Effect of Si soil amendments on As,Cd, and Pb bioavailability in contaminated paddy soils

Paddy and Water Environment - Numerous greenhouse and laboratory experiments have shown that the application of Si-rich materials may affect the mobility and transport of hazardous elements in the...     

Microwave Digestion for Colorimetric Determination of Total Si in Plant and Mineral Samples

A new method for determining the soluble silicon (Si) concentrations in nonliquid plant and mineral samples was developed using sodium hydroxide (NaOH)–hydrogen peroxide (H₂O₂) matrix for microwave digestion (MWD-Na) followed by colorimetric Si testing. MWD-Na was compared with autoclave-induced digestion and alkali fusion. The data have shown no significant difference between these three methods. HNO₃–H₂O₂ or HNO₃?–H₂O₂?–HF microwave technique results in Si loss. The reduction of the total Si can be realized via low solubility of Si in the acid solutions or silicon tetrafluoride formation. The Mullen and Riley method for colorimetric testing of Si in a solution that uses ascorbic acid to reduce the silicomolybdate complex formed under acid conditions to an intensely blue complex was modified using iron sulfate. The combination of MWD-Na and modified colorimetric blue method provides cheap and valid data on determining the total Si in both plant and mineral samples.     

Microbial biomass carbon and the microbial carbon dioxide production by soddy-podzolic soils in postagrogenic biogeocenoses and in native spruce forests of the southern taiga (Kostroma oblast)

In two layers of the humus horizons in soddy-podzolic soils of different biogeocenoses (Kostroma oblast) representing a succession series, the carbon content in the microbial biomass (C_mic) was determined using the method of substrate-induced respiration and the rate of microbial CO₂ production (basal respiration, BR). The C_mic content was from 110 to 755 μg/g soil, and the BR was from 0.40 to 2.52 μg CO₂-C/g/h. A gradual increase in the C_mic content and BR was found in the following sequence: cropland—fallow (7-year-old)—young (20- and 45-year-old) forests—secondary and native (primary) forests (90- and 450-year-old, respectively). In the litter, the C_mic content was higher in the 45-year-old forest than in the secondary and native forests: 10423, 6459, and 4258 μg C/g of substrate, respectively. The portion of C_mic in the soil organic carbon content in the upper layer of the soils studied varied from 1.3 to 5.4%; its highest value was in the soils under the secondary and native forests. The pool of microbial biomass carbon and the microbial CO₂ production in the upper 25-cm layer of the soils were calculated.     

The effect of optimization of silicon nutrition on the stability of barley DNA

Numerous studies on the use of silicon fertilizers indicate their positive influence on the resistance of plants to biogenic and abiogenic stress; nevertheless, the mechanisms of action of silicon on the plants have been little studied. Finely divided amorphous silica was used as a reference silicon fertilizer in microfield experiments that were carried out in the north of the Moscow region with a culture of barley. The strengthening of DNA molecules was shown to occur at doses of SiO₂ of 50, 500, and 1000 kg/ha, which provided higher concentrations of monosilicic acid in the soil than other doses. Therefore, the introduction of silicon improves the viability of the plants at the genome level and enhances the natural resistance of plants in agricultural lands.     

Remediation of Cadmium-Polluted Soil Using Plant Growth-Promoting Rhizobacteria and Natural Zeolite

Eurasian Soil Science - The impact of two strains of Pseudomonas bacteria and natural zeolite on the growth and elemental composition of barley plants was studied in an agrogray soil (Luvisol)...     

Mobile Si-rich compounds in the soil–plant system and methods for their determination

Different aspects of Si biogeochemistry in the soil have been reviewed. Interaction mechanisms of monosilicic acid with aluminum, phosphorus, and heavy metal compounds have been generalized. Polysilicic acids are chemically inert substances, but they participate in the formation of soil structure. Organosilicon compounds in the soil are very little investigated. From literature and our own data, the cycle of mobile Si forms in the soil–microorganism–plant system has been suggested, which shows the main fluxes of soluble Si migration and transformation. A new classification of the Si compounds based on their physicochemical and biological activities in the soil has been suggested as well as a method for the determination of mono- and polysilicic acids in the soil matrix.     

Effect of Moisture Deficiency and Increased Salt Content on Silicon State of Some Soils of European Part of Russia and Central China

Soluble forms of silicon affect a number of physical, chemical, and biological soil properties. Optimization of silicon nutrition enhances plant tolerance to biotic and abiotic stresses. Current climate change and anthropogenic impacts can alter the soil silicon state. Model laboratory experiments conducted with upper horizons of sod-podzolic soil, gray forest soil under different plant associations, chernozem, paddy soil, and red subtropical soil showed that insufficient soil moistening led to a reduction in soil monosilicic acid by 15 to 36% and simultaneous increases in polysilicic acid by 9 to 45%. Soil cultivation resulted in a decrease in plant-available soil silicon. An increase in NaCl concentration in the soil caused an increase in both monomers and polymers of silicic acid by 6 to 79%. The mobile equilibrium and lability of the numerical values of the parameters of the silicon state of the soil–plant system are revealed. These factors should be taken into account when implementing the 4R-STRATEGY for optimizing mineral nutrition in agricultural crops.     

施用活性硅降低重金属移动性的研究

该研究通过一系列的土柱实验研究土壤中硅和重金属的反应机制。土柱实验在可溶性镉、铜、镍和铅酸盐的情况下,用各种活性硅（硅藻土,沸石,无定形二氧化硅,浓缩单硅酸）处理灰森林土。所有富硅物质都用电子显微镜测试分析过。富硅物质对土壤中重金属的钝化试验结果表明：硅藻土和浓缩单硅酸比沸石和无定形二氧化硅更能降低重金属的移动性。重金属移动性的降低是由土壤溶液中单硅酸和重金属的反应,以及富硅物质表面对重金属的吸附实现的。重金属在土壤中移动的强度与自身种类有关。施用富硅物质可明显降低镉和镍的移动性,对铜和铅的效果不明显。     

Cadmium and arsenic adsorption in aqueous systems in the presence of monosilicic acid

The effect of different concentrations of monosilicic acid on the sorption capacity of quartz sand, diatomite, zeolite, and brown coal with respect to cadmium and arsenic has been studied in laboratory conditions. The applicability of different adsorption models, including exponential, semilogarithmic, and linear dependences, as well as the Langmuir and Freundlich equations, has been compared. An increase in monosilicic acid concentration from 0 to 2 mM increased the sorption capacity of all materials. It has been suggested that either the interaction of monosilicic acid with a pollutant takes place directly in the solution followed by sorption of the reaction products on the surface or in the pores of the sorbent, or first adsorption of the monosilicic acid by the sorbent occurs followed by interaction of the sorbed silicic acid with cadmium and arsenic; it is also possible that both process proceed in parallel.     

Silicon fertilizer efficiency

The role and function of silicon in plants and soil-plant system are investigated. It is shown that this element provides natural protection of cultivated plants from biogenic and abiogenic stresses, and silicon fertilizers allow producing a maximum yield with minimum cost.