Keeping K in Mind

Potassium management in potatoes

Published online: Jan 11, 2018 Articles, Fertilizer, New Products
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This article appears in the January 2018 issue of Potato Grower.

Potatoes use more potassium than any other nutrient, including nitrogen. Potassium is required for nutrient movement in the potato plant. It is essential for the makeup of over 40 different enzymes and is involved in more than 60 different enzyme systems in plants. Potassium is also important in the formation of sugars and starches in plants. All crops that produce a large amount of carbohydrates (sugars) such as cotton, almonds, alfalfa, grapes, cherries, peaches and especially potatoes, require large amounts of potassium. Specifically in potatoes, potassium influences tuber size, specific gravity, susceptibility to blackspot bruise, after-cooking darkening, reducing sugar content, fry color and storage quality.

Potassium is crucial in quality potato formation, as it promotes synthesis of photosynthates and their transport to the tubers. This enhances their conversion into starch, protein and vitamins. A deficiency of potassium affects many metabolic processes, like the rate of photosynthesis, the rate of translocation and enzyme systems. At the same time, the rate of dark respiration is increased. The result is a reduction in plant growth and in crop quality. Potassium influences on quality can also be indirect as a result of its positive interaction with other nutrients (especially with nitrogen).

Potassium is also used by plants to regulate the process of opening and closing the stomatal openings of their leaves. That process influences water use efficiency and carbon dioxide use in the plant. Potassium’s influence on cell turgor pressure and water relations in the plant helps the plants resist the effects of drought and temperature extremes, and aids resistance to many plant diseases

Depending on soil type, 90 to 98 percent of total soil potassium is unavailable. Feldspars and micas are clays that contain large amounts of potassium, but plants cannot use the nutrient if it is trapped between the layers of those clays. In persistently dry soils, potassium remains unavailable, as there is no water film surrounding the soil particles. Over time, these minerals break down, and the potassium is released. However, this process is too slow to provide crops the amount of potassium needed for optimal yield.

Typically only 1 to 2 percent of conventional potassium fertilizer applied to the soil is available at one time.

Plants lacking in potassium often display various signs of deficiencies, the most common being discoloration of older leaves on the plant as compared to younger leaves on the plant. The stem on affected tissue usually appears weak and is slender in size compared to healthy tissue. Other deficiency signs include inward curling of leaves, discolored leaf tips and marginal scorching. Another common sign of potassium stress is abnormally short internode length. A crop deficient in potassium may also display signs of various crop diseases.

As an essential major nutrient for crop production, potassium needs to be available to the plant at all stages of growth. Most potassium found in soils is unavailable to the plant; therefore, the nutrient may need to be supplied to the crop via fertilizer.

The need for potassium can and should be determined from soil and plant tissue analysis. Management recommendations for potassium in potato crops vary by region and specific soil conditions. It is often beneficial to split applications of potassium to match the optimal times of plant uptake in order to increase yield potential and quality. Proper potassium management can increase disease and pest resistance. In addition, this management practice can improve soil quality for sustainability, resulting in an overall increase in productivity.

Growers can provide the potassium their potato crop needs, when it needs it, by using efficient potassium nutrient products, such as Kalibrate and Sure-K from AgroLiquid, which provide available potassium to the plant at the right times in the growth cycle.

Kalibrate applied at planting time or side-dress is taken up from the soil along the length of young roots, particularly by root hairs. Potassium is transported in all directions between plant organs in response to metabolic demand. Kalibrate also contains 6 percent sulfur, another essential nutrient for potatoes.

Sure-K as a foliar application or fertigation enables the flexibility to provide available potassium, which is actively taken up by plant tissues. Once in the plant, Sure-K is rapidly transported and redistributed to areas of greatest metabolic demand. Sure-K can also be mixed with crop protection products, reducing the number of passes on the field.