PHYSICAL FACTORS INVOLVED IN THE FORMATION OF SOIL SHEATHS ON CORN SEEDLING ROOTS

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Abstract
A layer of soil (soil sheath) that is resistant to removal by shaking develops on corn seedling roots under a wide variety of environmental conditions. Low temperature (15 °C) and high soil moisture content (100% field capacity) promote the formation of the most substantial sheaths (> 11 mg of soil (dry weight) cm−1 root) in an Elora alfalfa soil. A diversity of corn genotypes and a teosinte form sheaths of comparable specific mass whereas much less soil adheres to pea and soybean roots in this soil. Cultivation history has a considerable influence on sheath mass. For example, at Elora, a soil under alfalfa for several seasons promotes sheaths of higher specific mass (9.9 ± 0.5 mg cm−1 root) than a continuous corn soil (7.1 ± 0.6 mg cm−1 root). Seeds inoculated with a fluorescent pseudomonad developed significantly more substantial sheaths in a 7-irradiated soil (11.2 ± 0.9 mg cm−1 root) than uninoculated, surface sterilized seeds (7.1 ± 0.6 mg cm−1 root). These observations suggest that a variety of factors influence the extent of sheath development. Key words: Soil sheath, temperature, soil moisture, soil type, fluorescent pseudomonads, corn