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Essential Plant Nutrients

Much has been researched and written about essential plant nutrients. Scientists have deemed that there are 20 mineral elements deemed to be essential for plant growth.

Plants get all their nutrition from minerals. They absorb these minerals as ions, dissolved in water and they are absorbed primarily via the plant roots.

A point to consider when thinking about plant nutrition is the is the application of Liebig’s law of the minimum. Baron Justus von Liebig, a German scientist in the mid 19th century, popularised the “law of the minimum,” which states that “plants will use essential elements only in proportion to each other, and the element that is in shortest supply—in proportion to the rest—will determine how well the plant uses the other nutrient elements.”

The law essentially states that a plant’s growth is limited by the lowest level of every essential element.

In other words, high levels of nutrients are wasted when any essential element is missing or supplied at a proportionately lower level. Lacking any essential mineral, no matter how seemingly insignificant, will affect the overall growth and health of the plant.

The 20 essential plant nutrients can be classified into the following 2 categories:

1. Macronutrients are used in large quantities by the plant.

  1. Structural nutrients.
  2. Primary nutrients.
  3. Secondary nutrients.

2. Micronutrients: used in small quantities by the plant.

Essential Plant Nutrients, Bio Leaf Plant Nutrients, New Zealand

 

1. Macronutrients:

a. Structural nutrients are utilised within the physical structure of a plant, namely:

  • Carbon (C).
  • Hydrogen (H).
  • Oxygen (O). 

These elements are obtained from the air (CO2) and water (H2O).

They form the building blocks 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.

b. Primary Nutrients:

  • Nitrogen (N): Component of proteins, hormones, chlorophyll, vitamins and enzymes. Promotes stem and leaf growth. The ammoniacal and nitrate forms are used directly by plants for stem and leaf growth. The urea form of nitrogen must be broken down by soil borne microorganisms or urease before it can be utilized by the plant. Urea can cause leaf tip and root burn. Deficiency symptoms: reduced yields, yellowing of leaves, stunted growth. Excess nitrogen can delay fruiting and flowering.

  • Phosphorus (P): Essential for seed germination, photosynthesis, protein formation, overall growth and metabolism, flower and fruit formation. Deficiency symptoms: purple stems and leaves, retarded growth and maturity, poor flowering and fruiting. Large amounts without zinc cause zinc deficiency. Low pH (<4) ties up phosphates in organic soils. Excessive amounts may be toxic to plants.

  • Potassium (K): Essential for formation of sugars, carbohydrates, proteins, cell division. Adjusts water balance; improves stem rigidity and cold hardiness; enhances flavor, color and oil content of fruits; important for leafy crops. Deficiency symptoms: spotted, curled or burned look to leaves; lower yields.

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 fertilisers.

c. Secondary Nutrients:

  • Calcium (Ca): Activates enzymes; structural part of cell walls; influences water movement, cell growth and division. Required for uptake of nitrogen and other minerals. Leached from soil by watering. Immobile: requires a constant supply for growth. Deficiency symptoms: stunting of new growth in stems, flowers, roots; black spots on leaves and fruit; yellow leaf margins.

  • Magnesium (Mg): Critical component of chlorophyll; needed for functioning of enzymes for carbohydrates, sugars and fats; fruit and nut formation; germination of seeds. Deficiency symptoms: yellowing between veins of older leaves; chlorosis; leaf droop. Leached by watering. Foliar spray to correct deficiencies.

  • Sulphur (S): Component of amino acids, proteins, vitamins, enzymes. Essential for chlorophyll. Imparts flavor to many vegetables. Deficiency symptoms: light green leaves. Water supply may contain sulfur. Leached by watering.

  • Silicon (Si): Component of cell walls; enhances resistance to sucking insects and fungi. Foliar sprays reduce populations of aphids on some plants. Enhances leaf presentation; improves heat, drought and cold tolerance; improves photosynthesis; extends bloom life. Deficiency symptoms: wilting, poor fruit and flower set, increased susceptibility to insects and disease. Disease resistance is enhanced by regular foliar feeding. (Si is a macronutrient for most plants.)

 

2. Micronutrients:

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

  • Boron (B): Affects at least 16 functions: flowering, pollen germination, fruiting, cell division, water relationships, movement of hormones, cell wall formation, membrane integrity, calcium uptake, movement of sugars. Immobile; easily leached. Deficiency symptoms: terminal bud die back causes rosette of thick, curled, brittle leaves or brown, discolored, cracked fruits, tubers and roots.

  • Chlorine (Cl): Involved in osmosis (movement of water or solutes in cells), ionic balance necessary to take up mineral elements and photosynthesis. Deficiency symptoms: wilting, stubby roots, yellowing, bronzing. Scents in some plants may be decreased. Leached by watering. Excessive amounts may be toxic to plants.

  • Cobalt (Co): Required by nitrogen fixing bacteria; formation of B12 vitamin; formation of DNA. Will extend life of cut flowers such as roses. Deficiency symptoms: may result in nitrogen deficiency.

  • Copper (Cu): Necessary for nitrogen metabolism; component of enzymes – may be part of enzyme systems that use carbohydrates and proteins. Bound tightly in organic matter. May be deficient in highly organic soils. Not readily lost from soil but may be unavailable. Deficiency symptoms: die back of shoot tips; terminal leaves develop brown spots. Excessive amounts may be toxic to plants.

  • Iron (Fe): Enzyme functions; catalyst for synthesis of chlorophyll; essential for new growth. Deficiency symptoms: pale leaves, yellowing of leaves and veins. Leached by water and held in lower parts of soil. High pH soils may have iron present but unavailable to plants.

  • Manganese (Mn): Enzyme activity for photosynthesis, respiration and nitrogen metabolism. Deficiency symptoms: young leaves are pale with green veins similar to iron deficiency; advanced stages-leaves are white and drop; brown, black or gray spots may appear next to veins. Plants in neutral or alkaline soils often show deficiencies. Acid soils may increase uptake causing toxicity.

  • Molybdenum (Mo): Structural part of enzymes that reduce nitrates to ammonia for amino acid development essential to protein formation; required by nitrogen fixing bacteria. Deficiency symptoms: pale leaves with rolled, cupped margins. Seeds may not form. Nitrogen deficiency may occur if plants are lacking Mo.

  • Nickel (Ni): Recently recognized as essential. Ni is an essential mineral for the urease enzyme which breaks down urea into usable forms of nitrogen. It is also essential for iron uptake. Seeds will not germinate without Ni.

  • Sodium (Na): Improves nitrogen metabolism in many plants, involved in osmotic (water movement) and ionic balance in plants. Deficiency symptoms: yellowing of leaves and leaf tip burn; may inhibit flower formation. Excessive amounts may be toxic to plants.

  • Zinc (Zn): Improves nitrogen metabolism in many plants, involved in osmotic (water movement) and ionic balance in plants. Deficiency symptoms: yellowing of leaves and leaf tip burn; may inhibit flower formation.

The above list of nutrients is known as the essential list of elements and represents the most important nutrients required for plant growth and health. In reality, there are many other nutrients used by plants and the law of the minimum applies to them as well. Deficiencies in these elements will also affect plant growth and health.


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