Magnesium deficiency

Magnesium deficiency is a nutritional disorder

Features

Central in chlorophyll structure and enzyme activation, Mg supports photosynthesis, carbon fixation (via RuBisCO), nitrogen assimilation, and ribosome stability in plant cells.

• Interveinal chlorosis: Older leaves display yellowing between veins with green veins remaining intact.

• Leaf drop & fruit impact: Progressive necrosis leads to premature leaf loss and may reduce fruit size or cause woody texture in berries.

• Leaf curling: Leaves may start to curl upward or become brittle.

• In vineyards like Napa or Balaton, Mg shortages often manifest post-veraison on basal leaves—a normal seasonal pattern exacerbated by soil conditions.

Causes

• Acidic, sandy soils leach magnesium easily, especially where high potassium fertilizer use compounds the issue.

• Low soil Mg availability or nutrient imbalances with K reduce uptake.

Consequences

1. Reduced Photosynthesis -> Magnesium is the central atom in the chlorophyll molecule. Deficiency leads to interveinal chlorosis (yellowing between leaf veins), especially on older leaves, which reduces the vine’s photosynthetic capacity.

2. Premature Leaf Senescence and Drop -> Affected leaves may become necrotic (dead tissue) and fall early. This weakens the vine by reducing leaf area needed for carbohydrate production.

3. Weakened Vine Vigor -> Magnesium-deficient vines show slower growth, poor canopy development, and reduced ability to recover from stress (like drought or disease).

4. Poor Fruit Quality -> Deficiency during berry development can result in: Smaller berry size, Lower sugar content (Brix), Poor color development in red varieties, Increased skin toughness or woody berries

5. Lower Yields -> Reduced photosynthesis and poor fruit set or berry development often translate to lower harvest yields.

6. Increased Susceptibility to Stress -> Vines become more vulnerable to: Drought, Heat stress, Fungal infections due to thin or poorly developed canopies

7. Nutrient Imbalances

Magnesium deficiency is often associated with excess potassium (K) or calcium (Ca), which can create ongoing nutrient antagonism and further block Mg uptake.

Treatment advices and Prevention

• Soil application: Epsom salts (magnesium sulfate) broadcast at 25–40 kg/ha effectively increases yield and must quality in trials. 

• Foliar sprays: Apply 25 g/L Epsom salt or chelated Mg solutions post-harvest or pre-veraison; foliar Mg nanoparticles show promise in saline soils. 

• Integrated fertility: Keep potassium and magnesium balanced; avoid excessive K to reduce competitive uptake