1 The Faculty of Engineering and Science, Aalborg University, VBN2 Department of Civil Engineering, The Faculty of Engineering and Science, Aalborg University, VBN3 Division of Water and Soil, The Faculty of Engineering and Science, Aalborg University, VBN4 Water and Environment Research Group, The Faculty of Engineering and Science, Aalborg University, VBN5 Urban Water and Environment Research Group, The Faculty of Engineering and Science, Aalborg University, VBN6 Department of Agroecology, Faculty of Science and Technology, Aarhus University, Tjele7 Institut for Agroøkologi - Jordfysik og Hydropedologi8 Shiraz University9 Univ Arizona, Dept Soil Water & Environm Sci, Tucson, AZ USA10 Shiraz University
Soil structure formation is essential to all soil ecosystem functions and services. This study aims to quantify changes in soil structure and microbial activity during and after field incubation and examine the effect of carbon, organic amendment and clay on aggregate characteristics. Five soils dominated by illites, one kaolinitic soil and one smectitic soil were sieved to 2 mm, and each soil was divided into two parts and one part amended with ground rape shoots (7.5 t ha−1) as an organic amendment. Samples were incubated in the field for 20 months with periodic sampling to measure water-dispersible clay (WDC) and fluorescein diacetate activity (FDA). After incubation, WDC and FDA were measured on air-dried 1–2-mm aggregates. Tensile strength was measured on four aggregate classes (1–2, 1–4, 4–8 and 8–16 mm) and results used to assess soil friability and workability. Intact cores were also sampled to determine compressive strength. During incubation, the amount of WDC depended on soil carbon content while the trends correlated with moisture content. Organic amendment only yielded modest decreases (mean of 14% across all sampling times and soils) in WDC, but it was sufficient to stimulate the microbial community (65–100% increase in FDA). Incubation led to significant macroaggregate formation (>2 mm) for all soils. Friability and strength of newly-formed aggregates were negatively correlated with clay content and carbon content, respectively. Soil workability was best for the kaolinite-rich soil and poorest for the smectite-rich soil; for illitic soils, workability increased with increasing organic carbon content. Organic amendment decreased the compression susceptibility of intact, incubated samples at smaller stress values (<200 kPa).
European Journal of Soil Science, 2014, Vol 65, Issue 2, p. 218-230