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Potassium

The role of potassium is directly related to the quality and production. The increment of the potassium levels improves the plant performance.

The essential roles of potassium are found in the protein synthesis, the photosynthetic processes and the sugars transport from the leaves to the fruits. A good potassium supply will sustain, therefore, from the beginning the leaf function in the fruit growing. This will contribute to the positive potassium effect in the plant yield and in the higher soluble solids´ content (more sugar) in the fruit at harvest time. Approximately 60 to 66% of the potassium absorbed by the plant is found in the fruit (Winsor et al, 1958). The potassium action in the protein synthesis reinforces the conversion of the nitrate absorbed in proteins, contributing to better efficiency of the supplied nitrogen fertilizer. Potassium is a cation involved in the maintenance of the plant osmotic potential (cell turgidity). An implication of this is the stoma movement; when stomata are open allow the plants to exchange gas and water with the atmosphere. This permits the plants to maintain an adequate hydration under stress conditions such as salinity or water shortage. In fact, the tomato crop with a high content of potassium generally shows a greater efficiency in the water use, this means, that this consumes relatively less water than potassium deficit crops for producing the same biomass quantity. In addition, potassium is involved in the fruit maturity processes such as the synthesis of the licopene pigment, which is responsible of the tomato red color. Potassium promotes a high acid content, which is essential for the good fruit flavor.

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Potassium deficiency symptoms in the plants:

• Leaves and stems.
• Young plants present dark green leaves, short stems and short internodes.
• Necrosis in the old leaves borders. Up side curling of the leaves.
• Interveinal necrotic spots in the old leaves.
• Weight reduction of the plant and foliar area.
• Fruit and reserve organs.
• Fruit fall during maturity.
• Spots during maturity.

 

• Insipid fruits (lack of flavor), low acidity.
• Appearance of yellow and green areas on the red surface of tomato fruits.
• Non uniform maturity.
• Glassy spots.
• Reduction of the fruit number per cluster.
• Reduction of the fruit set.
• Reduction of the average fruit weight.
• Reserve organs (example: potato tubers) with low dry matter content.

 

Deficiency is commonly noted by curling-up of the leaf edges (margins). This response occurs in most fruit tree types. Leaf margin chlorosis followed by necrosis (death) may subsequently occur. Symptoms generally manifest themselves first in mature leaves. New shoot extension may be reduced in affected trees. Fully-grown fruits may be smaller. Such fruits may also exhibit reduced colouration at maturation. Shelf-life may additionally be reduced.

Images from the book Symptons of Nutrient Imbalances in fruit trees, Bruno Razeto.


Early leaf symptoms of K-deficiency in 'Red Delicious' apple.

'Granny Smith' apple leaves showing advanced symptoms of K-deficiency.

Leaf symptoms of K-deficiency in 'Gala' apple (photo courtesy Gabino Reginato).

Leaf symptoms of K-deficiency in peach.

Leaf symptoms of K-deficiency in nectarine (photo courtesy Rafael Ruiz).

Leaf K-deficiency symptoms in cherry.

Leaf K-deficiency symptoms in 'D'Agen' prune.

Leaf K-deficiency symptoms in 'Thompson Seedless' ('Sultana') grape.

Leaf symptoms of K-deficiency in 'Chardonnay' grape.

Leaf K-deficiency symptoms in 'Thompson Seedless' grape.

Kiwifruit leaves showing initial signs of K-deficiency.

Leaf symptoms of K-deficiency in kiwifruit at the time of fruit set.

Fruits and leaves of 'Hass' avocado. Left - From a non-nutrient deficiency tree. Right - From a tree deficient in both K and Zn.

Leaf symptoms of K-deficiency in olive.

K-deficient olive leaves (increasing severity - left to right).

K-deficiency in a banana leaf (photo courtesy CORBANA and INPOFOS).

Leaf symptoms of K-deficiency in banana (photo courtesy CORBANA and INPOFOS).

Leaf symptoms of severe K-deficiency in banana.

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