ESSENTIAL NUTRIENTS FOR PLANTS AND DEFICIENCY SYMPTOMS

All plants require essential nutrients for healthy growth. There are in total seventeen different elements that make up these essential nutrients. Three of these elements: carbon, hydrogen and oxygen are absorbed from the air whereas the other fourteen elements are usually obtained from the soil.

The soil-less growing media such as bagasse, sawdust, coconut coir and rice hulls, typically used in grow boxes have little or no nutrients therefore, plants growing in these media types will need to be supplied with fertilizers to meet their nutritional requirements.

Nutrients from air and water

Carbon (C)

Plants absorb carbon from carbon dioxide (CO₂) in the atmosphere.

Hydrogen (H)

Hydrogen is obtained from water (H₂O) which is absorbed by the plant roots.

Oxygen (O)

Oxygen comes from gaseous oxygen (O₂)  and carbon dioxide (CO₂) in the atmosphere.

Nutrients from the growing medium

The nutrients that your plants require from their growing medium can be classified into two groups, namely macronutrients and micronutrients. 

Macronutrients

Macronutrients are nutrients that are required in large amounts by plants. Macronutrients can further be subdivided into primary plant nutrients and secondary plant nutrients.

Primary plant nutrients: 

There are three primary plant nutrients:

1. Nitrogen (N)

Nitrogen is required to promote the general vegetative growth of plants.  It is needed for protein synthesis and encourages fruit and grains' juiciness. It is a major component of chlorophyll which is required for photosynthesis.

 

Nitrogen Deficiency

Nitrogen deficiency is a condition that occurs in plants when they do not receive adequate nitrogen from the soil or other sources. Such plants often show signs of stunted growth, poor development of roots and shoots, yellowing of leaves, and reduced leaf size.

2. Phosphorus (P) 

Plants require phosphorus as an essential nutrient to promote the development of their root systems and speed up cell division.

Phosphorus Deficiency

 A phosphorus deficiency results in stunted growth, especially in the plant's root system. Additionally, the leaves tend to exhibit a purplish-green colour.

3.  Potassium (K) 

Potassium is essential for chlorophyll synthesis which is necessary for photosynthesis. Potassium also promotes the development of root systems and influences flower setting in plants.

Potassium Deficiency

When plants lack potassium, their leaves show discolouration, mottling and scorching at the edges. Additionally, flowering and fruiting plants experience premature bud falling.

What are the other essential macronutrients  that plants require apart from Nitrogen, Phosphorus, and Potassium? These are referred to as secondary plant nutrients.

 

Secondary plant nutrients

There are three secondary plant nutrients:

1. Calcium (Ca) in plants

Calcium plays an essential role in the growth and development of plants. It is an important nutrient for the growth and development of root tips in plants and for cell wall development.

Calcium Deficiency

Without adequate calcium, plants may experience stunted growth, yellowing leaves, and increased disease susceptibility. Therefore, it is crucial to ensure that plants receive sufficient calcium throughout their growth cycle.

2. Magnesium (Mg) 

Magnesium is an essential nutrient for chlorophyll synthesis and plays a critical role in numerous enzymatic reactions that are critical for the plant's growth and development.

Magnesium Deficiency

Without sufficient magnesium, plants may exhibit symptoms such as yellowing of leaves (chlorosis) and poor growth. It is therefore important to ensure that plants receive an adequate supply of magnesium, either through the soil or through fertilizers.

3. Sulphur (S) 

 Plants require sulfur as a nutrient for the production of proteins. It is an essential element that plays a key role in the growth and development of plants.

Sulphur Deficiency

 A sulfur deficiency can cause plants to become thin and slender in appearance, while their leaves turn pale green or yellow. Additionally, fruits may ripen late when there is not enough sulfur present.

Plants need more primary macronutrients than secondary macronutrients.

Micronutrients

Micronutrients are nutrients that plants require in small (trace) amounts. Although these nutrients are needed in minute amounts, they are still essential to the growth and development of the plant.

 

There are eight essential micronutrients required by plants: 

1. Boron (B)

Plants require Boron (B) to maintain normal cell division in the root and shoot tips.

Boron Deficiency

A lack of boron in plants can cause shoot tip death and abnormal growth. In celery plants, it can lead to "stem crack," while in beets, it can result in "heart rot."

2. Chlorine (Cl)

Plants need chlorine as it helps in the transportation of nutrients. Chloride, which is derived from chlorine, plays a vital role in regulating the opening and closing of stomata and also helps in the control of water within plant cells.

Chlorine Deficiency

Wilting of leaves, particularly at the edges, is an indication of a deficiency of chlorine. If the deficiency continues, the leaves may start curling, acquire a bronze colour, and display symptoms of chlorosis (yellowing of leaves), or necrosis (death of leaf tissue which appears as brown or black spots).

3. Cobalt (Co)

Cobalt is an important element for plant growth and development. It plays a crucial role in stem growth, as well as being an essential component of many plant enzymes, particularly those involved in nitrogen fixation in legumes. Additionally, it helps in the formation of healthy buds and is necessary for plants to mature properly. 

Cobalt Deficiency 

A deficiency of cobalt in plants is a bit unclear but may include reddening of stems, stunted growth, yellowing of leaves as well as chlorosis and necrosis.

High Levels of Cobalt

High levels of cobalt in plants, also referred to as cobalt toxicity, can result in leaves exhibiting a pale colour, discolouration of leaf veins and the loss of leaves. It can also cause iron deficiency in plants.

4. Copper (Cu)

Copper is required in plants for many enzymatic reactions, especially those that involve respiration. It is also needed for chlorophyll production and seed production.

Copper Deficiency

A lack of copper in plants can make them more vulnerable to diseases. Additionally, the leaves will appear darker with a purplish or bluish tint, and the edges and tips will start turning pale yellow or white. Also, the leaves may begin to wilt and droop.

5. Iron (Fe)

Iron is present in plant enzymes. It is essential for the formation of chlorophyll and is important for the maintenance of chloroplast structure and function.

Iron Deficiency

Young leaves turn yellow due to a lack of chlorophyll, then pale and white with dark green veins. Stunted growth and curling of leaves may occur.

6. Manganese (Mn)

Manganese is a vital micronutrient for plant development and growth. It is present in enzymes that facilitate respiration and is also used by plants for splitting water molecules during photosynthesis.

Manganese Deficiency

The most common symptom of manganese deficiency is yellowing of leaves between the veins and flexes (bends) appearing on leaves.

7. Molybdenum (Mo)

Molybdenum is an essential micronutrient which is involved in amino acid synthesis and nitrogen fixation in plants.

Molybdenum Deficiency

When molybdenum is deficient, plants exhibit reduced growth and their leaves turn pale green or yellow between veins, similar to nitrogen deficiency.

8. Zinc (Zn)

Zinc is a micronutrient that activates enzymes responsible for plant respiration and is essential for chlorophyll formation and photosynthesis.

Zinc Deficiency

When there is a zinc deficiency, plant growth is reduced. Leaves are smaller, discoloured, and yellow with green veins. They may also become distorted.

The choice of fertilizer depends on the crop's nutrient requirements.