Organic and Microbial Biomass Carbon Contents of Aggregates in a Toposequence of Pasture Soils

Abstract

The objective of this study was to determine changes in microbial biomass carbon (C<inf>mic</inf>) and organic carbon (C<inf>org</inf>) of soil aggregates along a pasture slope. Soil samples from 0-50 mm depth were taken from three landscape positions (shoulder, backslope and footslope) of a pasture in Samsun, Turkey. For each landscape position, soil aggregates were separated into eight aggregate size classes using a dry sieving method and then C<inf>org</inf> was analyzed. At all positions, macroaggregates (especially 841-1190 and 1190-1680 μ in sizes) were higher than microaggregates. The contents of C<inf>org</inf> varied between 0.65 and 2.08%. The highest C<inf>org</inf> contents were found in footslope position and the lowest contents in backslope. All properties are higher at footslope position than the other positions. Generally, C <inf>mic</inf> was greater in microaggregates of <250 μm, in macroaggregates of 250-420, 420-841, 841-1190 μm than in the other aggregate size at all positions, whereas C<inf>org</inf>:C<inf>mic</inf> was higher in macroaggregates of 1190-1680, 1680-2380, 2380-4760 μm than the other macro and microaggregate size. Consequently, in macroaggregates especially this class is relatively more C<inf>org</inf> than the microaggregates, even if the absolute values of C<inf>mic</inf> were lower.