Role of Potassium in Tomato Production

Potassium maintains the ionic balance and water status within the plant. It is involved in the production & transport of sugars in the plant; enzyme activation; and synthesis of proteins. Potassium is also required for pigment synthesis, notably lycopene.

Potassium effect at growth stages

Stage Potassium effect
Establishment Promote strong early growth
Vegetative Growth Maximize concentrations in leaf tissue prior to flowering
Flowering - Fruit Set Maintain plant growth and maximize flower numbers
Fruit Ripening - Maturity Maximize high potassium levels in the fruit and minimize disorders
See more on Tomato Growth Stages.

General guidelines for Potassium application

Tomatoes have a relatively high potassium requirement compared to nitrogen with over 267 lb/ac of potassium typically being utilized. Potassium is needed throughout the season and is a major component of the fruit at around 250mg K per 100g of fruit. It is essencial to maintain a good balance of potassium with magnesium and calcium. Too much potassium restricts the uptake of these other cations. Use of high levels of potassium is particularly important under saline conditions to maintain plant growth. Excess sodium reduces the uptake and transfer of potassium through the plant and thus potassium levels need to be increased in order to maintain plant growth.

Potassium deficiencies in Tomato

The leaves become dark green and yellowish to white necrotic dots develop near the leaf margins of the older leaves. These merge into brown necrotic areas around the leaf margins. Glasshouse grown tomatoes will often express K deficiency as ‘blotchy’ ripening. The fruit also lacks firmness and has low brix levels.

See more about potassium and other nutrients deficiencies in tomatoes on Tomato Crop Nutrition.