Effects of different land use managements on aggregate stability in Atasu-Galyan dam watershed

The main purpose of this study was to determine effects of different land use managements (forest, agriculture, pasture) on aggregate stability in Atasu-Galyan dam watershed, Trabzon. Total of 180 soil samples were collected from three different land use. The following soil properties were determined: electrical conductivity, pH, bulk density, particle density, porosity, lime, organic matter, aggregate stability, microbial biomass carbon and mechanical analyses. According to obtained data, forest had the lowest aggregate stability (for 1-2mm aggregates) while agriculture soils had the highest. High aggregate stability in soils under agriculture may be related to high clay content. There was not a significant relation between aggregate stability and organic carbon content. Generally, when the organic matter content is greater than 5-6%, it affects aggregate stability positively. Below that threshold, aggregation is mainly controlled by clay fraction of soil. In this study, the mean values for microbial biomass C were 295.6 ?g g-1, 376.6 ?g g-1, and 383.6 ?g g-1 in the agriculture, grassland and forest soils, respectively. One-way ANOVA demonstrated that forest and grassland soils contain significantly higher microbial biomass C than those in the agricultural soils. However, there was no significant relation between aggregate stability and soil microbial biomass carbon (r= 0.148P>0.05). In conclusion, mechanical composition of soil appear to contribute greatly to the stability of aggregates in humid region. Also, aggregate size that was used in this study (1-2mm), influenced cementation of soil particles and made clay minerals to be more effective on it rather than organic matter or biological characteristics of soil.