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General Agriculture

Major, Secondary and Trace Elements in Crop Nutrition

There are eighteen essential elements for crop nutrition, each with their own functions in the plant, levels of requirement, and characteristics. Plant growth and development depends on nutrients derived from the soil or air, or supplemented through fertilizer.

Nutrient requirements generally increase with the growth of plants, and deficiencies or excesses of nutrients can damage plants by slowing or inhibiting growth and reducing yield. Many deficiencies can be recognized by observing plant leaves.

The Essential Plant Nutrients

There are eighteen elements, without or with cobalt (Co) and/or nickel (Ni), as listed on Table 2, are identified as essential elements for plant growth, of which nine are required in macro (large) and seven in micro (trace) quantities. Hence, they are traditionally divided into two main groups, macronutrients and micronutrients, according to the quantities required by plants.

Carbon and O2 are obtained from the gas CO2 whereas H is obtained from water. As C, O and H are supplied by both air and water, they are therefore, not treated as nutrients by the fertilizer industry.

These three elements (C, H and O) are, however, also required in large quantities for the production of such plant constituents as cellulose or starch.

The other 13 are called mineral nutrients as they are absorbed in mineral (inorganic) forms. Regardless of the amount required, physiologically, all of them are equally important.

The 13 mineral elements are taken up by plants in specific chemical forms as shown in Table 1.1 (below) regardless of their source. The major aim of fertilizer industry is to provide the primary and secondary nutrients which are required in macro quantities.

When chlorophyll of plants is exposed to light, the three elements (C, H and O) are combined in a process of photosynthesis thereby making carbohydrates, with subsequent oxygen being released.

The water is, on the hand, brought into the plant by root absorption from the soil system. Carbon dioxide (CO2) enters plant through stomata, small leaf openings. The photosynthesis rate is directly controlled by the water and nutritional status of the plant. Maximum rates are ultimately, however, influenced by the plant genetics.

Table1.1 Essential plant nutrients and their chemical (elemental) symbol

Nutrients Supplied by Air and Water (Structural)Primary or MacronutrientSecondary nutrientsMicronutrients
Carbon (C)Nitrogen (N)CalciumZinc (Zn)
Hydrogen (H2)Phosphorus (P)MagnesiumChlorine
Oxygen (O2)Potassium (K)SulphurBoron (B)


Zinc (Zn)

Iron (Fe)

Manganese (Mn)

Cobalt (Co)*

Nikel (Ni)*
*These elements are among those regarded as beneficial, but not essential, by some authors. Others are Se, Si, Na and Al.

The 18 Elements Essential for Plant Nutrition

Carbon, H and O make up to 95 % of plant biomass, and the remaining 5 % is made up of all other elements. The difference in plant concentration, between macronutrients and micronutrients, is very large.

The relative contents of N and Mo in plants is in the ratio of 10,000:1. Plants need about 40 times more Mg than Fe. These examples indicate the significant difference between macronutrients and micronutrients.

Macronutrients: used in large quantities by the plant.

Structural nutrients: C, H, O Primary nutrients: N, P, K Secondary nutrients: Ca, Mg, S.

Micronutrients: used in small quantities by the plant Fe, B, Cu, Cl, Mn, Mo, Zn, Co, Ni.

Basic Classifications of Essential Elements

1. Structural Elements

Plants require eighteen elements found in nature to properly grow and develop. Some of these elements are utilized within the physical plant structure, namely carbon (C), hydrogen (H), and oxygen (O).

These elements, obtained from the air (CO2) and water (H2O), are the basis for carbohydrates such as sugars and starch, which provide the strength of cell walls, stems, and leaves, and are also sources of energy for the plant and organisms that consume the plant.

2. Macronutrients

Elements used in large quantities by the plant are termed macronutrients, which can be further defined as primary or secondary. The primary nutrients include nitrogen (N), phosphorus (P), and potassium (K).

These elements contribute to plant nutrient content, function of plant enzymes and biochemical processes, and integrity of plant cells.

Deficiency of these nutrients contributes to reduced plant growth, health, and yield; thus they are the three most important nutrients supplied by fertilizers. The secondary nutrients include calcium (Ca), magnesium (Mg), and sulfur (S).

3. Micro nutrients

The final essential elements are used in small quantities by the plant, but nevertheless are necessary for plant survival.

These micronutrients include iron (Fe), boron (B), copper (Cu), chlorine (Cl), Manganese (Mn), molybdenum (Mo), zinc (Zn), cobalt (Co), and nickel (Ni).

Table1.2: Essentiality and concentrations of essential elements in plants

Nutrient (symbol)Essentiality established byTypical concentration in plant dry matter

Nitrogen (N)de Saussure (1804)1.5 %
1 Phosphorus (P, P2O5)Sprengel (1839)0.1 – 0.4 %
Potassium (K, K2O1)Sprengel (1839)1 – 5%
Sulphur (S)Salm-Horstmann (1851)0.1– 0.4 %
Calcium (Ca)Sprengel (1839)0.2 – 1.0 %
Magnesium (Mg)Sprengel (1839)0.1 – 0.4 %

Boron (B)Warington (1923)6 – 60 μg/g (ppm)
Iron (Fe)Gris (1943)50 – 250.μg/g (ppm)
Manganese (Mn)McHargue (1922)20 – 500.μg/g (ppm)
Copper (Cu)Sommer, Lipman (1931)5 – 20.μg/g (ppm)
Zinc (Zn)Sommer, Lipman (1931)21 – 150.μg/g (ppm)
Molybdenum (Mo)Arnon & Stout (1939)below 1.μg/g (ppm)
Chlorine (Cl)Broyer etal., (1954)0.2 – 2 %
1 Oxide forms are used in extension and trade, 2ppm = parts per million = mg/kg = μg/g; 10, 000 ppm = 1 percent. Source: Roy etal., 2006.

Table1.3: Showing uptake form and mobility in plants and soil

NutrientsMacro/microUptake formMobility in plantsMobility in soil
CarbonMacroCO2, H2CO3

HydrogenMacroH+, OH, H2O


PhosphorusMacroHPO42-, H2PO4Somewhat mobileImmobile

PotassiumMacroK+Very mobileSomewhat mobile

CalciumMacroCa2+ImmobileSomewhat mobile

MagnesiumMacroMg2+Somewhat mobileImmobile


BoronMicroH3BO3. BO3+ImmobileVery mobile


IronMicroFe2+, Fe3+ImmobileImmobile



MolybdenumMicroMoO4ImmobileSomewhat mobile


CobaltMicroCo2+ImmobileSomewhat mobile

NickelMicroNi2+MobileSomewhat mobile

Read Also : List of Diseases Ruminant Animals (Livestock) Get from Feeds and Water

Functions of Nitrogen (N), Phosphorus (P), and Potassium (K) in the Plants

1. Nitrogen

Nitrogen availability limits the productivity of most cropping systems in Nigeria and all over the world. It is a component of chlorophyll, so when nitrogen is insufficient, leaves will take on a yellow (chlorotic) appearance down the middle of the leaf.

New plant growth will be reduced as well, and may appear red or red-brown. Because of its essential role in amino acids and proteins, deficient plants and grains will have low protein content.

Nitrogen excess results in extremely dark green leaves, and promotes vegetative plant growth. This growth, particularly of grains, may exceed the plant’s ability to hold itself upright, and increased lodging is observed.

Major, Secondary and Trace Elements in Crop Nutrition

Nitrogen is mobile both in the soil and in the plant, which affects its application and management, as discussed later.

2. Phosphorus

Phosphorus is another essential macronutrient whose deficiency is a major consideration in cropping systems. It is an essential part of the components of DNA and RNA, and is involved in cell membrane function and integrity. It is also a component of the ATP system, the “energy currency” of plants and animals.

Phosphorus deficiency is seen as purple or reddish discolorations of plant leaves, and is accompanied by poor growth of the plant and roots, reduced yield and early fruit drop, and delayed maturity.

Phosphorus excess can also present problems, though it is not as common. Excess P can induce a zinc deficiency through biochemical interactions. Phosphorus is generally immobile in the soil, which influences its application methods, and is somewhat mobile in plants.

3. Potassium

Potassium is the third most commonly supplemented macronutrient. It has important functions in plant metabolism, is part of the regulation of water loss, and is necessary for adaptations to stress (such as drought and cold).

Plants that are deficient in potassium may exhibit reductions in yield before any visible symptoms are noticed. These symptoms include yellowing of the margins and veins and crinkling or rolling of the leaves. An excess, meanwhile, will result in reduced plant uptake of magnesium, due to chemical interactions.

Distinguishing each macronutrient as mobile or immobile in the plant

The mobility of a nutrient in the soil determines how much can be lost due to leaching or runoff.

The mobility of a nutrient in the plant determines where deficiency symptoms show up.

Nutrients that are mobile in the plant will move to new growth areas, so the deficiency symptoms will first show up in older leaves.

Nutrients that are not mobile in the plant will not move to new growth areas, so deficiency symptoms will first show up in the new growth.

Nutrient mobility varies among the essential elements, and represents an important consideration when planning fertilizer applications. For instance, NO3 nitrogen is very mobile in the soil, and will leach easily. Excessive or improper application increases the risk of water contamination.

Meanwhile, phosphorus is relatively immobile in the soil, and is thus less likely to runoff. At the same time, it is also less available to plants, as it cannot “migrate” easily through the soil profile. Thus, P is often banded close to seeds to make sure it can be reached by starting roots.

Nutrients also have variable degrees of mobility in the plant, which influences where deficiency symptoms appear. For nutrients like nitrogen, phosphorus, and potassium, which are mobile in the plant, deficiency symptoms will appear in older leaves.

As new leaves develop, they will take the nutrients from the old leaves and use them to grow. The old leaves are then left without enough nutrients, and display the symptoms.

The opposite is true of immobile nutrients like calcium; the new leaves will have symptoms first because they cannot take nutrients from the old leaves, and there is not enough in the soil for their needs.

Read Also : Practices that Increase the Amount of Soil Organic Matter

Major, Secondary and Trace Elements in Crop Nutrition
Figure: Nutrient deficiencies in crops

Table: Showing the functions and plant-available forms of the nutrients

Nutrient ElementFunctions in PlantsPlant available form

Nitrogen (N)Promotes rapid growth, chlorophyll formation and protein synthesis.NO3, NH4

1 Phosphorus (P, P2O5)Stimulates early root growth. Hastens maturity. Stimulates blooming and aids seed formation.2–HPO4 , H2PO4

Potassium (K, K2O1)Increases resistance to drought and disease. Increases stalk and straw strength. Increases quality of grain and seed.K+
Calcium (Ca)Improves root formation, stiffness of straw and vigour. Increases resistance to seedling diseasesMg2+
Magnesium (Mg)Aids chlorophyll formation and phosphorus metabolism. Helps regulate uptake of other nutrients.SO4
Boron (B)Aids carbohydrate transport and cell division.H3BO3. BO3+
Iron (Fe)Chlorophyll formation.Cu2+
Manganese (Mn)Oxidation-reduction reactions. Hastens germination and maturation.Fe2+, Fe3+
Copper (Cu)Enzymes, light reactions.Mn2+
Zinc (Zn)Auxins, enzymes.Zn2+
Molybdenum (Mo)Aids nitrogen fixation and nitrate assimilationMoO4
Chlorine (Cl)Water use.Cl
CobaltEssential for nitrogen fixation.Co2+
Nickel (Ni)Grain filling, seed viabilityNi2+
Carbon (C)Component of most plantCO2, H2CO3
Oxygen (O2)Component of most plantO2
Hydrogen (H2)Component of most plantH+, OH, H2O

How Nutrient Demand Changes at Different Plant Growth Stages

In general, plant nutrient needs start low while the plants are young and small, increases rapidly through vegetative growth, and then decreases again around the time of reproductive development (i.e., silking and tasseling).

While absolute nutrient requirements may be low for young plants, they often require or benefit from high levels in the soil around them. The nutrient status of the early seedling will affect the overall plant development and yield.

Plants entering the reproductive stages have high nutrient requirements, but many of these are satisfied by redistributing nutrients from the vegetative parts.

In summary, soil is a major source of nutrients needed by plants for growth. The three main nutrients are nitrogen (N), phosphorus (P) and potassium (K). Together they make up the trio known as NPK.

Other important 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 are needed by the plant. The role these nutrients play in plant growth is complex.

Plants require 18 essential nutrients to grow and survive, classified by their importance into macronutrients (C, H, O, N, P, K, Ca, Mg, S) and micronutrients (B, Cu, Fe, Mn, Zn, Mo, Cl, Co, Ni). Study Tip!

Crop Nutrients may be mobile or immobile in the plant and in the soil, which influences redistribution of nutrients and display of deficiency symptoms, and the fertilization of crops.

Nutrient demands change throughout the life of the plant, in general increasing during vegetative growth but decreasing during reproductive development.

Read Also : Feed and Nutrition Management for Cattle


Benadine Nonye is an agricultural consultant and a writer with several years of professional experience in the agriculture industry. - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education - PhD Student in Agricultural Economics and Environmental Policy... Visit My Websites On: 1. - Your Comprehensive Practical Agricultural Knowledge and Farmer’s Guide Website! 2. - For Effective Environmental Management through Proper Waste Management and Recycling Practices! Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4Profits TV and WealthInWastes TV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

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