Deficiency or phytotoxicity of mineral elements

Kind of organism : Disorders and damages

Detection method : Visual

All diseases & pests

Fertilization management

The search of an optimal productivity and quality of patatoes involves, among other things, a good nutritional management of plants.

Deficiencies in macronutrients, which are required in large quantities or in micronutrients can reduce the growth of the vegetative system (haulm and underground organs) and the length of the growing cycle, and hence can reduce tuber growth and crop productivity. Some deficiencies (e.g. potassium) increase tuber susceptibility to damage such as internal blackspot.

Conversely, excessive application of fertilisers can also upset the nutritional balance and reduce tuber productivity.


Good nutritional management is required for the quality and the productivity of the potato crop and it must be adapted to the crop’s characteristics. These include the soil type, the type of production (seed, table or processed potatoes) and the expected yield.

The quality of fertilizer distribution in addition of the soil preparation and water management are important for the nutrient availability to the plants. This is particularly true for nutrients which are not very mobile in the soil. These factors are often predominant as severe direct nutrient deficiencies are quite rare in potato production.

Nutritional management of potato crops includes an adequate supply of fertilizers with macro and micronutrients, according to the nutrients availability in the soil, the soil type and the crop requirement. It is also related to a good soil structure, favourable to an efficient root system, to absorbable forms for optimal nutrient uptake and to chemical balance between the different nutrients. Acid or basic soils are more susceptible to nutrient deficiences.


The availability of mineral elements may cause symptoms on potato plants that are associated with either a deficiency or an excess (phytotoxicity) of certain nutrients.

Symptoms of deficiency are observed chiefly in filtering or sandy soils, which are prone to severe leaching, or in certain countries where crops are grown in pure sand and are fertigated.

The deficiency may be due to an insufficient supply of certain nutrients or because their availability is reduced by another factor (pH, chemical balance between elements, etc.).

The symptoms described in this chapter are given as a guideline and the confirmation of a deficiency or of an excess of nutrients usually requires further plant and/or soil analysis in a laboratory.

Nitrogen deficiency or toxicity

Phosphorus deficiency

Good phosphate nutrition is beneficial for the formation of thick and resistant skin on tubers as well as for starch quality (viscosity).

Potassium deficiency

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

Eléments secondaires et microéléments (micronutriments)

The main secondary elements or micronutrients include magnesium, calcium, iron, manganese, boron and sulphur. Although they are needed by the plants in much lower amounts than macronutrients, adequate supplies of these nutrients to the plants are required for quality crop production.

The availability of these nutrients in the soil depends on the pedoclimatic environment. For example, zinc is a not very mobile element and is concentrated in the soil’s organic matter close to the surface of the soil. Therefore, cool and humid weather reduces the availability of zinc and may cause deficiency.

The availability of micronutrients usually diminishes with a soil pH of over 7. Consequently, soils with a high pH level are more likely to suffer from a deficiency. Similarly, sandy soils are more likely to suffer from a deficiency than clay soils.

The main symptoms of deficiency in micro elements nutrients are described on the page opposite.

The use of micronutritional elements must be justified (by soil and plant tissue analysis or from meticulous visual examination of the plants) in order to avoid any extra or unnecessary cost, as well as limiting the possible toxic effects to the environment and adverse negative interactions with other elements. The choice of an effective method of application depends on the deficient micronutrient, local soil conditions and the phenological stage at which the deficiency is detected.

Boron deficiency

Toxicity: strong leaf deformation, similar to that caused by hormones, may be induced by severe boron toxicity.

Calcium deficiency

Iron deficiency

Magnesium deficiency

Manganese deficiency

Toxicity: excess of manganese, particularly in acidic soils, may cause the formation of pale green leaves and numerous necrotic spots on stems, petioles and can cover the entire leaf surface.

Sulphur deficiency

Salinity phytotoxicity

The potato is a highly salt susceptible crop and damage due to excessive salinity occurs in certain warm regions, where crops are irrigated with saline water and/or where high temperatures cause major evaporation and lead to the presence of high quantities of mineral salts on the soil’s surface. Excessive salinity, i.e. concentration of salts, in irrigation water or in the soil may be phytotoxic for some crops such as the potato and so reduces the plant’s growth and yield (photo 26).