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Manganese status of some Lower Fraser Valley soils developed from alluvial and marine deposits Safo, Ebenezer Yeboah

Abstract

A study was undertaken to determine the manganese status of some Lower Fraser Valley soils developed from alluvial and marine deposits. Mn fractions in six soils and in their particle size separates were determined by atomic absorption spectrophotometry. Water soluble Mn ranged from 0.5 to 1.4 ppm; Exchangeable Mn from 0.5 to 15.0 ppm; Hydroquinone reducible from 0.7 to 119.5 ppm; Total Mn from 82.0 to 957.5 ppm; and "Active Mn" from 3.2 to 129.8 ppm. These ranges were similar to reported values, except that.the study failed to find the high levels of total Mn reported by Baker on some soils from the same area. Generally water soluble and exchangeable Mn showed little variation within profile or between soils. In four out of the six profiles reducible and total Mn were higher in the parent material than in the surface horizons. However, there was no satisfactory fit for a number of the profiles to the four distribution patterns suggested by Leeper. Values for EDTA extractable and "active" Mn in two profiles suggest that both fractions of Mn represent the same chemical form. However, further results suggest that the two Mn fractions are different. In nearly all samples with high organic matter content EDTA extracted more Mn after removing "active Mn" than direct extraction with EDTA, supporting suggestions that EDTA extracts chelated Mn and also causes some dispersion of soil particles. Sonic dispersion led to increased recovery of all forms of Mn, more especially reducible and total Mn. The results suggest that until more is known about sonic dispersion it is unwise to assume that no modification of soil constituents takes place. Statistical techniques were used to examine the relationship between Mn distribution and parent materials, pH, organic matter content and cation exchange capacity. These analyses showed that the level of Mn fractions in the soil cannot be predicted by any single factor, but only by a number of soil factors in combination. The possibility of building up a computer model to predict Mn distribution is suggested. The significance of soil Mn distribution in terms of plant requirements is discussed. Plant available Mn in these soils, estimated by 0.02 M CaCl₂ extraction, ranged from 0.5 to 10.7 ppm. This was very similar to that for exchangeable. Based on data in the literature these soils were classified into manganese-deficient and-sufficient categories. Using extraction techniques only, various Mn pools were established for these soils according to the chemical pool concept proposed by Viets. These pools and their possible relation to Mn availability are discussed. It was suggested that a further study was necessary to establish a correlation between these Mn pools and plant Mn requirements and also to reveal the equilibria and rates of interconversion existing between the established pools as found under the soil conditions of the Lower Fraser Valley.

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