Micronutrients Point Wise Notes For Competitive exam-2


Ferrous sulphate is the most commonly used fertilizer which is sprayed on the crop to control iron chlorosis.

• When ferrous sulphate is applied to the soil, it is oxidized to ferric sulphate which is not readily available to plants.

• To overcome above problem, iron chelates are used both for soil and foliar application.

• Iron fruits which contain 22 % iron can be used for acid soils.

• Ferrous sulphate contains 19% Fe.

Potassium interacts positively with Fe.

Fe and Mn reach toxic levels under submergence.

• A negative interaction exists between P and Fe, Mn and Zn.

• Fe deficiency appears in younger leaves, while Mn deficiency appears in older leaves.

• DTPA-extractable CDL for Fe in soil is 2.5-4.5 mg/kg soil.

• CDL for Fe in plant leaves is 30-50 mg/kg drymatter.

Bronzing disease in rice is due to the toxicity of Fe.

• In plants Fe and Mn interact negatively.

• Fe should preferably be applied as foliar spray.

• With an increase in soil pH from 4 to 8, the concentration of Fe3+ ions declines from 10-8 to 10-20 M.

• The solubility of Fe decreases by 1000 fold for each unit increase of soil pH in the range of 4-9 compared to 100 fold decreases in the activity of Mn, Cu and Zn.

• Iron exists in Fe0 (metallic), Fe2+ (ferrous), and Fe3+ (ferric) forms.

• Under acidic conditions, Fe0 readily oxidizes to Fe2+, and Fe2+ oxidizes to Fe3+ as the pH increases above 5.

Ferric Fe (Fe3+) is reduced to Fe2+ and is readily available to plants in acidic soils, but precipitates in alkaline soils.

• Minimum Fe solubility occurs between pH 7.5 and 8.5, which is the pH range of many calcareous soils.

Iron deficiency, which occurs predominantly in calcareous and alkaline soils, is commonly enhanced by low soil temperature and high water or poorly aerated conditions.

• Fe plays a role in the synthesis of chlorophyll, reduction of nitrate and sulphate, and in N assimilation.

Interveinal chlorosis in the young leaves is the characteristic symptom of Fe deficiency and in extreme conditions the entire leaves may turn white.

• Sorghum is the indicator plant for Fe deficiency in soil.

• Fe deficiency is observed on neutral to alkaline soils.

Fe deficiency is more frequent on upland than on submerged soils.

• With the same calcareous soil, upland rice may suffer severe iron deficiency, while lowland rice may grow normally.

Fe toxicity occurs only in lowland rice. Fe toxicity is likely to occur in acid sandy, acid latosolic, and acid sulphate soils.

• Iron toxicity also occurs on some organic soils such as peaty soils.

• Iron deficiency is reported from Punjab, Haryana and Himachal Pradesh in the north and from Karnataka and Tamil Nadu in the south.

• In well-drained aerobic conditions under which crops other than rice are grown, Fe occurs in oxidized ferric (Fe3+) form which is insoluble and availability to crop plants is considerably reduced.

• Iron deficiency has been reported from upland nurseries and aerobic rice systems.

• Frequent irrigation of upland rice nurseries can easily overcome Fe deficiency.

Prolonged flooded conditions in rice fields can increase the content of ferrous (Fe2+) iron from 0.1 (under drained conditions) to 500-1000 mg/kg and may lead to Fe toxicity.

Crops generally absorb more iron than any other micronutrients.

• Among the cereals, maize absorb more Fe than rice, wheat, sorghum or pearl millet.

Ferrous sulphate heptahydrate (FeSO4.7H2O) containing 18-20% Fe, is the most popular Fe-fertilizer.

• Soil application of inorganic Fe sources is highly uneconomical because very high doses of Fe required to correct the deficiency.

• For foliar spray 1-2% solution of ferrous sulphate is recommended.

Iron chlorosis is observed in upland crops especially rice, sorghum, groundnut, sugarcane, chickpea etc. grown in highly calcareous soils.

• Zn and Mo reduce Fe uptake.

• Both Fe and Zn interact positively with N and inversely with P.

Fe and Mn interact negatively with each other as well as with several other nutrients, such as P, Zn and Mo.

• The soluble Mn2+ content decreased 100-fold for each unit increase in pH.

• Increase in soil pH decreases both the water-soluble and exchangeable Mn content in soils to produce Mn deficiency in alkaline soils.

Mn deficiency is very common in fine-textured soils in comparison to coarse-textured soils.

• Organic matter improves the availability of Mn particularly in acid sandy soils.

• The combination of flooding, organic matter, and high temperatures increases Mn2+ content in soil.

• In well drained aerobic conditions under which crops other than rice are grown, Mn occurs in manganic (Mn4+) form, being insoluble form and availability to crop plants is considerably reduced.

• Submerged condition in paddy soils, particularly in the presence of a high amount of organic matter, increases Mn concentration in soil solution to even a toxic level.

• Mn is essential for splitting the water molecule during photosynthesis.

Manganese deficiency occurs in young leaves which wither or produce interveinal chlorosis with prominent dark green spots along with major veins.

• In case of Fe deficiency, veins also become light yellow or yellow, which is the only visible difference between iron and Mn deficiency.

• In manganese deficiency, the veins remain green with a fine reticular pattern, with or without necrosis.

Deficiency of Mn is named as

a) Marsh spot of peas

b) Grey speck of oats

c) Speckled yellows of sugar beets

d) Crinkle leaf of cotton

e) Curly top of cotton

• Mn deficiency is seen in crops grown on alkaline soils.

• Mn toxicity in plants is associated with poorly drained acid soils.

Mn deficiency in wheat has been reported in punjab.

• Toxicity symptoms of Mn in rice are interveinal yellowish brown spots, stunted plants and reduced tillering.

• Silicon application reduces Mn toxicity.

Liming the soils reduce Mn toxicity.

Manganse sulphate tetrahydrate (MnSO4.4H2O) (23-28% Mn) is the most popular Mn-fertilizer.

0.1-1.0% solution of manganese sulphate is required for foliar spray.

• Over-liming acid soils may lead to Cu deficiency.

• Amount of exchangeable Cu decreases as the pH increases.

• DTPA extractable CDL for Cu in soil is 0.2 mg/kg soil.

• Copper is a part of plastocyanin.

• Copper sulphate contains 21% Cu.

Cu inhibits the uptake of Zn.

• Molybdenum is present in the chloroplast of leaves.

Molybdenum is a structural component of nitrogenase which plays an active role in nitrogen fixation by Rhizobium, Azotobacter and some algae and actinomycetes.

• Molybdenum interacts positively with P and negatively with S and N.

Molybdenum has deficiency symptoms similar to N.

Whiptail disease in cauliflower is due to the deficiency of Mo.

Pale yellow leaves despite high nitrate concentration indicate the deficiency of Mo.

Chlorine is involved in production of oxygen during photosynthesis.

• Chlorine is involved in Hill reaction in Photosystem II in photosynthesis.

• Deficiency of secondary nutrient sulphur is widespread in India.

• The deficiency of micronutrient Zinc is widespread in India.

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