Trials in South Africa show that phosphorus has a positive effect in fruit colouration. It does so by increasing the production of an enzyme involved in the production of anthocyanin, one of the main compounds in fruit that determines its red colour. Phosphorus source and timing are important. Foliar phosphate is very effective after flowering and at early ripening where there is a need to improve fruit colouration.
Improving Top Fruit Colouration
Colour of the skin is a very appealing apple and pear quality to consumers. Therefore, growers generally seek to improve fruit colouration. Crop nutrition can help to achieve the desired appearance.
Crop Nutrition and Top Fruit Colouration
Foliar application of a fertilizer containing phosphorus, calcium and magnesium, has also been shown to enhance red peel colour, and an increase in the concentration of flavonoids in ‘Fuji’ apples.
Nitrogen
Over-use or late applications of nitrogen reduces the red colouration of red apples. This can be advantageous in green apples, as it will improve greenness and minimize red colours.
Phosphorus
Paliyath et al. (2002) studied the effect of soil and foliar phosphorus supplementation on the post-harvest quality of apples (Malus domestica Borkh. cv. ‘McIntosh’ and cv. ‘Red Delicious’) and found that phosphorus fertilization increased the percentage of red skin on both varieties at harvest.
They have also found that fruit from sprayed sides of the trees subjected to foliar treatments with phosphorus and magnesium or phosphorus and calcium from blossom until a week before commercial harvest had increased red colour compared to those from the non-sprayed side.
Potassium
Potassium also increases anthocyanin content in apples, which improves the fruit colouration. However, supplies need to be in balance with other cations, particularly calcium, as preferential uptake of potassium over calcium can lead to quality problems such as bitter pit.
Zinc and Manganese
Zinc helps improve apple and pear fruit colour, while manganese helps improve background, green colour in apples.
Magnesium
Soil applied magnesium improves the colour of red fruit largely through the increased production of carbohydrates, which are the building block for red pigments.
Recommended Yara Fertilizers for Top Fruit
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YaraMila COMPLEX
12-4.8-14.9 + 8% S - Prilled NPK fertilizer which also contains magnesium and sulphur as well as micronutrients ideal for use on a wide range of arable and horticultural crops.
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YaraLiva TROPICOTE
15.5% N + 18.8% Ca - Granular calcium nitrate fertilizer for field application to a wide range of crops.
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YaraVita ZINTRAC 700
A fully formulated flowable liquid micronutrient fertilizer containing 700 g/l zinc for foliar application to prevent and treat zinc deficiency on a wide range of crops.
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YaraVita BORTRAC 150
A liquid micronutrient fertilizer containing 150 g/l boron for foliar application to provide additional boron or to treat boron deficiencies in a wide range of crops.
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YaraVita SENIPHOS
A liquid micronutrient fertilizer containing high concentrations of phosphate and calcium for foliar application to improve yield and quality in fruit and potatoes.
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YaraVita STOPIT
A liquid micronutrient fertilizer containing 160 g/l calcium for foliar application to control and reduce calcium related disorders in top fruit and other crops.
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YaraVita BUD BUILDER FL
A flowable liquid suspension fertilizer with nutrients and micronutrients including magnesium, zinc, nitrogen, boron and phosphate for foliar application to improve the flowering of top and soft fruit.