Moscow University Soil Studies Bulletin. 2019. 3.

The dynamics of mineralization of organic substances in soil solutions sampled by the tension lysimeters from podzolic soil has been studied. The stability of dissolved organic matter (DOM) varies with the horizon. The greatest content of resistant to biodegradation DOM (was mineralized less than 50%) was found in the upper organic horizons, down the profile it is decreased. The fraction of mineralized carbon is inversely proportional to the relative content of hydrophobic and phenolic fractions in DOM. The lowest percentage of mineralized carbon (23%) resides in the upper Elhi-horizon, where DOM is contained maximum of hydrophobic fraction (44%). In the course of oxidative transformation the degree of aromaticity of the DOM and the proportion of phenolic compounds increased (SUVA280 - by 2-12 times; phenols - 2 to 10 fold), while molecular masses decreased up to 5-5,5 kDa. These changes are manifested more intensively in solutions from the lower horizons, thus, the non-decomposable residue of this DOM is represented by substances most resistant to the decomposition.

Expression of the total chemical analysis in the form of oxides has significant drawbacks: this conditional form does not correspond to the actual content of soil minerals. Oxide form distorts the view of the relationship between the different elements in the soil. It is obvious that the total chemical composition should be expressed in the form of elements including oxygen - the element with the maximal Clarke. Thus it is necessary to consider the amendment on oxygen loss on ignition of the soil. The studied soil on amendments to oxygen can be divided into three groups. For spodosols of Russian plain after amendments oxygen content increases slightly and total chemical composition of practically does not change. For vertisols of southern Siberia after amendments oxygen content increases by 3 - 4%. Not accounting for this fact leads to a noticeable error in the content of K. For oxisols in Norfolk Island with a high proportion of unstable gibbsite after amendments content O increases by 7 - 8%. This leads to a noticeable error in the contents: O, Al, Fe and Ti in particular. For oxisols the amendment of oxygen is required.

The problem of elaboration and implementation of innovative, feasible, ecologically friendly nature-like technologies aiming at an increase in carbon (C) stock and significant reduction in greenhouse gas (GG) emission from all agricultural areas, including those under rice cultivation, is critically important. In field tests conducted in Hunan Province, China, carbon dioxide (CO₂) sequestration by roots of rice plants was evaluated as influenced by silicon (Si) fertilizers. The amount of additional CO₂ sequestrated was dependent on the content of plant-available Si in agrochemicals, frequency and duration of their application and granulometric composition of soil. The data obtained evidences the potential of Si fertilizers to promote the process of C sequestration and reduction in GG emission under rice cultivation. Their application provided an increase in rice yield by 12,1 to 71,2% and in the CO₂ fixation by root system by 0,95 to 14,9 t ha^-1 over one season. Returning C to soil and fertility reproduction could be provided via enhanced plant root system development and increased root debris after harvesting. Agrochemicals containing silicon available for plants should be included in the technology for the implementation of 4R-STRATEGY of mineral nutrition of agricultural crops.

An approach is proposed for the assessment of ecosystem services of various components of the landscape of urban forest parks. The methodology takes into account the environmental and recreational functions of the territory, is based on the interconnection of ecosystem services, ecological functions and the properties of individual components of the landscape. The assessment is carried out in a differentiated way, taking into account the decrease in the quality of the services provided in conditions of significant anthropogenic load. It is shown that the greatest contribution to the cost of services is made by the soil.

The application of the express method of indirect evaluation of the mobility of heavy metals by the index of specific electrical conductivity of soil in model experiments with given parameters and homogeneity is proposed. It was established that the electrical conductivity indices obtained with a direct measurement of the electric resistance of the soil are closely correlated with the data of the instrumental method of quantitative element analysis. The maximum efficiency of the sorbent is shown in relation to cadmium, the degree of absorption reaches 61,6% with the component composition of sorbent 1:3 (sapropel to lime). For plumbum, the effective composition of the sorbent at the ratio of sapropel and lime is 1:1 - 14,3% sorbed ions, for zinc, with a ratio of the ingredients 1:5 is 6,4%.

The ²²⁶Ra, ²³²Th, ⁴⁰K vertical profiles were studied in relation with the soil properties: pH_H2O, the sum of exchangeable Ca²⁺ and Mg²⁺, the degree of saturation with bases, the content of humus, mobile forms of phosphorus and potassium. An increase in the specific activity of ²²⁶Ra, ²³²Th, ⁴⁰K associated with the accumulation of humus and the biogenic accumulation of mobile forms of potassium and phosphorus in the upper 0-10 cm layer of horizon A in the soil of the oak forest was detected. The removal of ²²⁶Ra from the middle part of the profile of dark gray forest deep-carbonate soil was recorded. A positive correlation between the specific activity of ²²⁶Ra and the sum of the exchange bases Ca²⁺ and Mg²⁺ indicating the conjugate behavior of these elements-analogues in the horizons A, A(AE), AB and the lower horizons B1, B2, B3 was revealed. Removal of ²³²Th from horizon A(AE) and accumulation in horizon AB under conditions of local podzolization of dark gray forest soil in birch forest was observed.

Speciation of ²²⁶Ra and ²³²Th in sod-podzolic-gley concretionary soil are studied. It has been shown that with periodic overmoistening by surface waters and alternation of reducing and oxidizing conditions, the mobility and availability to plants of ²²⁶Ra is substantially higher than ²³²Th. The sum of fractions available to plants (water-soluble and exchangeable) and mobile (water-soluble, exchangeable and mobile) of ²²⁶Ra is 2-10 times higher than ²³²Th. Segregated ferruginous nodules formed in the eluvial horizons of this soil have a weak effect on the mobility of ²²⁶Ra, but significantly reduce the mobility of ²³²Th, much of which is substantially fixed inside the crystal lattices of newly formed minerals.