Turnover of organic matter in differently textured soils: I. Physical characteristics of structurally disturbed and intact soils

Soil type effects on organic matter turnover are most often ascribed directly to differences in soil clay content. Since soil texture determines the physical characteristics of soil, aggregation and water holding capacity may be more relevant to address in the search for controls of organic matter turnover. Most studies of microbial processes in soils are based on structurally disturbed soil, where the abiotic conditions for the microbial activity may be quite different from those in intact soils. In this study, basic physical characteristics were determined for structurally disturbed and intact soil samples from differently textured soils. Bulk soil was retrieved from 0–20 cm depth at six locations along a textural gradient in an arable field on Weichselian morainic deposits in Denmark. The samples (NA1 to NA6) ranged in clay from 11 to 45% and in silt from 7 to 15%. Clay and silt-sized organomineral complexes were isolated from NA2 soil by ultrasonic dispersion and sedimentation in water. The clay and silt fractions were added individually and in varying proportions to NA1 soil, providing three clay-amended (CL2, CL4 and CL6) and three silt-amended (SI2, SI4 and SI6) soils. All 12 soils were crushed in air dry state to