What is Magnesium?
Magnesium is a very mobile element that is important for plant growth and development. Its availability in soil depends on multiple factors: the source rock material, the degree of weathering, local climate and the specific agricultural system and its management practices, such as crop type, cropping intensity and rotation, and fertilization practices. Therefore, the amount of magnesium can vary highly depending on the soil type. Low amounts of Mg can be expected in tropical and sandy soils, while soils close to the sea marshland, peat soils, saline soils, and generally soils with high clay content tend to have higher amounts of magnesium.
How do plants use Magnesium?
Furthermore, it is also needed for cell division and protein formation, activation of several enzyme systems and is an essential component for plant respiration. In short, without magnesium, chlorophyll cannot capture solar energy for photosynthesis and the important metabolic functions related to carbohydrates and cell membrane stabilization cannot be performed by the plant.
What are the signs of magnesium deficiencies?
Magnesium deficiency commonly occurs in intensively used agricultural soils, but it can also be caused by weathering of soil. It is often seen in sandy, strongly leached and acid soils.
It is not easy to recognize Mg deficiency based on the symptoms. Due to its mobility within the plant, Mg deficiency symptoms will appear on the lower and older leaves first, before the
symptoms become visible on the younger leaves. Common deficiency symptoms include:
- slow growth and leaves to turn yellow, especially on the outer edges, which then develop
- newly growing leaves may become yellow with dark spots
- purple or reddish spots on the leaves
The visibility of symptoms is also often related to the amount of light the leaves or plant is exposed to. Plant or leaves exposed to high light intensity will show more symptoms than others.
Magnesium and its importance in crop production and agriculture has been overlooked for some time, even though it is an essential element for plant growth and development. This is due to the fact that it is difficult to detect latent Mg deficiency. The deficiency is often not directly visible but still negatively affects crop growth. Only acute deficiency, when it is too late for crop yield, shows visible signs like interveinal chlorosis and growth reduction.
Why is it important to know the Mg content in the soil?
Furthermore, magnesium is often subject to leaching in considerable amounts especially during autumn and winter month with heavy rains. Magnesium leaching is also influenced by soil acidity, Ca concentration (liming) and Cation Exchange Capacity (CEC) affected by organic matter and clay %. This further demonstrates the necessity of soil testing to know not only the Mg content before the next cropping season but also other parameters that influence the Mg availability for plants.