What is the pH value of magnesium

magnesium

Forms of magnesium binding in the soil

Levels of care of the soil

Magnesium in the plant

 

Forms of magnesium binding in the soil

In addition to the Mg2+-Ions, the magnesium in the soil is either exchangeably bound to the cation exchangers (organic substance or clay particles), or is permanently incorporated into the crystal lattice of the soil silicates. Only the first two fractions are available to plants.

Due to the large hydrate shell of the magnesium ion, the strength with which the Mg ions are bound to the exchanger surfaces is relatively low. This leads to an increased risk of leaching, especially on soils with poor sorption and low pH values.

Magnesium dynamics in the soil

  • The magnesium released during the silicate weathering represents a very slowly flowing Mg source for the plant-based diet.
  • The magnesites and dolomites that occur in some soils are no longer available as a source of magnesium from a pH value> 6, as they are hardly ever dissolved.
  • Many soils are naturally poor in magnesium. In particular on light and acidic soils, the plant-available magnesium in the soil is often insufficient to meet the needs of many agricultural crops
  • The Mg uptake by the plant is negatively influenced by a wide K / Mg and Ca / Mg ratio as well as a low pH value of the soil. Even with a high magnesium content in the soil, a latent or acute magnesium deficiency can occur for the plants.

Magnesium has an important function in maintaining the soil structure. Together with other polyvalent cations, above all calcium, magnesium also forms bridges between negatively charged clay minerals. This supports a stable, crumbly soil structure that prevents clogging. The soil fulfills its role of storing a large amount of plant-available water and plants can form a good network of roots in it for the development of water and nutrients.

 

Levels of care of the soil

For plant nutrition, the part of magnesium that can be easily absorbed from the soil solution by the plant is important. Based on the soil analysis, the supply status of a soil can be determined and the fertilizer requirement calculated. There are five salary classes from very low (A) to very high (E). The content class "C" is the target level of supply of the soil with nutrients. The nutrient contents of the individual content classes vary depending on the type of soil (light soils, medium-heavy soils, heavy soils).

 

Magnesium in the plant

The plants take magnesium from the soil solution only as Mg2+-Ion on. It is very mobile in the plant and is important for various areas of the plant's metabolism.

Functions of Magnesium in the Plant

  • Magnesium is a central component of chlorophyll (leaf green) and is therefore essential for the light reaction of photosynthesis.
  • Magnesium is indispensable for the synthesis and storage of important plant constituents (carbohydrates, proteins, fats).
  • Magnesium has an activating effect on various enzymes.
  • Magnesium regulates the energy balance of plants because it is necessary for the formation of bridges between enzymes and the energy carrier ATP.
  • Magnesium influences the formation of RNA and thus the conversion of genetic information into proteins.
  • Magnesium is a component of pectin substances and phytin. The former is important for the stability of the cell structure and the latter represents a low-energy phosphate store, which is of great importance for the germination of seeds.
  • Magnesium is a building block in the ribosomes and the cell nucleus matrix and helps stabilize the biological membrane.
  • Magnesium is involved in the structure of the cell walls.
  • Magnesium has hydrating properties and thus influences the water balance and the effectiveness of the enzymes.
  • Magnesium and manganese promote the concentration of value-determining ingredients such as citric acid and vitamin C. They promote the freezing quality of vegetables and the resistance of the potato to discoloration during processing into puree and dumpling flour.

Magnesium promotes root growth and yield formation

Magnesium plays an important role in the transport of carbohydrates within the plant. The assimilates formed in photosynthesis are only reliably brought to the growth organs if there is an adequate supply of magnesium. This is why root growth is inhibited when there is a magnesium deficiency. Before the first symptoms of deficiency become visible on the leaves, the roots are already impaired and with it the water and nutrient absorption.

Magnesium deficiency (left) leads to reduced root growth.

Magnesium also ensures the transport of carbohydrates to the harvest organs. For this purpose, the assimilates from the current photosynthesis as well as the carbohydrates temporarily stored in the shoot are mobilized with the help of magnesium, transported in grains, tubers or cobs and used there to generate yield.

Magnesium promotes the filling of the cob in corn. If there was a magnesium deficiency (left), some of the grains withered because not enough carbohydrates were transported to the cobs.

 

In the case of wheat, a good supply of magnesium increases the thousand grain weight and thus the yield. Source: Ceylan et al., 2016, Plant and Soil.

 

Magnesium protects the plants from stress

Plants that suffer from a magnesium deficiency are much more sensitive to drought, high temperatures and high light exposure than plants that are well supplied with magnesium.

Drought stress: Magnesium protects the plants through improved root growth and thus enables access to water in deeper soil layers.

High temperatures and light irradiation: High temperatures generally promote the growth of the plants and so the magnesium requirement increases, so that a deficiency situation quickly occurs. Scientists assume that the high sensitivity of magnesium-deficient plants to heat and light stress is also due to a higher concentration of oxygen radicals in the leaf cells.

 

The corn plant with a magnesium deficiency (-Mg) lags behind in its development compared to the plant that is well supplied with magnesium (+ Mg). The effect increases at high temperatures of 35 ° C.

 

The photosynthesis process is disturbed when exposed to high temperatures and insufficient magnesium is available, and the excess light energy leads to the formation of these aggressive oxygen compounds. They damage the cells and ultimately cause them to die - as a result, necroses form on the leaves.

In the shade, no symptoms of deficiency are visible on the leaves with a low magnesium supply. However, necroses develop when exposed to high levels of light.

 

Magnesium deficiency symptoms

  • Symptoms of deficiency can first be seen in the older leaves. There are chlorotic spots between the leaf veins.
  • If the deficiency persists, necrosis and red discoloration appear on the stems.
  • When exposed to strong sunlight, the entire plant appears wilted and limp (similar to the "wilted appearance" with K deficiency). This is due to a disturbed water balance. The single leaf looks stiff and brittle.
  • The chlorophyll content and the number of chloroplasts in the plant decrease.

Photos of magnesium deficiency in crops

Magnesium deficiency in grain (left), maize (middle) and rapeseed (right).