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 in tomatoes is also required for pigment synthesis, notably lycopene.
Potassium and yield
High levels of potassium provide high yields in tomato crops, as trial in UK shows. Tomatoes have a relatively high potassium requirement. There is usually 5.2 to 7.2lb of K taken into the plant for every tonne of tomato harvested.
Potassium and fruit ripening
Potassium has an important role in ensuring top quality fruit by determining the level of sugars, as well as ripening and storage characteristics. An inadequate supply of potassium in tomatoes can lead to uneven ripening (UK trials).
K and color defects - white tissue
An inadequate level of potassium in tomatoes can also lead to blotchy ripening and color defects such as internal white tissues, as shown in studies in USA.
K and color defects - yellow shoulder
Studies in US also show higher incidence of yellow shoulder as a result of lower than adequate levels of potassium.
Potassium and juice acidity
Higher levels of potassium in the tomato plant increases the acidity of the fruit and the resultant tomato juice, as can be seen in UK trials.
N:K balance and rots
Maintaining high levels of potassium can help alleviate problems of rots caused by high nitrogen levels, as studies in US show.
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 in tomatoes 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 at tomato growth stages
||Promotes strong early growth
||Maximizes concentrations in leaf tissue prior to flowering
|Flowering - fruit set
||Maintains plant growth and maximize flower numbers
|Fruit ripening - maturity
||Maximizes high potassium levels in the fruit and minimize disorders