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Development of standard methodologies for resident biomass and organic carbon

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Title: Development of standard methodologies for resident biomass and organic carbon
Author: Alder, V.; Charlton, D.; Gregorich, E. G.; King, D. J.
Abstract: The biologically active carbon fractions represent only a small proportion of the soil organic matter but they are dynamic and respond rapidly to changes in management or environmental conditions. Hence, the soil microbial biomass may be useful in assessing the impacts of management on long term changes in organic matter. The study examined components of soil carbon - microbial biomass, soluble organic, and total organic C - as well as other soil quality and productivity parameters such as soil strength, carbonates, density and crop yields. The relationship between soil properties and carbon components, and the implications for soil productivity were examined at various agricultural sites in Ontario. Soil redistribution due to topography and by agricultural practices will influence the distribution of soil properties in a landscape. Hence, soil properties were examined on the basis of landscape position within an agricultural practice. Effects of agricultural practices were examined at one location which consisted of adjacent farm fields under different long term crop and tillage management. Impacts of soil management and topography were reflected in the carbon components. No-till soils had about 1.5 times more organic carbon and about 2.5 times more microbial biomass carbon than conventionally tilled soils. The impact of landscape position within each management system was smaller than the effects of agricultural practices on carbon. All sites reflected higher organic carbon levels at lower slope positions but not alway higher microbial biomass carbon, though there tended to be more labile organic matter at the lower slope positions. Soil chemical, physical and productivity parameters were often less sensitive to soil management and landscape than the total and labile carbon components. That is, changes in soil organic carbon may be more readily reflected in the labile carbon components, than in, for example, bulk density. Seasonal differences in the levels of microbial carbon were not evident at all sites, and where temporal differences occurred, peak MBC levels did not coincide with the sampling date which approximated the initial reproduction stage of crop growth. However, more intensive sampling than was carried out in this study would be needed within a season, to determine when microbial populations are at a maximum. High variation in microbial biomass carbon underscores the fact that biomass measurements alone do not indicate much about soil quality. In order to characterize soil quality the biomass carbon needs to be compared with other measurements of labile carbon.
Date: 1997
Rights: In Copyright - Non-Commercial Use Permitted
Rights Holder: Agriculture Canada

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