Plant Nutrients

Science > Biology > Management of Crop Production > Plant Nutrients

Green plants are autotrophic. They require inorganic matter from outside and synthesize their own organic matter. Plant nutrients are mineral elements need by the plants for their growth, development, and maintenance.

Soil is a major source of plant nutrients needed by plants for growth. The three main plant nutrients are nitrogen (N), phosphorus (P) and potassium (K). Together they make up the trio known as NPK. Other important plant nutrients are calcium, magnesium, and sulfur. Plants also need small quantities of iron, manganese, zinc, copper, boron, and molybdenum, known as trace elements because only traces of them are needed by the plant.

Macronutrients: The mineral elements are the plant nutrients which are required by the plants in large quantities (more than 1 ppm) are called macronutrients. They include carbon, hydrogen, oxygen, nitrogen, phosphorous, potassium, calcium, magnesium and sulphur.

Micronutrients: The mineral elements are the plant nutrients which are required by the plants in small quantities (less than 1 ppm) are called micronutrients. They include copper, zinc, boron, molybdenum, chlorine, and iron.

Carbon and oxygen can be obtained from the air. Hydrogen and oxygen are obtained from the water while the remaining nutrients are obtained from the soil by plants.

Primary Nutrients (N, P, K)

Nitrogen (N):

Nitrogen is a key element in plant growth. it is the major component of amino acids, which are the building blocks of proteins, enzymes, and the green pigment chlorophyll. Crops with high nitrogen demands include grasses and leafy vegetables such as lettuce, spinach, and cabbage.

Nitrogen deficiency symptoms include stunted growth, yellowing or light-green colour in pastures because they are unable to make sufficient chlorophyll. Leaves in this state are said to be chlorotic. Other symptoms include the low protein content of grasses and crops and a lack of nodules or very small whitish nodules on clovers and other legumes.

The atmosphere contains a large reservoir of nitrogen, but most plants cannot use it. Pea, beans, clover and other legumes (dicots) have root nodules which contain symbiotic bacteria able to fix nitrogen gas as nitrates. They supply their own nitrogen fertilizer and enrich soil nitrogen if the roots are left in the soil after cropping.

Phosphorus (P):

Plants must have phosphorus for normal growth and maturity.  It is especially needed for seed germination, for healthy root growth and for hastening of the growth. Phosphorus atoms are needed to make important biological molecules such as ATP, DNA, RNA, and phospholipids.  It plays a role in photosynthesis, respiration, energy storage and transfer, cell division, cell enlargement and several other processes in plants. It increases vigour and disease resistance of plants. It helps to form and move starches, sugars, and oils in plants. It helps to improve fruit quality. Root crops such as carrot, parsnip, turnip, swede and fruit, and seed crops especially need adequate phosphorus. All manures contain phosphorus; manure from grain-fed animals is a particularly rich source.

Phosphorus deficiency symptoms include stunted growth, weak roots, and shoots, fewer tillers, Decreased yields. Some crops, such as corn, tend to show an abnormal discoloration when phosphorus is deficient.

Potassium (K):

Potassium is considered second only to nitrogen, when it comes to nutrients needed by plants, and is commonly considered as the “quality nutrient.” Potassium promotes flowering, fruiting and disease resistance. It is also important in cell wall development. It is needed to control both water uptake through roots and its loss from plants through the stomata in leaves. It is also needed in photosynthesis and respiration. As it is involved in sugar and starch production, it is especially needed by vegetables and fruits like carrot, parsnip, potato, tomato, and apple. Sufficient potassium in the soil is essential for the efficient plant use of nitrogen.

Potassium deficiency symptoms include reduced growth, yellowing and whitish spots along the outer margin of leaves, brown scorching and curling of leaf tips as well as chlorosis (yellowing) between leaf veins., reduced root, seed, fruit development.

Secondary Nutrients: (Ca, Mg, S)

Calcium (Ca):

Calcium plays a very important role in plant growth and nutrition, as well as in cell wall deposition. It is involved in the proper functioning of growing points (especially root tips), development of leaves, maintaining strong cell walls, and seed set in clovers. Calcium helps to control the transport of other nutrients in the plant. It is involved also in some enzyme processes. Lime, gypsum, dolomite, and superphosphate (a mixture of calcium phosphate and calcium sulfate) all supply calcium. It helps to maintain chemical balance in the soil, reduces soil salinity, and improves water penetration.

Deficiency symptoms of calcium are rare because it is common and abundantly available on the earth’s surface. In acute deficiency, localized tissue necrosis leading to stunted plant growth can take place. Other symptoms include curling of the leaves, the eventual death of terminal buds and root tips.

Magnesium (Mg)

Many enzymes in plant cells require magnesium in order to perform properly. It is needed for healthy leaves. It is an essential component of chlorophyll and is required for the transport of phosphorus around the plant. It is also needed in the production of ATP.

Magnesium (Mg), like calcium, is usually present in sufficient quantities in the soil for plant growth; and pasture deficiencies are rare.  If magnesium deficiency exists, then it can be overcome with dolomite (a mixed magnesium-calcium carbonate), magnesite (magnesium oxide) or Epsom salts (magnesium sulphate).

Magnesium deficiency symptoms include yellowing of leaves while the leaf veins remain green, abnormally thin leaves, and interveinal chlorosis.

Sulphur:

Sulphur is as necessary as phosphorus and is considered an essential mineral. It is required for the synthesis of several amino acids, proteins, and vitamins and chlorophyll. It also helps the plant to resist stress from weather, insects, and diseases. It is responsible for many flavour and odour compounds in plants such as the aroma of onions and cabbage.

Sulphur deficiency symptoms include: plants appear stunted with thin stems and petioles, small, pale, yellow-green leaves with lighter coloured veins, poor development and fewer numbers of nodules on legumes. Younger leaves suffer from chlorosis with their tips becoming necrotic. It is needed in very low amounts, but deficiencies can cause serious plant health problems and loss of vitality.

Trace Elements:

Iron (Fe):

Plants only need a small amount of iron to be healthy, but that small amount is crucial. It is a constituent of many compounds that regulate and promote growth. It is associated with the production of chlorophyll and helps to carry oxygen around the plant cells. Iron is also involved in reactions that convert nitrates to ammonia in the plant.

Iron deficiency symptoms include yellowing between the leaf veins of the youngest leaves (chlorosis), stunting and abnormal growth. plants with an iron deficiency, or chlorosis, show a sickly yellow color to their leaves because less chlorophyll is produced.

Manganese (Mn):

Many processes are dependent on manganese, Manganese helps with chloroplast formation, photosynthesis. nitrogen metabolism and synthesis of some enzymes. It is closely associated with iron, copper, and zinc as a catalyst in plant-growth processes. It is essential for rapid germination. It plays an important role in enzyme systems in seed and new tissues. Hence it is crucial for plants.

Manganese deficiency symptoms include yellowing between the veins of young leaves (chlorosis) due to immobility in plants, stunting of growth, and reduced flower formation.

Copper (Cu):

Copper activates some enzymes in plants which are involved in lignin synthesis and it is essential in several enzyme systems. Copper is an essential constituent of enzymes in plants for chlorophyll production, nutrient processing and the plant’s exchange of water and oxygen for carbon dioxide. Overuse of another trace element, molybdenum, can cause a copper deficiency in animals.

Copper deficiency symptoms are not very specific in plants.

Zinc (Zn):

Zinc (Zn) is associated with the formation of chlorophyll and of several enzyme systems required for protein synthesis. It also has a regulatory role in the intake and efficient use of water by plants. It plays an important role in a wide range of processes, such as growth hormone production and internode elongation.

Zinc deficiency symptoms include small bronze spots on older leaves of legumes; branching of small, dark green, distorted leaves in the centre of legume, white stripes in younger leaves of grasses. Its deficiency causes large losses in crop production and crop quality.

Boron (B):

Boron (B) is mainly involved in the movement of sugars throughout the plant and in seed production in legumes. It is also an important nutrient in the metabolism of nitrogen, carbohydrates, and hormones and is involved in the uptake and efficient use of calcium in the plant. Boron with calcium helps with the formation of cell walls in rapidly growing tissue. Deficiency reduces the uptake of calcium and inhibits the plant’s ability to use it. Boron requirements are much higher for reproductive growth so it helps with pollination, and fruit and seed development.

Boron deficiency symptoms include distorted and chlorotic leaves with darker pigmentation along the leaf margins, poor growth, and low seedset. Boron deficiency affects vegetative and reproductive growth of plants, resulting in inhibition of cell expansion, death of meristem, and reduced fertility.

Molybdenum (Mo):

Molybdenum is an essential component in two enzymes that convert nitrate into nitrite and then into ammonia before it is used to synthesize amino acids within the plant. Thus Molybdenum helps bacteria and soil organisms convert nitrogen in the air to soluble nitrogen compounds in the soil, so is particularly needed by legumes. It is also essential in the formation of proteins from soluble nitrogen compounds.

Molybdenum deficiency symptoms may look similar to a nitrogen deficiency and legumes will have green or grey to white nodules rather than the pinkish-coloured nodules of healthy plants. A lack of molybdenum will reduce the nitrogen-fixing ability and growth of legumes.

Nickel (Ni):

Nickel (Ni) is a component of the enzyme urease, it is involved in nitrogen metabolism. It is involved in nitrogen translocation within plants, in bacterial enzymes; including nitrogen fixation, and in the seed germination and vigour. It Influences plant disease resistance

Significant nickel deficiency will display visual symptoms typically in the old leaves of the plants as nickel is a mobile element. Deficiency  symptoms in legumes are exhibited as whole leaf chlorosis along with necrotic leaf tips (caused by the accumulation of toxic levels of urea)

Chlorine (Cl):

Chlorine is important for plant photosynthesis as it is involved in the opening and closing of stomata. It also ensures that the leaves are firm.

Chlorine deficiency symptoms include chlorotic leaves, leaf spots, brown edges, restricted and highly branched root system, as well as wilting of leaves at margins, and leaf mottling.

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