Fruit size in Citrus production has always been an important factor, but never more than in the current export environment. There has been a significant shift in the demand from small to medium-sized fruit to larger class 1 fruit, being sought after by buyers in overseas markets. This shift in demand for larger-sized fruit means as an industry we need to shift our focus from a production per hectare focus to Fruit size and fruit quality focus.

There are however many contributing factors affecting fruit size and Fruit quality.

Climatic conditions play an important role leading up to and during flowering and fruit set phases, while sufficient nutrient levels during cell division and cell enlargement also contribute to fruit development.

A tree with a healthy root system with adequate feeder roots will be able to utilize nutrients far more efficiently than a tree with a poor root system, for this reason taking care of root health is of paramount importance. Root health will impact the uptake of nutrients such as Potassium and Calcium which in turn is important in fruit size and fruit quality. Root health can be addressed by an increase in feeder root volume. Studies have shown that with the aid of mycorrhiza inoculants applied to the root system the uptake of elements such as Phosphorous can be improved while improving overall plant health. 

Potassium plays an important role in the cell enlargement phase and can be applied both to the soil as well as very effectively as a foliar spray on citrus-bearing trees. In the case of older orchards where feeder roots will be less and uptake may be reduced, foliar sprays can play a crucial role to ensure sufficient levels of elements such as potassium are available during cell enlargement. Average Nutrient withdrawal per ton of fruit produced must be considered when applying nutrients. Potassium applications can be applied during three development stages during the season, Pre Blossom, Cell division, and Cell enlargement phase.

Average accepted withdrawal of Potassium per ton of fruit per hectare

Oranges 2.3: kg/ha/ton, Mandarins 2.4: kg/ha/ton, Lemons: 2.0 kg/ha/ton

(Raath P.J, 2021)

Calcium is another element that plays a significant role in rind quality, and it is important to ensure Ca is available at cell division by starting with Calcium applications as early as mid-September to early October. 

Fruit at the end of the day is derived from flowers and the number of flowers is key, not only the volume of flowers but the quality of inflorescence, a “Green blossom” where leaves are present behind flowers is far more likely to bear fruit than a high volume of “white blossom”. In cases where the fruit set is excessive, fruit thinning techniques may be required, either by hand or by applying chemical thinning agents at the correct development stage. (Strict adherence to label instructions is critical to ensure the effective thinning of fruit)

Managing tree stresses with the correct use of Bio-stimulants leading up to flowering can also play a major role in the crop set.

Effective Irrigation is crucial especially during flowering throughout and cell enlargement phases where sufficient water is required to reduce drought stress. Soil pH will play an importantrole in the uptake potential of nutrients such as Potassium, which can be reduced in lower pH soils. It is advised to take note of soil pH before applying fertilizers to the soil as more is not always better in the case of N, P, and K. Excessive Nitrogen and Potassium levels can lead to thicker and coarser rinds in citrus.