Written by: Dr. Ragheb Al-Adly, Lecturer in the Lands Department, Faculty of Agriculture, Saba Pasha, Alexandria Universit

     Fertilizers

are natural (organic or inorganic) or manufactured substances added to the soil or directly to the plant to provide the plant with one or more nutrients necessary for plant growth. Fertilization gives the plant the necessary nutrients for its growth, production, and quality. This addition is done in different ways to fertilizers.

Essential nutrients

     It is defined as the element that performs a certain function in the life of the plant, such that if this element is absent or deficient, growth worsens or stops, and consequently the crop is reduced or non-existent.

In 1939, the scientists Arnon and Stout identified three conditions that must be met in an essential nutrient:

1. Must required for the completion of the life cycle of the plant.

2. Must not be replaceable by another element.

3. Must be directly involved in plant metabolism, that is, it must be required for a specific physiological function.

However, it was modified to include new conditions that scientists agreed upon, which was later called the general theory of the essentiality of nutrients. The theory is summed up in that an element becomes essential for the plant if it meets the following five conditions:

• The absence or deficiency of the element prevents the plant from completing its life cycle (vegetative or fruiting cycle).

• The absence or deficiency of an element results in its own deficiency symptoms, and these symptoms cannot be treated except by adding that element to the plant.

• That element cannot be replaced by another element.

• The element must have a specific physiological function or function in the plant, and this function or function must be known and specific.

• The element must be necessary for all elegant plants.

Accordingly, any element that does not meet the five conditions together cannot be considered an essential nutrient. Based on these rules, 17 elements have been identified that meet the previous conditions. There are 3 elements of the essential elements that represent 95% of the plant’s needs, which the plant obtains from Air and water, which are oxygen, carbon, and hydrogen. As for the rest of the nutrients (14 elements), the plant obtains them from the soil and fertilizers. These elements are divided into elements that the plant needs in large quantities, and they are called macronutrients, such as nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur, and elements that the plant needs in smaller quantities, and they are called micronutrients, such as iron, manganese, copper, zinc, molybdenum, boron, and nickel. The term micronutrient does not mean that these elements are of little importance to the plant. It does not grow naturally without sufficient amounts of these elements.

The macronutrients are divided into primary macronutrients, sometimes called fertilizer elements. They are nitrogen, phosphorus, and potassium, and they are usually not available in sufficient quantities to give the best plant growth. These elements are usually added to the ground through fertilization.

Secondary macronutrients, such as calcium, magnesium, and sulfur, are less susceptible to deficiency than these elements, as most lands have these elements in quantities suitable for absorption. A valid form of an element is the form or forms of an element that the plant can easily absorb and which, when a change in its quantity occurs, is accompanied by a change in the growth of the plant and also in its yield.

العناصر الضرورية للنبات

Some elements play a role in plant nutrition but are not essential. They are called beneficial elements. These elements can prevent or reduce the toxic effects of other elements or have important roles for some plants or under some conditions. For example, cobalt is essential for nitrogen fixation in legumes and the formation of root nodules (there is a trend to add cobalt to the essential elements so that the number of essential elements becomes 18 instead of 17). There is also silicon deposited in cell walls and it has been found to increase the plant’s resistance to heat, drought, insect, and fungal infection. It also works to reduce the toxic effects of manganese, iron, phosphorus, and aluminium.

Fertilization plays a fundamental role in feeding plants. If the fertilizer is supplied on a sound scientific basis, we obtain the optimal production. However, if there is an imbalance of excess or deficiency, symptoms of deficiency or poisoning appear.

Therefore, it is necessary to know the most important foundations on which fertilizer needs are determined:

1. The type of plants.

Plants differ in their nutritional needs due to the different nature of growth, the length of the growing season, and the compounds that must be formed to reach a crop. In general, we must know that the primary macronutrients for plant growth are phosphorus, potassium, and nitrogen. We must also know that the crops that need phosphorus the most are root crops, the roots of which are eaten, as well as crops from which we eat seeds. All plants at the beginning of their growth need phosphorus for the roots to grow properly and spread, to then obtain good vegetative and fruit growth. We must realize that what the plant misses in fertilizing with phosphorus at the beginning of its life is not compensated for by the late addition after that.

The plants that need the most potassium are Fruitful crops, tuber crops, and everything that has an enlarged economic part that stores food because it is the element responsible for the transfer of elements and materials that make up the shoot system and their transfer to the root system. It is also responsible for the hardening of the cells in the fruits and giving them a solid and taut appearance. It also enters into the construction of flavoring materials and sugars.

Nitrogen is necessary for the formation of vegetative growth. The need for it is confirmed in leafy crops, but excessive use of it may lead to undesirable consequences… such as the excitement of the vegetative group at the expense of the fruit and the increase in the moisture content of the fruits, which leads to a decrease in their storage capacity and rapid infection with diseases.

2. Irrigation system

The irrigation method affects the quantities of added fertilizers, as the quantities of added fertilizers increase in the flood irrigation to compensate for the loss of fertilizer as a result of washing.

3. Soil type

Sandy soils prefer to add slow-dissolving fertilizers in small quantities in close batches because they can immediately supply the plant with the elements they contain, unlike clay soil, which retains and holds onto the elements and the effect of adding them does not appear until after a period.

4. The age of the plant and its growth stage.

 At the beginning of the plant’s life, it needs nitrogen and phosphorus, as I mentioned previously. However, after flowering and fruit set, the need for potassium and calcium increases.

5. The type of the previous crop.

Some crops are stressful to the soil and consume its stock of nutrients. When planting after them, the nutritional needs of the planted crops must be increased so that symptoms of deficiency do not appear. They are added before planting at calculated rates.

In the end, we have explained that fertilization provides the plant with the necessary nutrients required for plant growth, including macronutrients that the plant needs in large quantities such as nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. There are also micronutrients that the plant needs in small quantities such as iron, zinc, manganese, boron, and molybdenum. Determining the plant’s fertilizer needs is very important so that there is no deficiency of a certain element or poisoning of the plant due to an increase in the concentration of a certain element, which leads to a decrease in the crop in the end. Therefore, determining the plant’s fertilizer needs leads to obtaining the optimal production from any plant.