Plant Nutrition - Macronutrients & Micronutrients - An Overview

17 February, 2022 by Seacliff Organics in Information

In plant nutrition, it is important that there are no deficiencies in primary or secondary macroelements or in essential microelements, these elements must be present in the proper proportions.

Plants consume primary macronutrients in large quantities, while their intake of secondary macronutrients is lower. Each of these nutrients has a distinct function, necessary for nourishing the plant. A shortage in any of them leads to deficiencies, with different adverse effects on the plant’s general state, depending upon which nutrient is missing and to what degree.

Of the 60 chemical elements that comprise plants, 16 of them are essential. Of those 16, some are extracted from the air in the form of CO2 or water. These are carbon (C), hydrogen (H), and oxygen (O). If for now we set aside leaf fertilization and the three above-mentioned elements, the remaining 13 are extracted from the soil. These are divided into macronutrients: Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S), and micronutrients: Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), Chlorine (Cl), all of which are essential for crops. The 2 elements that are not essential to plant nutrition, but are required by certain plants types in specific environments are Silicon (Si), and Cobalt (Co).

Primary Macronutrients

Macronutrients are essential for plant growth and a good overall state of the plant. The primary macronutrients are Nitrogen (N), Phosphorus (P), and Potassium (K).

N. Nitrogen

Nitrogen is essential for plant development, since it plays a fundamental role in energy metabolism and protein synthesis. Nitrogen is absorbed by the plant in the form of a nitrate. This macronutrient is directly related to plant growth. It is indispensable for photosynthesis activity and chlorophyll formation. Nitrogen is involved, above all, in the aerial zone, the part of the plant that a person sees. It promotes cellular multiplication.

P. Phosphorus

Phosphorus is involved in root growth, which it stimulates. In the aerial zone it favours flowering. Although phosphorus is also necessary during the plant’s growth period, it is much more involved in the flowering stage. Phosphorus is involved in transporting and storing energy. It improves the plant’s general state and increases the plant’s ability to withstand adverse climatological conditions. Phosphorus is essential in organic compound formation and the correct execution of photosynthesis. A shortage of phosphorous results in a late, deficient flowering, browning and wrinkling of the leaves, and a lack of vigour in general.

K. Potassium

Potassium is involved in the regulation of water and the transport of the plant’s reserve substances. It increases photosynthesis capacity, strengthens cell tissue, and activates the absorption of nitrates. Potassium stimulates flowering and the synthesis of carbohydrates and enzymes. This, in turn, provides an increase in the plant’s ability to withstand unfavourable environments such as low temperatures, and prevents withering. Therefore, a lack of potassium reduces plant resilience to dry spells and frosts or to a fungus attack. This, in turn, results in a lack of balance among other nutrients, such as calcium, magnesium, and nitrogen.

Secondary Macronutrients

Secondary macronutrients are also essential, even though they are consumed in smaller quantities than N, P, K, that is, primary macronutrients. The secondary macronutrients are Calcium (Ca) Magnesium (Mg) and Sulfur (S).

Ca. Calcium

Calcium attaches to the walls of plant tissues, stabilizing the cell wall and favouring cell wall formation. Calcium is also involved in cell growth and development. It improves plant vigour, activating the formation of roots and their growth. Calcium contributes to mineral retention in the soil and to the transportation of such minerals. It neutralizes toxic substances in plants and contributes to seed formation.

Mg. Magnesium

Magnesium constitutes the core of the chlorophyll molecule and is therefore essential for photosynthesis. This makes it an indispensable element for plant development. Magnesium promotes the absorption and transportation of phosphorus. It contributes to the storage of sugars within the plant. Magnesium performs the function of an enzyme activator, and in fact activates more enzymes than any other nutrient.

S. Sulfur

Sulfur participates in the formation of chlorophyll. It is necessary for performing photosynthesis and intervenes in protein synthesis and tissue formation. Sulfur is fundamental in the metabolizing of nitrogen, since it improves nitrogen efficiency. Sulfur also improves plant defences in general.

Plants need access to certain nutrients in order to be completely healthy and capable of contributing benefits to whoever consumes them.

In order to grow a verdant, healthy crop, a suitable contribution of micronutrients must reach the plants. For indeed, micronutrients provide plants with what they require in order to develop appropriately, attain a degree of immunity to fight off bacteria and pests, and weather the elements.

What are Micronutrients?

Micronutrients are elements required in small quantities, and are essential in order for plants to complete their life cycle. They are:

Fe. Iron

Iron is a central component of electron chains and a co-factor of many vital enzymes. Only a few bacteria are able to substitute iron with other metals, making it an essential element for virtually all life forms. In plants it is as basic as it can be: without iron a plant can’t produce chlorophyll, can’t get oxygen and won’t be green. The function of iron is to act much like it does in the human blood stream, helping to carry important elements through a plant’s circulatory system.

Zn. Zinc

Zinc is an important component of various enzymes that are responsible for driving many metabolic reactions in all crops. Growth and development would stop if specific enzymes were not present in plant tissue. Carbohydrate, protein, and chlorophyll formation is significantly reduced in zinc- deficient plants.

Mn. Manganese

Manganese is an important micronutrient for plant growth and development and sustains metabolic roles within different plant cell compartments. Manganese deficiency is a serious, widespread plant nutritional disorder in dry, well-aerated and calcareous soils, as well as in soils containing high amounts of organic matter, where bio-availability of manganese can decrease far below the level that is required for normal plant growth.

B. Boron

Boron is vital to plant health, due to its role in forming and strengthening cell walls. Low boron levels lead to poor growth of fast-growing tissues and plant development. Different plants need different amounts of boron, but for the most part, boron is not easily transported within the plants. For that reason, boron should continuously be available for uptake by the roots, and especially prior to flowering, as it is vital to the reproduction process.

Cu. Copper

Copper activates some enzymes in plants which are involved in lignin synthesis and it is essential in several enzyme systems. It is also required in the process of photosynthesis, is essential in plant respiration and assists in plant metabolism of carbohydrates and proteins. Copper also serves to intensify flavour and colour in vegetables and colour in flowers.

Mo. Molybdenum

Nitrogen is necessary for a plant to grow and molybdenum helps the plant to use nitrogen for compounds such as amino acids, proteins and chlorophyll, making the plants healthy and well fed. Without molybdenum, plants cannot perform the biochemical process of making essential nitrogen compounds.

Cl. Chlorine

Chlorine is important for plant photosynthesis as it is involved in the opening and closing of stomata (pores in leaves) that enable plants to take in and release carbon dioxide, oxygen and other gases as required. It also helps ensure leaves are firm.

Si. Silicon

Although deemed a non-essential nutrient for the majority of plants, the benefits of silicon include increasing pest and pathogen resistance, drought and heavy metal tolerance, and the quality and yield of agricultural crops.

Co. Cobalt

Cobalt plays a critical role in the overall growth process of plants. Cobalt is necessary for the processes of stem growth, elongating the coleoptiles, and expanding leaf discs. It is a critical element needed for a plant to reach maturity and for healthy bud development. Ruminant animals such as cattle and sheep produce vitamin B-12 in their digestive system when cobalt is available in their forage. Without cobalt they are subject to hookworm, bacterial infections, brucellosis, and neurological diseases.

Then there’s still a list of micro nutrients comprised of Iodine (I), Nickel (Ni), Vanadium (V), Chromium (Cr), Yttrium (Yt), Cesium (Cs), Strontium (Sr), Fluorine (Fl), and many more which each play their part in very small amounts in soil.

As mentioned above, a proper contribution of micronutrients to plants must be ensured. These elements are what nourish crops to a large extent and, above all, promote a crop’s well-being, health, and good development. Unlike products where a high percentage of chemicals are used, products where organic amendments are used act differently, since, with very small quantities of materials, all types of nutrients are provided. This instigates a gradual strengthening of the seeds or plants and is also reflected in the results of the productive area. After all, what is most important is for the crop to be at its peak when it is distributed in the market, and for it to meet quality needs.

A problem that farmers might face nowadays is that crop-growing soils are completely neglected. Some farmlands mainly consist of soils with more than a 75% deficiency in their natural components. Often, this is only discovered after having squandered a great deal of seeds. The idea, prior to planting any crop, is to properly study the soil’s quality. We test soil for pH, organic matter content, total exchange capacity, Mehlich 3 extractable macro- and micro-nutrients, base saturation, and we do saturated paste tests to determine what’s readily available to the plants and at what ratios. Healthy soil is vital for top quality production. Apart from soil testing we also look at the biology in the soil with a Soil Food Web assessment to determine if a complete Soil Food Web is present for consistent nutrient cycling.

Plant Nutrient Interactions

The Mulder’s chart allows us to see how nutrients in the soil can influence the availability and uptake of each other.

The chart shows some of the interactions between plant nutrients.

High levels of a particular nutrient in the soil can interfere with the availability and uptake

by the plant of other nutrients. Those nutrients which interfere with one another are said to be antagonistic.

For example, high nitrogen levels can reduce the availability of boron, potash and copper; high phosphate levels can influence the uptake of iron, calcium potash, copper and zinc; high potash levels can reduce the availability of magnesium. Thus, unless care is taken to ensure an adequate balanced supply of all the nutrients – by the use of analysis – the application of ever higher levels of nitrogen, phosphorus and potassium in compound fertilisers can induce plant deficiencies of other essential nutrients.

Stimulation occurs when the high level of a particular nutrient increases the demand by the plant for another nutrient.

Increased nitrogen levels create a demand for more magnesium. If more potassium is used – more manganese is required and so on.

Although the cause of stimulation is different from that of antagonism, the result is the same – induced deficiencies of the crop if not supplied with a balanced diet.

High levels of molybdenum in the soil and in the herbage reduce an animal’s ability to absorb copper into the blood stream, and ruminant animals grazing these areas have to be fed or injected with copper to supplement their diet (see Mo/Cu dotted line).

mulders chart mineral interactions Seacliff organics nz

ANTAGONISM: A decrease in availability to the plant of a nutrient by the action of another nutrient (see direction of arrow).

STIMULATION: An increase in the need for a nutrient by the plant because of the increase in the level of another nutrient.

FAQs

What are macronutrients and micronutrients in plant nutrition?

Plants require both macronutrients and micronutrients for their growth and development. Macronutrients are primary and secondary elements needed in larger amounts, including Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, and Sulfur. On the other hand, micronutrients are essential elements required in smaller quantities, such as Iron, Manganese, Zinc, Copper, Boron, Molybdenum, and Chlorine.

What happens when there is a deficiency in macronutrients or micronutrients?

A deficiency in these nutrients can negatively affect the plant's growth, development, and overall state. For instance, if a plant lacks nitrogen, it may exhibit stunted growth and yellowing of leaves, a condition called chlorosis.

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