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Ruhl G.,Julius Kuhn Institute | Hommel B.,Julius Kuhn Institute | Husken A.,Julius Kuhn Institute | Mastel K.,Agricultural Technology Center Augustenberg | And 3 more authors.
Crop Science | Year: 2011

In addition to or as substitution for a regulated isolation distance, conventional maize (Zea mays L.) border rows at the genetically modified (GM) maize field edge are considered as feasible measure to ensure coexistence between GM and conventional or organic maize. Therefore, we examined the effectiveness of 9-mand 18-m-wide non-GM maize borders at the GM maize field edge on out crossing rates into a neighboring non-GM maize field. One field experiment each was conducted in 2008 at three sites in Germany using a field orientation representing a worst-case scenario concerning wind direction. In each case, the distance between GM and non-GM maize fields was 51 m. At two sites, sizes of GM and non-GM maize fields were 0.8 ha, respectively, and at the third site 0.5 ha (GM) and 0.3 ha (non-GM). The GM percentages of individual samples taken at recipient field depths between 0 and 90 m were quantified by real-time polymerase chain reaction. Overall, no pollen-mediated gene flow reducing effect of border rows was observed in the present study, although synchrony of anthesis between GM maize and border row maize was given at each site. Calculated GM contents of the total non-GM fields harvest were always below the European Union labeling threshold of 0.9%. In consequence, planting 9-m- or 18-m-wide conventional maize border rows at the GM field edge is no reliable coexistence measure, at least if combined with an isolation distance. © Crop Science Society of America.


Georgiadis A.,University of Hohenheim | Sauer D.,TU Dresden | Herrmann L.,University of Hohenheim | Breuer J.,Agricultural Technology Center Augustenberg | And 2 more authors.
Soil Research | Year: 2014

The importance of silicon (Si) compounds in agriculture and geochemical cycles has received increasing attention over the last decade; however, quantitative data on non-crystalline pedogenic Si phases in soils are still rare. Recently, the authors developed a method for sequential Si extraction from soils, in order to improve the quantification of different Si compounds in soils. The method has been tested on samples of known composition. Here, the method is applied for the first time to complete soil profiles. Six different soil types from south-west Germany that have developed since the end of the last glacial period were selected. Most of the Si in these soils was bound in primary and secondary silicates. In mineral soil horizons, the second-highest proportion of Si was in precipitates of amorphous silica (minerogenic amorphous silica), whereas in some O horizons, the second-most important Si fraction was in biogenic amorphous silica. Topsoil horizons and clayey subsoil horizons of a Luvisol and a Stagnosol especially accumulate amorphous silica. Silicon from bio-opal contributed up to 14% to the total Si in Oa horizons of the studied soils. The smallest amounts of Si were found in the mobile and adsorbed Si fractions. Some methodological limitations are identified and discussed; however, the new sequential method of Si extraction enabled separation of different Si fractions in typical soils of a temperate-humid climate. © CSIRO 2014.


Georgiadis A.,University of Hohenheim | Sauer D.,TU Dresden | Herrmann L.,University of Hohenheim | Breuer J.,Agricultural Technology Center Augustenberg | And 2 more authors.
Geoderma | Year: 2013

In this paper, we introduce a new method for sequential extraction of different silicon (Si) fractions from soils. The method has been developed based on several series of extraction experiments on well-characterized isolated soil compounds and selected soil samples. Results and implications of these test series are presented, and reasons for the choice of methods for the single steps of the sequential extraction procedure are given.The sequential extraction method separates seven Si fractions. The first four extraction steps are performed on four replicates, which are then split into two by two replicates subjected to two different treatments in the following step. 1) The mobile Si fraction is obtained by extraction by weak electrolyte solution of CaCl2. 2) Si in adsorbed silicic acid is extracted by acetic acid through anion exchange. 3) Si in soil organic matter (SOM) is released by SOM oxidation with H2O2. 4) Si in pedogenic oxides and hydroxides is obtained by treatment with ammonium oxalate and oxalic acid solution under UV-light. 5) In step 5 amorphous silica of biogenic and minerogenic origin is specified. This separation is done in three sub-steps: 5.1) Two samples are directly subjected to NaOH extraction to obtain the total amorphous silica fraction; 5.2) the two other samples are first subjected to bio-opal separation with sodium polytungstate; 5.3) NaOH extraction is then applied to the bio-opal samples to obtain their Si content. The difference between the amounts of Si in the extracts of sub-steps 5.1 and 5.3 is interpreted as Si from minerogenic amorphous silica forming precipitates on surfaces of mineral grains. 6) In addition, total Si concentration is either determined by fusion of sub-samples with lithium borate, dissolution in nitric acid and ICP-OES analysis or by X-ray fluorescence analysis. The share of crystalline silicates is calculated as the difference between total Si and the sum of the Si fractions obtained in extraction steps 1 to 5.Potential drawbacks of the method include i) varying efficiency of the second extraction step, strongly depending on soil composition, ii) overestimation of Si in soil organic matter due to partial dissolution of clay minerals, pedogenic oxides and amorphous silica by H2O2, iii) underestimation of Si in pedogenic oxides and hydroxides due to incomplete destruction of highly crystalline pedogenic oxides or nodules. © 2013 Elsevier B.V.

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