Rheological parameters of some soil samples before and after H2O2 treatment


The effect of soil organic matter (SOM) on formation of inter-particle bonds was studied in soils with high organic and no mineral carbon content in the top (A1, Ap) layers of different origin and under various land uses. The first set of soil samples was collected in the Alekhin Central Chernozem Reserve (Kursk region, Russia): under native steppe vegetation and under 67-yearold bare fallow. The second set of samples was sourced from the Midlands of Kwa-Zulu Natal, South Africa: under pine plantation and under long-term maize monoculture. Soil organic matter was removed by of 30% hydrogen peroxide (H2O2) treatment for 20-40 days. The rheological behaviour of the capillary-wetted soil pastes was characterized by amplitude sweep test with the modular compact rheometer MCR-302 (Anton-Paar, Austria). The storage modulus in linear viscous-elasticity range (LVE-range) and crossover of storage modulus and loss modulus were determined. The samples treated with H2O2 in all cases except the Ferralsol under pine plantation, increased the storage modulus in the LVE-range. It shows more rigid particle interaction due to loss of SOM. The peculiarity of soil under pine plantation is very high resistance to stress in native state and loss of this resistance upon SOM oxidation or removal. We connect this with significant change in particle size distribution upon the H2O2 treatment. In contrast to other samples, this soil shows significant reduction in coarse silt fraction (from 44.5 to 23.2%) and an increase in clay content (from 10.8 to 36.5). We connect the observed differences to the type of organic matter inputs. Unlike the herbaceous vegetation, pine plantations lead to significant accumulation of plant litter on the soil surface. The dissolved organic matter (DOM) is leached out of the litter layer by percolating water. The sorption of DOM (ligand exchange, cation bridges, hydrophobic interactions) on the mineral surfaces contributes to particle aggregation.


Posted on

November 29, 2017