Soil micronutrients and their importance for plants

Micronutrients are important for plants because they contribute to many biological reactions, oxidation and reduction reactions that take place at the plant cell level.

 

The basic Micronutrients elements are iron, manganese, zinc, copper, boron and molybdenum

 

Plants need a small amount of the micronutrients elements, and the soil content is often sufficient to supply the plants with the quantities they need. These nutrients are found in the chemical fertilizers that are used to enrich the soil with large elements, but in some developed  agricultural countries, special fertilizers are used to enrich the soil with the micronutrients elements.

 

The main importance of micronutrients elements in plant nutrition

these elements are very necessary and their effectiveness appears especially after adding the major elements, as they work on the following:

 

• they greatly contribute to increase the effectiveness of nitrogen, phosphorous and potassium elements, and also increase the plant's utilization of them to obtain high-quantity and high-quality yields.
•  they increase the plant's ability to resist drought
•  they increase the plant's ability to resist high and low temperatures
• Some of them are involved in oxidation and reduction reactions that take place inside plants' cells
•  Many of them are included in the synthesis of various enzymes that stimulate biological reactions
•  they increase the amount of vitamins and proteins in addition to they increase the carbohydrate content of many plants
•  Protect plants from diseases and insects 

Factors affecting the availability of micronutrients 

• The most suitable pH for iron, manganese and boron availability is 5 - 6.5, while molybdenum is available at pH above 6.
•  The presence of calcium in high concentrations leads to the unavailability of micro elements, especially iron and manganese, due to the presence of antagonism between these elements
•  The degree of ventilation affects the state of valence of the element, as bivalent manganese is easier to absorb by plants in well-ventilated soils than triple and quadrivalent

 

The factors that led to the deficiency of micro elements on plants

1- Intensive agriculture: Intensive agriculture continuously consumes soil stock of these elements, which leads to a decrease in its concentration to less than the level required for other crops

 

2- Intensive use of macronutrients fertilizers: The excess use of N.P.K elements in order to obtain copious crop leads to a large consumption of the micronutrients that exceeds the soil content, which gradually reduces the natural stock of these elements.

 

3- Producing improved plant varieties with a high production capacity and these consume large quantities of the basic micronutrients.

 

4- The current industries tend to produce chemical fertilizers from the major elements free from impurities of the micronutrients that used to compensate the losses that occur during the growing seasons of crops 

Deficiency and toxicity 

Although the amount absorbed of micronutrients by the plants is small quantities that do not exceed tens to hundreds of grams per hectare annually, there are many soils that do not insure these simple required quantities.

 

When the required quantities are not available, the plants exhibit symptoms of deficiency of these elements, the degrees of deficiency vary according to the following criteria:

 

Obvious and severe shortage: it leads to a poor yield and a decrease in productivity, in which case the symptoms of deficiency appear clear on the plants

 

Hidden deficiency: the symptoms of deficiency here are not visible to the naked eye, but it can be identified by chemical analysis of plants and lead to a decrease in productivity

 

On the other hand, we note that an increase in the concentration of nutrients in the soil above the level required for crops leads to the emergence of toxic symptoms that are less dangerous than deficiency factors and appear in two forms:

 

Mild toxicity: It is caused by an excess of some elements inside the plants, and it does not show clear symptoms but causes a decrease in productivity

 

Obvious and severe toxicity: It causes the emergence of certain symptoms that differ in different elements and often causes implantation failure