Silicon fractions in Histosols and Gleysols of a temperate grassland site

Abstract

The importance of silicon (Si) in nutrition is currently being recognized by its beneficial effects on many crops. Therefore, it is important to determine the soil Si status and to examine different extractants for testing plant-available Si. Little information is available about the Si status of Histosols and C org -rich Gleysols in temperate climate. This study was undertaken (1) to characterize different Si pools in C org -rich groundwater soils of an experimental site and (2) to study the influences of small-scale variability on element distribution. At the experimental site, the thickness of the C org -rich layer ranges between 4 and 5 dm overlying fine-sandy fluvial sediments. Four extractants were evaluated: 0.01 M CaCl 2 , 0.5 M acetic acid, 0.1 M sodium pyrophosphate, and 0.1 M Tiron (C 6 H 4 Na 2 O 8 S 2 · H 2 O). Further, total element content was determined following HNO 3 /HF digestion. Calcium chloride-soluble Si shows no significant relations to other parameters analyzed. On the basis of published data, the soils investigated could be classified as Sideficient. The Si fraction extracted with acetic acid displays relations to C org content of the soil and a weak correlation to CaCl 2 -soluble Si, indicating that both solutions extract overlapping but not the same fractions. Sodium pyrophosphate extracts mainly organo-mineral Fe and Al complexes in the soils studied, which is reflected in a highly positive correlation to C org . Pyrophosphate-soluble Si showed a negative relationship to C org , which means a closer relation of this Si fraction to mineral matter than to C org . The Tiron solution extracted most Si of all extractants, but this amounts only 1% of the total Si content. Taking into account the element-specific relationship between pyrophosphate and Tiron-extractable Fe, Al, and Si, it can be concluded that Tiron dissolves mainly the opaline silica present in Histosols and C org -rich Gleysols. The distribution of C org and ash content shows clear spatial trend at the experimental site, which is correlated to pyrophosphate-extractable as well as total Si. This small-scale variability of soil parameters itself is related to a distinct microrelief.

Anthropogenic impact on amorphous silica pools in temperate soils

“…The weakest extractant (after water) is CaCl 2 , which only extracts this easily soluble Si pool (Berthelsen et al, 2001). In our measurements, 2 g of dried soil (<2 mm) was shaken (linear movement) for 16 h with 20 ml 0.01 M CaCl 2 extractant (1:10 ratio) in a 50 ml Nalgene tube at 20 • C (Höhn et al, 2008). After centrifugation at 4000 rpm for 30 min, the supernatant was filtered over 0.45 µm pore size (Chromafil ® A-45/25) and analyzed for Si by the automated molybdate-blue method.…”

“…Solubility is a function of temperature, particle size, pH, chemical composition (type of Al and Fe oxides), organic matter (OM) content and exposed surface area Höhn et al, 2008). In contrast to other factors like pH and clay, OC varied significantly between land use types (Table 1).…”

Grazers: biocatalysts of terrestrial silica cycling

“…All dried plant and faeces samples (2.0 g) from the summer campaign were shaken thoroughly for 16 h with 20 ml 0.01 M CaCl 2 solution in a 35 ml tube at 208C [25,38]. Extracted samples were then centrifuged at 4000 r.p.m.…”

Exchangeable silicon content of soil in a long-term fertilization experiment

“…Kaczorek and Sommer (2004) have shown that under the conditions of soil acidification, the amount of free silica increases. Similarly, Höhn et al (2008) reported an increase in the amount of silicon available in the soil with a decrease in pH. According to Miles et al (2014) where a large group of soils in a region of a country is surveyed, there is generally a positive relationship between pH and Si solubility/extractability.…”