Soil is not simply a physical anchor for plants; it is a complex and dynamic ecosystem that functions as the main reservoir of the essential nutrients that plants require to grow, flourish and reproduce. Proper nutrition is as critical for the health of a plant as it is for any living organism. Of the seventeen elements considered essential for plant life, most are supplied through root absorption from the soil solution.
These essential elements are classified, according to the amount that the plant needs, into macronutrients and micronutrients.
Macronutrients are those that plants require in relatively large quantities, although Carbon (C), Hydrogen (H) and Oxygen (O) are the most abundant and are obtained mainly from air (as CO2) and water (H2O), soil is the main source of the remaining six macronutrients, which are subdivided into primary and secondary.
These three elements are usually the most limiting in agriculture, which is why they are the basis of most fertilizers..
- Nitrogen (N): It is vital for vegetative growth, being a fundamental component of amino acids, proteins, enzymes and chlorophyll. A nitrogen deficiency typically manifests itself in pale or yellowish leaves (chlorosis), starting with the oldest leaves, the soil provides it in forms such as nitrate (NO3−) and ammonium (NH4+).
- Phosphorus (P): It is indispensable for the storage and transfer of energy (as a component of ATP and nucleic acids), cell division, the formation of robust roots, flowering and fruiting. Its deficiency often results in poor growth and a dark purple color in the foliage.
- Potassium (K): Known for its role in water regulation (cell turgor and opening/closing of stomata), potassium also activates more than 60 enzymes, improves resistance to diseases and strengthens the stems. A lack of potassium can lead to yellowing of the edges of older leaves.
The necessary secondary macronutrients are also found in smaller amounts than the primary ones, but equally crucial, these are :
- Calcium (Ca): Essential for the structure of cell walls and the stability of membranes. It is immobile on the plant, so its deficiency affects young growth spots, causing deformations.
- Magnesium (Mg): It is the central atom of the chlorophyll molecule, so it is vital for photosynthesis. The deficiency is seen as an intervenal chlorosis (yellowing between the veins) in the older leaves.
- Sulfur (S): Component of some amino acids (such as cysteine and methionine) and vitamins, it is crucial for the formation of proteins and the development of the chloroplast. Its deficiency symptoms are similar to those of nitrogen, but they appear first on young leaves.
On the other hand, micronutrients are required in minimal amounts, but their presence is as essential as that of macronutrients, they fulfill specific functions, often acting as enzyme cofactors.
- Iron (Fe): it is fundamental for the synthesis of chlorophyll and participates in energy transfer, despite being abundant in the soil, its availability decreases with a high pH, its deficiency causes interventional chlorosis in the youngest leaves.
- Manganese (Mn): It plays a key role in photosynthesis (water splitting) and activates numerous enzymes. its deficiency is similar to that of iron.
- Zinc (Zn): Necessary for the synthesis of auxins (plant growth hormones) and essential for carbohydrate metabolism. The lack of zinc reduces internodal growth, giving plants a "rosette" appearance.
- Copper (Cu): It participates in the metabolism of proteins and carbohydrates, and is a component of enzymes involved in photosynthesis and respiration.
- Boron (B): essential for cell wall formation, pollen germination, seed development and sugar transport.
- Molybdenum (Mo): necessary for the enzyme nitrate reductase (which converts nitrates into usable forms) and nitrogenase in legumes.
- Chlorine (Cl): It is involved in osmotic regulation and photosynthesis.
| Final considerations |
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The fertility of the soil depends not only on the amount of these elements, but on their availability.Plants absorb these nutrients in the form of ions dissolved in the soil solution. Factors such as soil pH, texture, moisture and organic matter directly affect the plant's ability to absorb them. A healthy soil, with a rich microbial activity, plays a crucial role in breaking down organic matter and releasing these elements, ensuring a constant and balanced supply that sustains plant life and productivity.
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| Bibliographic references |
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- Marschner, P. (2012). Marschner's Mineral Nutrition of Higher Plants (3ra ed.). Academic Press.
- Mengel, K. and Kirkby, E. A. (2000). Principles of Plant Nutrition (4th ed. in Spanish). International Potash Institute (IPI).
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