Magnesium (24.31)(+)

Magnesium is a secondary macro-nutrient in plants. Magnesium has good mobility in plants. It is an integral part of the make up of chlorophyll and is vital for photosynthesis in plants. It is is key to the plants ability to take up other nutrients and assist in the mobility of those nutrients throughout the plant (phosphorus) and assist the plant’s ability to use iron.

Factors affecting Magnesium availability

• Acidic Soils (below 6.5 pH).
• Good organic soils with a high CEC (Cation Exchange Capacity) are key to good Magnesium availability.
• High concentrations of Manganese &/or Potassium can lock out Magnesium.
• Low soil temperatures.

Magnesium deficiency

Magnesium deficiencies often present early spring and late autumn when soil temperatures are too cold or in instances where the soil is very acidic (below 6.5 pH). Poor quality soil with little organic content and high soil sodium can impact availability of magnesium.

Symptoms

Magnesium deficiency manifests as interveinal chlorosis on older leaves. This will develop to interveinal and marginal necrosis on leaf edges.

Treatment

Symptoms early season may be short-lived as temperatures rise. Mulching and black sheeting on the ground can help insulate and raise soil temperature. If symptoms manifest during the growing season, check soil pH (anywhere 6.8-7.2). Amending poor quality soil with good organic material and working this into the soil will help in the long run with magnesium availability. If you are using fertilisers, use a fertiliser low in potassium and manganese. Drip irrigation can help flush high concentrations of sodium from the root zone.

For a quick turn around Epsom Salt (Magnesium Sulphate) is a great choice as it is immediately available to plants both as a drench and as a foliar spray. But, Epsom Salt is NOT a miracle cure for everything (despite what the internet may tell you) and while it will very quickly fix any signs of chlorosis in the leaves – it will not fix the underlying issue. This will not go away. You will still need to address the underlying reason why the Magnesium deficiency is present in the first place. Acidic soil can be amended with Dolomitic Lime to raise soil pH and also give added Magnesium as Dolomitic Lime is high in Magensium.

Magnesium Toxicity

Magnesium toxicity is unlikely. Magnesium toxicity will bring about deficiencies in Calcium and Potassium. Establish the source of the excess Magnesium and address this. Flush out any excess magnesium in the soil with regular watering.