No 12 (2023)

Samples of the upper horizon of sod-podzolic virgin and arable soil were incubated with lime or superphosphate, then amorphous silicon dioxide was introduced in doses from 50 to 5000 kg/ha and incubated again for 2 weeks. The content of water-soluble and acid-soluble forms of silicon in soils was determined and the fractional composition of phosphorus compounds was analyzed. It is shown that an increase in the concentration of monosilicon acid in the soil solution of sod-podzolic soil initiated the processes of transformation of phosphorus compounds, leading to a decrease in the proportion of insoluble forms of phosphorus and an increase in the phosphorus content available to plants. The introduction of lime or phosphorus fertilizer contributed to the strengthening of these transformational processes, which is important for the development of recommendations for the practical application of silicon fertilizers and the reduction of doses of phosphorus fertilizers.

Over the past 25 years, the influence of siliceous rocks (diatomite, zeolite, flask) on soil properties (typical chernozem, leached chernozem), yield and quality of agricultural crops (cereals, potatoes and vegetables, technical) when used both in pure form and together with mineral fertilizers and bird droppings has been studied. The possibility of creating new types of more effective fertilizers based on siliceous rocks by enriching them with elements or compounds (in particular amino acids) that most fully meet the requirements of crops has been studied. Studies have shown that the yield of grain crops when using diatomite as a fertilizer is little inferior to mineral fertilizers. Thus, the increase in grain yield of winter wheat on average over all the years of research reached 0.60–1.30, spring wheat – 0.15–0.67, barley – 0.50–0.93 t/ha. The increase in corn grain yield, depending on the dose of zeolite application, ranged from 0.93 (dose of 500 kg/ha) to 1.36 (dose of 2000 kg/ha) t/ha. Potatoes and vegetables (cucumbers, tomatoes, carrots, table beets), as well as industrial crops (sugar beet, sunflower) are highly responsive to the use of siliceous products as fertilizers. In particular, the yield of sugar beet root crops increased by 6.5 t/ha on average when diatomite was applied at a dose of 3 t/ha, and in some years – up to 8.6 t/ha. The increase in crop yield increased very significantly when combined with nitrogen fertilizers from N30 to N60 – by 11.3 and 12.5 t/ha. The high efficiency of silicon-containing rocks as fertilizers of agricultural crops is due to their complex influence on the fundamental properties of the soil: physical (structural condition, soil density, structure of the arable layer), biological (activity of soil microorganisms), chemical (nutritional regime, environmental safety), as well as on the protective properties of plants.

The variability of the main indicators of acid-base buffering of sod-podzolic light-loamy soil was investigated, and the dynamics of the content of monomers and polymers of silicic acid and acid-soluble silica compounds in the soil under conditions of reclamation doses of various siliceous rocks (diatomite, zeolite and bentonite clay 3, 6, 12 t/ha) was described. Zeolite rock and bentonite had a positive effect on the anti-acid buffering ability of the soil, shifting the H⁺/OH^–equilibrium of the system by more than 160 and 20, respectively, depending on the applied dose of the material. The effect of diatomite was manifested in the anti-alkaline region of soil buffering, due to which the H⁺/OH^–-equilibrium index decreased by almost 40%. Against the background of the use of diatom rock and bentonite clay, the content of silicic acid monomers in the soil increased by more than 5 and 4 times, respectively, against the background of the use of zeolite – by more than 2 times. The content of silicic acid polymers in the soil increased up to 3 and 4 times with the use of zeolite and bentonite rocks, respectively. At the same time, the introduction of diatomite into the soil contributed to an increase in the content of H₄SiO₄ polymers by 5–10 times, depending on the dose of the material. The content of the acid-soluble fraction of silicon compounds in the soil increased by 1.4–2.8 times against the background of different doses of the studied rocks and, in general, had a different dependence depending on the composition of each of them. Based on the revealed irregularities in the content and dynamics of mobile silicon compounds in the soil (monomers and polymers of silicic acids, acid-soluble silica fractions), the characteristic is given and the value of the first proposed indicators describing their dynamic state and directions of transformation – the potential for the formation of monomers (M-A_Si) and polymers (P–A_Si) is disclosed. H₄SiO₄, the degree of polymerization (Pm-V_Si) and depolymerization (Dm-V_Si) of silicic acid, the total content of the loose-amorphous silica fraction (Si-AMF) and the degree of amorphousness of the Si-containing mineral phase of the soil (AMF-V_Si). The study of the influence of silicon materials in conditions of sod-podzolic soil revealed that, depending on the qualitative composition and dose of silicon rock, the M-A_Si index can increase by 30–80%, and the P-A_Si index can be in the range of increase from 0.3 to 3.0 or more times. The processes of polymerization of silicic acid and the decomposition of its polymers into monomers, expressed respectively by Pm-V_Si and Dm-V_Si, can also actively increase against the background of the interaction of soil with rocks, the measure of change of which is expressed in the order of 10–40% deviation relative to the control. The total content of loose-amorphous silica fraction in the soil, expressed by the Si_AMF index, can be determined by the composition of each siliceous rock used as a meliorant. If, when using diatomite, the indicator can decrease by almost 30%, then when using zeolite and bentonite clay, it can increase by 30–100%, depending on the dose. Similarly, the indicator of the degree of amorphousness of the silicon-containing part of the soil substance (AMF-V_Si) can also change.

In the soil and climatic conditions of the forest-steppe of the Middle Volga region, the effect and aftereffect of various doses of silicon-containing agro-ore (diatomite) and its combinations with bird droppings on the productivity of agricultural crops has been scientifically substantiated and experimentally proven. The highest effect on the productivity of corn, spring wheat, annual grasses was provided by the complex action and aftereffect of silicon-containing agricultural ore together with bird droppings. The yield of corn grain in these variants varied from 5.48 to 5.92, spring wheat – from 3.12 to 3.33, hay of annual grasses – from 9.15 to 10.2 t/ha. The total productivity of crops of the grain-to-crop rotation link when using silicon-containing agricultural ore (diatomite) mixed with bird droppings varied in the range from 13.0 to 14.1 tons of grain/ha, exceeding the control by 3.36–4.44 tons of grain/ha, or by 34.8–45.9%.

The responsiveness of flax to mineral fertilizers and foliar top dressing with an aqueous solution of the drug Controlfit-Si on sod-podzolic medium loamy soil was studied. It is shown that the reaction of flax to mineral fertilizers depended on the hydrothermal environmental conditions, doses and the ratio of nutrients. Excessive humidity and arid conditions negatively affected the productivity of crops. Foliar top dressing of plants with the drug Controlfit-Si leveled the negative impact of adverse weather conditions, increased the responsiveness of plants to mineral fertilizers, contributed to a more complete use of nutrients from fertilizers. On average, for 3 years on the backgrounds of full mineral fertilizer, top dressing increased the yield of flax straw by 25–30% with the best effect against the background of N48P48K48 (4.03 t/ha). Top dressing did not have a positive effect on the yield of flax seeds. It took 13.8 kg N, 5.9 kg P₂O₅ and 10.7 kg K₂O to form 1 ton of flax crop with the appropriate amount of seeds, regardless of plant nutrition conditions.

A set of methods for determining the active forms of silicon – monomers and polymers of silicic acid – in the soil–plant system is described in order to assess the silicon state of soils, the level of plant availability of silicon, as well as to assess the potential effectiveness of solid silicon-containing compounds as a source of bioavailable silicon. The parameter “active silicon” proposed to characterize the availability of bioavailable silicon in soils includes actual silicon, i.e. the content of monosilicon acid present in the soil solution at the moment, and “potential silicon” – monosilicon acid, which can pass into the soil solution from the solid phase. Based on the “active silicon” parameter, a classification of soils has been developed depending on the level of bioactive silicon deficiency.

Biostimulants are a new type of agrochemicals that are highly effective when applying low doses (up to 10 kg/ha). The interest in the use of biostimulants is confirmed by the appearance of not only scientific papers, but also the formation in various countries of legislative bases regulating the use and classification of this type of substances in agriculture. Thanks to the influence of silicon-containing compounds as biostimulators of plant growth, several tasks of modern agriculture can be comprehensively solved: to minimize the effects of stress factors, to reduce the use of pesticides and fertilizer doses, to improve the quality of products, to stop soil degradation. The range of global manufacturers of silicon biostimulants is represented by liquid (monosilicon acid) or solid (amorphous silica or silica gel) forms. There are several silicon-mediated mechanisms that provide plant protection in conditions of biotic and abiotic stress. There is a hypothesis of the influence of silicon on the signaling system of plants, which requires additional research.