SOIL BASAL RESPIRATION AND DEHYDROGENASE ACTIVITY OF AGGREGATES: A STUDY IN A TOPOSEQUENCE OF PASTURE SOILS

Abstract

The objective of this study was to determine changes in soil basal respiration (BR) and dehydrogenase activity (DHA) in soil aggregates along a pasture slope. Soil samples from 0-50 mm depth were taken from three landscape positions (crest, midslope 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 microbiological properties and organic carbon content (C(org)) were analysed. At all positions, the contents of macroaggregates (especially 841-1190 pm and 1190-1680 mu m) were higher than microaggregates. The contents of C(org) varied between 0.65-2.08%. The highest C(org) contents were found in footslope positions, and the lowest in midslope. All microbiological properties were higher at footslope position than at the other positions. Generally, BR and DHA were higher in microaggregates < 250 mu m, in macroaggregates of 250-420, 420-841, 841-1190 pm than in the other aggregate size classes at all positions, whereas C(org):C(mic) BR:C(mic) and DHA:C(mic) ratios were higher in macroaggregates of 1190-1680, 1680-2380, 2380-4760 mu m than the other macro- and microaggregate size. Consequently, macroaggregates had relatively more C(org) than the microaggregates, even if the absolute values of BR and DHA were the lower.