Fertilizers: Classification, Manufacture and Acidity | Soil Management

In this article we will discuss about:- 1. Meaning of Fertilizers 2. Classification of Fertilizers 3. Materials Used in Manufacturing of Fertilizers (Mixed) 4. Acidity and Basicity of Fertilizer.

Meaning of Fertilizers:

Liebig in Germany and Lawes in England developed independently the idea of treating phosphate with H₂SO₄ and producing a water soluble phosphate by about 1840. It is known as superphosphate or simply super. Lawes set up a factory at Deptford in 1843 for the production of super­phosphate. Possibly this was the first factory to be set up for the production of artificial fertilizers on a commercial scale.

Fertilizers are the organic or inorganic materials of natural or syn­thetic origin which are added to the soil to supply certain elements essential to the growth of plants. The term ‘Fertilizer’ is now commonly restricted to commercial products.

Amendments are the substances other than manures and fertilizers which are added to soils for the improvement of their condition.

Amendments are also termed as ameliorants, improvers or soil conditioners e.g. gypsum and lime though they supply nutrients but the main objective of applying them is for correcting the soil condition.

Classification of Fertilizers:

(a) Straight Fertilizers:

Such fertilizers has declarable content of only one major nutrient e.g. urea, ammonium sulphate.

(b) Binary Fertilizer:

It contains two major nutrients e.g. – Potassium Nitrate.

(c) Ternary Fertilizer:

It contains three major nutrients e.g. Ammonium potassium phosphate.

(d) Compound/Complex Fertilizer:

Such fertilizer has a declarable content of at least two of the major nutrients obtained chemically and generally granular in form. e.g. Nitro- phosphate, Amm- phos­phate and Diammonium phosphate (DAP).

(e) Mixed Fertilizer:

Individual or straight fertilizer materials are blended to­gether physically to permit application in the field in one operation. Such fertilizers supply two or three major nutrients in a definite proportion or grade e.g. – nitrophosphate with potash 15: 15: 15 of NPK.

(f) Complete Fertilizer:

They have all the three primary major nutrients viz. N, P, & K.

(g) Incomplete Fertilizer:

It contains any two primary nutrients.

(h) Low- Analysis Fertilizers:

They have less than 25% of the primary nutrients e.g. SSP (16% P₂O₅), sodium nitrate (16%N).

(i) High- Analysis Fertilizer:

They have more than 25% of the total primary nu­trient content e.g. urea, anhydrous ammonia (82.2%N), Ammoni­um phosphate (20% N + 20% P₂O₅), DAP (18% N + 46% P₂O₅).

Fertilizer Grade:

It refers to the guaranteed analysis of its plant nutri­ents. It is the minimum guarantee of the plant nutrient contents in the terms of N, available P₂O₅ and K₂O e.g. 6:24:24.

Fertilizer Ratio:

It refers to the relative percentage of N, P₂O₅ and K₂O i.e. 1:4:4 if fertilizer grade is 6:24:24.

Materials Used in Manufacturing of Fertilizers (Mixed):

1. Suppliers of Plant Nutrient:

Straight fertilizers are used for this purpose.

2. Conditioners:

To check absorbing moisture and making one, conditioners like straw, groundnut husk, paddy husk, peat soil etc. are used they just reduce caking and applied in drilling conditions and these conditioners are of low organic materials.

3. Neutraliser of Acidity or Basicity:

Dolomitic limestone is used to reduce residual acidity. Most fertilizers leave residual acidity or basicity.

4. Filler Material or Make Weight Material:

Sand, soil, earth, coal ash, charcoal such waste materials are added to make up the difference between the weight of the added fertilizers required to supply the plant nutrients and the desired quantity of the fertilizer mixture.

Precautions in Mixing Fertilizers:

1. Hygroscopic fertilizers should not be mixed because they form cakes after mixing.

Hygroscopic fertilizers are in descending order:

(a) NH₄NO₃ (Amm. Nitrate)

(b) Urea – CO(NH₂)₂

(c) Ammonium sulphate – (NH₄)₂SO₄

(d) Amm.sulphate nitrate – (NH₄)₂SO₄NH₄ NO₃

(e) Calcium ammonium nitrate (CAN)

The most hygroscopic fertilizers ammonium nitrate and urea stands second. All these fertilizers have NH⁺₄.

2. Fertilizers containing NH₄⁺ should not be mixed with basically reactive materials like lime, basic slag and rock phosphate because mixing results in the loss of N through escape of NH₃ gas.

3. All water soluble phosphatic fertilizers like super phosphate should not be mixed with those fertilizer that contain free lime because it will convert the soluble phosphate into insoluble form.

4. Slightly acidic fertilizer containing chloride may damage the gunny bags and drilling equipments.

Acidity and Basicity of Fertilizer:

Equivalent Acidity:

The amount of CaCO₃ required to neutralise the acid residue caused by application of acidic fertilizers in the soil e.g. 100kg (NH₄)₂SO₄ produces acidity which needs 110 kg of CaCO₃ to neutralise it. Therefore equivalent acidity of (NH₄)₂SO₄ is 110, Anhydrous NH₃ has more equivalent acidity than other fertilizer.

Equivalent Basicity:

Residual basicity caused by application of basic fertilizers, expressed in terms of CaCO₃ equivalent of basic residue left by a fertilizer material (in kg/100kg of fertilizer salt).

Commercial Nitrogenous Fertilizers:

Except paddy and potato, the ammoniacal form is not directly absorbed by crops. Ammonia always produces acidity. Except NO^–₃, CaCN and CAN; all other nitrogenous fertilizers are acidic in nature. NO^–₃ and CaCN are basic in reaction, whereas CAN is neutral.