Zinc is a micro-nutrient essential for the growth and development of plants, animals and humans.Zinc has several important functions in plants, including major roles in enzyme reactions, photosynthesis, DNA transcription and auxin activity. Of all micronutrients, zinc is the one most often deficient in corn production and most likely to elicit a yield response when applied as fertilizer. However, yield responses are only attainable when zinc is deficient and therefore limiting yield.
Role of Zinc in corn plant
- Synthesis (production) of growth hormones and proteins.
- Production of chlorophyll and carbohydrate metabolism.
- Essential for the transportation of calcium throughout the corn plant.
- Cell elongation, the increase in leaf and node size along with grain formation.
Factors Effecting Zinc Availability in soil
- Soil pH above 7.0 causes zinc to form compounds that are unavailable to plants and results in more zinc deficiency symptoms.
- Soils with low in organic matter have less zinc availability.
- The temporary deficiency is caused by slow root growth. As the temperatures rise and conditions improve, deficiency symptoms should disappear.
- Compacted soils reduce the corn plants rooting ability. The lack of roots, chance of intercepting zinc minerals is reduced and the corn plant is easily put into a zinc deficient state.
- Phosphorus levels increase, the mycorhizae population decreases, thus reducing the plants ability to uptake zinc, therefore high soil phosphorus levels tend to reduce the availability of zinc.
Occurrence of Zinc deficiency in maize
Zinc (Zn) deficiency in corn occurs at inter-veinal, light striping or a whitish band beginning at the base of the leaf and extending towards the tip. The margins of the leaf, midrib area, and the leaf tip usually remain green. Zinc deficiency may result in new leaves that are nearly white, an effect termed “white bud.” Zinc deficiency in corn results in a white or yellow band that runs parallel with the mid rib. Problems associated with zinc deficiency include Poor root development, Stunted growth, Small leaves, Shortened internodes, Delayed tasseling, Chalky kernels
Incorporation of Zinc
Zinc is one of the most important micronutrients for a high yielding corn crop. Zinc carriers, the very insoluble compounds, are effective sources of zinc for crops. Zinc materials may be broadcast on the soil and thoroughly incorporated or used in a band next to the seed at planting time. Broadcast application of an inorganic zinc material and thorough incorporation are the best means of rectifying the problem. Carriers and mobility of fertilizer in soil are
- Organic Zinc Sulphate (Zn EDTA) - High mobility
- Organic non-chelate zinc (Rayplex Zinc) - Low mobility
- Soluble Inorganic zinc( Zinc sulphate) - Low mobility
- Insoluble Inorganic zinc( Zinc oxide) - Very low mobility
Granular zinc sulphate or finely divided zinc oxide or carbonate are effective zinc carriers for broadcast treatment at minimal cost.The most common fertilizer sources of Zinc are Zinc chelates (contain approximately 14% zinc), Zinc sulphate (25-36% zinc) and zinc oxide (70-80% Zinc), where Zinc Sulphate is source of zinc.Zinc oxysulphate is a good Zn fertilizer with high percentage of Zn sulphate but Zn oxide is the predominant component not a good source of Zn.Organic sources of zinc used as chelates are zinc poly flavonoid and zinc sulfonate.
Zinc sulphate, apply 0.5 to 1 pound of actual zinc per acre (1.5 to 3pounds of material), zinc chelate is applied at the rate of 0.15 pounds of actual zinc per acre. The most cost-effective products available is zinc sulphate, which is considered an excellent sourceof zinc applied as a granular material in a bulk blend or incorporated into solid or liquid fertilizers. Foliar applications of zinc are not common in soil applications.
The Zn application provides a higher content of micronutrient in the soil and higher accumulation in the shoot reflected in the maize grain. The Zn application in the soil promotes a higher Zn uptake by the plants and maize yield.
Dr.A.G.Rajalakshmi1 K.Jeevika2 and A.Karmel Reetha3
1Senior Research Fellow, 2&3Assistant professor
Department of Soil Science and agricultural chemistry,
Vanavarayar Institute of Agriculture, Manakkadavu, Pollachi-642103