Potassium deficiency (K)
The overall need for K-fertilisation needs to be established in accordance with the specific crop and the yield level; for cabbage, the overall requirement is 250-300 kg K2O ha-1, to be divided into basal, starter and top dressings
A lack of potassium in vegetables will initially show as chlorotic tissue discolouration, beginning with the older leaves, and will eventually lead to necrosis of leaf tips and margins. In an advanced stage, chloroses and subsequent necroses will also appear between the leaf veins, with main veins remaining green for quite some time. Potassium deficiency will also increase the plants’ susceptibilty to drought, frost and plant pathogens. Additionally, this deficiency will seriously impair the transport, storage and processing qualities of nearly all important vegetable crops.
In cucumbers and tomatoes, potassium deficiency may stunt longitudinal growth as well as lateral shoot development. A lack of potassium in tomatoes will also result in irregular discolouration of the fruit, with green-brownish and brown-yellowish spots appearing around the stem. Carrots will show a pale root colour. A lack of potassium will cause melons to become more susceptible to fungi and bacterial diseases. It will also delay fruit maturity and impair taste. In peas and beans, potassium deficiency will cause chlorotic, respectively necrotic spots, rolling-in of leaves as well as internodal shortening. Potassium deficiency may also impair nitrogen fixation, so that legumes may also show symptoms of nitrogen deficiency.
All vegetables have high potassium requirements, often exceeding even their nitrogen requirements. It is therefore not possible to treat an acute lack of potassium with foliar applications. The focus should rather be on ensuring that a sufficient soil supply is available prior planting or sowing. Due to the chloride sensitivity of some vegetable crops, it is advisable to use a sulphate-based potassium fertiliser, such as Patentkali® or KALISOP®. Hinsichtlich der Höhe der K2O-Düngung muss je nach Kultur und Ertragsniveau unterschieden werden, bei Kohl beträgt diese 250-300 kg K2O ha-1, eingeteilt in Grund-, Start- und Kopfdüngung.