Manganese extracted from different chemical fractions of bulk and rhizosphere soil as affected by method of sample preparation

Abstract

Rhizosphere soils had higher amounts of 'readily soluble', 'weakly adsorbed', 'carbonate bound' and 'specifically adsorbed' Mn, but had lower amounts of 'oxide-Mn', than did bulk soils. This observation was true regardless of whether the comparison was based on values within moist or air-dried treatments. Observed trends in Mn distribution between different soil fractions were qualitatively similar regardless of method of sample preparation. However, there were substantial quantitative differences depending on the method of sample preparation. Air-dried samples increased significantly in the 'oxide-Mn' fraction and decreased in its soluble and adsorbed fractions relative to moist soil samples. There was a significant effect of method of air-drying on the distribution of Mn in rhizosphere samples. Samples that were extracted moist at first and then air-dried accumulated more adsorbed Mn and were depleted in 'oxide-Mn' relative to samples that were air-dried initially. There was a significant rhizosphere x airdrying interaction. Air-drying of some rhizosphere samples resulted in a significant underestimation of the 'readily soluble', 'specifically adsorbed', and 'oxide-Mn' fractions beyond the overall effect of air-drying. The results of this study suggested that soil samples used for Mn analyses be extracted immediately in a moist condition rather than air-dried, particularly for analyses of rhizosphere soil samples.

Redox transformations and plant uptake of selenium resulting from root-soil interactions

“…Root exudates also influence the forms of Mn in the rhizosphere. Warden (1991) found that rhizosphere soils had higher amounts of readily-soluble, weakly adsorbed, carbonate bound, and specifically adsorbed Mn and lower amounts of Mn oxide than bulk soils, as defined operationally with different extracting solutions.…”

Determination of trace elements bound to soil and sediment fractions (IUPAC Technical Report)

“…Usually, soil samples are air-dried prior to extraction. Although changes in the extractability of some elements (i.e., of Mn) have been reported earlier [49], this problem only recently received more attention [50][51][52][53][54][55]. Air-drying prior to extraction is a standard procedure, but leads to an increased extractability of Fe and Mn, whereas other metals are more or less unaffected [50][51][52][53][54][55].…”