Role of magnesium in apple production
Magnesium is a key constituent of the chlorophyll molecule; usually 15-20% of the tree’s Mg total is found in the chloroplast. It is also involved in various biochemical functions including activating enzymes involving phosphorylation, and protein synthesis.
Magnesium effect at growth stages
| Stage | Magnesium effect |
| Bud Burst – Start of Flowering | Promote strong early growth of new plant tissues and maximum tree productivity |
| Fruit Set to Fruitlet at 30mm | For reduced fruit drop |
| Post Harvest | Replenish reserves and strengthen new buds |
Magnesium deficiencies in apples
Interveinal chlorosis and bright yellowing develops first on older leaf margins and tip and spreads back to the main vein. The leaves often have a characteristic herringbone pattern of chlorosis on new year’s growth. Symptoms are normally most obvious later in the season during fruit fill.
In severe instances, leaves curl up, die and drop prematurely, leaving a few tufted leaves at the tip of the branches.
Magnesium and apple color
Studies in Poland show that soil applied magnesium can improve the color of red fruit largely through the increased production of carbohydrates, which are the building blocks for red pigments.
Magnesium uptake
Studies with Mcintosh apples in US show that regular soil application of magnesium ensures good leaf uptake and productive growth.
Magnesium and fruit drop
The same studies show that good leaf uptake of magnesium ensures a marked reduction in fruit drop.
Ca:Mg ratio and bitter pit
Care has to be taken since overuse of magnesium can restrict calcium uptake and increase the risk of bitter pit, as shown in studies with Jonagold apples in Poland.
Magnesium and fruit acidity
Magnesium has a slight effect on fruit acidity, as shown in trials with Golden Delicius apples in Italy.
