Clay mineralogy and potassium status of selected soils in the glacial LakeAgassiz region of central Manitoba

The clay mineralogy of the soil is important in that it can affect potassiu m (K) availability, particularly if vermiculite is present. Large areas of Glacial Lake Agassiz in Manitoba contain fine-grained lacustrine sediments that support boreal forest vegetation. The purpose of this investigation wa s to identify the clay mineralogy of several commonly occurring soils and d ocument its influence on soil fertility, particularly K availability. The s oils were classified as either Eluviated Eutric Brunisols or Orthic Eutric Brunisols. X-ray diffraction analysis verified that vermiculite, hydrous mi ca and kaolinite were the principal clay minerals in these soils. Vermiculi te was demonstrated to have hydroxy Al-interlayers and the amount of vermic ulite decreased in the deeper soil horizons. Smectite was present in the Bt j horizons of the Eluviated Eutric Brunisols, while trace amounts of chlori te were present in every inorganic horizon. Quantity/intensity curves for K and an experimental estimate of the K-fixation potential indicated that th e Ae horizons of several Eluviated Eutric Brunisols supported higher K acti vities in the soil solution and that K-fixation was greater in subsurface h orizons. Potassium fixation and the quantity/intensity curves for selected horizons of the Orthic Eutric Brunisols were nearly identical and each show ed a reduced intensity to maintain the aqueous activity of K.