MACRO NUTRIENTS

Plant nutrients occur in the soil in form of soluble substances. These substances are taken in by the plants in different quantities depending on their roles in the plant tissues.

Essential Elements

These are nutrients needed by plants for various uses.

They are divided into two broad categories namely:

1. Macronutrients
2. Micronutrients.

Macro-nutrients

–  These are also referred to as major nutrients.

–  They are required by the plant in large quantities.

They include;

1. carbon,
2. hydrogen,
3. oxygen,
4. nitrogen,
5. phophorus,
6. potassium,
7. sulphur,
8. calcium

Nitrogen, phosphorus and potassium are referred to as fertilizer elements,

Calcium, magnesium and sulphur, are referred to as liming elements.

ROLE OF MACRO NUTRIENTS IN PLANTS

Nitrogen (N03, NH4)

Sources

1. Artificial fertilizers
2. Organic matter
3. Atmospheric fixation by lightning
4. Nitrogen fixing bacteria.

Role of Nitrogen in Plants

1. Vegetative growth
2. Chlorophyll formation
3. Buildup of protoplasm.
4. Improves leaf quality in leafy crops such as tea and cabbages

Deficiency Symptoms

1. Yellowing of the leaves/chlorosis.
2. Stunted growth.
3. Premature ripening.
4. Premature shedding of the leaves.
5. Light seeds.

Effect of Excess Nitrogen

1. Scorching of the leaves.
2. Delayed maturity.

Loss of Nitrogen from the Soil:

1. Soil erosion.
2. Crop removal.
3. Used by microorganisms.

Phosphorus (H, P04, HPO”4 P105)

Sources:

1. Organic manures
2. Commercial fertilizers
3. Phosphate rocks

Role of Phosphorus

1. Encourages fast growth of the roots.
2. Improves the quality of the plant.
3. Hastens maturity of the crops.
4. Influences cell division.
5. Stimulates nodule formation in legumes.

Deficiency symptoms

1. Growth of the plant is slow.
2. Maturity is delayed.
3. Leaves become grey, purple in colour.
4. Yield of grains, fruits and seed is lowered.

Loss of Phosphorus from the Soil

1. Soil erosion.
2. Leaching
3. Crop removal
4. Fixation by iron and aluminum oxide.

Potassium (K‘, K20)

Sources

1. Crop residue and organic manures.
2. Commercial fertilizers
3. Potassium bearing minerals e.g. feldspar and mica.

Role of Potassium in Plants

1. Increases plant vigour and disease resistance.
2. Increases the size of grains and seeds.
3. Reduces the ill-effects due to excess nitrogen.
4. Prevents too rapid maturation due to phosphorus.

Deficiency Symptoms

1. Plants have short joints and poor growth.
2. Plants lodge before maturing.
3. Leaves develop a burnt appearance on the margin.
4. Leaves at the lower end of the plant become mottled, spotted or streaked.
5. In maize, grains and grasses firing starts at the tip of the leaf and proceeds from the edge usually leaving the midrib green.

Loss of Potassium from the Soil

1. Crop removal.
2. Soil erosion.
3. Fixation in the soil.

Calcium (Ca2+)

Source:

1. Crop residues and organic manures.
2. Commercial fertilizers.
3. Weathering of soil minerals.
4. Agricultural limes for example dolomite, limestone.

Role of Calcium in Plants

1. Improves the vigour and stiffness of straw.
2. Neutralizes the poisonous secretions of the plants.
3. Helps in grain and seed formation.
4. Improves the soil structure.
5. Promotes bacterial activity in the soil.
6. Corrects the soil acidity.

Deficiency symptoms

1. Young leaves remain closed.
2. There are light green bands along the margins of the leaves.
3. Leaves in the terminal bud become hooked in appearance there is a die-back at the tip and along the margins.

Loss of Calcium

1. Crop removal
2. Leaching
3. Soil erosion

Magnesium (Mg2+)

Sources:

1. Crop residues and organic manures
2. Commercial fertilizers
3. Weathering of soil minerals.
4. Agricultural limes.

Role of Magnesium in Plants

1. Forms part of chlorophyll.
2. Promotes the growth of the soil bacteria and enhances the nitrogen fixing power of the legumes.
3. Activates the production and transport of carbohydrates and proteins in the growing plant.

Deficiency symptoms

1. Loss in green colour which starts from the bottom leaves and gradually moves upwards.
2. The veins remain green.
3. Leaves curve upwards along the margins.
4. Stalks become weak and the plant develops long branched roots.
5. The leaves become streaked.

Sulphur (S04 2′, SO,)

Sources:

1. Commercial fertilizers.
2. Soil mineral containing sulphides
3. Atmospheric sulphur from industries.
4. Rain water

Role of Sulphur in Plants

1. Formation and activation of coenzyme-A.
2. Sulphur is a constituent of amino acids.
3. Influence plant physiological processes.

Deficiency Symptoms

1. Small plants/stunted growth.
2. Poor nodulation in legumes.
3. Light green to yellowish leaves/chlorosis.
4. Delayed maturity.