Top tips for improving apple skin colour
5th May 2023
With apple skin colour being a highly appealing quality to consumers, growers will generally seek to improve fruit colouration. Yara offers guidance on how crop nutrition can help to achieve the desired appearance.
Over-use or late applications of nitrogen reduces the red colouration of red apples, but can be an advantage in green apples – improving greenness and minimising red colours, Yara explains.
Phosphorous has also been shown to have a positive effect on colouration in trials in South Africa. It works by increasing the production of an enzyme involved in the production of anthocyanin, which is one of the main compounds that determines a fruit’s red colouration.
Foliar application of a fertiliser containing phosphorus, calcium and magnesium, has been shown to enhance red peel colour – and an increase in the concentration of flavonoids in Fuji apples.
The phosphorous source and application timings are important however – application of foliar phosphate is very effective after flowering and at early ripening where there is a need to improve fruit colouration, according to Yara.
Previous studies have also shown that phosphorous fertilisation increased the percentage of red skin on two varieties at harvest – Malus domestica Borkh. cv. ‘McIntosh’ and cv. ‘Red Delicious’.
Researchers also found increased red colour in fruit on the sprayed sides of trees given foliar treatments containing phosphorus and magnesium or phosphorus and calcium – from blossom until a week before commercial harvest – compared to the non-sprayed side.
Potassium also increases anthocyanin content in apples but supplies must be balanced with other cations, especially calcium, Yara warns, as preferential uptake of potassium over calcium can cause issues with quality, including bitter pit.
Meanwhile, zinc helps to improve apple colour and manganese improves background, green colour in apples.
Finally, soil applied magnesium improves the colour of red fruit, mainly as a result of the increased production of carbohydrates, which offer a building block for red pigments.
For further tips for apple growers, and information on recommended fertilisers, visit: https://www.yara.co.uk/crop-nutrition/apples/