Calcium is a vital nutrient for potatoes and most aspects of tuber quality can be improved by having a sufficient supply of calcium during growth. It is required in the crop for the maintenance of cell walls, healthy leaf and tuber development.
Calcium prevents a wide range of tuber quality problems
Calcium deficiency is widely known as internal rust spot - a physiological internal defect in which small small brown spots, due to cell death, appear in the tuber. This is directly related to a lack of calcium within the cell walls, meaning that they aren't strong enough and when cell expansion takes place they collapse and necrosis occurs.
Once calcium is incorporated into cell walls it can't be redistributed therefore it is important to have a sufficient supply as new cells develop. As mentioned already, calcium is integral to cell walls and give the cells, particularly the skin, strength. Therefore, a sufficient supply will help ensure the skin has a good finish as well as helping against physical damage which can occur during harvesting and handling.
Finally it can also help prevent bacterial diseases affecting the tubers. Strong skins mean less damage; which helps decrease bacterial infection through the broken surface. For potato nutrition 60-70% of the recommended nitrogen should be applied before tuber initiation and the remainder, top dressed in combination with calcium. YaraLiva Tropicote (15.5%N + 19%Ca) should be applied at tuber initiation, 200-300 kg/ha to supply over 40 kg/ha of readily available calcium as Ca2+
Potatoes need a soluble source of calcium
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 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 potato crop 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 and YaraLiva Nitrabor only require 1 litre of water to dissolve 1 kg of product, which means it has high calcium solubility.
As previously mentioned the timing of application to the potato crop is essential to flush the developing tuber with soluble calcium therefore the optimum application period is at tuber initiation.