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  • Soil Organic Matter
  • AGRIS (United Nations, Food and Agriculture Organization)  (4)
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  • 1
    Language: English
    In: Soil Science Society of America Journal, Sept-Oct, 2006, Vol.70(5), p.1731(10)
    Description: Uronates are important constituents of maize mucilage and polyuronates are used as a simplified model of the soil--root interface. We tested whether galacturonate (GA) and polygalacturonate (PGA) impair the diffusion of phosphate (P[O.sub.4]) into and out of pores of a synthetic goethite (147 [m.sup.2] [g.sup.-1]) and whether the effect of maize mucigel (MU) is comparable to PGA. We measured the P[O.sub.4] desorption kinetics of goethites in batch experiments over 2 wk at pH 5. One part of the goethite was equilibrated with organic substances before P[O.sub.4] addition, another part after addition of P[O.sub.4]. Before the desorption experiments, the porosity of our samples was analyzed by [N.sub.2] gas adsorption. In each treatment a rapid initial desorption was followed by a slow desorption reaction, which is assigned to the diffusion of P[O.sub.4] out of mineral pores. No consistent relation between the micro- and mesoporosity and the rate of the slow P[O.sub.4] desorption was observed. Compared with the C-free control, only PGA and MU affected the fraction of P[O.sub.4] mobilized by the fast and slow desorption reaction: when PGA was sorbed to goethite before P[O.sub.4], twice as much P[O.sub.4] was mobilized via the fast reaction than in the treatment where P[O.sub.4] was sorbed before PGA, suggesting a decreased accessibility of goethite pores to P[O.sub.4]. Mucigel, however, showed reversed effects, which is ascribed to its differing chemical composition. In conclusion, PGA seems inappropriate as a model substance for maize MU collected from non-axenic sand cultures. Under the experimental conditions chosen, the efficacy of all organic substances to increase P[O.sub.4] solution concentrations by pore clogging and sorption competition is small.
    Keywords: Phosphates -- Research ; Sorption -- Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 2
    Language: English
    In: Soil Science Society of America Journal, Nov-Dec, 2004, Vol.68(6), p.1853(10)
    Description: Recent [N.sub.2] adsorption studies have suggested a 'pore clogging' effect on mineral soil phases caused by organic matter coatings. For methodological reasons, this pore clogging effect has been studied only after drying. Our hypothesis was that pore clogging is affected by drying of organic coatings. In our study, we used AlOOH, which has been equilibrated with dissolved organic matter (DOM) and polygalacturonic acid [[PGA; [([C.sub.6][H.sub.8][O.sub.6]).sup.n]]. To test our hypothesis, we determined the porosity of moist and freeze-dried AlOOH samples. Freeze-dried samples were analyzed by [N.sub.2] adsorption, moist samples by [sup.1]H-nuclear magnetic resonance (NMR). In addition, the samples were characterized by environmental scanning electron microscopy--energy dispersive x-ray spectroscopy (ESEM-EDX). Both, DOM and PGA significantly reduced specific surface area (SS[A.sub.BET]) of AlOOH by 34 [m.sup.2][g.sup.-1](15%) and 77 [m.sup.2] [g.sup.-1] (36%). The reduction in SS[A.sub.BET] normalized to the amount of C sorbed was 1.0 [m.sup.2] [mg.sup.-1] DOM-C and 5.9 [m.sup.2] [mg.sup.-1] PGA-C. Dissolved OM reduced the pore volume of micro- and small mesopores 〈3 nm whereas PGA also reduced the volume of larger pores. The [sup.1]H-NMR results of moist samples showed that PGA sorption reduced the amount of water in pores 〈4 nm. In addition, the pore size maximum of AlOOH increased by 150%. Polygalacturonic acid coatings created new interparticle pores of about 10- to 70-nm size that are not stable upon freeze-drying. Porosity changes upon DOM-treatment were not commensurable by [sup.1]H-NMR. Our results indicate that clogging of micro- and small mesopores is not an artifact of freeze-drying. Polygalacturonic acid seems not only to cover the mouth of AlOOH-nanometer pores but also to fill them.
    Keywords: Soil Mineralogy -- Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 3
    In: Canadian Journal of Forest Research (Revue canadienne de recherche forestière), 2000, Vol.30(7), pp.1034-1040
    Description: Molybdenum plays an important role in the nitrogen turnover of ecosystems. However, very little is known about Mo availability in forest soils. We measured the oxalate-extractable Mo concentrations of acid forest soils, the Mo, nitrate, phosphate, and sulfate fluxes from the organic forest floor into the mineral soil using resin tubes and the Mo concentrations of the tree needles at 28 different Norway spruce ( Picea abies (L.) Karst.) sites in southern Germany. The supply of oxalate-extractable Mo varied from 51 to 3400 gha -1 , with the lowest values occurring in sandstone-derived soils (370 212 gha -1 ; mean SD). Molybdenum concentrations of current-year needles were in the range of 5 to 48 ngg -1 . The Mo needle concentrations and oxalate-extractable Mo of soils did not correlate. However, Mo fluxes (6-60 gha -1 a -1 ) from the organic forest floor into the mineral soils were correlated to needle concentrations and to the NO 3 fluxes. We conclude that Mo turnover within forest ecosystems is governed by Mo plant availability of mineral soils as well as by plant Mo uptake. In addition, Mo cycling strongly affects Mo distribution within soil profiles and Mo fluxes out of the organic layer.
    Description: Le molybdne joue un rle important dans le renouvellement de l'azote des cosystmes. Toutefois, on connat peu de choses au sujet de la disponibilit de Mo dans les sols forestiers. Nous avons mesur la concentration de Mo extractible l'oxalate dans des sols forestiers acides, les flux de Mo, de nitrate, de phosphate et de sulfate, de la couverture morte organique vers le sol minral, l'aide de tubes de rsines ainsi que la concentration de Mo dans les aiguilles d'pica commun ( Picea abies (L.) Karst.) dans 28 sites diffrents du sud de l'Allemagne. L'apport de Mo extractible l'oxalate variait de 51 3400 gha -1 avec les plus faibles valeurs provenant des sols drivs de grs (370 212 gha -1 ; moyenne ET). La concentration de Mo dans les aiguilles de l'anne courante variait de 5 48 ngg -1 . La concentration de Mo dans les aiguilles et le Mo extractible l'oxalate dans les sols n'taient pas corrls. Toutefois, les flux de Mo (6-60 gha -1 a -1 ) de la couverture morte organique vers le sol minral taient corrls aux concentrations foliaires et aux flux de NO 3 . Nous en concluons que le renouvellement de Mo dans les cosystmes forestiers est gouvern par le Mo des sols minraux disponible pour la plante autant que par le prlvement de Mo par la plante. De plus, le recyclage de Mo affecte fortement la distribution de Mo dans les profils de sol et le flux de Mo hors de la couche organique.[Traduit par la Rdaction]
    Keywords: Forest Floor ; Soils (Acid) ; Mobility ; Soil Profiles ; Molybdenum ; Minerals ; Nitrogen ; Sulfate ; Picea Abies ; Management and Conservation;
    ISSN: 0045-5067
    E-ISSN: 1208-6037
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  • 4
    Language: English
    In: Journal of environmental quality, 2009, Vol.38(3), pp.933-9
    Description: Liming is a common technique suggested for the stabilization of shooting range sites. We investigated the effect of an increase in pH on the mobilization of soluble and dispersible (colloidal) Pb, As, and Sb. Our hypothesis was that the addition of divalent cations counteracts the pH-induced mobilization of soluble and colloidal metal(loid)s. We determined soluble (operationally defined as the fraction 〈 10 nm obtained after centrifugation) and dispersible (filter cut-off 1200 nm) As, Pb, Sb, Fe, and C(org) concentrations in the filtered suspensions of batch extracts of topsoil samples (C(org): 8%) from a former shooting range site following a pH increase to values between 3.5 and 7 by adding a monovalent (KOH) or a divalent (Ca(OH)(2)) base. In the Ca(OH)(2)-treated samples, dissolved metal(loid) concentrations were 62 to 98% lower than those titrated with KOH to similar pH. Similarly, Ca reduced the concentration of dispersible Pb by 95%, but had little or no impact on dispersible As and Sb. We conclude that the counterion valency controls the mobility of metal(loid)s by affecting the mobility and sorption capacity of the sorbents (e.g., colloids, organic matter).
    Keywords: Antimony -- Chemistry ; Arsenic -- Chemistry ; Cations, Divalent -- Chemistry ; Lead -- Chemistry ; Soil -- Analysis
    ISSN: 0047-2425
    E-ISSN: 15372537
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