Dissolved Organic Matter in a Grassland Soil Profile: A Pilot Study Based on Lysimeter and Water Extraction Approaches

Dissolved organic matter (DOM) is a key component of soil systems and plays an important role in soil solution chemistry and organic matter transport. This study focuses on the comparison of DOM obtained by two different approaches: soil solution sampling and water extraction from soil. The aim is to characterise and compare dissolved organic matter collected from the same site and from identical depths of the soil profile.
Soil solution samples were collected using lysimeters installed at depths of 20, 40, and 60 cm. Water-extractable dissolved organic matter (WEDOM) was obtained from soil samples collected at the same depths and locations. The study site is a permanently grassed area managed by annual mowing, where the cut biomass is left on the surface without further intervention. This management represents a stable system with continuous organic matter input.
The physicochemical characterisation of DOM was based on a set of complementary analytical methods. Basic properties were determined by measuring pH and electrical conductivity. Dynamic light scattering (DLS) was used to assess particle size distributions, while zeta potential measurements were applied to evaluate surface charge and colloidal behaviour. UV–Vis spectroscopy was used to calculate selected absorbance coefficients related to aromaticity and the degree of humification.
By combining field-based lysimeter sampling with laboratory water extraction and multiple analytical techniques, this study provides a methodological framework for the comparison of different DOM fractions along the soil profile.

Acknowledgement
This work was supported by The NATO Science for Peace and Security Programme, project Nr. G6296. https://land-security.org/.