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Secondary Nutrients Next Secondary Nutrients Introduction Calcium, magnesium and sulphur are considered as secondary nutrients for plants; however, they play no secondary role in plant nutrition. They are just as essential for plant nutrition as any of the other 14 essential plant nutrients. Although, secondary nutrients are needed in lesser amounts than that of primary nutrients but they are important for plants. They have been called the “synthesizers” because of their functions in living organisms. End Previous Next Secondary Nutrients Introduction Many factors can affect the availability of these three nutrients to plants. The best estimates of their availability can be determined by soil analysis or a combination of soil and plant analyses. However, field observations and deficiency symptoms are also important diagnostic tools. End Previous Next Secondary Nutrients Sulphur (S) Sulphur is becoming more of a limiting nutrient in crop production than in the past, for several reasons Higher crop yields require more S Increased use of high analysis fertilizers containing little of no S Reduced amounts of atmospheric S fallout from the sky Reduced soil S reserves from organic matter losses due to mineralization and erosion. End Previous Next Secondary Nutrients Sulphur (S) Most S in the soil is tied up in organic matter and cannot be used by the plant until it is converted to the sulphate (SO4) form by soil bacteria. That process is known as mineralization. Sulphur can be applied as broadcast or banded fertilizer material or applied through irrigation systems (furrow and sprinkler). Sulphur is also an important nutrient for proper nutrition of forage crops that will be consumed by livestock. End Previous Next Secondary Nutrients Sulphur (S): Role in Plants Sulphur (S) is an essential part of amino acids cysteine, cystine and methionine. Hence, it is essential for protein production. S is involved in the formation of chlorophyll and in the activation of enzymes. It is a part of the vitamins biotin and thiamine (B1). In most plants it makes up 0.2 to 0.3 per cent of dry matter. Thus, it is as important in plant growth as phosphorus and magnesium; but its role is often underestimated. End Previous Next Secondary Nutrients Sulphur (S): deficiency symptoms As the supply of S becomes more limiting, young leaves lack S and, hence, show deficiency symptoms. In many ways, S deficiency resembles that of N. Unlike N deficiency, S-deficiency symptoms in most cases appear first on the younger leaves, and are present even after N application. Plants deficient in S are small and spindly with short and slender stalks. Their growth is retarded, and maturity in cereals is delayed. End Previous Next Secondary Nutrients Sulphur (S): Role in Plants It is needed for the formation of mustard oils, and the sulphydryl linkages that are the source of pungency in onion, oils, etc. S is required by comparable with P. End crops Previous in amounts Next Secondary Nutrients Sulphur (S): deficiency symptoms Nodulation in legumes is poor and N fixation is reduced. Fruits often do not mature fully and remain light green in colour. Oilseed crops deficient in S produce a low yield and the seeds have less oil in them. End Previous Next Secondary Nutrients Sulphur (S): deficiency symptoms In Tomato With Sulphur Source: http://5e.plantphys.net/image.php?id=373 End Previous Without Sulphur Sources: http://www.sulphurindia.com/Images/10.jpg Next Secondary Nutrients Areas affected by deficiency (S) Light textured soils with low organic matter Canal irrigated areas Areas where S-free fertilizers are used Acid soils are more prone to S-deficiency due to stronger adsorption of SO4. Wheat is more prone to S deficiency than rice End Previous Next Secondary Nutrients Sulphur Toxicity symptoms S toxicity can occur under highly reduced conditions, possibly as a result of sulphide (H2S) injury. Most plants are susceptible to high levels of atmospheric SO2. Normal SO2 concentrations range from 0.1 to 0.2 mg SO2/m3, and toxicity symptoms are observed when these exceed 0.6 mg SO2/m3. S-toxicity symptoms appear as necrotic spots on leaves, which then spread over the whole leaf. End Previous Next Secondary Nutrients Magnesium Involved in phosphate metabolism, plant respiration, and activation of enzyme systems. Magnesium can be added to deficient soils by applying Mg-containing fertilizers or dolomitic limestone. Dolomitic limestone contains both Ca and Mg carbonates (for neutralizing value), whereas calcitic limestone contains only Ca carbonate. End Previous Next Secondary Nutrients Magnesium Availability of Mg is often related to soil pH. Other situations also increase needs for Mg: . sandy soils with low cation exchange capacity, low Mg-supplying power, and a high Mg leaching potential application of calcitic limestone on low Mg soils crops with high Mg requirements; high application rates of ammonium-N and K. End Previous Next Secondary Nutrients Magnesium: role in plants Mg ranks with Ca, P and S in the group of least abundant macronutrients in plants. Plants take up Mg in the form of Mg2+. Mg occupies the centre-spot in the chlorophyll molecule and, thus, is vital for photosynthesis. It is associated with the activation of enzymes, energy transfer, maintenance of electrical balance, production of proteins, metabolism of carbohydrates, etc. Mg is mobile within the plants. End Previous Next Secondary Nutrients Magnesium: deficiency symptoms As Mg is readily translocated from older to younger plant parts, its deficiency symptoms first appear in the older parts of the plant. A typical symptom of Mg deficiency is the interveinal chlorosis of older leaves in which the veins remain green but the area between them turns yellow. As the deficiency becomes more severe, the leaf tissue becomes uniformly pale, then brown and necrotic. Leaves are small and break easily (brittle). Twigs become weak and leaves drop early. End Previous Next Secondary Nutrients Magnesium: deficiency symptoms Magnesium deficiency symptoms in maize End Previous Next Secondary Nutrients Magnesium: deficiency symptoms Magnesium deficiency in tomato: Source: http://5e.plantphys.n et/image.php?id=368 End Previous Next Secondary Nutrients Calcium Calcium (Ca) is sometimes considered a “low key” nutrient, but it carries a heavy load in plant growth. Calcium availability is adequate for most crops when soils are limed to properly adjust soil acidity. Deficiencies of Ca are most likely to occur on acid, sandy soils from which available Ca has been leached by rain or irrigation water, and on strongly acid peat and muck soil where total soil Ca is low. High exchangeable soil sodium (Na) may depress plant uptake of Ca. End Previous Next Secondary Nutrients Calcium: role in plants Calcium (Ca) ranks with Mg, P and S in the group of least abundant macronutrients in plants. It is absorbed by plant roots as the divalent cation Ca2+. Ca is a part of the architecture of cell walls and membranes. It is involved in cell division, growth, root lengthening and activation or inhibition of enzymes. Ca is immobile in the phloem. End Previous Next Secondary Nutrients Calcium: deficiency symptoms Ca deficiency is seen first on growing tips and the youngest leaves. This is the case with all nutrients that are not very mobile in the plants. Ca-deficient leaves become small, distorted, cupshaped, crinkled and dark green. They cease growing, become disorganized, twisted and,under severe deficiency, die. Although all growing points are sensitive to Ca deficiency, those of the roots are affected more severely. Groundnut shells may be hollow or poorly filled as a result of incomplete kernel development. End Previous Next Secondary Nutrients Calcium: deficiency symptoms Calcium deficiency in maize End Previous Calcium deficiency in tomato Next Secondary Nutrients Let us sum up Secondary nutrients are considered secondary because while they are essential to crop development, seasonal crop uptake is usually lower than for the primary nutrients N,P, and K but considerably higher than the micro-nutrients. The secondary plant nutrients (calcium, magnesium and sulphur) are equally important to the plant growth. In case of their deficiency the plants will suffer. The most common sources of calcium are gypsum and lime. Gypsum is a mined product that contains both calcium and sulphur, making it good for providing calcium. Lime is available in the form of ground oystershells and mined limestone. A source of magnesium is magnesium sulphate, otherwise known as epsom salts. Sulphur is available by itself in a granulated form, and in ammonium sulphate, etc. End Previous Next