Management effects on carbon distribution in soil aggregates and its consequences on water repellency and mechanical strength
The purpose of this study was to investigate the physico-chemical heterogeneity of structured soils by analysing bulk soil, soil aggregates and homogenized material from arable soils (conservation and conventional tillage) in comparison to grassland soils. The organic carbon distribution of the investigated soils showed not only higher contents in the topsoil, but also smaller aggregates contained more Corg after segregation by dry sieving. The determination of carbon using δ13C identified that in the smallest fraction mostly fresh deposited organic carbon was accumulated. After Na-pyrophosphate percolation the smallest aggregate were the most influenced by percolation and most of the organic carbon was lost. The determination of organic carbon distribution and the δ13C signal within soil aggregates have shown only a slight tendency of higher Corg accumulation in the exterior aggregate region in comparison to the interior regions. Most investigated soil aggregates showed higher amounts of hydrophilic groups in the exterior regions of aggregates than in the interior regions. In addition K, Fe and Al have shown reduced contents in exterior regions in comparison to the interior regions, in contrast to the Na enrichment on the aggregate surface. The tensile strength of air dry aggregates was affected by the moisture content, depth of the soil and the size of the aggregates. The largest differences considering soil management were found between grassland and arable soil, while the differences between conventional and conservation tillage systems were less pronounced.