There is a widespread use of magnesium fertilizers in turf, since magnesium is the central atom of chlorophyll. Only a small proportion of the total magnesium is bound to chlorophyll (around 25%) and about 70% is relatively mobile being dissolved in plant sap. The magnesium ion is also involved in protein synthesis and many enzyme reactions.
Soil texture and soil organic matter content both influence magnesium availability. The actual type of clay present also has a major influence as although the soil may contain similar clay content, magnesium availability to turf can vary.
Soils that are sandy, low in organic matter, and contain a large amount of kaolinitic clay require more frequent application of magnesium fertilizer. This contrasts directly with heavy soils and those with a high CEC, which generally require larger and less frequent applications.
Figure showing how temperature effects Magnesium tissue content
The first symptoms are interveinal chlorosis and as the deficiency becomes more severe, the leaves may turn reddish-purple.
When does it occur?
The following conditions inhibit magnesium uptake:
- Low soil pH;
- The presence of high levels of ammonium, potassium, calcium, and manganese depressing shoot and leaf levels;
- In highly leached sandy soils and
- Following liming.
A response to a magnesium fertilizer is likely when:
- Soil magnesium levels are low;
- The soil pH is high or it has been raised by liming;
- Applying nitrogen as ammonium leads to antagonism between ammonium and magnesium;
- Compaction exists and finally
- There is a spell of wet/cold weather leading to low magnesium soil mobility.
Commonly used magnesium fertilizers and their characteristics.
These can be either quick-release soluble salts such as sulphate and nitrate or slow-release forms like oxides.
- Magnesium sulphate, in the form of Epsom salts (10% magnesium) and magnesium nitrate (11% magnesium).
- Kieserite (16% magnesium).
- Magnesium carbonate also known as dolomitic lime, contains 3–12% magnesium and Granomag® contains 57% magnesium.
So why use Kieserite?
- It produces a consistent supply of magnesium.
- The release pattern of kieserite corresponds best with turf demand.
- As It moves gradually down the soil profile it optimizes uptake and lastly
- It is extremely user-friendly as it can be applied as a granular or as a fine powder.
Epsom salts contain 10% magnesium and is also known as magnesium sulphate. It is highly soluble and used to prevent and correct magnesium deficiency. However, due to its this high solubility, it will be likely to leach especially on sandy soils.
Granomag containing 57% magnesium, is commonly used in fertilizer blends. However, it is insoluble and not readily available to the turf as it takes so long to break down. The other disadvantage is that due to its large particle size, it is not suitable for use on closely mowed turf, such as greens, unless during renovation following hollow tine aeration.
A foliar application of magnesium nitrate-containing both 10% nitrogen and 11% magnesium is an ideal way to deliver magnesium and nitrate-nitrogen. Consequently, rate reductions can be made of 30–50% comparative to epsom salts (magnesium sulphate). As it is sulphate free it also does not have issues with tank compatibility, unlike epsom salts.
A simple method for identifying the correct fertilizer type for a given soil type and condition (courtesy BASF).