Managing Citrus Fruit Acidity
During the ripening process fruit acids are degraded, the sugar content increases and the sugar/acid ratio reaches a higher value.
A high level of acidity - common in under-ripe fruit - makes the fruit taste sour. Conversely, over-ripe fruits have very low levels of fruit acid and therefore lack characteristic flavor.
For lemons, a higher level of acidity is particularly important. Lemon varieties have between 5-7% (mostly citric acid), compared with around 1% in oranges.
Crop Nutrition and Citrus Fruit Acidity
Nitrogen and potassium increase fruit acidity, whereas calcium and copper will reduce acidity. Other nutrients have little effect.
Nitrogen
In trials, increasing the nitrogen rate to 364Kg/ha significantly improved the TSS/acid ratio of the fruit.
Potassium
Potassium increases the content of organic acids in fruit juice, reducing the TSS/Acid ratio. Thus, the correct potassium regime is important and will differ for the production of sweet oranges, mandarins, or acid lemons.
Copper
While copper deficiencies are rare, trials in India indicate that copper reduces acidity and increases the TSS/Acid ratio in mandarins. Excessive use of copper may delay fruit ripening.
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