Potash fertilizers for potatoes

In a ton of quality potatoes – an average of 4-4,3 kg of potassium. A certain amount of this trace element also contains withered tops, which are usually destroyed. In order to harvest a good harvest next season, it is necessary to restore soil fertility by adding potash fertilizers for potatoes to it.

Potassium ions are found in the cytoplasm of potato tops and tubers. Scientists have found that potassium:

  • normalizes the water balance of the potato bush;
  • increases plant resistance to drought and frost;
  • stimulates the process of photosynthesis, improves the absorption of nitrogen;
  • promotes the accumulation of starch in tubers;
  • accelerates the growth of the root system and strengthens it;
  • enhances the immunity of potatoes to rot, rust, powdery mildew;
  • improves the keeping quality of ripe tubers.

The faster a potato grows, the more potassium it needs. Therefore, for feeding the very early varieties, the usual dose of potash fertilizers is increased by 20–30%. Young sprouts especially need such feeding.

If there is not enough potassium, then the tops of the shoots pull it away from the lower, older leaves. Potassium starvation begins: a brown border appears on the lower leaves – marginal burns, leaf plates are covered with rust-colored spots. With potassium starvation, undecomposed ammonia accumulates in the tissues, protein synthesis in cells slows down, the stems become frail and susceptible to disease.

But an excess of potassium in the soil is also harmful: the leaves become lighter, thinner, chlorosis spots appear between the veins. On soils overly fertilized with potassium, the assimilation of other microelements by plants is hampered: nitrogen, phosphorus, magnesium, calcium. This impairs the taste of the tubers, reduces the keeping quality, and sometimes leads to rotting of the lentils.

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Organic sources of potassium

In organic fertilizers, there is enough potassium to make up for its deficiency in the soil:

  • straw contains up to 0,8% potassium. If used as a mulch, it quickly decomposes, releasing all the nutrients into the soil;
  • there is a lot of potassium in rotted manure from cattle that feed on fresh grass, hay and silage. In addition, straw is laid for animals as bedding, and then, together with waste, they are piled up in heaps;
  • in fresh chicken manure – up to 0,8% potassium;
  • effective potash-phosphorus fertilizer – ash. However, only ash from burnt wood and plant residues is suitable for enriching the soil with potassium. For example, in ash from birch and pine firewood – up to 12% potassium, in ash from sunflower tops – up to 30%. There is no potassium in peat and coal ash.

Manure is applied to the soil both in the fall, after harvest, and in the spring before planting potatoes. The norm, depending on the fertility of the soil, is 100–300 kg. If there is little manure, they put it in a glass or half-liter jar in each hole when planting potatoes. Instead of manure, it is allowed to throw a handful of dried chicken manure into the holes. The only limitation: if the soil is infected with a nematode, it is not recommended to use manure and droppings, you will have to feed the plants with mineral fertilizers.

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Ash can be added to the soil when digging or plowing a plot (consumption – 10 kg per hundred square meters). Fertilizer not only enriches the soil with potassium and phosphorus, but also alkalizes it. But in this way, ash is used in the same area no more often than once every 3 years. But it is allowed every year, when planting, to throw handfuls of ash into the holes. It is important to remember that excess ash will spread scab.

manure and ash are the best organic potash fertilizers for potatoes

Mineral potash fertilizers

Mineral potash fertilizers are better absorbed by potatoes if they are applied in several steps, for example, in the fall, during fall plowing, or in the spring, directly into the holes, then with additional fertilizing. The fertilizer dose must be calculated so that the amount of potassium oxide is 2–2,5 kg per hundred square meters.

It should be borne in mind that the lighter the soil, the more it needs potash fertilizers. For loam, the dose should be less than for light sandy loam soils. Peat soils are especially affected by the lack of potassium. Almost all potash fertilizers (except for cement dust) acidify the soil, therefore, dolomite flour is added to the soil together with them.

Chlorine-containing potash fertilizers

The most common and affordable are potash fertilizers with chlorine:

  • potassium chloride, potassium content in terms of oxide (K2O) – up to 63%);
  • 30% potassium salt;
  • 40% potassium salt.
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As far as potassium is useful for potatoes, chlorine, which slows down the development of plants, is harmful. Therefore, all chlorine-containing fertilizers are applied to the soil in autumn, so that chlorine is washed out by spring waters, and by the time the potatoes are planted, its concentration is minimal.

Potassium dissolves in most soils, but is not washed out. An exception is sandy soil. For such soils, chlorine-containing potash fertilizers cannot be used, since potassium is not stored until spring.

Potassium chloride

These are small crystals of pink or light gray color. The light gray powder is very hygroscopic and, when stored in a damp warehouse, quickly cakes and loses its beneficial properties. Pink crystals are more resistant to moisture, but they are also best stored in a completely dry room.

The rate of application of potassium chloride is 1,5–2 kg per hundred square meters. It goes well with urea or superphosphate (urea and superphosphate cannot be mixed).

Potassium salts

30% potassium salt is a mixture of potassium chloride with the mineral kainite, 40% – with sylvinite. 40% salt for fertilizing potatoes is used extremely rarely, only if there are no other fertilizers: it contains more chlorine than pure potassium chloride.

In addition to potassium and chlorine, 30% salt contains magnesium. Fertilizer is applied at the rate of 2,5-3,5 kg per hundred square meters. This type of salt is used to fertilize light soils: sandy loam and peat.

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Chlorine-Free Potash Fertilizers

Potash fertilizers without chlorine are more expensive than chlorine-containing ones, but they can be used in spring and summer for top dressing.

Potassium sulphate (potassium sulphate)

Potassium sulfate contains 45-50% potassium oxide, 18% sulfur, 3% magnesium, some calcium. The fertilizer is suitable for all soils. It is brought in in the spring, for digging (2,5-3,5 kg per hundred square meters), or put in the holes when planting. During budding, fertilizing is carried out: per linear meter of the garden – 3 tablespoons of ash are mixed with 1 teaspoon of potassium sulfate. The mixture is shallowly embedded in the soil between the rows.

photo of potassium sulfatePotassium sulfate – universal fertilizer

Potassium nitrate

The fertilizer contains 13% nitrogen and 38% potassium. Potassium is poorly absorbed by plants in alkaline soil, nitrogen in acidic soil. Therefore, potassium nitrate is used only on neutral soils. Application rates – 2-3 kg per one hundred square meters.


The fertilizer contains 10% magnesium, up to 28% potassium, up to 17% sulfur. Dosage: 3-4 kg per 1 hundred square meters during the spring digging of the site. During budding, foliar feeding is useful: 20–25 g of potassium magnesium per 10 liters of water.

Cement dust

Cement dust contains 10–35% potassium, as well as various sulfates and carbonates. Fertilizer is applied in spring or autumn, at the rate of 4–5 kg per one hundred square meters. It alkalizes the soil.

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Complex fertilizers

Potassium is part of the triad (nitrogen, phosphorus, potassium), which is part of most complex fertilizers. The most popular complex fertilizers with potassium:

  • nitroammofoska – introduced in the fall, for plowing, the rate is up to 3 kg per hundred square meters. Fertilizer goes well with superphosphate or urea. If you need to increase the dosage of potassium, add 1–2 kg of potassium sulfate. Summer top dressing – 10-15 g of nitroammofoska per 10 liters of water;
  • nitrophoska – applied in the spring, dosage – 2-3 kg per hundred square meters, goes well with potassium sulfate, superphosphate and ammonium nitrate. Summer root dressing – 7-10 g of nitrophoska under each bush (at a distance of 5-6 cm from the stem).

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Anna Evans


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