Co-treatment with silicon and quicklime in pig manure application as a promising option of environmnetal management.

Manure utilization is the most important current practices economically and, ecologically. The combined use of active forms of silicon together with other types of soil amendments or fertilizers has been shown to reduce P, N and K leaching from upper soil horizon or fixation, which positively affect crop production. The present study evaluated the performance of pig manure co-treated with quicklime (calcium oxide - CaO) and monosilicic acid (Si(OH)4) as sources of nutrients for rice production conducted in greenhouse and field tests for the reduction of negative environmental effects through the soil-plant system. Results indicated that quicklime/monosilicic acid-treated pig manure reduced the phosphorus and potassium leaching and phosphorus fixation which resulted in an increase in the biomass of rice by 38.3-52.3% in greenhouse and rice yield in field increased by up to 17.4%. Phosphorus plant-availability in the soil and its uptake by rice plants were enhanced by the mixture of treatments. Furthermore, quicklime/monosilicic acid -treated pig manure enhanced the accumulation of potassium in rice leaves.

Growth of Bacillus amyloliquefaciens as influence by Si nutrition.

The aim of study was to determine the influence of soluble and solid forms of Si on the growth of B. amyloliquefaciens. The experiment was conducted at two regimes: under sterile conditions (without B. amyloliquefaciens) and infected conditions (with B. amyloliquefaciens). New formed silica gel, diatomite and monosilicic acid at 1 mM Si and 2 mM Si were used as source of Si. The concentration of monosilicic acid in the solution was measured on second and tenth days of experiment. The total carbon in the solution before and after centrifugation was determined on day 10 of the experiment. The experiment has demonstrated a significant positive effect (by 4.7-41.2%) on B. amyloliquefaciens growth in water system. The presence of B. amyloliquefaciens in Si-rich solution reduced the concentration of monosilicic acid in the solution up to 16.2%. About 13.5-30.7% of B. amyloliquefaciens can be attached to the Si-rich surface without formation of cell clusters. Si can be classified as a beneficial nutrient for B. amyloliquefaciens. The tested strain of Bacillus can form channels in silica gel. The presence of monosilicic acid resulted in the formation of an aligned positioning of cells in water-based solution. This study is the first to demonstrate the direct influence of active Si forms on bacteria growth. The research showed that monosilicic acid or Si-rich solid substances with high solubility on Si can be recommended to increase B. amyloliquefaciens growth in soil, water or reactors.

Effect of silicon on barley growth and N2O emission under flooding.

The global climate change is related with greenhouse gas emission from cultivated soils - carbon dioxide, methane and nitrous oxide. The emissions of N2O also have negative influence on ozone layer of our planet. The major source of the nitrous oxide is denitrification process in soil, which controlled by specific soil microbe society. The pot experiment with flooding to accelerate the denitrification process and the application of the monosilicic acid as a source of soluble form of Si was carried out with barley. Several forms of nitrous oxide emission (unlimited carbon denitrification and potential denitrification with or without ethylene application) were measured. The obtained data showed that the application of monosilicic acid to brown soil when growing barley under conditions of soil flooding has a significant effect on nitrogen emission and can change the N2O:N2 ratio. The application of the monosilicic acid reduced the uC-D N2O emission, while increased the PD N emission. Generally the application of the water soluble Si decreased the N2O:N2 ratio. We suggested that the presence of monosilicic acid in the system provides a more complete denitrification process with the formation of N2 in the NO3- → NO2- → NO→N2O → N2 reaction sequence, while the deficiency of bioactive Si mainly provides the formation and emission of N2O. Considering that N2 is not a greenhouse gas, we can conclude that application of monosilicic acid to the soil can reduce greenhouse gas emissions and reduce the impact of global climate change on agricultural activity.

Binding of transition metals to monosilicic acid in aqueous and xylem (Cucumis sativus L.) solutions: a low-T electron paramagnetic resonance study.

The supplementation of monosilicic acid [Si(OH)4] to the root growing medium is known to protect plants from toxic levels of iron (Fe), copper (Cu) and manganese (Mn), but also to mitigate deficiency of Fe and Mn. However, the physicochemical bases of these alleviating mechanisms are not fully understood. Here we applied low-T electron paramagnetic resonance (EPR) spectroscopy to examine the formation of complexes of Si(OH)4 with Mn(2+), Fe(3+), and Cu(2+) in water and in xylem sap of cucumber (Cucumis sativus L.) grown without or with supply of Si(OH)4. EPR, which is also useful in establishing the redox state of these metals, was combined with measurements of total concentrations of metals in xylem sap by inductive coupled plasma. Our results show that Si(OH)4 forms coordination bonds with all three metals. The strongest interactions of Si(OH)4 appear to be with Cu(2+) (1/1 stoichiometry) which might lead to Cu precipitation. In line with this in vitro findings, Si(OH)4 supply to cucumber resulted in dramatically lower concentration of this metal in the xylem sap. Further, it was demonstrated that Si(OH)4 supplementation causes pro-reductive changes that contribute to the maintenance of Fe and, in particular, Mn in the xylem sap in bioavailable 2+ form. Our results shed more light on the intertwined reactions between Si(OH)4 and transition metals in plant fluids (e.g. xylem sap).

Efficacy of Si fertilization to modulate the heavy metals absorption by barley (Hordeum vulgare L.) and pea (Pisum sativum L.).

Silicon-based fertilizers and soil amendments can have direct and indirect positive influences on cultivated plants. The solid forms of Si-based substances, the most widespread in use, are efficient only at high application rates due to their low level of solubility. Several types of Si-based substances such as fumed silica, slags from the iron and steel industry, modified slags, and a Si-rich product were tested using barley and pea as silicon accumulative and non-accumulative plants, respectively, at two application rates. The plants were grown under toxic concentrations of heavy metals in a greenhouse. Si-rich materials high in water-soluble Si had a positive effect at both the low and high application rates, and for both plant species. This type of substance can be regarded as Si fertilizer, demonstrating greater efficiency at a low application rate and lessened efficiency at a high application rate for protection of the cultivated plants against accumulation of the heavy metals.

Monosilicic acid potential in phytoremediation of the contaminated areas.

The contamination of agricultural areas by heavy metals has a negative influence on food quality and human health. Various remediation techniques have been developed for the removal and/or immobilization of heavy metals (HM) in contaminated soils. Phytoremediation is innovative technology, which has advantages (low cost, easy monitoring, high selectivity) and limitations, including long time for procedure and negative impact of contaminants on used plants. Greenhouse investigations have shown that monosilicic acid can be used for regulation of the HM (Cd, Cr, Pb and Zn) mobility in the soil-plant system. If the concentration of monosilicic acid in soil was increased from 0 to 20 mg L(-1) of Si in soil solution, the HM bioavailability was increased by 30-150%. However, the negative influence on the barley by HM was reduced under monosilicic acid application. If the concentration of monosilicic acid was increased more than 20 mg L(-1), the HM mobility in the soil was decreased by 40-300% and heavy metal uptake by plants was reduced 2-3 times. The using of the monosilicic acid may increase the phytoremediation efficiency. However the technique adaptation will be necessary for phytoremediation on certain areas.

Prospective for remediation and purification of wastes from Xikuangshan mine by using Si-based substances.

Heavy metal mining includes several procedures producing water and solid wastes. These wastes may have high content of heavy metals and other pollutants. Usually, traditional technologies for purification of solid and liquid wastes are expensive and require a lot of special constructions. Recent investigations have shown that some Si-rich substances enable to regulate the mobility of pollutants in soil and water and enhance the plant resistance to its toxicity. Based on these findings, new way for purification of waste-waters and detoxification of pollutants can be elaborated. Laboratory test was conducted with contaminated solid and liquid wastes from Xikuangshan mine. In column and incubation tests, the contents and mobility of the following pollutants were evaluated in Si-treated and untreated samples: As, Cd, Co, Cr, Cu, Hg, Pb, Ni and Zn. The investigations have shown that the Si-rich substances can be used for filtration of contaminated waste-water. The concentrations of soluble pollutants were reduced by 5-10 times and more. The incubation tests with solid wastes and Si-rich compounds have demonstrated that some Si-based substances reduced the contaminant mobility by 2-4 times. The efficiency of tested substances depended on their solubility on Si. The data has demonstrated that some types of local materials including industrial wastes can be used for purification of waste-waters and detoxification of solid wastes.

Pb detoxification in Equisetum diffusum.

Current research highlights the use of aquatic macrophyte Equisetum diffusum (Himalayan horsetail) for lead detoxification. This plant species can grow in waste cathode ray tube (CRT) powder and absorbs its Pb. X-ray fluorescence spectroscopy (XRF) analysis of plant ash shows that 68 mg/kg lead concentration in the untreated plant was improved to 7600 mg/kg in CRT powder after 90 days. The role of monosilicic and/or monoplumbic acid as reaction intermediates for Pb detoxification and associated bioaccumulation is proposed. Pb detoxification in E. diffusum is mainly rendering around the iso-electronic nature of Pb and Si and forms similar phytochelatin (PC) complexes with available family of peptide ligands. The study focuses on the underlying functions of silicon containing plants in metal detoxification.