Onions with the correct amount of nitrogen to support strong and fast leaf growth and early bulb formation have better storage quality as they suffer less from weight loss and sprouting.
Nitrogen can also help to increase the specific weight of the outer skin. This can improve the bulb’s resistance to pressure, reducing damage during handling and storage. Too much nitrogen softens the bulb and increases storage rot diseases.
Phosphorus has a positive effect on storage quality of onions, especially when high rates of nitrogen have been used. Where phosphorus supply is adequate, there is lower weight loss, less sprouting and reduced rot.
The use of potassium allows growers to maintain high rates of nitrogen for yield with reduced risk of storage problems such as rot or sprouting. Potassium also needs to be balanced with phosphorus inputs.
While only relatively low levels of calcium are found in the bulb, these levels are critical for storage quality, improving the strength of cell walls. Trials show that magnesium, applied alongside calcium, helps improve the shelf life of onions by reducing the level of rot during storage.
Trials confirm Boron's effects on yield and also on improving storage quality. The effect of boron on storage quality could be associated with the micronutrient’s role in improving calcium accumulation in the bulb.