Se‐Fixierung durch Tonminerale und Fe‐oxide
Bei der Untersuchung der Se‐Fixierung lag das Hauptaugenmerk darauf festzustellen, welche Bodenbestandteile zur Se‐Bindung befähigt sind. Hierbei wurde die Bedeutung der Fe‐hydro‐oxide für die Se‐Fixierung besonders herausgestellt. Die gewöhnlichen Bodentonminerale wie Kaolinit, Montmorillonit und Vermiculit zeigen sämtlich Se‐Fixierung; jedoch trat bei Tonmineralen des 1:1‐Schichttyps stärkere Fixierung ein als bei solchen des 2:1‐Typs. Versuche mit feingemahlenen Mineralen zeigten einen starken pH‐Einfluß auf die Fixierungsgeschwindigkeit. Das Maximum wurde zwischen pH 3 und 5 erreicht; bei weiter ansteigendem pH trat ein starker Rückgang der Fixierung auf. In dem Fe2O3‐System trat bei pH > 8 ein leichter Rückgang der Se‐Fixierung ein.
Anhand der Extrahierbarkeit des Se aus den Tonmineralen ließ sich erkennen, daß Tonminerale vom 1:1‐Schichttyp Selenit in schwerer löslicher Form festlegen als solche des 2:1‐Typs, und daß Selenit an Tonen hauptsächlich durch eine Oberflächen‐Austauschreaktion adsorbiert wurde. Der überwiegende Anteil des zugesetzten Selenits war in dem Fe2O3‐System in potentiell und schwerverfügbarer Form vorhanden. Danach ist zu vermuten, daß die Se‐Fixierung sowohl durch Austauschreaktion als auch durch Fällung auf Fe‐selenit stattfindet.
N-PAC (azaarenes) occur in the environment at levels that are 1-10% of the analogous polycyclic aromatic hydrocarbons (PAH), e.g. from the production and use of creosote and tar. In this investigation navew (Brassica campestris L.), Italian rye-grass (Loliurn multiporum L.) and barley (Hordeurn uulgare L.) were grown in two different soils containing concentrations of 0, 1 and 100 ppm acridine. The observations reveal that acridine inhibits the seed production of navew and the growth of Italian rye-grass. Inhibition was noted at 1 ppm level. At 100 ppm nawev seeds either did not germinate or the sprouts did not survive.
The uptake of added Se from selenite and selenate by barley and red clover was investigated in a pot experiment. Much more of selenate than of selenite was taken up but the Se concentrations in the plants declined more with time when selenate was the source. Increasing sulphate addition to the soil decreased the uptake of Se from selenate greatly and from selenite to a lesser extent. The ratio Se in the roots/Se in the tops shows that Se is more readily translocated from the roots when taken up from added selenate than from selenite.On the basis of these and other investigations it is concluded that selenite is a better source than selenate when the Se concentration in the plants has to be raised to a level sufficient for livestock nutrition.
A pot experiment was initiated to measure the influence of varying pH and clay content of soils low in native selenium on the uptake of added selenium by ryegrass (Lolium multiflorum). The results showed a general decrease in selenium uptake with increasing clay content, and there was a strong interaction between the pH, clay content, and time.It is concluded that a somewhat smaller amount of selenite might be used on sandy soils than on loamy soils to raise the selenium concentration in farm crops to a desirable level. The results showed also an influence of pH and clay content on the relative availability of selenium and sulfur.In an earlier experiment (Bisbjerg and Gissel-Nielsen, 1969), a negative correlation was found between plant uptake of added selenium and the clay content of the soils used. However, in the same experiment there was a correlation between plant uptake of selenium and soil pH. Many authors have described the availability of selenium from soils where these two factors varied (Davies and Watkinson, 1966;Kubota et al., 1967). Geering et al. ( 1968) measured the solubility of selenium in soils as a function of pH, and they found the lowest solubility when the soil solution was slightly acid to neutral, and when there was increasing solu-
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