Plant Nutrients: Meaning, Role and Deficiency Symptoms

Everything you need to learn about Plant Nutrients:- 1. Meaning of Plant Nutrients 2. Classification of Plant Nutrients 3. Physiological Roles 4. Deficiency Symptoms 5. Symptoms under Abundant (Excess) Supply 6. Control of Deficiency 7. Foliar Nutrition of Plants.

Meaning of Plant Nutrients:

The normal green plant is autotrophic that means it can synthesise all its organic substances; provided it is supplied with all the inorganic elements and growth under normal condition. The nutrition of green plant is therefore, solely inorganic. It is, in fact, commonly called mineral nutrition. Elements absorbed from the soil by the roots are generally known as Plant nutrients or Mineral nutrients.

Classification of Plant Nutrients:

The plant nutrients may be classified in two ways.

They are:

(1) Classification of plant nutrients on the basis of their availability.

(2) Classification of plant nutrients on the basis of mobility in plant.

Physiological Roles of Plant Nutrients:

The effect of nutrients on plant growth (crop production) are as follows:

(A) Major Elements:

(a) Nitrogen:

(1) Nitrogen makes plants dark green

(2) Increases vegetative growth

(3) Increases the protein content of some food and feed crops

(4) Encourages the formation of good quality foliage

(5) Nitrogen increases the cation exchange capacity of plant roots and these makes them more efficient in absorbing other nutrient ions like phosphorus, potassium, calcium etc.

(6) Nitrogen is an important constituent of chlorophyll, thus increases photosynthesis process in plant.

(b) Phosphorus:

(1) Stimulates root formation

(2) Helps in cell division and stimulates growth

(3) Hastens maturity

(4) Makes plants more drought-resistant and winter hardy

(5) Gives tolerance against insect and disease

(6) Increases the percentage of phosphorus and calcium in plants

(7) Increases nodule formation in legume (pulse) crops which fix nitrogen.

(8) Increases protein and mineral contents in plant

(9) Increases the number of tillers in cereal crops

(10) Increases the ratio of grain to straw in cereals and thus increases the yield of grain.

(c) Potassium:

(1) Helps in moving the manufactured food (translocation)

(2) Imparts vigour to the plants

(3) Favours the growth of legume crop

(4) Imparts drought resistance and winter hardiness

(5) Imparts resistance to diseases and insects

(6) Produces stiff stalks and stems, and thus reduces lodging

(7) Increases the availability of other elements like nitrogen and potash

(8) Increases the size of root and tuber e.g., potato.

(b) Secondary Nutrients:

(a) Calcium:

(1) Promotes early root growth

(2) It is constituent of cell wall, it therefore, helps in increasing stiffness of straw or stem

(3) Encourages seed production

(4) Increases the calcium content in plants

(5) Increases the nodulation of legumes

(6) Improves soil structure

(7) Keeps soil neutral.

(b) Magnesium:

(1) Important constituent of chlorophyll, therefore, increases photosynthesis in the plant

(2) Regulates the uptake of other plant nutrients, particularly nitrogen and phosphorus

(3) Acts as a carrier of phosphorus in the plant

(4) Promotes the formation of oils and fats.

(c) Sulphur:

(1) Helps in chlorophyll formation

(2) Stimulates root growth, seed formation and nodule formation

(3) Encourages more vigorous plant growth

(4) Sulphur is a constituent of enzymes and other proteins

(5) Increases oil content in mustard and soya-bean.

(c) Micronutrients:

(a) Iron:

(1) Helps in chlorophyll formation

(2) Acts as oxygen-carrier in oxidation- reduction re action

(3) Helps in protein synthesis and several metabolic reactions.

(b) Manganese:

(1) Acts as a catalyst in oxidation-reduction reaction

(2) Acts as an activator of many enzymes

(3) Helps in chlorophyll synthesis.

(c) Boron:

(1) Helps in the uptake of calcium

(2) Encourages efficient utilisation of calcium in plant

(3) Helps in protein synthesis.

(d) Copper:

(1) Helps oxidation-reduction reaction

(2) It is a constituent of certain protein.

(e) Molybdenum:

(1) Helps in the fixation of atmospheric nitrogen in the roots of legume by nodule bacteria

(2) Helps in protein synthesis.

(f) Chlorine:

(1) Essential for the photosynthesis process

(2) Keeps osmotic pressure normal in cell sap

(3) Encourages growth in cabbage, carrot, lettuce, wheat etc.

(g) Zinc:

(1) It is a constituent of a number of enzymes e.g. carbonic anhydrase, alcohol dehydrogenase, and various peptidases.

(2) Helps in the formation of growth hormones (auxines)

(3) Enhances heat and frost resistance of plant

(4) Affects the uptake of phosphorus by plants

(5) Acts as a catalyst in chlorophyll formation

(6) Deficiency of zinc in plant leads to reducing sucrose and starch content, decreasing auxin, upsetting protein synthesis and increasing organic acid content.

Deficiency Symptoms of Nutrients:

(a) Nitrogen:

(1) The lower leaves turn yellow and in some crops they quickly start drying up as if suffering from shortage of water

(2) Growth stunted

(3) Leaves and fruits shedding

(4) Whole plant becomes yellow.

(b) Phosphorus:

(1) Growth is stunted

(2) Leaves become smaller in size

(3) Delay in maturity

(4) In corn (maize) leaves and stems become purple.

(c) Potash:

(1) The margin of leaves turn brown and dry up

(2) The older leaves develop brown colour starting from tip and margin

(3) Stunted growth

(4) In maize, the edges and lips become dry and appear scorched or fired.

(d) Calcium:

(1) Symptoms are localized in new leaves and in bud leaves of plants

(2) In tobacco, terminal bud dies

(3) The leaves have wrinkled appearance.

(e) Magnesium:

(1) Symptoms are first appeared on older leaves

(2) Yellow streaks develop between parallel veins in the leaves and veins remain green.

(f) Sulphur:

(1) The whole leaf in tobacco plant has light green colour

(2) The chlorosis of younger leaves take place.

(g) Copper:

(1) In tobacco and potato, the young leaves remain permanently wilted

(2) The tip of the leave may turn white.

(h) Iron:

(1) The new leaves show chlorosis in between veins. The veins remain green.

(i) Boron:

(1) The leaves thicken and margins roll upward

(2) The leaf tip and margin of older leaves die prematurely

(3) Terminal bud dies

(4) The younger leaves are dwarfed

(5) Diseases due to boron deficiency are—top rot of tobacco, heart rot of sugar beet, lack of head formation in cauliflower.

(j) Manganese:

(1) Small brown patches develop on leaves (Potato)

(2) In cotton, the upper leaves become yellowish-grey while veins remain green

(3) ‘Grey speck’ of Oat disease caused by manganese deficiency.

(k) Molybdenum:

(1) Curling of leaves

(2) Petiole of leaves remain intact but shedding of margin and other parts of leaves.

(l) Chlorine:

(1) Yellowing of leaves (whole plant).

(m) Zinc:

(1) Stunted growth

(2) Reddish-brown spots appear on lower leaves

(3) Later on the whole leaf becomes rusty brown in colour

(4) The mid rib of the younger leaves, especially at the base, become chlorotic

(5) Deficiency of zinc in rice is called ‘khaira disease’.

Deficiency indicators plants:

Certain plants are suited as indicators for specific nutrient deficiencies. The indicator plants are susceptible to such deficiencies and develop clear symptoms, which are not shown by other deficiencies.

Some of the common crops suitable as indicator plants are given as follows:

Why Deficiency Symptoms are Not So Scientific?

1. Some hunger signs are common for more than one elements e.g., all the elements which govern the chlorophyll content such as N, Fe and Mg show similar symptoms (chlorosis).

2. An attack of insect-pest and disease or mechanical injury may cause yellowing and wilting which may be the symptom for certain deficient elements.

3. Higher availability of micronutrients may-, cause toxicity which may become the deficiency symptoms of certain plant elements.

Symptoms under Abundant (Excess) Supply of Nutrients:

(a) Nitrogen:

(1) Delays maturity of plants

(2) Encourages lodging

(3) Depresses root growth

(4) Makes plants more susceptible to attacks by insects and diseases.

(b) Micronutrients Toxicity:

Micronutrients above the sufficient level, the microelements may be poisonous to the plants. Boron is toxic when the water-soluble form is too high. In very acid soils iron and aluminium are often harmful. Toxicity due to molybdenum and copper, cause ill health in live-stock grazed on herbage. Manganese toxicity is common in highly acidic soils.

Iron:

(1) Tiny brown spots lower leaves, starting from the tips and spreading towards the base

(2) In severe cases, the entire leaves become purplish-brown

(3) Leaf usually remains green.

Manganese:

(1) Brown spots on the veins of the leaf blade and the leaf sheath, especially on the lower leaves

(2) Stunted plant growth

(3) Production of tillering limited.

Boron:

(1) Chlorosis at the tips of the older leaves, especially along the margins

(2) Later large, dark brown elliptical spots appear in the affected parts, which turn brown and dry up

(3) The first symptoms of boron toxicity is a yellowish-white discolouration of the tips of the older leaves.

Sulphur:

(1) In flooded soil, sulphate is reduced to sulphide, which inhibits the respiration and oxidative power of the roots

(2) Retards the uptake of various elements

(3) Hydrogen sulphide is considered the major cause of disorder in rice crop.

Control of Deficiency:

The following measures may be applied for correcting deficiency through soil and foliar application:

1. Nitrogen:

Nitrogen deficiency can be corrected by the use of nitrogenous fertilizers like urea, ammonium sulphate etc., in the soil. The application of urea as foliar spray on the leaves also gives good responses. Other N-fertilizers cause scrotching of leaves.

2. Phosphorus:

Application of phosphatic fertilizers (super phosphate) in the soil. Phosphorus is capable of being utilised by the plant when it is sprayed on the leaves. Although the practice is not common.

3. Potassium:

Use of potassic fertilizers e.g., Muriate of potash in the soil may cure potassium deficiency. Application as foliar sprays have been made, using potassium sulphate fertilizer. Some leaf injury resulted and the conclusion was reached that soil applications are far more satisfactory.

4. Calcium is seldom applied as a foliar spray because it can be efficiently applied to the soil. Calcium carbonate, calcium oxide, calcium hydroxide can be applied to the soil.

5. Magnesium is now commonly applied to plant foliage as solutions of magnesium sulphate. Soil application of magnesium takes long time to correct deficiency.

6. Sulphur:

S-sprayed on leaves is readily absorbed by the plants. Soil application of sulphur in form of sulphate is equally effective.

7. Iron:

Spraying of 5% ferrous sulphate on foliage is an effective method in controlling its deficiency. Iron is trans-located very slowly, as a result, after spraying chlorotic- spots may still be in evidence in places which did not receive iron spray. On alkaline soils where iron chlorosis is common, application of iron compounds to the soil have not been very successful because iron is soon rendered insoluble.

8. Copper:

Copper sulphate is commonly used for the correction of deficiency of copper. It may be applied in soil or used as foliar spray. Solution of copper sulphate and calcium hydroxide is prepared in water for spraying. Without the calcium hydroxide, the copper sulphate injures the foliage.

9. Boron:

Boric acid or borax (sodium tetra borate) is used as a foliar spray. Boron is also satisfactorily applied to the soil, either alone or in mixed fertilizers.

10. Manganese:

Soil application of manganese sulphate @ 20-100 kg per hectare was found effective. Spraying is economical since much smaller amount can be employed. The concentration used is 0.2-0.5 per cent manganese sulphate solution at the rate of 500- 1000 litre of water per hectare-. Manganese chloride solution may also be used in correcting the deficiency.

11. Molybdenum:

Sodium molybdate, ammonium moly dated are used in soil and spray application. Its translocation in plant is slow.

12. Zinc:

Mitigating the zinc deficiency are as follows:

In case of soil application method, 25 to 50 kg zinc sulphate per hectare is applied at the time of final land preparation. Its residual effect remains in the soil for 3-4 years.

Zinc sulphate is also applied in liquid form on foliage 5 kg zinc sulphate and 2.5 kg lime (calcium hydroxide) are dissolved in 1000 litre of water and spraying of this solution is done over standing crops.

Addition of organic matter to soil or growing green manure crops frequently improves crops subject to zinc deficiency.

Foliar Nutrition of Plants:

The plants are able to absorb essential elements through their leaves. The absorption takes through the stomata of the leaves and also through the leaf cuticle. Movement of elements is usually faster through the stomata, but the total absorption may be as great through the cuticle. Both woody and herbaceous plants are also capable of absorbing nutrients through the surface of their stems.

The following elements supply nutrients for plant growth by applying them as foliar sprays to the leaves:

Available Form in Which the Nutrients Occur in Soil:

Plants take carbon, hydrogen and oxygen chiefly from air and water. Some amount of carbon is also absorbed through roots. Other nutrients are taken from the soil mostly in the form of ions.

The 16 elements move into the plant primarily in the following forms: