Modern agriculture strongly relies on mineral fertilizers that make it possible to increase the arable land productivity fast and cost-effective. The traditional use of fixed doses of mineral fertilizers under a free market economy is ineffective, as it does not reflect the character of soil fertility. The article explores the causes of hereditary links between nutrient removal and harvest elements. To plan the activities of agricultural enterprises it is required to use mathematical models for calculating the doses of mineral fertilizers. As initial data, the authors used the results of long-term experiments conducted at the Department of Soil Science and Agrochemistry of the Northern Trans-Ural State Agricultural University. The scheme of the experiment included the application of mineral fertilizers to the planned yield in spring wheat 3.0; 4.0; 5.0 and 6.0 t/ha. Mineral fertilizers were applied taking into account soil fertility that was estimated annually. In experiments, the content of nutrients in straw and grain was determined annually; removals were calculated. The data obtained shaped the basis for the development of a mathematical model for spring wheat feeding. There was revealed: a high correlation between nutrients and biogenic removal; the ratio of grain to straw; yield of the byproducts at harvest. Regression equations can be used to calculate the doses of mineral fertilizers for the planned yield in grain crops. A high approximation coefficient confirms the reliability of the derived equations. A regression mathematical model of correlated indicators is presented. The indicators can be used to optimize the fertilizer system, to plan agricultural enterprises and in studies as well.

The purpose of the study was to assess the availability of phosphorus and potassium mobile forms in the humus layer of virgin gray forest soils in the western part of the West Siberian Lowland. The results of laboratory tests were processed using mathematical methods of variational statistics in Microsoft Excel. It was revealed that gray forest soils have low availability of mobile phosphorus in the humus layer (light gray - 34±17 mg/kg, gray - 44±23 mg/kg, dark gray - 52±24 mg/kg of soil). For that reason, when they are involved in arable land, continuous phosphorization or constant application of phosphorus fertilizers will be required. Also, during agricultural use, a high degree of variation in the content of mobile phosphorus should be considered (variation coefficient is 45% for dark gray and 51% for light gray and gray forest soils). Gray forest soils are characterized by a fairly good supply of mobile potassium, which content in humus layer of light gray soils is 133±45 mg/kg, gray - 140±49 mg/kg, dark gray - 164±51 mg/kg of soil. This is due to the peculiarities of the mineralogical composition of parent rock materials of gray forest soils. The variation of the content of potassium mobile forms in all subtypes is estimated as average. The research results can be applied in the development of agrochemical measures aimed at increasing the fertility of gray forest soils.

The aim of the study was to study the variability of the microaggregate composition of the soil profile of virgin gray forest soils in the western part of the West Siberian Lowland. 330 soil sections were studied, covering all subtypes of gray forest soils. Empirical data were processed using mathematical methods of variation statistics. The results of the research showed that the humus horizon of light gray forest soils is characterized by good water resistance of microaggregates - the dispersity factor on average for the sample is 14.6%, the variation is small (Cv = 19%). Gray forest soils in the humus horizon have, on average, a dispersity factor of 12.2%. This subtype, in comparison with light gray soils, has a higher variability of the dispersity factor (Cv = 24%), which is due to the variety of combinations of soil formation factors, mainly relief and vegetation. The dispersity factor of the humus horizon of dark gray forest soils averages 7.9% for the sample, which is typical for medium structured soils; the variation is estimated as small (Cv = 18%). The microaggregate composition of gray forest soils is characterized as satisfactory throughout the entire soil profile, which makes it possible to improve structure formation during agricultural development and maintain the optimal structural-aggregate composition for a long time. The results obtained can be used in the development of an adaptive-landscape system of agriculture.

The paper identifies the main criteria defining the competitiveness of milk producers in the market. They include the level of marketability, selling price, cost, profitability, and quality of milk. The differentiation of southern areas of Tyumen region from the perspective of milk production competitiveness was carried out by clustering analysis in the Statistica program via the Ward's method. Five clusters are found on the basis of hierarchical classification. The mean cluster values are calculated and analyzed, thus resulting in the definition of the most competitive and noncompetitive areas of the region. The solution of the task related to competitiveness enhancement of dairy products in the south of Tyumen region requires certain measures connected with state support and innovations, which, if applied, will provide the region with high-quality and inexpensive milk according to scientifically grounded food standards.