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 (Cmic) and organic carbon (Corg) 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 Corg was analyzed. At all positions, macroaggregates (especially 841-1190 and 1190-1680 ? in sizes) were higher than microaggregates. The contents of Corg varied between 0.65 and 2.08%. The highest Corg 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 mic was greater in microaggregates of <250 ?m, in macroaggregates of 250-420, 420-841, 841-1190 ?m than in the other aggregate size at all positions, whereas Corg:Cmic was higher in macroaggregates of 1190-1680, 1680-2380, 2380-4760 ?m than the other macro and microaggregate size. Consequently, in macroaggregates especially this class is relatively more Corg than the microaggregates, even if the absolute values of Cmic were lower.