Phosphatic
fertilisers:
The
nutrient phosphorus present in phosphate fertilizers are usually expressed in terms of
phosphoric anhydride or simply as phosphorus pentaoxide, P2O5. The
availability of phosphorus in which it is present. The amount of phosphorus available to
the plants depends upon the extent to which the fertilizer supplies HPO4----or
H2PO4 ions. According to the solubilities, the phosphatic
fertilizers are divided in following groups.
Water
soluble phosphatic fertilizers: These fertilizers contain phosphorus in available form in
neutral soils, which can be readily absorbed by young plants. In acid, soils and free
iron, aluminium hydroxy phosphates but in alkaline and calcareous soils, water soluble
phosphorous is converted into insoluble calcium phosphate. The common examples of these
fertilizers are:
Sr. No. |
Fertiliser |
% P2O5 |
i |
Single
Superphosphate (CaH2PO4)16 |
18% P2O5 |
ii |
Double
superphosphate CaH4(PO4) 2 |
32% P2O5 |
iii |
Triple
superphosphate Ca(H2 PO4) 2 |
46 to
48% P2O5 |
iv |
Ammonium
phosphate |
20% P2O5 |
Citric
acid soluble Phosphatic Fertilizers: The citric soluble fertilizers are suitable for
acidic soils because at low pH citrate soluble phosphorus is converted to monocalcium
phosphate not as water soluble phosphate and therefore, phosphorus is not fixed as iron
and aluminium phosphate.
Sr. No. |
Fertiliser |
% P2O5 |
i |
Dicalcium
phosphate, CaHPO4 |
14% P2O5
extract soluble |
ii |
Basic
slag (CaO) 5P2 O5. SiO2 17 |
20% P2 O5
extract soluble |
iii |
Calcium
metaphosphate Ca (PO3) 2 |
60 to 64%P2 O5
extract soluble |
Water
and citrate insoluble phosphatic fertilizers: These mineral fertilizers contain
phosphorus, which is insoluble in water as well as in citric acid. They are suitable in
strongly acid soils or organic soils. These fertilizers are given in green manured fields.
The phosphorus is very slowly released by microbes at action and remains in soil for long
time.
Sr. No. |
Fertiliser |
% P2O5 |
i |
Rock
Phosphate Ca3 (PO4)2CaF2 |
20 to
30% P2O5extract soluble |
ii |
Bone
meal (Ca(PO4) 2) 3 CaF2 |
21 to
25% P2O5 extract soluble |
(d) Other phosphatic fertilizers: Following are the other phosphatic fertilisers.
Sr. No. |
Fertiliser |
% P2O5 |
i |
Kotka
phosphate |
26% P2O5 |
ii |
Rhenmia
phosphate |
26 to
28% P2O5 |
iii |
Thermophos |
18.3%
P2O5 |
iv |
Pelophos |
18% P2O5 |
v |
Coronat
phosphate |
21% P2O5 |
|