Magnesium’s Role in Soybean Nodulation

April 29, 2022

Magnesium (Mg), like nitrogen (N), is essential to soybean growth because it is required to produce chlorophyll, which plants need for photosynthesis. That said, the physiological mechanisms involved in nodulation that depend on magnesium still remain largely unknown. 

Nonetheless, studies have highlighted both the consequences of magnesium deficiency and the benefits of receiving an optimal external supply of magnesium. Let’s take a look at how supplying magnesium affects the growth and development of soybean nodules.

Magnesium: a vital component of chlorophyll

Chlorophyll is what gives plants their dark green colour, and magnesium is the central element of a chlorophyll molecule. This means that an unavailability or imbalance of magnesium will affect chlorophyll production, which is critical to nitrogen fixation.

The consequences of a magnesium deficiency in soybean nodulation

If there’s not enough magnesium in the soil, the soybean will have a lighter green colour and frail appearance. In addition to the direct effects on plant growth, a limited supply of magnesium can also affect the biological fixation of dinitrogen (N2) in the nodules formed by symbiotic interactions between legumes and rhizobia.

The benefits of an external magnesium supply on soybean nodulation

An external supply of magnesium improves nodule production in conditions where there is a limited or low availability of nitrogen. An optimal external supply of magnesium also promotes dinitrogen fixation and the growth of the soybean plants. 

What’s more, an external supply of magnesium promotes nodule growth, in turn causing an increase in the number of larger nodules, without changing their structure.

An adequate supply of magnesium also helps reduce starch and sucrose buildup in the leaves of soybean plants while increasing their concentrations in the roots. This phenomenon helps improve the carbohydrate supply in the colonized (infected) area where nodules have formed. 

Magnesium’s importance in soybean nodulation

Soybean plants need a lot of nutrients for healthy growth and magnesium is one of them. Any conditions that limit this nutrient’s supply are likely to harm the plants’ growth and viable seed production. 

To recap, magnesium deficiency can lead to:

  • Less productive and lower-quality soybean crops
  • A negative impact on biological fixation of dinitrogen

On the other hand, an external magnesium supply promotes:

  • Nodule growth when nitrogen availability is limited
  • Dinitrogen fixation and soybean plant growth
  • Larger nodules
  • Less starch and sucrose accumulation in the leaves

To learn more about nutrient deficiencies in soybean crops, check out our article Nutrient deficiencies in soybeans.