Potassium and Nitrogen Fertilization of Fruiting Vegetables

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Many fruiting vegetable crops are receiving additional nitrogen and potassium applications as sidedressings or as fertigation through drip irrigation systems at this time. Specific nitrogen and potassium recommendations can be found in the commercial vegetable production recommendations for Delaware which are online at http://ag.udel.edu/extension/vegprogram/publications.htm.

Balancing nitrogen and potassium properly is critical for high yields and good quality in fruiting vegetables. Growers understand the critical role of nitrogen for plant growth. Potassium is equally important for many vegetable crops such as tomatoes, cantaloupes, and watermelons which benefit from additional applications of potassium, even if soil potassium levels are high. High rates of nitrogen can be utilized by the plant and transformed into high yield only in the presence of high potassium levels.

Although potassium does not form part of the structure of vegetable plant, it is important for regulating sugar production, translocation of proteins and sugars, water balance, cell turgor, and stomatal activity. Potassium improves the quality of fruits by maintaining desirable sugar to acid ratio and improving the ripening of fruits.

The “take home” message is that nitrogen should be balanced with potassium during the cropping season with sidedressing or fertigation in fruiting vegetable crops. A 1:1 or 1:2 ratio of nitrogen to potassium should be used depending on the crop.