Deficiency Symptoms of Essential Elements

Deficiency and the Critical Concentration

When the supply of an essential element falls, plant growth suffers. The concentration below which growth is noticeably held back is called the critical concentration, and once an element's level drops below this point, the element is said to be deficient. Because every essential element plays one or more specific roles, its shortage produces a particular, recognisable pattern of abnormal growth — a deficiency symptom — rather than a generic decline. These symptoms vary from element to element, go away once the missing nutrient is supplied again, and can eventually kill the plant if the deficiency is not corrected.

Why Symptoms Show Up Where They Do

Where a deficiency symptom appears on the plant depends on how mobile that element is inside the plant:

• Mobile elements — such as nitrogen, potassium and magnesium — can be broken down out of old tissue and exported to actively growing young tissue. So when these elements are deficient, the plant strips them from its older, senescing leaves first to feed its younger leaves, and the deficiency symptom shows up first in the older leaves.
• Relatively immobile elements — such as sulphur and calcium — are locked into structural parts of the cell and cannot easily be withdrawn and moved once they are laid down. Their deficiency symptoms therefore appear first in the young, growing tissue, which is where the ongoing shortage is felt directly.

The Main Symptom Types

• Chlorosis — loss of chlorophyll causing leaves to yellow — caused by deficiency of nitrogen, potassium, magnesium, sulphur, iron, manganese, zinc or molybdenum.
• Necrosis — death of tissue, particularly leaf tissue — caused by deficiency of calcium, magnesium, copper or potassium.
• Inhibited cell division — caused by low nitrogen, potassium, sulphur or molybdenum.
• Delayed flowering — caused by low nitrogen, sulphur or molybdenum. …