• Organic compounds like EDTA (Ethylene Diamine Tetra Acetic acid), DTPA (Diethylene Triamine Penta Acetic acid), Cyclohexane diamine tetraacetic acid have the ability to chelate or loosely hold metallic ions in their cyclic structure and these metal-organic complexes are called metal chelates.
• Metal chelates are soluble in water, but they do not ionize in soil solution. Metal ions, therefore, do not react with soil constituents.
• Chelate forms of nutrients are more soluble than those from ordinary salts.
• Iron, copper, zinc and manganese fertilizers are available in chelated forms.
ZINC
• Nearly half of the Indian soils are poor in available Zn.
• Zinc deficiency is less prevalent in the western states of Rajasthan and Gujarat.
• Zn deficiency was first detected in rice at Pantnagar, Uttarakhand in 1965 by Nene (plant pathologist) and given the name Khaira.
• The solubility of Zn is highly pH dependent and decreases 100fold with each unit increase in soil pH.
• Zn deficiency is most prevalent in calcareous soil due to
a) Increase in pH decreases Zn availability
b) Zn is directly sorbed on carbonates
c) Calcium carbonate can form insoluble calcium zincate
• Lack of moisture leads to Zn deficiency in soil and plants. Thus, more Zn deficiency is reported in aerobic rice systems.
• Zn is relatively immobile in plants, so deficiency symptoms generally appear on the growing young tissue.
• In rice the characteristic symptom of Zn deficiency is bronzing.
• Zinc interacts positively with N and K and negatively with P.
• Zn reacts antagonistically with all 3 secondary nutrients (Ca, Mg and S).
• Phosphate application decreases the uptake of Zn.
• Zn shows negative interaction with Fe, Cu and Mn.
• Zinc Sulphate is the most commonly used zinc fertilizer which contains 36% Zn.
• Zinc Oxide (ZnO) contains 50-80% Zn and is used for seed treatment. It is not soluble in water.
• Soil application of 10-25 kg/ha zinc sulphate is the most common recommendation.
• For foliar spray 0.5% solution of zinc sulphate mixed with a small quantity of lime is the general recommendation.
• For foliar application, zinc chelates are a better source, although they are more expensive. Zn chelates are better for fruit orchards.
• Zinc sulphate heptahydrate (21% Zn) is the most popular Zn fertilizer in India.
• Zinc is taken up by crop plants as Zn2+.
• Concentration of Zinc in soil solution is 2×10-9 M.
• Zinc removal by a 5 tonnes/ha grain producing rice crop is 200 g/ha.
• Zinc coated urea was first tested in agronomic experiments at IARI, New Delhi.
BORON
• Essentiality of Boron was established by K. Warington in 1923.
• Boron is taken up by most plants as H3BO3.
• Common soil B mineral is tourmaline.
• Maximum toxic element (Arsenic) is found in B fertilizer Colemanite.
• Boron is a non metal micronutrient.
• Boron is neither a constituent of enzymes nor it directly affects the enzymatic activities in plants.
• Boron helps in germination and growth of pollen grains.
• Boron also acts as fuel pump, aiding the transmission of sugars from older leaves to new growth areas and root-system.
• Boron helps in uptake of calcium.
• Boron moves in plant through phloem.
• Boron deficiency causes cracking in fruits.
• Average concentration of B in plants is 20ppm.
• Boron deficiency is wide spread in soils of humid zone.
• Boron content is more in igneous rocks.
• Maximum B deficiency is reported in soils of Karnataka.
• The deficiency of micronutrient Boron is prominent in eastern India.
• The magnitude of B deficiency in crops is almost similar to that of phosphorus (P) and zinc (Zn) and even more than sulphur (S) deficiency.
• Average boron deficiency in soils of whole India is 42-52%.
• Wide-spread deficiency of B is found in calcareous soils.
• Boron deficiency is widespread when soil had 25% CaCO3.
• Boron deficiency can be corrected by application of Granubor.
• Optimum concentration of Solubor solution for foliar spray on crops is 1 g/L.
• Borax is the most commonly used boron fertilizer which contains 11% B.
• Borax is highly soluble in water and is lost by leaching.
• To avoid leaching losses of boron, boron frits are developed which contains 2 to 6% B.
• Boric acid and solubor are boron fertilizers for foliar application.
• Boric acid contains 17% B.
• Boron solubility is maximum for Solubor.
• General dose of borax pentahydrate (14.6%) is 2 kg/ha.
• Boron is approved for fortification with DAP.
• Fortified fertilizers are allowed by ministry in agriculture.
• Boron foliar sprays are more beneficial than soil application to litchi.
• Boron foliar sprays response can be seen on early growth plus maturity.
• Contribution of irrigation water is important in correcting B deficiency.
• Boron toxicity in crops occurs in salt affected soil
