Chemical fertilizers

Chemical fertilizers

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Chemical fertilizers: what they are and how they work

When we talk about chemical fertilizers we refer to products treated at an industrial level through transformation or refining processes, or obtained synthetically, used in gardening and in the agricultural sector as fertilizers in order to provide the soil with nutrients that can be used by the plants. Nutrients are distinguished according to the functions performed, the quantities absorbed and essentiality: based on this last parameter, we speak of non-essential, essential for a few species and essential for all species. While non-essential substances are passively absorbed and can sometimes have a phyto-toxic effect (this is the case of fluorine) or in any case do not perform any function, the essential elements for all species are sixteen: molybdenum, oxygen, carbon, boron, sulfur , manganese, hydrogen, iron, nitrogen, potassium, phosphorus, copper, zinc, chlorine and magnesium. In reality, hydrogen, oxygen and carbon are not considered nutritional elements in the strict sense, as a result of the methods of intake with which plants absorb them. In particular, carbonic nutrition involves gas exchanges via stomatal pathways with the atmosphere, which allow for the absorption of carbon dioxide. Water nutrition, on the other hand, takes place through the roots, stomata and lenticels, and obviously concerns the absorption of water. Finally, mineral nutrition concerns the absorption, in the form of minerals, of the remaining nutritional elements, dissolved in water, through the roots and the stomatal openings.

Fertilize the land with chemical fertilizers

The use of chemical fertilizers, therefore, is aimed at fertilization, and determines a change in the chemical composition of the soil in order to favor the nourishment of crops (and in this sense the fertilization is different from the amendment, since it does not have the purpose of improve the physical properties of the soil, and from the correction, since it is not intended to alter the pH). This does not mean that there are chemical fertilizers characterized by a corrective or amending secondary effect. In particular, the amending effect is rarely obtained with chemical fertilizers, and more often with organic fertilizers, which incorporate rather large quantities of fertilizer, so as to improve the overall structure of the soil after humification. However, it should be specified that the amending effect given by mineral fertilization occurs only when chemical fertilizers rich in calcium are supplied, within acid soils. Here, in fact, the mineral colloids characterized by a reduced degree of basic saturation determine the structural state of the soil; the structure, therefore, is improved by football. From a quantitative point of view, the supply of mineral fertilizers is limited to a few quintals per hectare of land, which makes it clear that any corrective effects or secondary amendments are in any case not very long-lasting and rather mild. In reality, agricultural lime is both a fertilizer, a soil improver and a corrective: but it is a particular case, the proverbial exception that confirms the rule.

Macroelements and microelements

Within chemical fertilizers, a distinction is made between oligodynamic elements (the so-called microelements) and macroelements, depending on the quantities used by the plant. In fact, macroelements make up plant tissues in quantities greater than one part in a thousand, while microelements make up tissues in quantities less than one part in a thousand. It should be noted, in any case, that the microelements are as important as the marks: in fact, in the absence of the oligodynamic elements, the plants can face deficiency physiopathies, affections which, depending on the case, can be more or less serious. A further distinction provides for the subdivision into dynamic elements and plastic elements, based on the function held in the body. The plastic elements, in particular, are those that participate in the construction of tissues when they become part of the composition of lipids, carbohydrates and structural proteins: this is the case of sulfur, phosphorus, hydrogen, carbon, oxygen and nitrogen. The dynamic elements, on the other hand, participate in physiological processes by becoming part of hormones, enzymes and coenzymes: this is the case of magnesium, potassium, calcium and microelements.

The administration of nutritional elements: the importance of nitrogen

The function of chemical fertilizers (whose prices on the market vary significantly depending on the type: to buy them, it is advisable to listen to the suggestions of a nurseryman), therefore, is to make these elements available, according to the measures and quantities specific to the needs of the various species. Plants, as a rule, respond positively to the administration of the elements in an artificial way, especially when they, either by immobilization or by real deficiency, are present in the soil in small quantities. In any case, it can also happen that there are no answers: for example when the soil is excessive, or when a species does not need a certain element. Just think of legumes, which do not respond to the supply of nitrogen simply because they already autonomously exploit the symbiont nitrogen fixing. In conclusion, it is good to specify the importance of nitrogen, an essential element for almost all plants (with the exception of carnivorous species), which is absorbed mainly in nitric form.

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