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The Ultimate Guide to Micronutrient Fertilizer

Explore the essential guide to micronutrient fertilizers, their roles, deficiency signs, and application methods for optimal plant health and growth.

We often talk about macronutrients as the most essential nutrient pack for the plants. While their significance cannot be undermined, there are other equally important nutrients. These are called micronutrients. 

These elements for plant nourishment make up less than 1% of the plant’s dry weight and play a key role in processes that run a plant’s life. To elaborate more, here is an article dedicated to these nutrients. 

Keep reading to learn who these are, what they do, how they affect plant life, and how to supplement a plant if it needs it. There’s also much more…

What are Micronutrients?

What are Micronutrients

Micronutrients are yet another set of essential nutrients your plant requires to ensure it is healthy and can carry out its functions optimally. 

A plant requires seven micronutrients: boron, copper, chloride, iron, molybdenum, manganese, nickel, and zinc. 

In the next section, we will discuss each one of them in detail.

7 Essential Plant Micronutrients 

Boron 

Symbol: B

Plants receive boron through organic matter or boron-containing minerals. These can be added to the soil for easy access as they are mobile and available in the form of borate (BO3 3- ) anion. However, this form is prone to leaching from the surface of the soil. 

When the soil boron level falls below 0.1 pounds per acre, it is said to be low or insufficient. This concentration can also be affected by the calcium, potassium, or nitrogen levels in the soil. Of these, the calcium: boron ratio is the most significant.

Signs of boron deficiency

  • Leaves turn yellow leaves, especially the young ones. The main growing point (terminal bud) dies.
  • Whitish-yellow spots might appear at the bases of leaves.
  • Leaves can develop dark brown, irregular spots. These may turn into dead tissue (necrosis) if the deficiency is severe.
  • Due to issues in the cell wall growth, leaves and stems may become brittle and distorted.
  • The tips of the leaves may thicken and curl.
  • Affected plants grow slowly and look smaller. This is because the spaces between leaves (internodes) are shorter.
  • The flower buds may not form correctly as boron collects in reproductive parts or may be shaped oddly.
  • Seed quality and pollination are poor.

How to detect boron deficiency: The soil boron test level and crop’s requirements are the two determinants for deciding whether or not to add boron to the soil. Plant tissue analysis can also be done. 

How to fix it: Use superphosphate, animal manure, and liming materials for soil application.  

Boron fertilizer is recommended for alfalfa, apple, broccoli, cotton, root crops, peanuts, cabbage, and cauliflower.

Zinc

Symbol: Zn

The macronutrient zinc is needed for several cellular functions in plants, including homeostasis, enzyme activation, chlorophyll formation, and more. It is an important fertilizer for producing edible beans, corn, and sweet corn.

Signs of zinc deficiency

Signs of zinc deficiency

  • Again, leaves that lack zinc show a yellowish tinge between the veins. It is visible as stripes starting midway from the edge to the center.
  • Sometimes, patches of different colors, such as pale green, yellow, or white, can be seen.
  • Severe deficiency converts the leaves from grayish-white to yellow and may drop off early or die.
  • Zinc helps in the growth of stem segments. Therefore, zinc deficiency makes the plant short.
  • Flowers and seeds may not develop properly.
  • Fewer side shoots appear in wheat and similar plants.
  • Zinc deficiencies are prevalent in those parts of the field, where the top layer of soil is taken away.

How to detect zinc deficiency: An easy way to know about zinc insufficiency or deficiency is a soil test that reveals that the zinc levels have fallen below 2.0 pounds per acre with soil pH at 6.1. Also, adding too much zinc can cause zinc toxicity, which can be removed by raising the soil pH to 6.5.

How to fix it: for a good crop yield, apply zinc sulfate (35%) as a dry fertilizer using the broadcast method. Remember, when spraying zinc fertilizer on foliage, do not add any fertilizer to the soil as this may cause zinc toxicity. 

Zinc fertilizer is recommended for peach, plum, or nectarine trees and peanuts. 

Manganese

Symbol: Mn

Manganese helps plants grow and develop optimally. It also plays important roles in various parts of the plant cells. An example of this is a part of the plant that helps produce oxygen during photosynthesis, a process plants use to make their food.

You know it is time to add manganese to the soil when the extractable manganese is < 4.0  

lbs per acre, and the soil pH is < 5.6.

Signs of manganese deficiency

  • We know that chloroplasts are the parts of plants where photosynthesis takes place. Mn deficiency affects chloroplasts the most among all the cell organelles.
  • Young leaves suffer interveinal chlorosis. In iron deficiency, there is a clear difference between veins and interveinal areas affected by chlorosis. Here, the effect is more spread out.

Some examples of Mn deficiency symptoms in crops include grey spots in oats, marsh spots in peas, white streaks in wheat, and interveinal brown spots in barley.

How to detect manganese deficiency: Take soil samples and plant tissues to learn about the manganese levels in the plant.

How to fix it: Both soil and foliar manganese fertilization work to control manganese deficiency. For soybean crops, use 1 pound of manganese per acre in the form of MnSO4.4H2O as a foliar spray. This can be done with two applications throughout the growing season.

Manganese fertilizer is recommended for soybeans, peanuts, small grains, oats, wheat, cotton, onions, cucurbits, peas, beans, and radishes.

Iron

Symbol: Fe

While iron helps maintain the physical structure of chloroplast, it is also known for its role in chlorophyll synthesis. Iron deficiency in plants is not a result of an iron deficiency in plants but due to the soil conditions. 

For example, high soil pH, high soil temperatures, and higher concentrations of other micronutrients such as copper, manganese, phosphorus, and zinc.

Signs of iron deficiency

Signs of iron deficiency

  • An insufficient amount of iron means plants produce less chlorophyll.
  • The leaves display a yellowish hue between the veins.
  • In young leaves, there are clear lines between the green veins and yellow areas.
  • Severe iron deficiency turns the entire leaf whitish-yellow, and it may even die.
  • Plants’ growth slows down when they don’t have enough iron.
  • Fields that do not have enough iron display irregular yellow patches. This is more visible where the soil is exposed.

How to detect iron deficiency: A simple soil test or physical analysis of the plant leaves can give you an idea of iron levels in the plant. Other than this, tissue analysis can also be carried out. 

How to fix it: Foliar application of iron (1% ferrous sulfate solution) is considered to reduce low iron levels in the vegetation.

Iron fertilizer is recommended for azaleas, gardenias, camellias, philodendrons, hydrangeas, citrus trees, and roses, as well as several Australian native plants. 

Copper 

Symbol: Cu

Yet another element essential for chlorophyll synthesis is copper. It is also found essential in several enzymatic activities that take place within a plant. So, if copper levels are low in plants, it can lead to diseases such as ergot (a disease well-known for leading to grain loss).

While copper is easily leached from sandy soils that have low concentrations of copper, the clayey soils retain them well. 

Signs of copper deficiency

  • Young leaves turn yellow due to chlorosis.
  • The plant experiences stunted growth.
  • Grain crops take longer to reach maturity.
  • Plants may either bend or fall over.
  • Sometimes, there’s brown discoloration (also known as melanosis).
  • In wheat, grain production, as well as filling, can be poor. They may be empty sometimes.
  • Plants get sick more easily.

How to detect copper deficiency: Conduct a soil test, as this will help you ascertain the type of response the plant has for particular soil types.

How to fix it: It can be corrected by using a foliar application of 1 to 2 pounds of CuSO45H2O per acre or 20 to 50 pounds of copper sulfate (CuSO45H2O) per acre. 

However, one must remember that there is a slight variation between variation and toxicity. Therefore, the application should be based on the evaluation of the plant tissue that is most affected.

Copper fertilizer is recommended for onion, beet, spinach, lettuce, tomato, and sunflower.

Molybdenum

Symbol: Mo

A plant requires molybdenum to synthesize the enzyme nitrate reductase. It is also needed for nitrogen fixation in legumes by Rhizobia bacteria. It also helps root nodule bacteria to fix atmospheric nitrogen. In the soil, it is present in the form of molybdate (MnO42-) anion.

Generally speaking, molybdenum deficiency is rarely found in plants. 

Signs of molybdenum deficiency:

  • It resembles signs of nitrogen deficiency in the leaves.
  • The plant experiences stunted growth.
  • Rolled, scorched, or cupped leaves that are also pale in color
  • Thick, brittle leaves eventually dry up, leaving only the midrib

How to detect molybdenum deficiency: An easy way to know whether Mo application is required is to test the soil pH. If the pH is above 6, then the possibility of the deficit is low. However, when the pH is less than 6, your plant is more likely to develop signs and require immediate attention. 

Sap nitrate concentration is one way to measure molybdenum deficiency. This is because nitrate accumulates in the leaves, but it cannot be used to build proteins.   

How to fix it: Use dolomite or lime to correct low molybdenum quantity in plants. 

Note: Molybdenum should never be applied to non-legume plants.  

Molybdenum is recommended for lucerne, clovers, peas and beans. 

Chlorine

Symbol: Cl

Chlorine has several growth and development-related roles in the plant. The first and foremost is osmoregulation, and the other is the opening and closing of stomata. It is also helpful in the use of oxygen in the photosynthesis process. 

In addition, chlorine makes plants resilient to stress and diseases. When the soil has sufficient chlorine, the quality of the crop improves. In the soil, chlorine occurs as a chloride (Cl-) anion.

Signs of chlorine deficiency

Signs of chlorine deficiency

  • Plants have yellow and dead spots on their leaves. The line between the dead spots and the healthy parts of the leaves is clearly visible.
  • The edges of the leaves might also start to sag. Also, the roots can become very branched. These symptoms are often seen in cereal crops such as wheat or barley.
  • Different plant types have different reactions to Cl deficiency; sometimes, this may look like they have a leaf disease.

How to detect chlorine deficiency: Apart from acknowledging the physical changes, plant tissue is a great idea for unraveling the hidden chloride deficiency in plants. 

How to fix it: Use potassium sulfate or potassium nitrate for tobacco, potatoes, and tomatoes. Apply fertilizers that make the soil more acidic and have no chloride in them if you are fertilizing mulberries.

Chlorine fertilizer is recommended for tobacco, potato, and tomato.

The Best Application Method for Micronutrients

By far, the foliar application is considered to be the most effective way to add micronutrients to the plants that need it. By doing so, the plants will absorb the nutrients through their leaves and roots. This also means that plants can take them instantaneously. 

Seaweed fertilizer or fish emulsions are used mostly to prepare micronutrient fertilizers. 

Challenges in Detecting Micronutrient Deficiencies

  • Many nutrient deficiencies and toxicities can take place simultaneously. For example, excessive phosphorus can lead to zinc deficiency.
  • Crop species belonging to the same plant family can have different sensitivities towards micronutrients. In corn and barley, for instance, corn is more sensitive to zinc.
  • False deficiency symptoms may also appear. These may look like nutrient deficits but may happen due to drought, excess water, herbicide or pesticide residues, disease, genetic abnormalities, compaction of soil, or infestation by insects. 
  • The real symptoms may be different from the field symptoms.
  • Sometimes, no symptoms may appear. While the plant may have one or more deficiencies, they stay hidden and do not show up until late. Not only this, but the time lapse between the nutrient deficiency and when the signs actually start appearing can be damaging to the plant. This is because, by the time you learn about the plant’s requirement, it may have lost its health considerably. 

Parting Thoughts 

That’s about the main micronutrients, but the list doesn’t end here. There are a few more micronutrients, such as calcium, sulfide, nickel, etc., and they hold an importance of their own. Yet, if you pay attention to the presence or absence of these micronutrients, your plants will thank you. If you still have any queries regarding micronutrient fertilizers get in touch with our experts.

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