Role of Secondary Nutrients in Crops

Role of Secondary Nutrients in Crops:

Secondary-Nutrients:

The nutrients are essential for plant growth but required in comparatively less amount than macro-nutrients and required in larger quantity than micro-nutrients, which are called secondary nutrients.

Calcium (Ca), Magnesium (Mg), and Sulfur(S) are categorized as Secondary nutrients for plants.

Although plant uses these nutrients in plant growth, compounds of one or more of these elements are also used as soil conditioner as well, rather than strictly used for plant nutrients.

Secondary elements affect the PH of the soil as well, Ca. and Mg. increases the soil PH on the other hand Sulfur increases the soil PH from some source.

Availability of Ca, Mg, and Sulfur in soil depends upon the nature and category of the Soil at your farm.

Understanding of the availability of the secondary nutrients in the soil can be assessed based on soil type will be discussed in a separate blog in the future.   

Micro-Nutrients:

These essential elements for crop optimum growth/yield but are required in smaller amounts hence called micronutrients. Each has it is specific   

Zinc (Zn), Iron (Fe), Copper (Cu), Manganese (Mn), Nickel (Ni), Boron (B), Cholerine (cl), Molybdenum (Mb), Cobalt (Co).

Secondary Nutrients:

Sulfur (S):

It is 4^th major nutrient in crop production. Oil crops, forages, legumes and some vegetables need in considerable amounts. In some crops it needs the same as phosphate needed. Sulfur is a part of every cell and essential in the production of three amino acids which are building blocks for proteins formation. Sulfur is not a part of chlorophyll, but it is essential in the formation of chlorophyll, especially in winter crop hardiness.     

Sulfur is very important in seed production as well in oil crops. It is also very important in the process of nitrogen fixation in leguminous crops. Sulfur performs an important role in the metabolism of nitrogen.

Plant can uptake sulfur in the form of SO₄^2- from the soil and So₂ (gas) from the atmosphere through leaves. Unlike Calcium and Potassium, Sulfur absorbed as anion.  

Sulfur is deficient in the soils having organic matter less than 2%, and under high irrigation frequency lands.

Sulfur is immobile in the plant structure and not easily translocated from older leaves to younger leaves. Therefore, sulfur deficiency appears on younger leaves.

Green to yellow color is a deficiency symptom and stunted growth.

The soils with the desired level of organic matter has enough sulfur but it is not in a useful form for plants, first that sulfur undergo through the process of mineralization (microbial activity and affected by temperature and moisture) then sulfur converts into sulfate which is useful form for plants.

Immobilization of sulfur is the opposite process in which sulfate again converts into organic form.  

Calcium (Ca):

Calcium in Plants Health plays a very important role indirectly contributes to yield increase by encouraging the roots and leaf development. Calcium helps to form those compounds which are part of the compounds to form cell wall, indirectly calcium helps in to strengthen the plant structure.   

Calcium protects the plant from heat stress, it improves the stomata function and participates invasion of the heat shock protein.

Calcium protect the plant from disease attack, Calcium make possible such stronger cell walls those can stop the invasion of many fungi and bacteria secret enzymes that weaken the cell wall.

Calcium helps to balance the organic acids in the plants, as well as, it also excites the activities of enzymes and improves availability of the Molybdenum (Mo) and uptake of other nutrients.

Calcium helps rhizobium(Nitrogen-fixing bacteria) to form nodules on the roots of the leguminous crops that enables the crop to capture the Nitrogen gas from the air and convert it in the useful form, so the plants can use it. 

Plant can uptake Calcium in the form of Ca²⁺, its movement in plants is passive because it does not require energy input, Uptake mainly occurs through the xylem, so it directly relates with the transpiration rate of the crop.

Deficiency occurs in high humidity, cold climate, low transpiration of the crop.

In saline soil conditions calcium availability reduces because in this condition water uptake by plant reduces.

Calcium(Ca²⁺) compete other positive ions like Sodium(Na⁺),Potassium(K⁺), and Magnesium(Mg²⁺), applying too much  of these ions decrease the availability of calcium to the plants, Sodium(Na⁺) replace the absorbed calcium (Ca²⁺)  ions and deteriorate the soil structure and reduces the calcium availability as well.

Calcium deficiency mostly occurs in acidic and sandy soils by excess irrigation/rain, water by which it leaches down from root zone of the crop.

Magnesium (Mg²⁺):

Magnesium is at the core of each chlorophyll cell. Magnesium is combined with four Nitrogen atoms in chlorophyll, so it is directly involved in photosynthesis. It also serves in the plant to capture the sunlight to utilize in photosynthesis and crop growth.

Magnesium participate in the phosphate metabolic activities, it  serves as phosphate carrier in the plant, contributes  in the root formation and improves the utility of nutrients and water in the plants, it  gives green hue to leaves and It is a catalyst for many enzymes to participate in plant growth while synthesis the protein and balances the nucleic acid in plants.

Dolomitic limestone (the compound is a combination of Calcium Carbonate and Magnesium carbonate.) It serves in the growing medium as neutralizing the acidic content in the medium as well as the source of calcium and magnesium.

The plant can uptake Magnesium in the form of Mg²⁺, plant uptake magnesium in two ways passively by transpiration dissolved in water, and actively in the forms of magnesium ions by diffusion, Magnesium ions diffuse from high concentration to low concentration.

It abundantly available in clay soil and organic matter.

Magnesium primarily available in soil minerals, breakdown of minerals is very slow therefore that magnesium is not available to plants.

Magnesium availability becomes limited, while low PH, Low temperature, poor moisture levels of the soil, and imbalance of competing elements like Calcium and potassium.

It is actively mobile element and can easily move from older leaves to younger leaves.

Deficiency of magnesium appears on older leaves first.