Managing Citrus Total Soluble Solids (TSS)

The TSS content of the fruit is usually obtained from assessing the degrees Brix of the fruit. The TSS or sugar content measures and includes the carbohydrates, organic acids, proteins, fats and minerals of the fruit. It represents from 10-20% of the fruit's fresh weight and increases as fruit matures to produce a less acidic, sweeter fruit. It is important that the grower aims to produce an acceptable balance of TSS and fruit acidity (see TSS/Acid ratio).

Crop Nutrition and Citrus TSS

Potassium and nitrogen have a relatively minor effect on TSS. However, boron, iron, manganese and zinc all increase TSS. Molybdenum, on the other hand, will induce a reduction in TSS.


Boron increases the levels of sugars in the fruit. In these trials - particularly on sweet orange - there was almost a 50% increase in TSS from use of a 0.6% application.



Use of iron effectively increases the level of sugars in the fruit. Trials show increases where iron is deficient across Pineapple oranges, Washington navels, and Balady mandarins.


Manganese and zinc

Manganese - often in association with zinc - increases TSS contents of the fruit. It can also help improve the ascorbic acid content of the fruit. As a result, manganese has little influence on the TSS/Acid ratio and this combination of improved sugars and acidity content produces more desirable fruit for the consumer.