Potassium deficiency

• Role in the plant: the potato needs a large amount of potassium (K), as this element is essential for metabolic functions such as the transfer of leaf sugars to the tubers and the conversion of the sugars into starch. It is also important for the osmotic potential of cells and related water balance. Potassium deficiencies adversely affect the yield, the size and the quality of the tubers. A lack of potassium also reduces the dry matter content of the tubers. Potassium deficiencies also lessen the plant’s resistance to biological stresses (diseases or pests) and to climatic conditions such as drought and cold.

• Symptoms of deficiency: this deficiency is manifested firstly on the older leaves because potassium is highly mobile inside the plants. Symptoms begin with discoloured then necrotic brown spots firstly at the leaf margins, then spreading across the leaf blade within the veins. Leaves become deep veined, deformed and with a dark-green colour and shiny and metallic aspect (“bronzing”) (photos 1 to 3).

The availability of potassium is essential to the quality of the tubers, particularly regarding their resistance to mechanical damage like internal black spot bruising.