Total Si Content Research Articles

Release of labile Si from forest and agricultural soils

Despite the importance of silicon (Si) as benefecial nutrient for many plants, including economically-important cereals, the reactivity of various Si pools in soils (silicate minerals, amorphous compounds, phytoliths, organic litter) is not fully quantified which does not allow predicting the capacity of agricultural or forested soil to provide soluble Si to soil porewaters where it can be used by plants. Towards better understanding of factors controlling bioavailable Si in soils, here we quantified the release rate of Si from several pairs of French forest and agricultural topsoils, developed on calcareous or loess parent material. We used mixed-flow and column reactors, in acetate and carbonate buffers and distilled water, at various pH (4–8) and time of reaction (day to month).The rate of Si release from soil (RSi) exceeded that of crystalline clay minerals by 1–2 orders of magnitude, being 5–10 times lower than that of various allophanes. The rates were weakly dependent on pH (compared to clays or phytoliths) and varied from 5 × 10−7 to 2 × 10−6 mol/gsoil/day at 4 < pH ≤ 8. In terms of Si reactivity, four studied soil groups followed the order: “calcaric cambisols ≈ hypereutric cambisols ≥ luvisols ≥ albeluvisol”. Calcaric and hypereutric cambisols as well as luvisols exhibited a weak decrease of RSi with pH increase. The rate of Si release from albeluvisol increased 2 times with a pH increase from 4 to 8. There was no measurable difference in RSi between agricultural and forest soils.The pool of labile Si in forest soils was quantified via soil column flow-through experiments. The breakthrough curves of Si demonstrated high concentrations (1.6–5.7 mg/L) over first several hours of reaction in the soil column. The water leachable Si pool ranged from 0.04 to 0.08 mg Si gsoil−1, corresponding to labile Si stock in the 0–20 cm soil of 80–160 kg ha−1. These values can meet the annual requirements of plants in forests and cultivated soils. The pool of labile Si correlated (RPearson > 0.90; p < 0.05) with Si associated with amorphous Fe and Al compounds and soluble bioavailable Si extracted using CaCl2 method, but negatively correlated with total Si content in soils and Si of phytoliths. The main pools of soil labile Si could be allophanes, organo-Fe-Al-Si compounds and adsorbed forms of Si onto Fe and Al hydroxides. We hypothesize that, because of low sensibility of RSi to type of soil and fluid pH, the majority of soils regulate Si release at some ‘universal’ rate which is further reflected in relatively narrow range of riverine Si concentrations and export fluxes across the world. Therefore, the modeling of chemical weathering and element export flux in the watersheds should incorporate the experimentally measured reactivity of the whole soil rather than individual constituting primary or secondary minerals.

Modeling the Composition of the Earth’s Liquid Outer Core

The paper suggests expressions, coherent with experimental data, for the calculation of the sound velocity and the temperature of a condensed medium under pressures in the Earth’s liquid outer core through parameters of the shock Hugoniot of the medium. Additives to the Earth’s liquid outer iron-nickel core were fitted so that the calculated pressure, density and sound wave velocity corresponded to geophysical values and the temperature did not exceed the admissible limits. It was established that the iron carbide Fe3C containing (4.0 ± 0.5) wt.% carbon with additives of FeS2 and SiC with a total content of Si and S up to 1.5 wt.% meets the required criteria as the main light additive in the upper layers of the Earth’s core. Less probable is the additive of carbon in the diamond phase up to 0.5 wt.%. In the Earth’s outer core, at the boundary with the solid inner core, among the possible light additives are the iron carbide Fe3C with (3.5 ± 0.4) wt.% carbon or diamond phase carbon of (4.0 ± 0.5) wt.%. Additives at the bottom of the Earth’s liquid outer core, containing significant amounts of Si, S, are hardly probable. The content of H in the Earth’s liquid outer core can be significant at the minimum possible core temperatures. The content of O is insignificant.

The impact of pine self-afforestation on podzolization process in semi-natural grassland areas of Volyn Polissya (Ukraine)

Background. Several theories have been proposed to explain the podzolization process. Currently, the role of organic matter in both weathering and immobilization in the illuvial horizon is clearly stated. The origin of soil organic matter and, accordingly, the various mechanisms of its influence on the soil material, create the basis of these theories. We assume that in the base-poor sandy soils under rich herbaceous vegetation with a well developed sod layer, the process of podzolization may also depend on CO2 soil formation agent . Materials and Methods. Four localities along a Pinus sylvestris L. self-afforestation chronosequence with pine stands of 10, 20, 40 yrs and an adjacent semi-natural grassland area were investigated in order to determine the patterns of podzolization process on sandy glacial till deposits. Soil pH, exchangeable base, soil cation exchange capacity, total content of soil organic carbon, amorphous Fe, Si and Al and total contents of Al, Fe, Mn, Zn, Cd, Pb, Cu, Co, Ni, Na, K were determined. Statistical analysis of the results was performed using LibreOffice for Linux. Results. During the pine succession, a previously well differentiated into horizons podzolic soil under the grassland vegetation community gradually degrades. Previously well-defined albic and spodic diagnostic horizons disappear, the soil profile becomes more acidic, the soil organic carbon, the base cation content and the base cation saturation decrease, the leaching rate of aluminium and iron increases. Secondary podzolization features in the soil profiles were detected 40 years after the onset of afforestation. The podzolization has not been intensive enough to develop fully fledged albic and spodic diagnostic horizons over such a short period. Conclusions. Based on the obtained soil morphological, physical and chemical properties, three most important agents of podzolization are proposed as principal for the studied area. The main gent under pine forest is fulvic acids that are produced during coniferous litter decomposition. Low molecular weight organic acids and carbon dioxide produced to the rhizosphere by roots and a root associated microbiota are mainly involved in the podzolization process under the grassland ecosystem.

Postharvest application of potassium silicate improves keeping quality of banana

ABSTRACTGRAS (General-Regarded-As-Safe) compounds play a considerable role in food industry to secure the food safety and environmental sustainability. Soluble silicon (Si) acts as a disease control agent for many plants. Climacteric pattern of ripening and postharvest diseases limit the shelf life of banana during transportation to local and overseas destinations. The ability of banana fruit to absorb Si upon postharvest dip treatment and if so, the absorption of Si confers any effects on disease reduction and keeping quality, were investigated. Banana dipped in 1500 µg mL−1 silicon for 20 minutes showed longer shelf life among different Si concentration × dipping time treatment combinations. Si treatment resulted significantly lower rates of ethylene production, respiration and delayed time taken for fungal rot development compared to non Si-treated (control) fruit. Total soluble silicon content in peel tissues was significantly higher [0.54% dry weight (dw)] in Si-treated versus control fruit (0.13% dw). Si treatment had no effect on total Si content, total soluble solids (TSS) content, titratable acidity (TA) or antioxidant activity in banana fruit pulp. This indicates that dip-treatment allowed Si to penetrate and remain in peel without reaching fruit pulp while extending the shelf life without altering the organoleptic properties of banana fruit pulp.

In-situ alloying of AlSi10Mg+Si using Selective Laser Melting to control the coefficient of thermal expansion

Selective Laser Melting (SLM) was investigated as new processing route for strongly hypereutectic AlSi alloys for thermal management applications in space industry. Processing conditions, microstructure and thermal expansion behavior were analyzed for AlSi10Mg + Si alloys with 25 wt% and 50 wt% Si fabricated by in-situ SLM of powder mixtures. For both Si compositions parts with densities ≥ 99% could be achieved using laser power ≥ 275 W and scan speeds ≥ 1500 mm/s for the alloy containing 25 wt% Si and laser power of 400 W and scan speeds ≥ 1500 mm/s for the alloy containing 50 wt% Si. Considerable refinement of primary and eutectic Si was achieved for both Si compositions due to the high cooling rates of SLM. The mean particle size for the coarse primary Si of the 50 wt% Si containing alloy was below 10 μm. Additionally, unmolten Si powder particles were observed. Measurements of the coefficient of thermal expansion (CTE) showed the tailorability of CTE with adjustment of Si content. A decrease in CTE of 43% compared to pure Al was achieved at a total Si content of 50 wt%. Experimental data was close to model calculations based on the rule of mixture and the Turner model depending on the different microstructures of the two alloy compositions.

Using chemical experiments and plant uptake to prove the feasibility and stability of coal gasification fine slag as silicon fertilizer.

Coal gasification fine slag (CGFS) is a kind of industrial waste that is generated from entrained-flow coal gasification with a high content of 0.5M hydrochloric acid (HCl)-extractable silicon (Si). Si fertilizer has been widely used in agriculture to enhance the mechanical properties and yield of crops. An evaluation was actualized by analyzing HCl-extractable Si fractions and X-Ray diffraction (XRD) of different treatments (acid, alkali, salt, grind, calcination, temperature, and time) for CGFS samples and other Si source materials. The results showed that CGFS had stable HCl-extractable Si concentrations of 60 ± 2g/kg except in the calcination treatment, which decreased the content of extractable Si by 28.2%. Furthermore, under the same processing conditions, CGFS showed a higher content of extractable Si than other Si source samples. Moreover, a rice growth experiment was carried out for 120days in a different mass incorporation of CGFS in the greenhouse. The strength index and total Si content of the stem proved that using CGFS at 5wt.% markedly promoted the growth of rice. The study indicated that an appropriate application of CGFS as a Si resource to an agricultural field could be considered as a viable option for safe disposal of this industrial waste.

Acquiring Information on the Total Content and Speciation of Silicon in Petroleum Products/Fuels Using High-Resolution Continuum Source Flame Atomic Absorption Spectrometry and Wavelength-Dispersive X-ray Fluorescence

Various chemical forms of silicon (Si) possibly present in petroleum products/fuels were investigated in this work: low-molecular-mass species with different compositions, structures, and volatilities, as well as a Conostan oil standard, polysiloxanes, and silicon dioxide. Analysis in xylene solutions was accomplished using wavelength-dispersive X-ray fluorescence (WD XRF) or high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS). Samples were also analyzed using HR-CS FAAS in aqueous solutions after mineralization in a closed microwave-heated system, mineralization in an open system, or mineralization combined with fusion using lithium metaborate. It was found that none of the applied procedures was suitable for the accurate determination of Si in all the tested forms. The total content of Si can only be determined if various methodological variants are applied. Using WD XRF, similar signals are obtained for all the investigated organic Si forms. The procedure is also helpful ...

Phytolith‐rich biochar increases cotton biomass and silicon‐mineralomass in a highly weathered soil

AbstractNon‐essential silicon (Si) is beneficial to plants. It increases the biomass of Si‐accumulator plants by improving photosynthetic activity and alleviating stresses. Desilication, however, takes place because of natural soil weathering and removal of harvested biomass. Pyrolysis transforms Si‐rich biomass into biochar that can be used to supply bioavailable Si.Here, we applied two biochar materials differing in Si content on soils differing in weathering stage: a young Cambisol and a highly weathered Nitisol. We studied the impact of biochar supply on the bioavailability of Si, cotton biomass, and Si mineralomass. The biochar materials derived from, respectively: Miscanthus × giganteus (Mi; 34.6 g Si kg−1 in biochar) and soft woody material (SW; 0.9 g Si kg−1 in biochar). They were compared to conventional Si fertilizer wollastonite (Wo; CaSiO3). Amendments were incorporated in soils at the rate of 3% (w/w). The content of bioavailable Si in soil was determined through 0.01 M CaCl2 extraction.In the Cambisol, the proportion (CaCl2 extractable Si: total Si content) was significantly smaller for Mi (0.9%) than for Wo (5.2%). In the Nitisol, this proportion was much larger for Mi (1.4%) than for Wo (0.7%). Mi‐biochar significantly increased Si‐mineralomass relatively to SW‐biochar in both soils. This increase was, however, much larger in the Nitisol (5.9‐fold) than in the Cambisol (2.2‐fold).Mi biochar is thus an alternative Si fertilizer to Wo to supply bioavailable Si, increase plant biomass, and promote the biological cycle of Si in the soil‐plant system in the Nitisol. Besides, it increased soil fertility and soil organic carbon content.

Uptake of Silicon by Sugarcane from Applied Sources May Not Reflect Plant-Available Soil Silicon and Total Silicon Content of Sources.

Soils of the tropics and sub-tropics are typically acid and depleted of soluble sources of silicon (Si) due to weathering and leaching associated with high rainfall and temperatures. Together with intensive cropping, this leads to marginal or deficient plant Si levels in Si-accumulating crops such as rice and sugarcane. Although such deficiencies can be corrected with exogenous application of Si sources, there is controversy over the effectiveness of sources in relation to their total Si content, and their capacity to raise soil and plant Si concentrations. This study tested the hypothesis that the total Si content and provision of plant-available Si from six sources directly affects subsequent plant Si uptake as reflected in leaf Si concentration. Two trials with potted cane plants were established with the following Si sources as treatments: calcium silicate slag, fused magnesium (thermo) phosphate, volcanic rock dust, magnesium silicate, and granular potassium silicate. Silicon sources were applied at rates intended to achieve equivalent elemental soil Si concentrations; controls were untreated or lime-treated. Analyses were conducted to determine soil and leaf elemental concentrations. Among the sources, calcium silicate produced the highest leaf Si concentrations, yet lower plant-available soil Si concentrations than the thermophosphate. The latter, with slightly higher total Si than the slag, produced substantially greater increases in soil Si than all other products, yet did not significantly raise leaf Si above the controls. All other sources did not significantly increase soil or leaf Si concentrations, despite their high Si content. Hence, the total Si content of sources does not necessarily concur with a product's provision of soluble soil Si and subsequent plant uptake. Furthermore, even where soil pH was raised, plant uptake from thermophosphate was well below expectation, possibly due to its limited liming capacity. The ability of the calcium silicate to provide Si while simultaneously and significantly increasing soil pH, and thereby reducing reaction of Si with exchangeable Al3+, is proposed as a potential explanation for the greater Si uptake into the shoot from this source.

Silicon Induces Resistance to Bacterial Blight by Altering the Physiology and Antioxidant Enzyme Activities in Cassava

Cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis (Xam) is a devastating disease limiting cassava production. The potential effect of Si application on the physiological and biochemical mechanisms attributed to Si-mediated resistance of cassava to Xam was evaluated. The optimal concentration of Si in enhancing resistance to CBB without detrimental effects on plant growth was determined using cultivars TME14 and TMS60444 known for their susceptibility to Xam. Varied concentrations of Si (0.7 to 2.1 mM) were administered by watering the plants three times per week before and after Xam inoculation. The optimized Si concentration was used to evaluate the effect of Si supplementation on resistance to CBB disease using eight farmer-preferred cassava cultivars. The population of Xam, cultivar resistance, chlorophyll content, lipid peroxidation, H2O2 content, activity of antioxidant enzymes and total Si content in cassava cultivars were quantified 21 days post inoculation. Silicon concentration of 1.4 mM was optimal in enhancing cassava resistance to Xam. Silicon-treated plants of all cassava cultivars showed significantly (P ≤ 0.05) lower Xam population ranging from 5% to 26.7% compared to non-Si treated control plants. Activities of antioxidant enzymes, malondialdehyde, H2O2 and chlorophyll contents were significantly (P ≤ 0.05) higher in Si treated plants than non-Si treated plants. Silicon accumulation in leaves of Si treated plants was higher compared to non-Si treated control plants.

Evaluation of available silicon content and its determining factors of agricultural soils in Japan

ABSTRACTTo evaluate the available silicon (Si) content in agricultural soils in Japan and to investigate the determining factors of this content, we collected 180 soil samples from the surface layer of paddies and upland fields in Japan and determined their available Si contents. A phosphate buffer (PB; 0.02 M, pH 6.9) or an acetate buffer (AB; 0.1 M, pH 4.0) was used to extract available Si from the soil samples, and the Si concentrations in the extracts were determined by inductively coupled plasma-atomic emissions spectroscopy (ICP-AES). The total Si content and selected physicochemical properties were also determined for the soil samples. The median values of the available Si contents by the PB and AB methods were 48.8 and 79.7 mg kg−1 and corresponded to 0.017% and 0.027% of the total Si content, respectively. The overall data showed log-normal distributions. The available Si content of the upland soils was significantly higher than that of the paddy soils by both the PB (p < 0.01) and AB methods (p < 0.05). The available Si contents by the PB and AB methods had a significant positive correlation (p < 0.01) and they had significant negative correlation with the total Si content (p < 0.01). The values of the available Si contents by the PB and AB methods correlated positively with the pH, total carbon (C) content, and dithionite-citrate bicarbonate extractable iron (Fed) and aluminum (Ald), acid oxalate extractable iron (Feo) and aluminum (Alo), Fed-Feo and Alo+1/2Feo values (p < 0.01). A multi-regression analysis indicated that pH, amorphous minerals and crystalline iron (Fe) oxides were the dominant determining factors of available Si in the soils, and these three variables explained approximately two thirds of the variation of available Si content in agricultural soils in Japan. In terms of soil type, Terrestrial Regosols, Dark Red soils and Andosols had relatively high available Si contents, whereas Sand-dune Regosols, Red soils and Gray Lowland soils had relatively low contents. In terms of region, the soils in the Kanto and Okinawa regions had relatively high available Si contents and those in the Kinki, Shikoku and Chugoku regions had relatively low contents. In conclusion, the available Si content and its determining factors for agricultural soils in Japan were quantitatively elucidated, and this will contribute to the establishment of rational soil management —including the application of silicate materials, taking into account the Si-supplying power of the relevant soils—for sustainable and productive agriculture in Japan.

Some biochemical defense responses enhanced by soluble silicon in bitter gourd-powdery mildew pathosystem

Silicon (Si) has been exploited for its beneficial effects in terms of disease control in many plants. Added Si was found to accumulate beneath the cuticle and act as a barrier against pathogen penetration, and also induce biochemical defense responses in plants. This study investigated the effect of soluble silicon (Si) supply on biochemical defense responses against powdery mildew pathogen (Erysiphe sp.) in bitter gourd (Momordica charantia L.), an intermediate Si accumulator. Supplying the sand-based growth medium with 200 ppm potassium silicate (Si+) significantly reduced the severity of powdery mildew infections, elevated the activities of enzymes peroxidase, polyphenol oxidase and pathogenesis-related proteins; chitinase and β-1,3-glucanase in bitter gourd leaves after challenged by Erysiphe sp. compared with those grown in control mix (Si−). After 7 weeks growth in Si-amended medium, leaves accumulated nearly seven times as much silicon (3.36 % dry weight) as those grown in control mix (0.44 % dry weight). The total Si content in leaves gradually decreased after the Si amendment was ceased. Si + plants exhibited a stronger antifungal activity against Cladosporium cladosporioides. Three zones with antifungal activity were revealed after separation of methanolic leaf extracts on thin-layer chromatography plates, out of which one compound was found to have induced by Si and/or Erysiphe infection, and another induced only by Si amendment. These results suggest that Si would play an active role in strengthening resistance in bitter gourd plants against powdery mildew by stimulating expression of several biochemical defense reactions.

Silicon application enhances resistance to xanthomonas wilt disease in banana

Silicon (Si) has been reported to be a beneficial element and shown to enhance disease resistance in many crops, although it is not regarded to be critical for plant growth and development. In this study, the potential effect of Si supplementation on resistance to banana xanthomonas wilt (BXW) disease was evaluated using various banana cultivars. Si application at a concentration of 200 mg per plant per week was found to be optimal in enhancing resistance to BXW without any detrimental effects on plant growth. The effect of varying the duration of Si application showed continuous supply of Si before and after pathogen inoculation led to a significantly higher level of resistance to BXW in all the banana cultivars tested in comparison to non‐Si‐treated inoculated plants. Banana plants treated with Si before pathogen inoculation only, also exhibited high protection against BXW similar to plants treated continuously with Si. The total Si content in leaves increased significantly in Si‐treated plants in comparison to non‐Si‐treated control plants. The amount of Si accumulation was directly correlated to the duration of application; plants treated with Si continuously showed significantly higher amounts of Si accumulation in leaves than plants where Si application was terminated following bacterial inoculation or when Si application started immediately after pathogen inoculation. The Si‐treated plants also showed higher activity of the peroxidase enzyme in comparison to non‐Si‐treated control plants. This study confirms that application of Si enhances resistance to BXW and may provide an alternative disease management strategy.

Synthesis of SAPO-34 using metakaolin in the presence of β-cyclodextrin

SAPO-34 molecular sieves were synthesized by the addition of β-cyclodextrin (β-CD) as crystal growth inhibitor using metakaolin as silicon and aluminum sources. Properties of the obtained samples were characterized by XRD, SEM, N2 adsorption–desorption, FTIR, XRF, EDX, NH3-TPD and 29Si MAS NMR. When β-CD was added, crystal size of the SAPO-34 crystals decreased. Variation of Si content from the crystal center to surface decreased while total Si content hardly changed. 29Si MAS NMR results showed that β-CD contributed to better Si dispersion and decreased the size of Si(4Si) patches. Moreover, the MTO (methanol-to-olefin) process was conducted to investigate the influence of β-CD on catalytic performance. The synthesized sample with molar ratio of β-CD/Al2O3 equaling 0.055 remained active for 610 min while the sample synthesized without β-CD for only 280 min, which indicates that the lifetime of catalyst synthesized with β-CD is greatly prolonged.

The Influence of the Chemical Composition on the Corrosion Performances of Some Al-Fe-Si, Al-Mg-Si and Al-Mg-Mn Type of Alloys

Paper presents the results on the corrosion behavior of some Al-Fe-Si, Al-Mg-Si and Al-Mg-Mn alloys in their final commercially usable tempered state. Durability of alloys was quantified and compared in the sense of corrosion rates in aqueous solutions while also having in mind the role of alloy chemistry. Open circuit corrosion potential (OCP) measurements, linear polarization and potentiodynamic anodic/cathodic polarization was employed in order to determine the corrosion behavior of samples in the mixture of chloride ions containing aqueous corrosion ambient. We found out that AlFe0.83Si0.18(AA8079), AlMg0.63Si0.72 (AA6005) and AlMg4Mn (AA5182) alloy exhibited the highest rates of passivation in 0.51 mol NaCl solution. The group of Al-Fe-Si alloys exhibited the greatest sensitivity to the changes in chemical composition under potentiodynamic polarization. Artificially aged Al-Mg-Si extruded profiles and fully annealed (after cold rolling) Al-Mg-Mn sheets exhibit very similar levels of equilibrium potentials E(I=0) in 0.51 mol NaCl solution. In the case of Al-Fe-Si alloys, we found that Fe/Si ratio also plays an important role, next to the total content of Fe and Si. Alloys with high Fe/Si ratios showed almost 30 % lower polarization resistance compared to the alloys with balanced Fe/Si, even in the case of the equal total content of alloying elements. The AlMg0.7Si1.2Mn0.8 alloy aged after quenching in the sprayed water and AlMg4Zn1.3Mn0.4 annealed sheet exhibit very similar levels of corrosion rates in 0.51 mol NaCl solution.

Changes in texture and retorting yield in oil shale during its bioleaching by Bacillus Mucilaginosus

Bioleaching of oil shale by Bacillus mucilaginosus was carried out in a reaction column for 13 d. The pH value of the leaching liquor decreased steadily from 7.5 to 5.5 and the free silicon dioxide concentration reached approximately 200 mg/L in it. Scanning electron microscopy(SEM) observations revealed that a mass of small particles separated from the matrix of oil shale. Energy dispersive spectrometry(EDS) analysis implied that the total content of Si,O, Al was decreased in the particle area of the matrix. These facts indicate that the silicate was removed, leading to the structural transformation of oil shale. Comparison of the shale oil yields before and after bioleaching illustrated that approximately 10% extra shale oil was obtained. This finding suggests that the demineralisation of the oil shale by silicate bacteria improves shale oil yield.

Evaluation of industrial wastes as sources of fertilizer silicon using chemical extractions and plant uptake

AbstractSix inorganic industrial‐waste materials (coal fly ash, bauxite‐processing mud, steel slag, two samples of air‐cooled blast furnace [BF] slag, and one sample of water‐cooled BF slag), along with wollastonite, were evaluated as fertilizer‐Si sources. Evaluation was carried out by analyzing total and extractable Si fractions in the materials, by incubating them at two rates with a Si‐deficient soil and measuring potentially available extractable Si and by measuring yield and Si uptake by two successive rice crops grown in the fertilized soils. Of the waste materials used, fly ash had the highest total Si content (29%) but a negligible quantity was present in extractable forms. Steel slag and bauxite‐processing mud had only 5%–7% Si content while BF slags contained 14%–18% Si. All materials, other than fly ash, increased the amount of extractable Si present in the soil. Additions of steel slag and bauxite‐processing mud caused greater increases in Si extractability than the air‐cooled BF slags while water‐cooled BF slag–treated soils contained notably high acid‐extractable Si. Because of the alkaline nature of the materials, and their reaction products, there was a positive relationship between extractable soil Si and soil pH. However, an equilibration experiment using NaSiO3 as the Si source confirmed that Si solubility in the soil decreased with increasing pH. Dry‐matter yields of rice, at the lower rate of Si addition, were increased by all treatments other than fly ash. The higher rates of steel slag and bauxite‐processing mud caused yield depressions. Total Si uptake by rice was increased by all treatments, other than fly ash, and was greater at the higher rate of Si addition. It was concluded that the BF slags are the most effective waste materials as fertilizer‐Si sources and that, in slag‐amended soils, CaCl2 and NH4 acetate are the most reliable soil‐test extractants.

INFLUENCE OF PLANT ASSOCIATIONS ON THE SILICON CYCLE IN THE SOIL-PLANT ECOSYSTEM

Soluble Si compounds such as monosilicic and polysilicic acids affect chemicals and physical properties of the soil. The main aim of this study is to evaluate Si cycle in the various soil-plant s ystems via the determination of mobile Si forms in the soi l and of the total content of Si in the plant assoc iations. The concentrations of monosilicic acid, polysilicic acids and acid-extractable Si in unmowed meadow, mowed meadow, birch-aspen forest, spruce wood and agricultural land soil-plant systems, were tested at the soil depths of 0-10, 20-30 and 50-60 cm in a Ru ssian region, south of Moscow. The annual content o f Si within the investigated soil-plant systems was c alculated. Forty to 80 kg ha -1 of Si is annually removed from Grey Forest Soil (Luvisol). The concentration of monosilicic acid in the upper soil horizon depended on the type of plant association and on th e total content of adsorbed Si. The removal of plan t remains from the ecosystems resulted in decreased monosilicilic acid concentration in the upper soil horizon. The ecosystems which utilize annual plant remains increased the content of monosilicilic acid of the surface soil horizon. The concentration of mono silicic acid in the upper soil layer can be used as indicator of the stability of plant association. Th e unmowed meadow and the birch-aspen forest were characterized as ecosystems with accumulative type of Si cycle. The agricultural land, the mowed

Plant Alkaline Fusion Technique Followed by Colorimetric Procedure for the Detection and Quantification of Total Silicon in Ornamental Plants

Silicon (Si)–determination procedures currently available require expensive equipment and must be modified to assess Si concentrations in plant tissues. A Si-determination procedure referred to as the plant alkaline fusion technique, or PAFT, was developed to assess total Si concentrations, specifically in plant tissue. The procedure consists of dry-ashing the plant material, alkaline fusion, solubilization of the fusion cake, dilution, and colorimetric determination to quantify total Si content. The fusion technique for solubilizing plant Si can be performed using sodium hydroxide (NaOH), nickel crucibles, and Bunsen burners. Silicon concentrations of two National Institute of Standards and Technology (NIST) standard reference materials (SRM) [pine needles (SRM 1575) and peach leaves (SRM 1547)], a rice straw standard (LSU#5), an NIST soil standard (SRM 2709), and five ornamental plant species were all assessed using the PAFT procedure, and then these values were compared to two different inductively coupled plasma–optical emission spectroscopy (ICP-OES) procedures conducted by independent laboratories. The PAFT Si determination procedure typically reported the greatest value or was within 15% of the two ICP-OES procedures while costing significantly less than both ICP-OES procedures.

Effect of geo-pedological conditions on the distribution and chemical speciation of selected trace elements in forest soils of western Alborz, Iran

Geologic and pedologic controls have an important influence on the abundance, distribution and behavior of elements in natural soil environments. In order to assess the role of these factors on distribution and chemical speciation of selected trace elements in soil, soils on six parent materials including phyllite, tonalite, peridotite, dolerite, shale and limestone were sampled in western Alborz in Iran. Soil genesis and development of representative residual pedons were studied for each parent material and the total content of Si, Al, Fe, Ca, Mg, Co, Cr, Cu, Mn, Ni, Pb, V and Zn were compared. Enrichment/depletion patterns of trace elements were assessed using Ti as the reference element and lowest horizon as the reference layer. A modified BCR (European Community Bureau of Reference) sequential extraction procedure was used to fractionate the elements into four operationally defined species. The total contents of Co, Cr, Ni and V are highest in soils derived from peridotite (53, 984, 285, and 204 mg kg − 1 , respectively) and dolerite (39, 1023, 176, and 185 mg kg − 1 , respectively). Lead and Zn contents are highest in soils derived from shale (27 and 106 mg kg − 1 , respectively), which is probably due to the high sorption capacity of clay. Different elements exhibited very different enrichment/depletion patterns in a given pedon. Moreover, depth distribution patterns differed also for a given element among soils with different parent material and even showed considerable variation among soils with similar lithology. Lead, Zn, Cu and Mn have been generally enriched in most pedons, except in some acidic and strongly leached soils, whereas Co, Cr, Fe, Ni and V have been leached, especially from Dystrudepts and Eutrudepts. The latter elements, however, showed enrichment trend in Hapludalfs and Argiudolls parallel to the development of illuvial B horizons. Iron, Cr, Cu, Ni, V and Zn are present primarily in the residual fraction, independent of soil and parent material type, whereas Mn, Pb and Co were mainly present in the non-residual fractions of most pedons. Trace element concentrations in the soils of the study area are related primarily to the parent material type while pedogenic processes appear to have played a minor role.