Potatoes are an extremely important crop in the agricultural production of the Udmurt Republic and show high responsiveness to mineral fertilizers [1, 4]. The application of biological fertilizers in potato cultivation technology is of great practical importance since it opens up the possibility of reducing the doses of applied mineral fertilizers, which in difficult economic conditions and when prices constantly growing can reduce the cost of production and increase the profitability of production. According to Yu. N. Pleskachev and O. N. Skvortsova, the application of Azotovit and Phosphatovit fertilizers increased the photosynthetic activity of potato plants by 25–41 % [2]. In the studies of L. S. Fedotova, A. V. Kravchenko, due to the application of these fertilizers, an increase in potato yield of 4.9 t/ha to the control was obtained [3].

In the conditions of the Udmurt Republic, such studies are carried out for the first time. The results obtained can be applied to obtain environmentally friendly products in case of transfer to organic farming systems.

The purpose of the research is to study the effect of biological fertilizers Azotovit and Phosphatovit on the yield and quality of potato tubers.

The field experiment scheme included the following options:

1. Control (without fertilizers).

2. Azotovit.

3. Phosphatovite.

4. Azotovit + Phosphatovite.

Biological fertilizers were used for the pre-planting treatment of tubers and when watering plants in the budding phase for inter-row cultivation. Replicated four times. Potato variety is Red Scarlet.

The field experiment was carried out on the land of the Udmurt Federal Research Centre of the Ural Branch of the Udmurt Agricultural Research Institute on sod-medium podzolic medium loamy soil (the agrochemical characteristics are presented in the table).

The soil is close to neutral, with a very high content of mobile phosphorus and medium content of mobile potassium. The growing season of 2019 differed from the average long-term data in terms of agrometeorological conditions. Thus, during the entire growing season of plants, the average monthly temperature was significantly lower than the norm — by 0.8–3.3 °С. Especially low temperatures were recorded in May, July and August. At the same time, during these months, precipitation significantly exceeded the average annual norms. In August, precipitation was 2.5 times higher than the average annual rate, which contributed to the development of late blight. However, the studied variants had no effect on the phytopathological state of plants.