of bones destroys almost half the nitrogen.

Phosphatic Fertilizer # 3. Triple Superphosphates:

Triple superphosphate is manufactured by treating rock phosphate with phosphoric acid:

Triple superphosphate (also called concentrated super phosphate) contains 43 per cent water soluble P₂O₅. It reacts with the soil the same way as single superphosphate.

Phosphatic Fertilizer # 4. Basic Slag:

Basic slag is a byproduct of the steel industry, where the original iron ores contain appreciable amounts of phosphorus. It is a greyish black powder with a very high specific gravity. Some chemists consider it to be the silicate and phosphate of lime of the formula (CaO)₅P₂O₅SiO₂. It contains 8 to 12 per cent P₂O₅ Basic slag produced in Tata Iron & Steel Company contains 3 to 4 percent of citrate soluble P₂O₅.