Question

What are the symptoms of a phosphorus deficient plant? Where do these symptoms first appear in plants?

Answer 1

Phosphorus deficiency is seen in leaves and stems of plants in the form of abnormal discoloration. Plants with phosphorus deficiency show dark bluish-green coloration with purplish leaves.

Complete answer:
One of the initial symptoms of phosphorus deficiency include stunted growth of the plant. Some crops such as corn, tend to show abnormal discoloration in various parts of the plant (mostly leaves). In the early vegetative stages, the plants turn dark bluish-green in colour with leaves and stems becoming purplish. This purple colour is due to accumulation of sugars in the leaves which favour the synthesis of anthocyanin (a purple coloured pigment). In the late stages of plant growth, phosphorus demands are high and phosphorus deficiency affects both seed development and normal crop maturity.
Phosphorus is highly mobile in plants. Therefore, phosphorus deficiency may translocate from old plant tissues to actively growing young tissues. These symptoms first appear in the older tissues of the plant. Older plant leaves are affected before the younger actively dividing leaves due to redistribution of phosphorus. Corns may display a purple or reddish colour on the lower leaves and stems.

Additional information:
Phosphorus is an essential nutrient in plant growth and development. It is the second most limiting macronutrient after nitrogen. It plays a major role in catalysis of various biochemical reactions as well as development of plant structural components. It is responsible for capturing and converting solar energy into useful plant components. Factors contributing to phosphorus deficiency include soil pH, type of clay, presence of organic matter in soil, soil temperature, aeration, moisture and composition, application timing etc.

Note:
Diagnosis of phosphorus deficiency is more difficult than nitrogen or potassium deficiency. Usually, crops don’t show any obvious symptoms other than stunted plant growth during early stages of growth. By the time visual phosphorus deficiency is detected it might be too late to correct it.