Soil Structure Formation Through The Action Of Plants

During soil formation, the interaction of different biota with weathered mineral material shape characteristic structures of pores and solid. We here explore soil structure formation on a chronosequence of recultivation sites where loess material has been used for 24 years in a standardized recultivation process. Thus, it is an ideal site for studying soil structure formation as a function of time.

Changes in soil pore system are characterised by parameters such as connectivity and pore size distribution. To derive these undisturbed soil columns (10 cm Ø) were taken from two depths (0-20; 40-60 cm) for 0, 1, 3, 6, 12 and 24 year old sites. X-ray µCT is used for scanning the original columns as well as subsamples of 3 and 1 cm Ø. This hierarchical sampling scheme was developed to overcome the trade-off between sample size and resolution. Subsamples therefore reveal information on micropores and small roots. In detail, image analysis is used to derive porosity, pore size distribution, connectivity and biopore density. The data are complemented by destructive sampling and determination of root length with WinRHIZO.

First results show an increase of macropores and connectivity over time. Especially under the ploughed layer a marked increase of biopore density during the first 12 years could be observed. However, in topsoil the effect of soil management is stronger than the effect of time, leading to a decrease of connectivity in the first 20 cm compared to soil samples from 40–60 cm depth.

For the first time, we were able to quantify how roots change the pore structure and how fast a dynamic balance of biopores in soils can develop.

The study is part of the DFG-Project Soil Structure (AOBJ:628683).

Fig.1: Biopores in a 3x3 cm soil column after a) 3 years and b) 12 year after reclamation (50 cm depth).