Agronomy advice | Calcium and boron improve onion storage

Crop nutrition influences dry matter content, firmness and storability. Several key nutrients are involved but none more so than calcium and boron which are particularly associated with quality.

Calcium is probably the third most important nutrient needed by onions and has a key role to play in maintaining crop quality. Calcium is a key component of cells maintaining the structure of cell walls and stabilising cell membranes. Calcium is important in onions as it improves skin finish and reduces bulb decay.

Calcium nitrate treated onions will store longer with less rotting problems

Calcium is particularly important for bulb density, integrity and long-term storage with minimal disease problems. Calcium has a major role to play in promoting long-term storage quality with minimal diseases problems. Trials confirm that onion crops with high levels of calcium in the bulbs have reduced levels of black rot due to Aspergillus niger and also fewer neck rots such as Botrytis allii.

Boron often works synergistically with calcium and trials have shown an effect of boron on storage quality due to the micronutrient’s role in improving calcium accumulation in the bulb. While boron is quickly taken up from the
soil, it is relatively immobile in the plant, so foliar sprays are often more effective.

There is also a close relationship between calcium uptake and nitrogen uptake, reminding of the importance to apply both nutrients together at the same time as the N:Ca ratio will influence uptake and availability.

Calcium needs to be soluble to get into the plant

However, it’s not only the timing of calcium that needs to be right but also the source of calcium that is being applied. There is a misconception sometimes that liming materials will contain and provide enough calcium for the crop but many liming materials are calcium carbonate based. This means that they aren’t very water-soluble and consequently not freely available to the crops through the growing season.

For example Lime is calcium carbonate – it requires 66,000 litres of water to dissolve 1 kg of calcium carbonate; which means it would take a long time to become plant-available. Whereas YaraLiva Tropicote only requires 1 litre of water to dissolve 1 kg calcium nitrate, which means it has high calcium solubility.

Yara's recommendation is to apply 400-600 kg/ha YaraLiva Tropicote post-emergence at the bulb formation stage which will supply calcium together with nitrate nitrogen. Alternatively, to apply additional boron YaraLiva Nitrabor applied at 400-600 kg/ha will supply calcium and boron together with nitrate nitrogen

Check out our onion crop programme