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  • 1975-1979  (3)
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  • 1
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    SOIL BACTERIAL CHANGES AS AFFECTED BY GROWING SEASON WEATHER CONDITIONS: A FIELD AND LABORATORY STUDY (1976)
    Canadian Science Publishing
    Details
    Publication Date: 1976-08-01
    Description: During the 1972 and 1974 growing season, soil bacteria, actinomycetes, moisture and temperature in the top 15 cm of a Wood Mountain loam were monitored regularly under sheltered and unsheltered summer-fallow and cropped conditions. The 1972 temperatures and rainfall were later simulated in the laboratory and their effects on the bacterial population in the Wood Mountain loam, a Sceptre heavy clay, and a Melfort silty clay loam determined. Multiple regression was used to quantify the relationships between the different microbial populations and several selected environmental variables. Microbial change was generally directly proportional to moisture change, the latter being the main factor influencing response. The effect of moisture change was usually dependent on the temperature and/or the initial moisture content prior to the change. Soil microbial populations increased in response to both increases and decreases in temperature. The inverse relationship with temperature appeared to be the result of the dry soil surface being wetted by dew which accompanied low night temperatures. Microbial responses were greater in the top 2.5 cm than in the 2.5- to 15-cm segment. Bacteria and actinomycetes responded to environmental stimuli in a similar manner but the response of bacteria was usually greater than that of actinomycetes. The bacteria: actinomycetes ratio was 3:1 in the top 2.5 cm but only 1.3:1 in the 2.5- to 15-cm segment. Cropping the soil had no effect on microbial numbers. In the laboratory study, denitrifier response was more closely related to rainfall than were bacterial or actinomycetal response. Denitrifier response was greatest in the clay and least in the loam.
    Print ISSN: 0008-4271
    Electronic ISSN: 1918-1841
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 2
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    SIMULATED DEW FORMATION AND MICROBIAL GROWTH IN SOIL OF A SEMIARID REGION OF WESTERN CANADA (1977)
    Canadian Science Publishing
    Details
    Publication Date: 1977-05-01
    Description: To simulate the effect of dew formation on microbial growth in semiarid soils, air-dry loam was exposed to moisture condensation by incubating soil in a sine wave temperature incubator in which the diurnal temperature was 27.5 and 4 C and the relative humidity was 45% at 27.5 C. In an open system, condensation increased the soil moisture from about 1.4 to 4% (by weight) which is equivalent to a moisture suction of −1,930 and −200 bars, respectively. Even at such high suctions, condensation caused marked increases in bacteria and actinomycetes as assessed by plate and direct counts. A pure culture of Arthrobacter oxidans, a typical nonsporeforming soil bacterium, responded in a manner similar to the natural bacterial flora. Neither temperature per se, spore germination, nor contamination by airborne microorganisms was responsible for these increases. It was hypothesized that at such high suctions, moisture distribution in the soil must be heterogenous in order to permit bacterial growth.
    Print ISSN: 0008-4271
    Electronic ISSN: 1918-1841
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 3
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    RELATIONSHIPS BETWEEN NITRATE IN SUMMER-FALLOWED SURFACE SOIL AND SOME ENVIRONMENTAL VARIABLES (1975)
    Canadian Science Publishing
    Details
    Publication Date: 1975-05-01
    Description: Multiple regression was used to quantify the relationships between NO3 in surface soil versus several selected environmental variables. Measurements were made on summer-fallowed Wood Mountain loam in the field. The temperatures and moisture conditions measured during one growing season were simulated in the laboratory using three soils. The most important factor influencing NO3 change was wetting and drying. The latter's effect was dependent on the soil moisture content just before the change occurred and/or the temperature during the period of change. Nitrification accounted for 12% of the increases in NO3 in the top 2.5 cm of soil; 88% of the increase resulted from upward movement of NO3-salts into the surface layer of soil as a result of evaporation. Of the NO3 produced by nitrification in the Wood Mountain loam, about 17.4% was credited to temperature effects. Thus only about 2.1% of the NO3 increase in the top 2.5 cm of soil in the field was due to temperature. In the simulation study, 19 C appeared to be a critical temperature above which the rate of nitrification was sufficient to counterbalance NO3 losses resulting from leaching and/or denitrification. The effect of moisture change on NO3 change appeared to be directly proportional to the total C and total N content of the three soils.
    Print ISSN: 0008-4271
    Electronic ISSN: 1918-1841
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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