Climate, Time, and Organisms in Relation to Podzol Development in Michigan Sands: I. Site Descriptions and Microbiological Observations 1

Direct microscopic counts of microflora, nitrification patterns, and water-soluble organic matter production in upper humic horizons of seven soils were studied in an attempt to determine the processes responsible for correlations between forest types and Podzol development in Michigan. The volume and surface area of fungal mycelia, the number of bacterial cells, and the length of actinomycete filaments per gram of organic matter were substantially greater in a mull humus horizon under 100% northern hardwoods than in a mor humus horizon under a forest stand dominated by hemlock. Maximum crenic acid production occurred in the mor humus horizons, these being associated with forest stands dominated either by hemlock or white pine. Leachates from these horizons contained no nitrate until incubated with periodic leaching for over 5 months. In a mull and a duff mull horizon, nitrification was nil during the period of maximum crenic acid production and the initial appearance of nitrate was closely accompanied by sharp decreases in pH of the leachates and sharply reduced production of crenic acid. Data obtained in these studies point to mor humus layers (Oh or O2 horizons) as a major site of production of water-soluble organic materials having properties which suggest that they may be active agents in podzolization and contribute to the composition of Podzol illuvial horizons. Production of these materials is intimately linked with patterns of nitrogen transformation peculiar to forest soils, notably under conifers.