The article presents data on the content of agrochemical and physico-chemical, absorption capacity, composition of water-soluble salts, carbonate content of irrigated meadow-takyr soils in the lower reaches of the Zarafshan River. The article highlights the agrochemical, physicochemical properties of irrigated meadow-takyr soils of the lower flowing river. Zarafshon. The results of the study showed that in the profile of irrigated meadow-takyr soils there are excretions of iron oxides, which indicates an earlier, hydromorphic stage of these soils. Irrigated meadow-takyr soils contain 0.95-1.12 % humus, to the bottom the amount of humus drops sharply to 0.66 %. Nitrogen in the upper horizons fluctuates 0.06-0.08 %, its content is evenly distributed throughout the soil profile. Mobile forms of phosphorus are average and increased-provided. Its content in the arable horizon varies within 50-60 mg/kg of soil. The availability of mobile potassium is average 209.0 - 260.1 mg/kg of soil. Absorption capacity in irrigated meadow-takyr soils varies across horizons within 7.8 mg/eq. per 100 grams of soil. The composition of the absorbed bases is dominated by magnesium (Mg) cations, which is 41.7-57.0 %, then calcium (Ca) is 36.7-53.3 %, potassium (K) is 4.5-5.3% and sodium (Na) 0.3-.0 % of the sum of absorbed bases. The absorbed bases are dominated by magnesium (Mg) cations, which is 41.7-57.0 %, then calcium (Ca) is 36.7-53.3 %, potassium (K) is 4.5-5.3 % and sodium (Na) 0.3-.0 % of the sum of absorbed bases. In the old irrigated meadow-takyr soils occurs magnesium alkalinity is highly carbonate. These soils have a rather high moisture capacity and low water permeability, slopes to crust formation.

The article presents agrophysical, agrochemical, water-physical data of solonchak soils of the Kashkadarya region. The research results showed that the salt content in the salt crust reaches 30.3 % of the solid residue. The composition of water-soluble salts is dominated by magnesium sulfates. In the lower horizons, the distribution of salts is almost united form and their amount is 4-5 % with an increased chlorine content (0.8-1.2 %). Soil-forming rocks for solonchak soils are mainly river terraces and deltas on the proluvium of the piedmont plains, on the alluvium of the bedrocks of the plateau. The essence of the solonchak process lies in the strong salinization of the entire soil-ground layer with a maximum accumulation of salts in its upper part, where they form a puff or crust. The content of salts in the salt crust reaches 30.3 % of the solid residue; magnesium sulfates predominate in the composition of water-soluble salts. The amount of humus in the salt horizon varies over a very wide range from 0.7 to 1.4 %. The thickness of the humus horizon varies from 3 to 59 cm. According to the mechanical composition, solonchaks are heterogeneous, they are divided into light, sandy and loamy soils. Solonchak soils are characterized by low absorption capacity, which reaches 9 mg/eq per 100 g of soil. The absorbed bases are dominated by alkaline earths (the amount of Mg is 82.8 % of the total of absorbed bases, of which Ca accounts for 6.2 %, K – 5 % and Na - 6.0 %).

As is well known, the content of organic matter (humus) in the soil is the most important indicator of its fertility. The transformation of organic residues into humic substances is directly related with the activity of biological factors of soil formation. This article is devoted to this actual problem. We tried to consider this issue using the example of gray-brown (chestnut) soils of semi-humid subtropics (Jalilabad) of Lankaran region. The article presents data on the amount of humus in individual horizons of gray-brown soils and its individual subtypes – ordinary, light, dark, as well as in irrigated variants of these soils. The dynamics of changes in the humus content in these soils were studied and their distinctive features were analysed. The relationship between the humus content and some biological indicators, in particular, phytomass and microorganisms, was carried out. In general, a comparative theoretical analysis is carried out between our results and the data given in the literature.

The article presents the results of a study of the agronomic role of root and crop residues under conditions of soil flooding. It has been established that the humus state of rice-marsh soils under rice, subject to the alternation of crops in the crop rotation, does not undergo drastic changes. There is a positive correlation between the amount of humus and the content of root masses. The biogenicity and fertility of soils under rice cultivation is directly dependent on the predecessor and the mechanical composition of the soil. The highest content of the root mass in the original samples was in the field, where the predecessor layer was alfalfa, but the sowing of rice in the layer led to a decrease in it by the end of the season (in autumn) by more than 2 times, which indicates a high rate of mineralization of organic residues in rice soils. Thus, there is a constant transformation of organic residues, which depends on the predecessor and crop rotation. During the entire growing season, aerobic fiber-decomposing microorganisms predominated in the soils under rice sowing along the alfalfa layer.Aerobic forms of fiber-decomposing microorganisms also dominated in the soils under rice sowing along the turnover of the alfalfa layer. In seasonal dynamics, there was a sharp increase in the number of fiber-decomposing microorganisms.The conducted studies showed that in the soils with alfalfa crops under the cover of barley in the spring, fungi of the Mucor Trichoderma genera predominated. Actinomycetes Act. albus and fungi Trichoderma dominated in the soils along the alfalfa layer, and mucosal fungi and actinomycetes (Act. albus) dominated in the soils along the turnover of the alfalfa layer.

Heavy metals refer to special pollutants, monitoring of which is obligatory in all environments. In this regard, the study of soil contamination with heavy metals is one of the urgent issues. The research results showed that the amount of heavy metals in samples from sites located along the Tashkent tract was several times higher than the norm. The study of anthropogenic impact on soil microbiota is a necessary element of any biomonitoring study. Heavy metals already rank second in terms of danger, inferior to pesticides and well ahead of such well-known pollutants as carbon dioxide and sulfur. In the future, they may become more dangerous than nuclear power plant waste and solid waste. Contamination with heavy metals is associated with their widespread use in industrial production. Due to imperfect cleaning systems, heavy metals get into the environment, including soil, polluting and poisoning it.

The paper presents studies on the effect of various hydrothermal conditions, precursors and mineral fertilizers on the yield and removal of macroelements by spring soft wheat. Wheat was cultivated in crop rotation with zero tillage technology on calcareous chernozem at N.P. A.I. Baraev. It has been established that the maximum content of productive moisture in a meter layer of soil before sowing wheat for peas was observed in 2018 - 130 mm, the minimum in 2020 - 84.5 mm. On wheat sown on flax, the largest amount of productive moisture was noted in 2017 - 125.1 mm, and the smallest in 2012 - 58.9 mm. The maximum yield of spring wheat sown on pea and flax stubble in the control variant was obtained in 2018 - 21.0 and 19.2 c/ha, and the minimum in 2012 - 6.5 and 2.6 c/ha. Peas as a precursor for wheat provided an impact on its yield in comparison with flax stubble only in 50% of the studied years. According to the two predecessors, a significant increase over the four studied years was obtained when ammophos P20 was introduced into the rows during sowing, which, depending on the hydrothermal conditions of the growing season, ranged from 1.1 to 5.7 c/ha. The humidity of the growing season, the predecessor and fertilizers did not have a significant effect on the content of macronutrients in wheat grain. The removal of nitrogen, phosphorus and potassium by wheat grain depended on the yield, the level of which was influenced by the weather conditions of the predecessor and fertilizers. The largest removal of macronutrients for the two predecessors and variants of the experiment was noted in 2018, and the smallest - in 2012.

The paper presents classical and modern concepts of modeling enzymatic processes and determining the initial rate of an enzymatic reaction by graphical and analytical methods. Methods for determining the initial rate of the enzymatic reaction in soils are given. In contrast to the Newton-Gregory analytical method, a new method is proposed for determining the initial rates of reactions catalyzed by enzymes. For this purpose, the most commonly used in modeling are recommended: hyperbolic, binomial, binomial-parabolic polynomials of the 5th and 6th degree, pseudopolynomials of the 5th and 6th degree of the model. It is proposed to use a batch program on a computer to calculate the kinetic parameters. The prospects of using mathematical modeling in the study of enzymatic reactions in soil are shown.

The article is devoted to the study of the impact of oil pollution on the soil-plant system. Estimation of technogenic pollution of Zhanazhol field by oil products is given. Oil products have a negative impact on both the plant system and the soil structure. The impact of spilled oil on plants occurs in different ways - physical, chemical and physiological, which leads to damage to lipid membranes, disruption of cell membrane conductivity. Oil pollution has an inhibitory effect on the development of soil microorganisms and soil enzymes. It is established, that influence of pollution on biological activity (microorganisms, enzymes) is connected with concrete oil fraction. Literature data on the impact of oil contamination of soil on plants are given. Considered the main mechanisms of the impact of oil pollution on the soil-plant system Described: measures for environmental monitoring of soil cover and restoration of soils affected by oil pollution, given the spectral characteristics of plants and soils contaminated with oil, as well as remote sensing data with a view to identifying the reflective properties of oil pollution. It has been revealed that the main factors of the negative impact of oil pollution on the soil-plant system, as noted in the literature, are the toxic effects of oil hydrocarbons and changes in the physical and chemical properties of the soil.