Role of Potassium in Citrus Production

Alongside nitrogen, potassium is one of the most important nutrients for citrus production. It is needed for enzyme activation, cell division, photosynthesis, photosynthate transport and osmoregulation.

Potassium on yield and quality

Potassium has a big impact on leaf size, and tree health and vigor. It is also largely responsible for many important internal and external fruit quality characteristics including fruit size and rind thickness and color.

Trials with sweet oranges confirm the positive effect of K on yield, fruit size and quality. The improved yield is due, in part to improved fruit set but more commonly as a result of an increased fruit size.

Potassium and foliar sprays

In some cases, soil K-application can be ineffective, e.g. on clay soils with high K-fixation capacity and where high levels of Ca, Mg, Na in the soil or irrigation water compete for K-uptake. In this situation foliar sprays should be used to supplement basal applications of K.

Potassium and fruit number

The improved yield is due, in part to improved fruit set, as studies in California with Valecia oranges show.

Potassium effect on diseases

Some fruit disorders are likely to occur under low potassium conditions or high leaf N:K ratios, like plugging and creasing. These result in less marketable fruit.

Potassium and juice content

Potassium nutrition positively influences fruit size, rind thickness, and fruit color. Trials also confirm a positive effect on juice content in lemons and lime and also on sweet oranges.

Potassium on TSS and acidity

Potassium increases the content of organic acids in fruit juice. This increase in acidity may also reduce the TSS/Acid ratio. Therefore, the correct K-regime is important and will differ for the production of sweet oranges, mandarins or acid lemons.

General guidelines for Potassium application

Citrus fruit takes up more potassium than any other nutrient. Application rates can be calculated based upon leaf or soil analysis – the latter being most commonly used. Rates of 0.8 - 1.4 lb K₂O/tree are generally applied in 3 - 5 splits during the growing season. The main potassium uptake occurs during late fruit growth and application rates should be increased to meet this need.

Potassium at citrus growth stages
Flowering	Establish good early growth
Fruit Set	Continued strong growth
Fruit Enlargement and Maturation	Maximize fruit fill and fruit size, productivity, skin quality and vitamin C content and reduce granulation and fruit splitting
Post Harvest	Maintain long-term fruit productivity