Role of Phosphorus in Onion Production

Phosphorus is a component of nucleic acids (DNA and RNA) and essential for energy transfer within the plant. Thus it has a direct effect on yield and quality.

Phosphorus effect at growth stages

Stage Phosphorus effect
Pre-Planting Maximize root development and to supply reserves for season long growth and good bulbing
Bulb Fill Encourage ripening, early maturity and a big bulb size
See more on Onion Growth Stages.

General guidelines for Phosphorus application

Phosphorus is rarely required in large quantities. However, where crops are grown on soils with very low natural P levels, higher rates are required to boost yield and bulb size. It is important that phosphorus is available early season in order to encourage growth, particularly of the root system. Placement of phosphorus within the root zone has been shown to work better than when P-fertilizer is broadcast.

Phosphorus deficiencies in onion

Plant growth and establishment slows and rooting is adversely affected and stunted. Leaves are mottled green/yellow brown. Maturity can also be delayed and crops tend to have a thicker neck at harvest.