Phosphorus toxicity

The first signs of phosphorus (P) toxicity occur as a mottled chlorosis just behind the tip of the oldest leaf and along the margin of the leaf. The tip itself rapidly becomes necrotic. Within a few days, the progression of symptoms leads to the chlorosis turning a bright yellow along the margins leaving a green arrow effect and increased necrosis of the tip. The base of the leaf remains green and healthy.

In the case of severe P toxicity, a similar series of symptoms appear on the second oldest leaf and will progress to all leaves in time with subsequent death of the plant. In many cases in the field, plants may initially show toxicity symptoms due to high levels of P near the germinating seed, but will grow out of the toxicity with no apparent detrimental effect on yield.

Phosphorus Toxicity