Printer Friendly

Optimising the extraction of amorphous silica by NaOH from soils of temperate-humid climate.

Introduction

Silicon (Si) is the second most abundant element (28.8 mass%) in Earth's crust after oxygen (Wedepohl 1995). It takes part in buffer reactions in soils, thus decelerating soil acidification, and decreases the toxicity of aluminium (Al) and other metals for soil organisms and plants (Schindler et al. 1976; Gerard et al. 2001; Matichenkov and Bocharnikova 2001; Ma and Yamaji 2006). Moreover, Si plays multiple roles in plant growth and crop health (Epstein 2001; Tavakkoli et al. 2011). Its availability can positively influence the yield of crops such as rice (Korndorfer and Lepsch 2001), wheat (Rafi and Epstein 1999) and sugarcane (Savant et al. 1999; Meyer and Keeping 2000). Despite the important role of Si in biogeochemical cycles and biological processes (Derry et al. 2005), specific knowledge about Si pools and dynamics in soils is still lacking (Sommer et al. 2006).

The study presented here focuses on extracting Si from amorphous silica in soils ([Si.sub.a]), because this fraction is assumed to play a major role in Si availability and cycling (Alexandre et al. 1997) and because it is more soluble than crystalline minerals (Gebhardt 1976; Her 1979).

Extraction of Sia is usually carried out at high temperatures by using alkaline extractants, such as [Na.sub.2]C[0.sub.3] (e.g. Follett et al. 1965; Arnseth and Turner 1988; Clymans et al. 2011), NaOH (e.g. Foster 1953; Hashimoto and Jackson 1960; Koning et al. 2002) or a complexing agent, e.g. Tiron ([C.sub.6][H.sub.4][Na.sub.2][0.sub.8][S.sub.2]) (Biermans and Baert 1977; Kodama and Ross 1991). The results obtained by these methods depend on (i) on the chemical process (protonation, complexation, ligand exchange, etc.) and the efficiency of the extracting agent; (ii) the effective surface available for chemical reactions; and (iii) the degree of crystallinity of the different Si phases that are present in the soil.

The alkaline extractants [Na.sub.2]C[0.sub.3] and NaOH are commonly used at varying concentrations, extraction times, solid : solution ratios (SSR) and temperatures (e.g. Chadwick et al. 1989; Herbauts et al. 1994; Conley 1998). Several studies showed that these extractions are not sufficiently selective and that clay minerals are easily attacked by the extractants (Follett et al. 1965; Wada and Greenland 1970; Krausse et al. 1983; Breuer and Herrmann 1999). Hence, the contribution of silicate Si to the amounts of Si measured in extracts should be considered when these high-temperature extractions are applied (Sauer et al. 2006). Consequently, correction methods for mineral Si have been developed (DeMaster 1981; Kamatani and Oku 2000). The DeMaster (1981) technique is based on the observation that at high pH (using 1% [Na.sub.2]C[0.sub.3]) and elevated temperature (80-85[degrees]C), most amorphous silica completely dissolves within the first 2 h of extraction, whereas it is assumed that Si release from silicates is constant over the entire extraction time of usually 5 h. These differences in dissolution behaviour are utilised to determine the amounts of [Si.sub.a] by linear extrapolation of Si release from silicates (2-5 h extraction time) back to t = 0 to correct for mineral dissolution. The method of DeMaster (1981) is commonly used in marine sedimentology and has been applied more recently to soils (e.g. Conley and Schelske 2001; Saccone et al. 2008; Comelis et at. 2011; Meunier et al. 2014). The [Na.sub.2]C[0.sub.3] method may severely underestimate the amounts of amorphous silica in soil (Saccone et al. 2007; Meunier et al. 2014). On the other hand, [Na.sub.2]C[0.sub.3] partially dissolves poorly crystalline minerals (Comelis et al. 2011; Georgiadis 2011).

According to Hashimoto and Jackson (1960), the ratio of extracted Si: Al (extractions with 0.5 n NaOH) reflects the relative contributions of amorphous Si phases and allophanes. Based on the assumption that Al and Si release from silicates proceeds linearly over time, Kamatani and Oku (2000) developed a procedure to calculate Sia based on the amounts of extracted bulk Al. Si is plotted against Al, and Al concentration (on the x-axis) is linearly extrapolated to its intercept with the v-axis. The intercept is interpreted to represent the Sia content of the sample. This correction method, however, requires that the Si: Al ratio from silicate dissolution remains constant during the extraction (Koning et al. 2002) and that no co-precipitation of Al with amorphous Si phases takes place in the soil.

Biermans and Baert (1977) used an alkaline-complexing Tiron solution that simultaneously extracts amorphous Al, iron (Fe) and Si phases from soils. Kodama and Ross (1991) showed that the amounts of allophane, imogolite and weakly crystalline Fe oxides extracted by Tiron arc similar to those extracted by ammonium oxalate solution (Tamm 1932; modified by Schwertmann 1964). They also obtained amounts of Sia similar to those obtained by NaOH extraction (Kodama and Ross 1991). According to Guntzer et al. (2010), the Tiron method is suitable for the quantifying fresh phytoliths and extracting Si in amorphous components from soils. However, considerable smectite dissolution by Tiron was detected by Georgiadis (2011). Because of its strong disposition to form Al-organic complexes, Tiron can break down smectite, which is a disadvantage when studying soils dominated by 2: 1 layer clay minerals.

As shown above, the various existing methods for chemical extraction of Sia from soils all have specific constraints. Therefore, we carried out a series of extraction experiments with 0.2 m NaOH (modified after Kamatani and Oku 2000) on a variety of well-characterised substances, in which we systematically varied the extraction conditions. The aim of these experiments was to identify a set of conditions at which 0.2 m NaOH dissolves amorphous silica in soils from a temperate-humid climate, while minimising the attack of other Si compounds.

Materials and methods

Model compounds and soil samples used for the test series

Effects of different extraction conditions were tested on selected model compounds. These included two clay minerals (kaolin and smeetite; CH Erbsloh, Krefeld, Germany), one kind of feldspar (microcline, Dr F. Krantz, Bonn, Germany), and two types of amorphous silica: silica gel (Merck, Kenilworth, NJ, USA) and bio-opal (amorphous silica of biogenic origin) obtained from Equisetum fluviatile (water horsetail) following the procedure of Bartoli and Wilding (1980). The model compounds and soil samples selected for the experiments have been characterised in terms of pH, mineralogy and element composition in previous publications (Georgiadis et al. 2013, 2014) (Table 1).

Soils were sampled in four regions in south-west Germany. Soil included: two Podzols (one on the upper slope, the other on the foot slope) on Triassic sandstone under a forest of silver fir and Norway spruce in the northern Black Forest; two Cambisols (one on the upper slope, the other (Chromic) on the lower slope) on gneiss under a spruce forest in the southern Black Forest; a Stagnosol on periglacially reworked loess under a mixed forest of spruce, fir and beech; and a Luvisol on loess under a woodruff beech forest in the Kraichgau region. In total, 42 mineral horizons were analysed (FAO Guidelines for Soil Description 2006).

Mobile Si (extracted by Ca[Cl.sub.2] solution), adsorbed Si (extracted by acetic acid), Si in soil organic matter (released by [H.sub.2][O.sub.2]) and Si in pedogenic oxides (released by N[H.sub.4] oxalate under UV radiation) were removed from the soil samples before the extraction of Si from amorphous silica, according to the sequential Si extraction introduced by Georgiadis et al. (2013). Silica gel and bio-opal were employed to test the efficiency of NaOH solution in dissolving amorphous silica, whereas the crystalline materials were used to test the aggressiveness of the extractant against these minerals. Mixtures of clay minerals and silica gel (using ratios of clay mineral to silica gel of 9: 1 and 1:1) were used to test whether the extraction behaviour of the compounds in mixtures differs from that of the pure compounds. The software SigmaPlot 11.0 (Systat Software, San Jose, CA, USA) was used for statistical analyses.

A first-order dissolution model was used to describe the dissolution of tested materials (Koning et al. 2002):

[A.sub.t] = [A.sub.0] x [e.sup.-kl]

Here, [A.sub.t] is the Si amount of the sample at time t (h), [A.sub.0] is the initial Si amount of the sample, and k is the rate constant ([h.sup.-1]).

Extraction conditions tested

Pre-trials with silica gel demonstrated the importance of high pH for efficient silica gel dissolution (lh, 85[degrees]C, SSR 1 MOO, Georgiadis 2011; no. 1 in Table 1). Silica gel was dissolved below pH 12 only up to 20% and at pH [greater than or equal to] 13 to [greater than or equal to] 80%. A 0.2 m NaOH solution at pH 13.3 completely dissolved the silica gel. Therefore, 0.2 m NaOH was applied at different SSRs, temperatures and extraction times. Polyethylene ware was employed instead of glassware, in order to minimise Si contamination.

We tested SSRs of 1 :50, I : 200, 1 :300, 1 :400, 1 :600, 1:800 and 1:1000. Temperatures were 100[degrees]C, 85[degrees]C, 65[degrees]C (water bath and shaking at 90rpm) and room temperature (horizontal shaker at 250 rpm). The extraction lasted 10 min, 30 min, 1 h, 3h, 5h, 15h, 24 h, 48 h and 72 h. In addition, extraction times of 120 h, 144h and 168 h at room temperature were applied to water horsetail bio-opal and soil samples.

After the hot extractions (>65[degrees]C), the samples were cooled down for 10 min in a cold water bath. All extracts were centrifuged at 3000 rpm for 5 min and the supernatant was filtered through paper filters (12[micro]m), then, if the filtrate was not clear, through membrane filters (0.2 pm). Concentrations of Si and A1 in the filtrate were determined by inductively coupled plasma-optical emission spectrometry (Vista Pro; Varian, Palo Alto, CA, USA). Two replicates were used for all extractions and analyses.

Results and discussion

Effect of SSR on Si extraction

The SSR was identified as a crucial factor for efficiency of extraction of bio-opal. Increasing the ratio from 1 : 100 to 1:300 considerably enhanced the extraction efficiency (Fig. 1; no. 2 in Table 1). At SSR of 1 :300, water horsetail bio-opal was almost completely extracted within 3 h; by contrast, only 20% of the bio-opal was dissolved at a ratio 1:100 within the same timespan.

In a subsequent step, an extraction series with SSRs ranging from 1 :50 to 1 : 1000 was carried out on silica gel. Complete dissolution of silica gel (>90%, which is within the limit of the analytical accuracy) was achieved with a ratio of 1 :200 and higher (Fig. 2; no. 3 in Table 1). An SSR value of 1 :400 appeared the best option, because the maximum extraction efficiency was reached with this variant after only 1 h of extraction time. Higher SSRs did not increase extraction efficiency further. The dissolution rate of silica gel and bioopal depended on the SSR. Increasing the SSR from I : 100 to 1:300 increased the rate constant (k) by a factor of ~ 1.3 for silica gel (from 3.3 to 4.4 [h.sup.-1] [R.sup.2] = 0.99) and by a factor of ~40 for bio-opal (from 0.06 to 2.3 [h.sup.-1], [R.sup.2] = 0.99), assuming first-order Si-dissolution kinetics (Koning et al. 2002).

The SSR of 1 :400 was, however, unlikely to be high enough to dissolve bio-opal (obtained by density separation from soil samples) completely from some organic topsoil (O) horizons (Georgiadis etal. 2014). Bio-opal solubility depends on specific surface area, water content, degree of internal order (e.g. due to ageing), and the presence of other soil components (Kamatani and Oku 2000; Koning et al. 2002). The solubility of soil-derived bio-opal that had experienced previous alteration in the soil environment might be lower than that of the plant bio-opal and silica gel used in the experiments introduced at the beginning of this section. In conclusion, SSR should potentially be higher than 1 :400 for Si extraction from soil-derived bio-opal.

However, since the optimum soil-sample weight is ~1 g (a lower sample weight results in a larger variation of laboratory readings), SSRs higher than 1 :400 are hardly practicable. In addition, the extraction of smectite and kaolin samples revealed that a high SSR increased Si release not only from amorphous silica, but also from clay minerals (Fig. 3; no. 5 in Table 1). During the first 10-20 min of smectite extraction, Si release exceeded that of Al. The same observation was made by Koning et al. (2002) during continuous clay mineral extraction (leaching method with 0.5 m NaOH, adapted from Muller and Schneider (1993). This can be explained by the 2 : 1 layer structure of smectite, in which the Al octahedron sheet is not exposed to the extractant during the initial extraction phase. Alkaline solutions generally break down the Si tetrahedron sheets in smectites first (Borchardt 1989).

Release of Si from clay minerals during the first hour of alkaline extraction was not linear (Fig. 4a; no. 6 in Table 1). This is in agreement with Kamatani and Oku (2000), who reported a parabolic Si-release from clay minerals under similar conditions, but at SSR of 1 : 1300-1 :2000. Silicon release from both clay minerals followed first-order kinetics (k = 0.05 [h.sup.-1], [R.sup.2] = 0.99).

The Si release curves of clay mineral-silica gel mixtures at a ratio of 9 : 1 (Figs 4b, 5a; nos 6, 9 in Table 1) showed a different behaviour from clay mineral-silica gel mixtures at a ratio of 1 : 1 (Fig. 5b; no. 9 in Table 1). Concentrations of Si in the extracts remained constant after 30 min extraction time, resulting in lower Sia values (80-88%). The release from I : 1 mixtures demonstrates that dissolution of crystalline minerals is not relevant if samples contain large amounts of amorphous silica. Such conditions may occur in O horizons, which are typically enriched with biogenic amorphous silica (Golyeva 1999).

Effect of temperature on Si extraction

Extraction from silica gel at varying elevated temperatures (65[degrees]C, 85[degrees]C and 100[degrees]C) resulted in very similar behaviours of Si release, with maxima reached after ~1 h. By contrast, silica gel dissolution at room temperature was completed after 5h (Fig. 2b; no. 4 in Table 1). The silica gel rate constant at room temperature (k = 0.58 [h.sup.-1], [R.sup.2] = 0.97) was about one-tenth of that at 85[degrees]C (k=5.7 [h.sup.-1], [R.sup.2]= 0.99).

Silicon release from clay minerals was much lower at room temperature (no. 7 in Table 1). The Si concentration in the extract after 24 h at room temperature was decreased by factors of 45 (kaolin) and 13 (smectite), relative to 5h extraction at 85[degrees]C. Although Si release from smectite during extraction at room temperature was larger than from kaolin, Si extracted from smectite after 24 h was only 2.55 mg [g.sup.-1] compared with 33mgg 1 after 5h extraction at 85[degrees]C. The Si: Al ratios in the extracts obtained at room temperature were very large (~275 : 1), indicating that silicate dissolution was considerably less extensive than under hot extraction. No Al release from kaolin or feldspar was detected after 5 h of extraction at room temperature, whereas after 5 h of extraction at 85[degrees]C, the kaolin extract represented 13 mg [g.sup.-1] and the feldspar extract 1.5 mg [g.sup.-1] Al (Georgiadis 2011).

The clay mineral extractions with 0.2 m NaOH at 85[degrees]C and at room temperature were then extended to 6h and 75 h, respectively (no. 8 in Table 1). The clay minerals were etched with 0.2 m NaOH for 5 h at room temperature before the extractions, in order to remove potential amorphous silica precipitates from the clay mineral surfaces. Then the residues were washed twice with deionised water and dried at 40[degrees]C. Amounts of Si extracted after 6 h at 85[degrees]C exceeded those after 75 h extraction at room temperature (Georgiadis 2011) by a factor of 10 for smectite and by a factor of 30 for kaolin.

Clay mineral-silica gel mixtures (ratio 9:1) were then extracted at room temperature. The Si concentration in the extract of the kaolin-silica gel mixture approached a constant value after 5 h of extraction at room temperature, whereas the Si concentration in that of the smectite-silica gel mixture remained constant after 9h (Fig. 5c; no. 9 in Table 1). The measured Si concentrations were equivalent to 73-78% of the expected amount of Sia from silica gel.

These results indicate Si-extraction efficiency of 0.2 m NaOH after 5-9 h at 25[degrees]C similar to that after 1 h at 85[degrees]C (Fig. 5a, c). An advantage of the extraction at 25[degrees]C is that only minor amounts of Si were released from the silicates. This is indicated by the Si concentration in the extract, which remained constant after dissolution of silica gel. No further dissolution of clay minerals was measured. Therefore, the amounts of Si from amorphous silica could be obtained directly from the maximum Si concentration measured in the extract without applying a correction for Si from dissolved silicates. On the other hand, Sia extraction at room temperature was apparently not complete.

Extraction with 0.2 m NaOH at room temperature depended on the type of amorphous silica. The release of Si from silica gel finished after 5 h extraction time, whereas water horsetail bioopal continued to dissolve for up to 168 h (no. 10 in Table 1), which is demonstrated by their rate constants (0.025 [h.sup.-1], [R.sup.2] = 0.97 for bio-opal, 0.58 [h.sup.-1], [R.sup.2] = 0.97 for silica gel). A mixture of bio-opal and silica gel (1 : 1) dissolved in 0.2 m NaOH to ~90% after 168 h at room temperature with k = 0.006 [h.sup.-1], [R.sup.2] = 0.99 (Georgiadis 2011).

The pH values of the extracts of clay minerals and clay mineral-silica gel mixtures did not change considerably during extraction, irrespective of the temperature. The difference in pH before and after the extractions was at most 0.3 units, and pH remained at 13 in almost all samples (pH 13.3 at the beginning of the extraction). Hence, any influence of changes in pH on the extraction capacity of 0.2 m NaOH is excluded.

Extracts of soil samples generally exhibited constant Si concentrations after ~120h extraction time at room temperature (Table 2; no. 11 in Table 1). The rate constant for the O and Ah horizons of the Podzols, Cambisols and the Luvisol was -0.02 [h.sup.-1] ([R.sup.2]2 >0.9, n = 7), which was similar to the dissolution rate of pure bio-opal (0.025 IT1). This may indicate that Si extracted from the O and Ah horizon samples originated from bio-opal. The rates for the subsoil samples were lower, 0.01-0.02 [h.sup.-1], ([R.sup.2] > 0.9, n =19). The lowest rates were calculated for the eluvial horizons of the Podzols and the Luvisol (0.011-0.015 [h.sup.-1]), but rates were enhanced for the spodic and argic horizons (0.013-0.019 [h.sup.-1]). These soil horizons are supposed to accumulate amorphous, nonbiogcnic silica (Georgiadis et al. 2014).

The O horizon of the Cambisol (Chromic) contained 10 mg Si [g.sup.-1] whereas the O, A and E horizons of the other soils contained only 2.5-3 mg Si [g-.sup.1 ](Table 2). Saccone et al. (2007), who applied an automated alkaline extraction procedure according to Koning et al. (2002) to Oa--A horizon material of a Podzol, observed constant Si release at ~10 mg Si [g.sup.-1 ]as well, which they interpreted to be derived from bio-opal.

The large Si: Al molar ratios after 120 h extraction time of topsoil samples (10-60) relative to those of subsoil samples (1-3) also strongly suggest that Si in topsoils was mainly derived from bio-opal (Gcorgiadis et al. 2014). Bio-opals are usually poor in Al (Conley et al. 2006), thus with typical Si: Al ratios of 8-20 (Bartoli and Wilding 1980; Bartoli 1985).

In the subsoil samples, Si may be released from various compounds, including, for example, short-range-order silicates in spodic horizons, which is indicated by the large Al amounts in the Bs horizon or from intermediate products of clay transformation (Gebhardt 1976). The source of Si and Al extracted with NaOH may therefore be a mixture of poorly crystallised silicates (sources of Si and Al) and/or bio-opal (source of Si) transported downwards by processes such as illuviation and/or bioturbation (Saccone et al. 2008).

Based on the results of the experiments reported above, we suggest extracting Sia from soils from temperate-humid climate with 0.2 m NaOH at room temperature, since dissolution of crystalline silicates is negligible under these conditions.

Conclusions and recommendations

In this study, we have shown that the required solid: solution ratio and extraction duration depend on the sample. A ratio of 1 :400 is suitable for amorphous silica extraction from soils. Complete dissolution of pure water horsetail bio-opal required an extraction time of 168 h in the test series reported here; 5 h was needed to dissolve silica gel. For detailed investigations, Si concentrations in the extract should be analysed after 5 h and at regular intervals thereafter, e.g. every 10-12 h, to ensure complete dissolution of amorphous silica. The constant Si concentration in the extract, reached after -120-168 h, is considered to be Si released from different amorphous silica compounds in the soil sample.

The calculation of the rate constant for Si dissolution can help to indicate different amorphous silica compounds in soils and related soil processes.

During lengthy extraction at room temperature, samples should be shaken very slowly end-over-end instead of horizontally to avoid abrasion of soil particles and at the same time ensure immediate dispersal of released Si in the extract (McKeague and Cline 1963). The Si extraction at room temperature is probably too weak to dissolve silica efficiently from soils characterised by extreme silica accumulation, especially from silcretes, because silica in silcretes is often partially dehydrated and transformed into more stable, mostly microcrystalline phases (Sauer et al. 2015). Therefore, the method at room temperature is recommended primarily for soils in temperate-humid climate where such extreme accumulations generally do not occur.

http://dx.doi.org/10.1071/SR14171

Acknowledgements

This study was part of the project 'Development of a method for fractionated Si analysis in soils' funded by the German Research Foundation (DFG STA 146/48-1), which is gratefiilly acknowledged. It was a sub-project of the DFG project bundle 'Multiscale analysis of Si cycling in terrestrial biogeosystems'. We also thank the Alfred Toepfer Stiftung F.V.S. for financial support. Special thanks go to Katie Mackie for correcting the manuscript's English grammar.

References

Alexandre A, Meunier J-D, Colin F, Koud J-M (1997) Plant impact on the biogeochemical cycle of silicon and related weathering problems. Geochimica et Cosmochimica Acta 61, 677-682. doi: 10.1016/S0016703 7(97)00001-X

Arnseth RW, Turner RS (1988) Sequential extraction of iron, manganese, aluminum, and silicon in soils from two contrasting watersheds. Soil Science Society of America Journal 52, 1801-1807. doi: 10.2136/ sssaj 1988.03615995005200060052x

Bartoli F (1985) Crystallochemistry and surface properties of biogenic opal. Journal of Soil Science 36, 335-350. doi:10.1111/j. 1365-2389.1985. tb00340.x

Bartoli F, Wilding LP (1980) Dissolution of biogenic opal as a function of its physical and chemical properties. Soil Science Society of America Journal44, 873-878. doi:10.2136/sssajl980.03615995004400040043x

Biermans V, Baert L (1977) Selective extraction of the amorphous Al, Fe and Si oxides using an Alkaline-Tiron solution. Clay Minerals 12, 127-135. doi: 10.1180/claymin. 1977.012.02.03

Borchardt G (1989) Smectites. In 'Minerals in soil environments'. 2nd edn (Eds JB Dixon, SB Weed) pp. 675-727. (Soil Science Society of America: Madison, WI, USA)

Breuer J, Herrmann L (1999) Eignung der extraktion mit natriumbikarbonat fur die charakterisierung von bodenbildenden prozessen. Mitteilungen der Deutschen Bodenkundlichen Gesellschaft 91, 1375-1378.

Chadwick OA, Hendricks DM, Nettleton WD (1989) Silicification of Holocene soils in Northern Monitor Valley, Nevada. Soil Science Society of America Journal 53, 158-164. doi: 10.2136/sssaj 1989.036 15995005300010030x

Clymans W, Struyf E, Govers G, Vandevenne F, Conley DJ (2011) Anthropogenic impact on amorphous silica pools in temperate soils. Biogeosciences 8, 2281-2293. doi: 10.5194/bg-8-2281-2011

Conley DJ (1998) An interlaboratory comparison for the measurement of biogenic silica in sediments. Marine Chemistry 63, 39-48. doi: 10.1016/ S0304-4203(98)00049-8

Conley DJ, Schelske CL (2001) Biogenic silica. In 'Tracking environmental change using lake sediments. Terrestrial, algal, and siliceous indicators, Bd. 3'. (Eds .IP Smol, HJB Birks, WM Last) pp. 281-293. (Kluwer Academic Publishers: Dordrecht, The Netherlands)

Conley DJ, Sommer M, Meunier J-D, Kaczorek D, Saccone L (2006) Silicon in the terrestrial biogeosphere. In 'The silicon cycle: Human perturbations and impacts on aquatic systems'. SCOPE 66. (Eds V Ittekot, D Unger, C Humborg, NT An) pp. 13-28. (Island Press: Washington, DC)

Cornelis JT, Titeux H, Ranger J, Delvaux B (2011) Identification and distribution of the readily soluble silicon pool in a temperate forest soil below three distinct tree species. Plant and Soil 342, 369-378. doi: 10.1007/sl 1104-010-0702-x

DeMaster DJ (1981) The supply and accumulation of silica in the marine environment. Geochimica et Cosmochimica Acta 45, 1715-1732. doi: 10.1016/0016-7037(81)90006-5

Derry LA, Kurtz AC, Ziegler K, Chadwick OA (2005) Biological control of terrestrial silica cycling and export fluxes to watersheds. Nature 433, 728 731. doi:!0.1038/nature03299

Epstein E (2001) Silicon in plants: facts vs. concepts. In 'Silicon in agriculture'. (Eds LE Datnoff, GH Snyder, GH Komdorfer) pp. 1-15. (Elsevier Science B.V.: Amsterdam)

FAO Guidelines for Soil Description (2006) 'Guidelines for soil description.' 4th edn (FAO: Rome)

Follett EAC, Mchardy WJ, Mitchell BD, Smith BFL (1965) Chemical dissolution techniques in the study of soil clays: Parts 1 and II. Clay Minerals 6, 23-34. doi: 10.1180/claymin.1965.006.1.04

Foster MD (1953) Geochemical studies of clay minerals 111. The determination of free silica and free alumina in montmorillonites. Geochimica et Cosmochimica Acta 3, 143-154. doi: 10.1016/00167037(53)90003-9

Gebhardt H (1976) Bildung und Eigenschaften amorpher Tonbestandteile in Boden des gemaBigt-humiden Klimabereichs. Zeitschrift fiir Pflanzenernahrung und Bodenkunde 139, 73-89. doi: 10.1002/jpln. 19761390108

Georgiadis A (2011) Entwicklung einer methodc zur fraktionierten Sibestimmung in boden des feucht-gemaBigten klimas. Hohenheimer Bodenkundliche Hefte, 100. PhD Dissertation, University of Hohenheim, Germany.

Georgiadis A, Sauer D, Flerrmann L, Breuer J, Zarei M, Stahr K (2013) Development of a method for sequential Si extraction from soils. Geoderma 209-210, 251-261. doi:10.1016/j.geoderma.2013.06.023

Georgiadis A, Sauer D, Herrmann L, Breuer J, Zarei M, Stahr K (2014) Testing a new method for sequential Si-extraction on soils of a temperate-humid climate. Soil Research 52, 645-657. doi: 10.1071/ SR 14016

Gerard F, Boudot J-P, Ranger J (2001) Consideration on the occurrence of the All3 polycation in natural soil solutions and surface waters. Applied Geochemistry 16, 513-529. doi:10.10l6/S0883-2927(00)00048-2

Golyeva AA (1999) The application of phytolith analysis for solving problems of soil genesis and evolution. Eurasian Soil Science 32, 884-891.

Guntzer F, Keller C, Mcunier JD (2010) Determination of the silicon concentration in plant material using Tiron extraction. New Phytologist 188, 902-906. doi: 10.1111/j. 1469-8137.2010.03416.x

Hashimoto I, Jackson ML (1960) Rapid dissolution of allophane and kaolinite-halloysite after dehydration. In 'Proceedings of the 7th National Conference on Clays and Clay Minerals', pp. 102-113. (Pergamon Press: Washington, DC)

Herbauts J, Dehalu FA, Gruber W (1994) Quantitative determination of plant opal content in soils, using a combined method of heavy liquid separation and alkali dissolution. European Journal of Soil Science 45, 379-385. doi: 10.1111/j. 1365-2389.1994.tb00522.x

Iler RK (1979) 'The chemistry of silica.' (Wiley-Interscience: New York)

Kamatani A, Oku O (2000) Measuring biogenic silica in marine sediments. Marine Chemistty 68, 219-229. doi: 10.1016/S0304-4203(99)00079-1

Kodama H, Ross GJ (1991) Tiron dissolution method used to remove and characterize inorganic components in soils. Soil Science Society of America Journal 55, 1180-1187. doi: 10.2136/sssaj 1991.03615995 005500040047x

Koning E, Epping E, Van Raaphorst W (2002) Determining biogenic silica in marine samples by tracking silicate and aluminium concentrations in alkaline leaching solutions. Aquatic Geochemistry 8, 37-67. doi: 10.1023/A: 1020318610178

Korndorfer GH, Lepsch I (2001) Effect of silicon on plant growth and crop yield. In 'Silicon in agriculture'. (Eds LE Datnoff, GH Snyder, GH Korndorfer) pp. 133-147. (Elsevier Science B.V.: Amsterdam)

Krausse GL, Schelske CL, Davis CO (1983) Comparison of three wetalkaline methods of digestion of biogenic silica in water. Freshwater Biology 13, 73-81. doi:10.1111/j. 1365-2427.1983.tb00658.x

Ma JF, Yamaji N (2006) Silicon uptake and accumulation in higher plants. Trends in Plant Science 11, 392-397. doi:10.1016/j.tplants.2006.06.007

Matichenkov V V, Bocharnikova EA (2001) The relationship between silicon and soil physical and chemical properties. In 'Silicon in agriculture'. (Eds LE Datnoff, GH Snyder, GH Komdorfer) pp. 209-219. (Elsevier Science B.V.: Amsterdam)

McKeague JA, Cline MG (1963) Silica in soil solutions: I. The form and concentration of dissolved silica in aqueous extracts of some soils. Canadian Journal of Soil Science 43, 70-82. doi:10.4141/cjss63-010

Mcunier JD, Keller C, Guntzer F, Riotte J, Braun JJ, Anupama K (2014) Assessment of the 1% Na2C[O.sub.3] technique to quantify the phytolith pool. Geoderma 216, 30-35. doi:10.1016/j.geoderma.2013.10.014

Meyer JH, Keeping MG (2000) Review of research into the role of silicon for sugarcane production. Proceedings of the South African Sugar Technologists Association 74, 29-40.

Muller PJ, Schneider R (1993) An automated leaching method for the determination of opal in sediments and particulate matter. Deep Sea Research Part I: Oceanographic Research Papers 40, 425-144.

Raft MM, Epstein E (1999) Silicon absorption by wheat (Triticum aestivum L.). Plant and Soil 211, 223-230. doi:10.1023/A:1004600611582

Saccone L, Conley DJ, Koning E, Sauer D, Sommer M, Kaczorek D, Blecker SW, Kelly EF (2007) Assessing the extraction and quantification of amorphous silica in soils of forest and grassland ecosystems. European Journal of Soil Science 58, 1446-1459. doi: 10.1111/j. 1365-2389,2007.00949.x

Saccone L, Conley DJ, Likens GE, Bailey SW, Buso DC, Johnson CE (2008) Factors that control the range and variability of amorphous silica in soils in the Hubbard Brook Experimental Forest. Soil Science Society of America Journal 72, 1637-1644. doi:10.2136/sssaj2007.0117

Sauer D, Saccone L, Conley DJ, Herrmann L, Sommer M (2006) Review of methodologies for extracting plant-available and amorphous Si from soils and aquatic sediments. Biogeochemistry 80, 89-108. doi: 10.1007/ si 0533-005-5879-3

Sauer D, Stein C, Glatzel S, Kuhn J, Zarei M, Stahr K (2015) Duricrusts in soils of the Alentejo (southern Portugal)-types, distribution, genesis and time of their formation. Journal of Soils and Sediments 15, 1437-1453. doi: 10.1007/sl 1368-015-1066-x

Savant NK, Komdorfer GH, Datnoff LE, Snyder GH (1999) Silicon nutrition and sugarcane production: A review. Journal of Plant Nutrition 22, 1853-1903. doi:10.1080/01904169909365761

Schindler PW, Furst B, Dick R, Wolf PO (1976) Ligand properties of surface silanol groups. I. Surface complex formation with [Fe.sup.3+], [Cu.sup.2+], [Cd.sup.2+], and [Pb.sup.2+]. Journal of Colloid and Interface Science 55, 469-475. doi: 10.1016/0021 -9797(76)90057-6

Schwertmann U (1964) Differenzierung der Eisenoxide des Bodens durch Extraktion mit Ammoniumoxalat-Losung. Zeitschrift fiir Pflanzenernahrung und Bodenkunde 105, 194-202. doi: 10.1002/jpln. 3591050303

Sommer M, Kaczorek D, Kuzyakov Y, Breuer J (2006) Si pools and fluxes in soils--A review. Journal of Plant Nutrition and Soil Science 169, 310 329. doi: 10.1002/jpln.200521981

Tamm O (1932) Uber die oxalatmethode in der chemischen bodenanalyse. Meddelanden fran Statens skogsforsdksanstalt 27, 1-20.

Tavakkoli E, Lyons G, English P, Chris N, Guppy CN (2011) Silicon nutrition of rice is affected by soil pH, weathering and silicon fertilisation. Journal of Plant Nutrition and Soil Science 174, 437-446. doi: 10.1002/jpln.201000023

Wada K, Greenland DJ (1970) Selective dissolution and differential infrared spectroscopy for characterization of amorphous constituents in soil clays. Clay Minerals 8, 241-254. doi:10.1180/claymin,1970. 008.3.02

Wedepohl KH (1995) The composition of the continental crust. Geochimica et Cosmochimica Acta 59, 1217-1232. doi: 10.1016/0016-7037(95) 00038-2

Anna Ceorgiadis (A,D), Daniela Sauer (A,B), Jorn Breuer (C), Ludger Herrmann (A), Thilo Rennert (A), and Kad Stahr (A)

(A) Institute of Soil Science and Land Evaluation, Soil Chemistry and Pedology Section, University of Hohenheim, Emil-Wolff-Str. 27, D-70593 Stuttgart, Germany.

(B) Institute of Geography, Dresden University of Technology, Helmholtz-Str. 10, D-01069 Dresden, Germany.

(C) Center for Agricultural Technology Augustenberg, Section 12 Agroecology, NeSlerstr. 23-31, D-76227 Karlsruhe, Germany.

(D) Corresponding author. Email: Anna.Georgiadis@uni-hohenheim.de

Table 1. Conditions tested in the extraction experiments

Expt no.   Material                               Temp. ([degrees]C)

1          Silica gel                                     85
2          Bio-opal (water horsetail)                     85
3          Silica gel                                     85
4          Silica gel                              Room temp., 65,
                                                       85, 100
5          Kaolin, smectite                               85
6          Kaolin, smectite, kaolin + smectite            85
             (1:1) Mixtures: kaolin: silica
             gel (9:1), smectite: silica gel
             (9:1), kaolin + smectite: silica
             gel ([SIGMA]9:1)
7          Pure minerals                              Room temp.
8          Pure minerals                                 Room
                                                    temp.(etching)
                                                  [right arrow] 85,
                                                      Room temp.
9          Mixtures: kaolin: silica gel (9: 1,           85,
             1:1), smectite: silica gel               Room temp.
             (9: 1, 1:1)
10         Bio-opal (water horsetail)                 Room temp.
             Mixture: bio-opal: silica gel
             (1:1)
11         Soils                                      Room temp.

Expt no.   Solid: solution ratio     Extraction     Reference
                                      time (h)

1                 1 :400;                 1         Georgiadis 2011
              pH range 5-13.7
2               1:100 1:300               5         Fig. 1
3          Range: 1 :50 to 1:1000         5         Fig. 2 a
4                  1 :400                 5         Fig. 2b
5          Range: 1 :50 to 1:1000         5         Fig. 3
6                  1:400                 72         Fig. 4
7                  1 :400               5, 24       Georgiadis 2011
8                  1 :400            5 (etching)    Georgiadis 2011
                                    [right arrow]
                                          6
                                         75
9                  1 :400                5,         Fig. 5
                                         24
10                 1 :400                168        Georgiadis 2011
11                 1:400                 168        Table 2

Table 2. Silicon release (mg [g.sup.-1]) and Si: A1 molar ratios in
the extracts of soil samples, extracted by 0.2 m NaOH at room
temperature, solid: solution ratio 1: 400

Mobile Si (extracted by Ca[Cl.sub.2] solution), adsorbed Si
(extracted by acetic acid), Si in soil organic matter (released by
[H.sub.2][O.sub.2]) and Si in pedogenic oxides (released by
N[H.sub.4]-oxalate under UV radiation) were removed from the soil
samples before extraction with 0.2 m NaOH (Georgiadis et al. 2013).
n.d, not determined

Time    Hor.          Si          Si/Al
(h)             (mg [g.sup.-1])

Podzol on sandstone, upper

5        Oa          0.34          14
24                   1.24          35
72                   2.35          62
128                  2.89          53
146                  2.83          56
168                  n.d.         n.d.

5        AE            0           --
24                   0.55          11
72                   1.15          26
128                  1.44          37
146                  1.51          29
168                  n.d.         n.d.

5        EA            0           --
24                   0.23           4
72                   0.38          10
128                  0.36          11
146                  0.32          13
168                  n.d.         n.d.

5        E           0.14           3
24                   0.20          10
72                   0.20          10
120                  0.23          11
144                  0.22          14
168                  n.d.         n.d.

5        Eg          0.27          3.5
24                   0.48          3.1
72                   0.48          3.1
120                  0.53          2.5
144                  0.56          2.4
168                  n.d.         n.d.

5        EB          0.27          2.8
24                   n.d.         n.d.
72                   0.48          2.7
120                  0.52          2.2
144                  0.56          2.0
168                  n.d.         n.d.

5       Bsl          0.21          4.4
72                   0.32          4.0
120                  0.38          3.5
144                  0.35          3.0
168                  n.d.         n.d.

5       Bs2          0.23          3.4
24                   0.33          3.0
72                   0.33          3.0
120                  0.39          2.7
144                  0.39          2.2
168                  n.d.         n.d.

5        BC          0.38          2.6
72                   0.62          1.9
120                  0.71          1.8
144                  0.72          1.7

5        2C          0.48          2.4
72                   0.73          1.7
120                  0.79          1.6
144                  0.84          1.5

Time    Hor.          Si          Si/Al
(h)             (mg [g.sup.-1])

Podzol on sandstone, footslope

5        Oa          0.45          ii
24                   0.59          15
72                   1.57          25
128                  1.75          27
146                  1.75          21
168                  n.d.         n.d.

5        EA            0           --
24                   0.02         0.87
72                   0.79          19
128                  1.01          17
146                  0.98          18
168                  n.d.         n.d.

5      EA/Bsl          0           --
24                     0           --
72                   0.72         1.98
128                  0.62         1.87
146                  0.61         1.53
168                  n.d.         n.d.

5       Bsl            0           --
24                     0           --
72                   0.56         0.65
128                  0.63         0.66
146                  0.59         0.57
168                  n.d.         n.d.

5       Bs2          0.28         0.58
24                   0.43         0.53
72                   1.09         1.06
128                  1.19         1.04
146                  1.16         1.01
168

5        C           0.63         1.98
24                   n.d.         n.d.
72                   0.95         1.72
120                  1.00         1.45
144                  1.04         1.57
168                  n.d.         n.d.

Time    Hor.          Si          Si/Al
(h)             (mg [g.sup.-1])

Cambisol on gneiss, upper slope

5        Oa          1.95          135
24                   2.86          48
72                   11.97         25
120                  13.78         25
144                  13.31         23
168                  13.92         27

5        Ah          0.38          4.1
24                   0.71          4.3
72                   2.55          3.8
120                  3.08          4.5
144                  3.09          3.1
168                  3.04          3.0

5       AB/B         0.30         0.69
24                   0.57         0.96
72                   2.15         1.07
120                  2.54         1.07
144                  2.71         1.11
168                  2.77         1.10

5        Bw          0.34         0.31
24                   0.67         0.47
72                   2.24         0.90
120                  2.64         1.01
144                  2.64         0.90
168                  2.93         0.97

5        BC          0.44         0.34
24                   0.79         0.49
72                   2.32         0.96
120                  2.77         1.03
144                  2.91         1.01
168                  2.91         0.99

5        CB          0.75         1.07
24                   1.01         0.91
72                   2.39         1.15
120                  2.80         1.39
144                  2.86         1.18
168                  2.98         1.17

Time    Hor.          Si          Si/Al
(h)             (mg [g.sup.-1])

Cambisol (Chromic) on gneiss,
lower slope

5        Oa          1.99          14
24                   3.43          14
72                   8.50          10
120                  9.39           9
144                  9.56           8
168                  9.56           8

5        Ah          0.37         2.31
24                   1.02         2.57
72                   3.13         2.80
120                  3.71         2.68
144                  3.72         2.57
168                  3.82         2.47

5       BAg          0.17         0.44
24                   0.52         0.74
72                   2.06         1.22
120                  2.44         1.63
144                  2.53         1.22
168                  2.66         1.22

5        Bg          0.12         0.18
24                   0.42         0.37
72                   1.71         0.77
120                  2.06         0.82
144                  2.12         0.83
168                  2.22         0.84

5       BCg          0.44         0.88
24                   0.76         0.85
72                   2.17         1.23
120                  2.51         1.20
144                  2.64         1.15
168                  2.72         1.17

5       CBg          0.61         1.32
24                   1.09         1.14
72                   2.45         1.37
120                  2.77         1.31
144                  2.86         1.29
168                  3.01         1.24

Time    Hor.          Si          Si/Al
(h)             (mg [g.sup.-1])

Luvisol on loess, plateau

5        Ah          1.56          68
24                   2.27          48
48                   2.76          40
120                  3.42          22
144                  3.43          18
168                  3.30          22

5        E           0.74         6.71
24                   1.06         6.21
48                   1.42         5.67
120                  2.16         4.00
144                  2.29         4.57
168                  2.27         4.65

5       Bt1          1.93         4.04
24                   2.66         3.25
48                   3.23         3.07
120                  4.54         2.32
144                  4.68         2.55
168                  4.59         2.53

5       Bt2          1.65         4.32
24                   2.31         3.53
48                   2.73         3.38
120                  3.95         2.46
144                  4.05         2.69
168                  3.97         2.73

5       Bt3          1.48         6.23
24                   2.00         4.14
48                   2.34         3.80
120                  3.11         2.83
144                  3.29         3.08
168                  3.21         2.98

5        Ck          0.33         9.94
24                   0.55         6.26
48                   0.74         5.37
120                  1.31         4.49
144                  1.28         4.58
168                  1.33         4.45

Time    Hor.          Si          Si/Al
(h)             (mg [g.sup.-1])

Stagnosol on periglacially
reworked loess, plateau

5        Ah          0.46         3.12
24                   0.64         4.97
48                   n.d.         n.d.
120                  2.97         5.67
144                  2.87         6.06
168                  2.94         5.93

5        E1          0.36         0.99
24                   0.67         1.46
48                   n.d.         n.d.
120                  2.41         2.59
144                  2.40         2.83
168                  2.48         2.86

5        E2          0.33         1.26
24                   0.61         1.42
48                   n.d.         n.d.
120                  3.53         1.94
144                  3.47         2.22
168                  3.56         2.19

5        E3          0.27         1.86
24                   0.52         1.74
48                   n.d.         n.d.
120                  4.19         2.09
144                  4.28         2.29
168                  4.31         2.25

5       Cg1          0.30         1.67
24                   0.61         1.75
48                   n.d.         n.d.
120                  3.74         2.10
144                  3.74         2.36
168                  3.87         2.29

5       Cg2          0.32         2.02
24                   0.61         1.91
48                   n.d.         n.d.
120                  3.60         2.16
144                  3.70         2.64
168                  3.68         2.38

5       Cg3          0.35         1.61
24                   0.71         1.63
120                  3.61         2.26
144                  3.48         2.41
168                  3.55         2.32

5       Cg4          0.46         1.46
24                   0.90         1.46
72                   n.d.         n.d.
120                  3.56         2.13
144                  3.58         2.32
168                  3.63         2.25
COPYRIGHT 2015 CSIRO Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2015 Gale, Cengage Learning. All rights reserved.

 
Article Details
Printer friendly Cite/link Email Feedback
Author:Georgiadis, Anna; Sauer, Daniela; Breuer, Jorn; Herrmann, Ludger; Rennert, Thilo; Stahr, Karl
Publication:Soil Research
Article Type:Report
Date:Jul 1, 2015
Words:7157
Previous Article:Weighting the differential water capacity to account for declining hydraulic conductivity in a drying coarse-textured soil.
Next Article:Trace elements in road-deposited and waterbed sediments in Kogarah Bay, Sydney: enrichment, sources and fractionation.
Topics:

Terms of use | Privacy policy | Copyright © 2018 Farlex, Inc. | Feedback | For webmasters