Micro nutrient fertilizer

Micronutrient Fertilizers

The importance of fertilization of crops with micro-nutrients is increasing mainly because of greater removal from the soil, intensive liming of soil, intensive drainage of soil, higher use of nitrogenous, phosphatic and potassic fertilizers etc.
There are seven essential micronutrients required by plants.

These are iron, manganese, zinc, copper, chlorine, boron and molybdenum.

a. lron fertilizers

These are generally water soluble substances, predominantly sprayed as foliar nutrients on the crops.
Plants absorb iron in the form of Fe2+.

Commonly used iron fertilizers are as follows.

Ferrous sulphate
(FeSO4 7H2O) It is a water soluble fertilizer containing 20 % Fe

Fe – Chelates
Fe-EDTA
Fe-EDDPA Suitable for application as foliar nutrients

b. Manganese fertilizers

The manganese (Mn) fertilizers are as follows:

Manganous Sulphate
( MnSO4 7H2O) It is the well known water soluble Mn fertilizer.

It is pink salt containing 24 % Mn.
It dissolves in water and is suitable for foliar application.

Mn – chelates (Mn – DTA) It contains 13 % Mn.
It plays an important role in the crop function.

Zinc fertilizers
Zinc (Zn) fertilizers play an important role in Zn deficient areas.

Zinc sulphate
(ZnSO4 7H2O) It is water soluble whitish salt containing 23 % Zn.
It is applied as foliar nutrient.
Its acidic action causes corrosion damage to plants

Zinc-oxide(ZnO)

It contains 70 % Zn.
It is slightly soluble in water
It is used as slow acting foliar nutrient

Copper Fertilizers

Copper fertilizers have been used to correct copper (Cu), deficiencies.
Copper sulphate (CuSO4 5H2O) – 25 % Cu
Copper sulphate (CuSO4 H2O) – 36 % Cu

Boron Fertilizers

Borax (Na2B4O 10H2O) It contains 11 % B
It is water soluble white salt
It can be applied as a soil dressing or foliar

Boric acid (H3BO3)

It contains 18 % B
It is a white crystalline powder
It is applied as a foliar nutrient

Molybdenum Fertilizers

Sodium molybdate

(Na2MoO42H2O) It contains 40 % Mo

Ammonium molybdate
(NH4)6Mo7O244H2O) It contains 54 % Mo

These are water soluble salts which contain Mo
They are suitable for soil application and foliar application as well

The need for the micronutrient fertilization has been increasing due to the following causes:

1. Change in the plants : Change in the plant varieties from traditional to high yielding varieties (HYV). HYV have a capacity to remove more nutrients both major and minor. HYV have low mobilizing capacity of micro nutrients from the soils hence they are to be applied through external application.

2. Changes in soil: Change in soil condition from acid to alkaline (Increased soil reaction) and aeration cause greater immobilization of most micronutrients except molybdenum (Fe, Zn, Cu and Mn). High acidic nature of the soil induces both calcium and magnesium deficiency.

3. Changes in fertilization: Using high doses of NPK in the form of complex fertilizers, induces deficiencies of secondary and micro nutrients. Antagonistic action due in part to excessive fertilization with NPK eg. Higher K content in soils effects the uptake of Fe, Mn, and B.

Excess P leads to deficiencies of Zn, Fe, Cu and increases Mo availability. More the sulphate present in the soils, lesser the availability of Mo. Lesser or least micronutrient constituents in multinutrient fertilizers.

4. Changes in overall growth conditions.

1. Intensive cultivation: Intensive cultivation leads to micro nutrient deficiencies

2. Non availability and application of organic manure.

3. Under/ over limed condition.

4. Parent material: Most of the micronutrients originates from parent material and influences the availability or deficiency of micronutrients to plants

5. Land leveling and shaping: Most of the micronutrients are concentrated on the surface soil except Molybdenum. Leveling of land and deep tillage operations leads to deficiencies.

6. Low Si/Mg ratio: Leads to fixation of Zn in soil.

7. Calcium carbonate: More the CaCO3 in soils lesser the availability of Fe, Cu, Mn, Zn.

8. Soil texture: Boron availability is more in coarse textured soils and in finer textured soils it gets fixed, unavailable to plants.

9. Secondary clay minerals: Montmorillonite clay adsorbs more of Zn, Cu and leads to deficiency or unavailability to plants.

10. Soil moisture: Dry conditions of soil fix more of Boran and are released under wet conditions. Presence of more moisture reduces the availability of Mn.

11. Interaction with macronutrients: Heavy nitrogen interferes with availability of Cu, Mn, Zn and leads to deficiencies in plant.

12.Liming reduces the availability of Mn, Zn, Fe, Cu.

13. Seasonal variation: Nutrient deficiencies are more during cold season.

Out break of B deficiency is common in dry seasons

Summer drought aggravates Fe chlorosis.

High and low soil temperatures induce Zn deficiency in soils having low Zn.