Plant nutrients are the chemical elements that are essential to the nourishment of plant health. Plant nutrients fall into three categories, all of which are based on the amount a plant needs. Each plant nutrient performs a crucial role in plant growth and development. There are two categories of plant nutrients ,macro and micro and the other division is that of non-minerals and minerals. The non-mineral nutrients are hydrogen, oxygen and carbon. These nutrients are found in the air and water. In the process called Photosynthesis (making things with light), plants use energy from the sun to change carbon dioxide and water into starches and sugars, which are the plant’s food.
The fourteen mineral nutrients which come from the soil, are dissolved in water and absorbed through a plant's roots. There are not always enough of these nutrients in the soil for a plant to grow healthy. This is why many farmers and gardeners use fertilizers to add the nutrients to the soil. Macro nutrients can be classified as primary and secondary nutrients. The primary nutrients are nitrogen (N), phosphorus (P), and potassium (K). These essential elements are required by plants in higher quantities than elements that fall into the other category. Additionally, each of these three elements perform crucial functions in plant biology. Nitrogen is necessary for building proteins, produces carbohydrates, and is essential for plant growth. Phosphorus effects root growth, seed formation, and plant maturity. Potassium is important in disease resistance, fruit formation, and effects plant enzymes.
Secondary plant nutrients are calcium (Ca), magnesium (Mg), and sulphur (S). These elements, although not needed in such high quantities, are necessary for plant health. Sulphur helps develop vitamins, aids in seed production, and is an integral part of forming amino acids. Magnesium is a key component in chlorophyll production, and helps plants to utilize phosphorus and iron. Calcium plays many roles in regulating plant system functions like respiration and cell division and in some plants it is essential for nut development . Calcium and Magnesium are added when lime is applied to acidic soils. Sulphur is usually found in sufficient amounts from the slow decomposition of soil organic matter.
The micronutrients are needed in much smaller quantities , but are necessary for growth and development. The plant micronutrients are boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) zinc (Zn) and nickel. Among these, copper, play a major role in photosynthesis and reproduction. Others aid in the absorption and utilization of other elements.
Plants can receive nutrients from the soil, fertilizers, or through individual nutrient application. For example, to increase plant flowering and fruiting, gardeners can use PK Boosters to give plants more phosphorus and potassium; both of which are essential to fruit/flower growth and development. Recycling organic matter such as grass clippings and tree leaves is an excellent way of providing micronutrients as well as macronutrients to growing plants. In general, most plants grow by absorbing nutrients from the soil. Their ability to do this depends on the nature of the soil. Depending on its location, a soil contains some combination of sand, silt, clay, and organic matter.
The soil texture and its pH determine the extent to which nutrients are available to plants. Soil Texture is the amount of sand, silt, clay, and organic matter available in the soil. Soil texture affects how well nutrients and water are retained in the soil. Clays and organic soils hold nutrients and water much better than sandy soils. As water drains from sandy soils, it often carries nutrients along with it. This condition is called leaching. When nutrients leach into the soil, they are not available for plants to use.
An ideal soil contains equivalent portions of sand, silt, clay, and organic matter. Sometimes, the nutrients that plants need occur naturally in the soil. Otherwise, they must be added to the soil as lime or fertilizer. Soil pH is one of the most important soil properties that affects the availability of nutrients. Macronutrients tend to be less available in soils with low pH. Micronutrients tend to be less available in soils with high pH. Lime can be added to the soil to make it less acidic and also supplies calcium and magnesium for plants to use. Lime also raises the pH to the desired range of 6.0 to 6.5. In this pH range, nutrients are more readily available to plants, and microbial populations in the soil increase. Microbes convert nitrogen and sulphur to forms that plants can use. Lime also enhances the physical properties of the soil that promote water and air movement.
Macronutrients
Nitrogen (N)
Nitrogen is a part of all living cells and is a necessary part of all proteins, enzymes and metabolic processes involved in the synthesis and transfer of energy. It is a part of chlorophyll, the green pigment of the plant that is responsible for photosynthesis. Nitrogen also helps plants with rapid growth, increasing seed and fruit production and improving the quality of leaf and forage crops. It often comes from fertilizer application and legumes get their N from air.
Nitrogen deficiency symptoms
Plants having less than 1 percent N – content are usually regarded deficient in Nitrogen. Nitrogen deficiency will cause stunted growth. Symptoms first appear on the older leaves in the form of light green to pale yellow colouration with intensity depending upon severity of N-deficiency. Reduction in flowering and crop yields and low protein content are associated with N- deficiency. It can be managed by the foliar spray of 2 percent urea or water soluble nitrogeners . Excess consumption of nitrogen will result in the increase of succulence , tallness in plants and heavier heads that may tend to cause lodging . A nitrogen rich, luxuriant succulent crop is susceptible to insect ,pest and disease attack.
Phosphorus (P)
Like nitrogen, phosphorus (P) is an essential part of the process of photosynthesis. It involves in the formation of all oils, sugars, starches, etc. Phosphorus helps with the transformation of solar energy into chemical energy; proper plant maturation; withstanding stress. It effects rapid growth, encourages blooming and root growth. Phosphorus often comes from fertilizer, bone meal, and superphosphate.
Phosphorus deficiency symptoms
Plants having less than 0.01 % or 1000 ppm P are P- deficient. Deficiency symptoms appear first on the older leaves. P-deficient plants have dark green or bluish green coloured older leaves. Under conditions of continued deficiency, older leaves become bronzed or develop reddish –purple tips and leaf margins. It will end in restricted growth of plant tops and roots. P-deficient plants are thin, erect and spindly with sparse and restricted foliage . Development of lateral buds is suppressed, leaves become narrow, making an acute angle with stem-axis. It can be managed by foliar spray of 2 percent DAP(Diammonium phosphate) and application of recommended dose of phosphorus along with other major nutrients.
Potassium (K )
Potassium is absorbed by plants in larger amounts than any other mineral element except nitrogen and, in some cases, calcium. It helps in the building of protein, photosynthesis, fruit quality and reduction of diseases. Potassium is supplied to plants by soil minerals, organic materials and fertilizer.
Potassium deficiency symptoms
Potassium concentration in healthy plant tissues varies from 1 to 5 %. Deficiency symptoms of potassium develop first on older leaves. Chlorosis along the leaf margins is followed by scorching and browning of tips of older leaves which gradually progresses inwards. Slow and stunted growth of plants is another symptom. Plants lodge easily. Potassium deficient seeds and fruits are shrivelled. It can be managed by soil application of recommended dose of potassium. Foliar sprays of 1% Muriate of potash or Potassium nitrate can also be done.
Calcium ( Ca)
Calcium, an essential part of plant cell wall structure, provides for normal transport and retention of other elements as well as strength in the plant. It is also thought to counteract the effect of alkali salts and organic acids within a plant. The main sources of calcium are dolomitic lime, gypsum, and superphosphate.
Calcium deficiency symptoms
Calcium in Ca- sufficient plants ranges between 0.2 to 1 %. Usually plants having Ca- content of less than 0.1% or 1000ppm are calcium deficient. Calcium deficiencies are common in acid soils of the tropics. Ca- deficiency symptoms appear on younger leaves. Young leaves distorted , small and abnormally green. Leaves become cup shaped and crinkled and the terminal buds deteriorate with some break-down of petioles. Desiccation of terminal buds and weakening of the stem structure is another symptom. Pops in ground nut, blossom end rot in tomatoes and bitter pith in apples are due to Ca- deficiency.Ca- deficiency occur in acid soils. Application of lime to acid soils based on soil test will solve the deficiency.
Magnesium (Mg)
Magnesium is part of the chlorophyll in all green plants and essential for photosynthesis. It also helps activate many plant enzymes needed for growth. Soil minerals, organic material, fertilizers, and dolomitic limestone are sources of magnesium for plants.
Magnesium deficiency symptoms
Magnesium deficient plants usually have less than 0.1% Mg. Magnesium deficiency symptoms appear on older leaves .Symptoms include , interveinal chlorosis and streaked or patchy effects on older leaves. Affected leaves turn small in final stages and curve upwards at margin. Interveinal chlorosis with tints of red, orange and purple colours is observed in some of the vegetables. Deficiency occur in acid soils. This can be managed by applying dolomite to acid soils based on soil test. If Mg deficiency is observed in plants growing on neural to alkaline light textured soil, spray 1% MgSO4 or apply MgSO4 to soil based on soil test.
Sulphur (S )
Sulphur is an essential plant food for production of protein. It promotes activity and development of enzymes and vitamins. Sulphur helps in chlorophyll formation. It improves root growth and seed production and helps with vigorous plant growth and resistance to cold. Sulphur may be supplied to the soil from rainwater. It is also added in some fertilizers as an impurity, especially the lower grade fertilizers. The use of gypsum also increases soil sulphur levels.
Sulphur deficiency symptoms
Plants having less than 0.1 to 0.2 % S-content suffer from S – deficiency. Crop plants having N:S ratios more than 16:1 also can be suspected to be deficient in Sulphur. Sulphur deficiencies are similar to N deficiencies but, first appear on the younger leaves as it is immobile in plants. The fading of the normal green colour of the young leaves , followed by chlorosis is the most common deficiency symptom. Brassicas are susceptible to S –deficiency, S- deficient plants have restricted lamina, leaves show cupping owing to the curling of the leaf margins and arresting of the growing points. The older leaves become puckered with inward raised areas between the veins. The older foliage develops orange or reddish tints and may shed permanently. Soil application of 100-200 kg/ha of gypsum based on soil test and crop requirement will cure the disease. Foliar spray of 1% water soluble S fertilizers is also advisable
Micro nutrients
Boron (B )
Boron helps in the use of nutrients and regulates other nutrients. It aids production of sugar and carbohydrates. Boron is essential for seed and fruit development. Main sources of boron are organic matter and borax.
Boron deficiency symptoms
Plants having B concentrations of the order of 5 to 30 ppm are suspected to be B- deficient. Critical deficiency range of B varies from 5 to 10 ppm in graminaceous plants, 20 to 70 ppm in most of the dicotyledonous plants. Boron deficiency symptoms become conspicuous on the terminal buds or young leaves , which become discoloured and may die under acute conditions of B-deficiency. Internodes become shorter and give appearance of a bushy or a rosette . Increased diameter of stem and petioles gives rise to the typical cracked stem of celery. Major diseases due to deficiency of B are heart rot of sugar beet and mangold, browning or hollow stem of cauliflower, top sickness of tobacco, internal cork of apple. Foliar spray of 0.2% Borax or soil application of Borax@5-10 kg/ha mixing with vermi compost or FYM(1:1) will solve the deficiency.
Copper (Cu)
Copper is important for reproductive growth. It aids in root metabolism and helps in the utilization of proteins.
Copper deficiency symptoms
Plants having less than 5 ppm Cu are regarded as Cu-deficient. Chlorosis of the younger shoot tissues, white tips, reclamation disease, necrosis, leaf distortion and die back are the characteristic Cu- deficiency symptoms. Necrosis of the epical meristems results in elongation of the shoots in cereals and auxillary shoots in dicotyledonous plants. Symptoms sterility in male flower, delayed flowering and senescence are the most important effects of Cu-deficiency. Foliar spray of 0.1% CuSO4 +0.5% lime water or soil application of CuSO4@20-25 kg/ha mixing with vermicompost or FYM(1:1) will solve the deficiency
Chloride ( Cl )
Chloride aids plant metabolism. It is found in the soil.
Chloride deficiency symptoms
Wilting, restricted and highly branched root system, often with stubby tips are the major symptoms. Leaf mottling and leaflet blade tip wilting with chlorosis has also been observed. It can be managed by a using a fertilizer that specifically includes chloride as an ingredient.
Iron ( Fe )
Iron is essential for formation of chlorophyll. The best sources of iron are the soil, iron sulphate and iron chelate.
Iron deficiency symptoms
Plants having less than 30 ppm of Fe2+ are usually deficient in iron. Deficiency of iron results in inter veinal chlorosis appearing first on the younger leaves with leaf margins and veins remaining green. Under the conditions of severe deficiency, growth cessation occurs with the whole plant turning necrotic. Foliar spray of 0.2% FeSO4 +0.02% lime water or soil application FeSO4 @20-25 kg/ha, mixing with vermicompost or FYM(1:1), Aeration (drain, standing water ) and application of lime based on soil testing can be used
Manganese (Mn )
Manganese functions with enzyme systems involved in breakdown of carbohydrates, and nitrogen metabolism. Soil is a source of manganese.
Manganese deficiency symptoms
Manganese deficient plants contain less than 25 ppm Mn. Deficiency symptoms of Mn are more severe on middle leaves than on the younger ones. Interveinal chlorosis in dicotyledonous plants is characterised by the appearance of chlorotic and necrotic spots in the interveinal areas. In the monocotyledonous plants like cereals , manganese deficiency symptoms appear as greenish grey spots, flecks and stripes on the more basal leaves. Chlorotic leaf areas soon become necrotic and turn red , reddish brown or brown. Symptoms of Mn – deficiency are popularly known as grey speck of oats, speckled yellow of sugarbeet, marsh spot of peas, phala blight of sugarcane and frenching of tung trees. Foliar spray of 0.6% MnSO4+ 0.3% lime water or soil application of MnSO4@20-25 kg/ha mixing with vermicompost or FYM(1:1) are effective.
Molybdenum ( Mo )
Molybdenum helps in the use of nitrogen. Soil is a source of molybdenum.
Molybdenum deficiency symptoms
The critical concentration of Mo- deficiency in plants is usually less than 0.1 ppm. Molybdenum deficiencies resemble N- deficiencies. In plants with reticulate venation, the earlier effects of Mo – deficiency appear as chlorotic mottling between the veins on old or middle leaves all over the surface. In Brassica spp, symptoms appear on 3 to 4 week old plants. The Mo- deficient cauliflower plants exhibit chlorotic mottling and cupping of the middle leaves. Severely affected leaves show scorching and withering starting from the margins and extending to the entire lamina leaving behind only petioles. Mo-deficiency in cauliflower is termed as whip-tail. Foliar spray of 0.1 -0.2% sodium molybdate or soil application of sodium molybdate @ 0.5-1 kg/ha mixing with vermicompost or FYM(1:1) can be applied.
Zinc ( Zn )
Zinc is essential for the transformation of carbohydrates. It regulates consumption of sugars. Zinc is part of the enzyme systems which regulate plant growth. The sources of zinc are soil, zinc oxide, zinc sulphate, zinc chelate.
Zinc deficiency symptoms
Plants containing less than 15 ppm Zn are deficient in Zn. Common deficiency symptoms of Zn are intervenial chlorosis, first appearing on the younger leaves. The first symptoms of Zn deficiency appear in 3 to 4 weeks old seedlings when the young leaves develop reddish- brown pigmentation. This pigmentation which first appear in the middle of the leaf intensifies and covers the entire lamina. In dicotyledonous plants, symptoms include short internoded and decrease in leaf expansion. Names given to Zn deficiency are Khaira disease in rice, white bud of maize, frenching of citrus and little leaf of cotton. Foliar spray of 0.5% ZnSO4+0.25% lime water or soil application of ZnSO4 @ 20-25kg/ha mixing with vermicompost or FYM(1:1) will solve the deficiency.
Nickel ( Ni )
Nickel is a component of some plant enzymes, most notably urease, which metabolizes urea nitrogen into useable ammonia within the plant. Without nickel, toxic levels of urea can accumulate within the tissue forming necrotic legions on the leaf tips.
Nickel deficiency symptoms
Nickel deficiency will reduce growth and yield of plants. In legumes, whole leaf chlorosis along with necrotic leaf tips will happen. In woody ornamentals,shortened internodes, weak shoot growth, death of terminal buds and eventual death of shoots and branches may happen.Since Nickel is needed in small quantities only, it can be applied as a single element application as nickel sulphate or in a chelated form.
Presence of nutrients
Micronutrients stay beneath soil as salt. So plants consume these elements as ion. The macronutrients are consumed in larger quantities and contribute to over 95% of a plants' entire biomass on a dry matter weight basis. Micronutrients are present in plant tissue in quantities measured in parts per million, ranging from 0.1 to 200 ppm, or less than 0.02% dry weight. Most soil conditions across the world can provide plants adapted to that climate and soil with sufficient nutrition for a complete life cycle, without the addition of nutrients as fertilizer. However, if the soil is cropped it is necessary to artificially modify soil fertility through the addition of fertilizer to promote vigorous growth and increase or sustain yield. This is done because, even with adequate water and light, nutrient deficiency can limit growth and crop yield.
Plants take up essential elements from the soil through their roots and from the air through their leaves. Nutrient uptake in the soil is achieved by cation exchange, wherein root hairs pump hydrogen ions (H+) into the soil through proton pumps. These hydrogen ions displace cations attached to negatively charged soil particles so that the cations are available for uptake by the root. In the leaves, stomata open to take in carbon dioxide and expel oxygen. The carbon dioxide molecules are used as the carbon source in photosynthesis.
The root, especially the root hair, is the essential organ for the uptake of nutrients. The structure and architecture of the root can alter the rate of nutrient uptake. Nutrient ions are transported to the centre of the root, the stele, in order for the nutrients to reach the conducting tissues, xylem and phloem. The casperian strip, a cell wall outside the stele but within the root, prevents passive flow of water and nutrients, helping to regulate the uptake of nutrients and water. Xylem moves water and mineral ions within the plant and phloem accounts for organic molecule transportation. Water potential plays a key role in a plant's nutrient uptake. If the water potential is more negative within the plant than the surrounding soils, the nutrients will move from the region of higher solute concentration—in the soil—to the area of lower solute concentration - in the plant.
Nutrients uptake
There are three fundamental ways plants uptake nutrients through the root:
Simple diffusion occurs when a non polar molecule, such as O2, CO2, and NH3 follows a concentration gradient, moving passively through the cell lipid bilayer membrane without the use of transport proteins.
Facilitated diffusion is the rapid movement of solutes or ions following a concentration gradient, facilitated by transport proteins.
Active transport is the uptake by cells of ions or molecules against a concentration gradient; this requires an energy source, usually ATP(Adenosine tri phosphate), to power molecular pumps that move the ions or molecules through the membrane.
Nutrients can be moved within plants to where they are most needed. For example, a plant will try to supply more nutrients to its younger leaves than to its older ones. When nutrients are mobile within the plant, symptoms of any deficiency become apparent first on the older leaves. However, not all nutrients are equally mobile. Nitrogen, phosphorus, and potassium are mobile nutrients while the others have varying degrees of mobility. When a less-mobile nutrient is deficient, the younger leaves suffer because the nutrient does not move up to them but stays in the older leaves. This phenomenon is helpful in determining which nutrients a plant may be lacking.
Symbiosis
Many plants engage in symbiosis with microorganisms. Two important types of these relationship are with bacteria such as rhizobia, that carry out biological nitrogen fixation, in which atmospheric nitrogen (N2) is converted into ammonium (NH+)and with mycorrhizal fungi, which through their association with the plant roots help to create a larger effective root surface area. Both of these mutualistic relationships enhance nutrient uptake.
Though nitrogen is plentiful in the Earth's atmosphere, relatively few plants harbour nitrogen-fixing bacteria, so most plants rely on nitrogen compounds present in the soil to support their growth. These can be supplied by mineralisation of soil organic matter or added plant residues, nitrogen fixing bacteria, animal waste, through the breaking of triple bonded N2 molecules by lightning strikes or through the application of fertilizers.
Functions of nutrients
Plant nutrition is a difficult subject to understand completely, partially because of the variation between different plants and even between different species or individuals of a given clone. Elements present at low levels may cause deficiency symptoms, and toxicity is possible at levels that are too high. Furthermore, deficiency of one element may present as symptoms of toxicity from another element, and vice versa. An abundance of one nutrient may cause a deficiency of another nutrient. For example, K+ uptake can be influenced by the amount of NH+ available.
Nutrient deficiency
The effect of a nutrient deficiency can vary from a subtle depression of growth rate to obvious stunting, deformity, discoloration, distress, and even death. Visual symptoms distinctive enough to be useful in identifying a deficiency are rare. Most deficiencies are multiple and moderate. However, while a deficiency is seldom that of a single nutrient, nitrogen is commonly the nutrient in shortest supply.Chlorosis of foliage is not always due to mineral nutrient deficiency. Solarization can produce superficially similar effects, though mineral deficiency tends to cause premature defoliation, whereas solarization does not, nor does solarization depress nitrogen concentration.