Optimum soil acidity for growing potatoes

The optimum soil acidity for potatoes is 5,2–5,7 pH. If the acidity is too high (pH <4,5), then the soil, as a rule, contains an excess amount of aluminum, due to which the plants poorly absorb potassium, magnesium, phosphorus and calcium. The roots cannot properly absorb water, grow slowly, thicken, branch poorly.

At low acidity (pH> 7), beneficial trace elements form insoluble compounds. Potatoes growing on alkaline soils poorly absorb magnesium, phosphorus, boron, zinc. In addition, potatoes need a lot of nitrogen. And the bacteria that enrich the soil with it develop most rapidly in a weakly acidic environment.

How to determine the acidity of the soil

To measure soil acidity in large farms, it is better to purchase a special device or periodically take soil samples for analysis to a laboratory. It is not profitable for owners of small areas to buy a device. It is easier to determine the pH using folk methods or using litmus paper.

An example of a device for determining the acidity of the soil

PH values ​​depending on the type of soil:

  • moderately acidic soil – 4,0–4,5;
  • medium acid – 4,6–5;
  • slightly acidic – 5,1-6,0;
  • neutral – 6,1-7,0;
  • slightly alkaline – 7,1–8,0;
  • alkaline – more than 8,0.

Folk methods for determining acidity

  1. If among the weeds there are a lot of horsetail and woodlice – the soil is acidic, coltsfoot, clover and nettles like neutral soils, field bindweed – alkaline.
  2. Take 2 bowls, pour a handful of earth into each. In one container, pour a little vinegar, sprinkle the earth in the second with soda. If, when the ground comes into contact with vinegar, bubbles appear and a hiss is heard, the soil is alkaline. If the same happens upon contact with soda, the soil is acidic. If there are no visible signs of reaction, the soil is neutral.
  3. In a bottle, mix 2 tbsp. spoons of earth with 5 tbsp. tablespoons of water and a teaspoon of crushed chalk. Put a rubber fingertip on the neck. Shake the bottle several times and leave for 20-30 minutes. If the fingertip begins to fill with escaping gases, it means that the soil is acidic.
  4. Brew several (4–5) black currant leaves in a glass of boiling water. When the broth has cooled, throw a pinch of earth into it. If the water remains green, the soil is neutral, if it turns pink, the soil is acidic, the alkaline soil will color the water blue.
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Determination of soil acidity by litmus test

A hole 15–20 cm deep is dug on the plot. A pinch of earth is scraped off the walls (at least in 4 places). Soil samples (about 80–100 g in total) are moistened with boiled or distilled water and mixed thoroughly.

Sprinkle a strip of litmus paper with damp earth and press firmly. After a few minutes, the color of the strip will change, and it can be compared with the scale that is sold with the paper.

photo litmus testLitmus test

Soil deacidification

If the soil is too acidic, it is recommended to add slaked lime (fluff), ground chalk, cement dust, dolomite flour to it every few years. Ash, bone meal and fish meal also help. The frequency of application is once every 4–6 years, for weakly acidic soils – once every 10 years. The dosage depends on the pH value. In strongly acidic soils, add up to 4 glasses of lime per 1 m², for weakly acidic – 1 glass is enough.

If the soil is slightly acidic, it is enough to throw a handful of ash, bone or fish meal into each hole when planting potatoes. To gently deoxidize the soil, in the fall, the site is sown with green manure: rye, phacelia, oats, legumes.

Soil acidification

Natural means for acidifying alkaline soil – manure, compost, sawdust of coniferous wood and needles (as mulch). But organics are best used on loose soils.

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If the alkaline soil is heavy, clayey, mineral fertilizers are used to acidify it, primarily nitrogen-containing fertilizers (urea, ammonium nitrate). However, mineral fertilizers with potassium hardly increase the acidity of the soil: potassium has alkalizing properties.

If potash mineral fertilizer needs to be added to alkaline soil, potassium chloride is preferred, since chlorine is an effective acidifier. But it slows down the growth of potatoes, so fertilization is applied only in the fall.

Sometimes there is advice for acidifying the soil to spill it with water and vinegar (100 g of 9% vinegar per 10 liters of water). But this method is only good for indoor plants, since vinegar is extremely harmful to the soil microflora. After watering with water and vinegar, most of the beneficial soil bacteria die.

Fertilizers with sulfur effectively acidify soil – colloidal sulfur and ammonium sulfate. Sulfur dissolves very slowly in water, so the acidity rises gradually, without causing discomfort to the plants.

Colloidal sulfur is a fungicide that helps with scab and powdery mildew. Usually, the fertilizer is used as part of foliar dressing (about 300 g per hundred square meters). But you can add sulfur in the fall, at the rate of 1–1,5 kg per hundred square meters.

Ammonium sulfate is applied at the rate of 3-4 kg per hundred square meters. Fertilizer significantly acidifies the soil. To reduce its effect, ammonium sulfate is even mixed with chalk or fluff: for neutral soils – in equal parts, for slightly alkaline – add no more than 10-25% of chalk to the mixture.

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Anna Evans


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