Forms and extractability of manganese in potting media

Abstract

Abstract Sequential extraction of pine bark medium alone and after amendment with either manganese sulfate (MnSO4), composted rice hulls, or soil showed that at pH 5.5–7.0 most of the manganese (Mn) exists in a form that is extracted by acidic hydroxylamine hydrochloride, and which could therefore be in oxide or strongly‐bound forms. Acidification to pH 4.5–5.0 transferred large amounts of this ‘oxide’ Mn into ‘readily available’ and ‘weakly adsorbed’ fractions. Similar extractions of Sitka spruce bark showed that most of its Mn was extracted by weak cationic reagents ('readily available’ and ‘weakly adsorbed’ fractions). Growth of oats in pine bark, peat, and eucalypt sawdust media, with and without MnSO4 amendment, lowered the amounts of Mn in ‘readily soluble’ and ‘weakly adsorbed’ fractions and caused some loss of ‘oxide’ Mn. Comparison of data for Mn extracted by 2 mM DTPA (1:1.5 v/v) with Mn in sequential fractions showed that DTPA dissolves some ‘oxide’ Mn. The data further suggest that up to about...