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A study of soils and leachates from two forest sites using tension lysimeters Bourgeois, William W.

Abstract

A study of the soils and leachates of two ecologically different forest sites was started in September, 1968 with an object of evaluating soil factors as to site differentiation. Tension lysimeters with silicon carbide powder, as a contact material, were used to collect water passing through the soils of the two sites at a soil water tension of less than 0.10 bar. As the study was performed on sloping topography, tension lysimeters were required to measure both the down slope pathway and the vertical percolation of the soil water. The leachates from the master horizons of the two soils were collected weekly. The anion and cation content of the leachates was determined along with electrical conductivity, pH and total volume of water. The two soils, Whatcom series and Blaney series, were sampled according to their morphological characteristics. The samples were analyzed for selected physical, chemical and mineralogical properties. The properties selected were such that soil characterization was accomplished and information was provided for leachate interpretations. A greater volume of water passed through the Whatcom soil (permanent seepage site) than through the Blaney soil (mesic site). This was reflected in the genetic and morphologic characteristics of the two soils. The largest quantity of leachate was collected immediately above the compacted material under the solum. The cation concentrations of the leachates from these zones were similar in both the Whatcom and Blaney soils. Higher cation concentrations were observed in the leachates from the spodic horizons. Sodium was the cation of highest concentration in all the leachates and calcium, magnesium and potassium occurred in decreasing order. Seasonal trends seemed to appear to be present in both the anion and cation concentrations. The principal causes of these trends appeared to be the quantity and rate of water passing through the soil and soil temperature, although the latter was not measured directly it was inferred from the seasonal patterns. Soil water relations and associated soil properties appeared to be the main reasons for better tree growth on the Whatcom soil. The exchangeable calcium and magnesium content of the Whatcom soil may also have an influence. Field evaluation of forest sites may be accomplished using soil morphological characteristics as these are reflections of the important soil properties desirable for Douglas-fir growth.

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