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

Abstract

The objective of this study was to determine changes in microbial biomass carbon (C_mic) and organic carbon (C_org) 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_org was analyzed. At all positions, macroaggregates (especially 841–1190 and 1190–1680 μm in sizes) were higher than microaggregates. The contents of C_org varied between 0.65 and 2.08%. The highest C_org 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 μm, in macroaggregates of 250–420, 420–841, 841–1190 μm than in the other aggregate size at all positions, whereas C_org : C_mic 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_org than the microaggregates, even if the absolute values of C_mic were lower.