Magnesium in the soil and its effect on the roots
Magnesium is an element little considered in fertilization plans, even though numerous physiological processes have been identified in which it intervenes, for example, it participates in: phosphorylation (formation of ATP in chloroplasts), photosynthetic fixation of carbon dioxide ( CO2), protein synthesis, chlorophyll formation, phloem recharge, partition and assimilation of photosynthesis products, and photo-oxidation of leaf tissues. Also the enzyme ribulose1,5-bisphosphatecarboxylase (RuBP), commonly known as RuBisco, is only activated in the presence of Mg, this is very important to carry out the photosynthesis process.
The symptoms of Mg deficiency in plants, include interveinal chlorosis and red spots on old leaves. However, the appearance of these symptoms is a function of the intensity of the light intercepted by the plant, since it is believed that under conditions of high light intensity, plants require greater amounts of this nutrient.
It is known that up to 35% of the Mg contained in plants is linked to thylakoids, located in chloroplasts (cellular organelles that transform light into energy for the plant).
The Mg in the soil
In intensive production schemes fertilized exclusively with nitrogen (N), phosphorus (P) and potassium (K), Mg has become one of the limiting factors, due to depletion in a large number of soils.
The absorption of Mg is influenced by the amount of the element available in the soil solution, the pH of the soil, the percentage of saturation of Mg in the total cation exchange capacity, and the type of soil.
The losses of Mg in the soil can be given by leaching, the absorption of microorganisms, little retention of cations in the soil, and precipitation by secondary minerals; The latter is very common in arid soils.
Most of the Mg contained in the soil comes from the decomposition of minerals, soils located in temperate climates have concentration ranges from 5 to 50 ppm and in arid climates it ranges from 120 to 2400 ppm. Losses due to leaching depend on the concentration of the element in the soil and the rainfall regime, the reported values range from 5 to 68 kg / ha / year of losses, with sandy soils being the most affected. Excessive potassium fertilizations can decrease Mg availability, just as an excess of Ca inhibits the absorption of the element and it can also be lost due to erosion.
Mg in Acid Soils
Some soils subjected to high precipitation regimes, little cation retention and with an acidic pH, are frequently deficient in Mg, a product of leaching and antagonistic interactions that occur with Aluminum (Al).
Despite being an element frequently absent in acidic soils, it has been found that like Ca, Mg can also alleviate Al toxicity. The mechanisms of action are completely different, in the case of Mg its beneficial effects are very specific in the protection of plant roots. Today the benefits of adding Mg to crops established in this type of soils are well documented, allowing the effective release of organic anions (exudates from the roots), which provide protection to plants through the chelation of Al, neutralizing it and suppressing its phyto-toxic effects that occur in the rhizosphere (part of the soil near the roots).
Cakmak (2010) reports that there is a positive effect between the amount of Mg that a crop absorbs and the growth of the root and aerial parts of a plant. The same author demonstrated that the relationship between the area on the roots increases in plants with deficiency (aerial part / root), this adverse effect develops long before chlorosis is seen in the leaves. On the other hand, it has been found that in Mg deficiency, the concentrations of carbohydrates, reducing sugars and starches increase in the leaves.
Fageria (2013), reports that there is a very close relationship between the presence of Mg in the soil and the weight of the root in crops such as beans, peas and rice established in acid soils (oxisols).
It can be concluded that a critical aspect for obtaining good yields is that the plant has an adequate root system, and an adequate transport of carbohydrates, therefore, it is necessary to periodically monitor the state of nutrition with Mg in the soil and in the plant. before they see deficiency symptoms.
Source: Intagri
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