Density separation of soil organic matter across three land uses in calcareous soils of Iran

ABSTRACT

The aim of this study was to examine the usefulness of physical and chemical fractionation in quantifying soil organic matter (SOM) in different stabilized fraction pools. Soil samples from three land use types in Lorestan province, Southwest Iran were examined to account for the amount of organic carbon and nitrogen in different SOM fractions. Size/density separation and chemical oxidation methods were applied to separate the SOM fractions including particulate organic matter (POM), Si + C (silt and clay), DOC (dissolved organic C), rSOM (oxidation-resistant organic carbon and nitrogen) and S + SA (sand and stable aggregates). The values obtained for TOC, TN, and HWC were highest in forest lands followed by the range and agricultural lands. Among the SOM fractions, S + SA showed the highest values (5.75, 5.77 and 20.6 g kg⁻¹ for agriculture, range and forest lands respectively) followed by POM, Si + C, rSOM, and DOC. The concentrations of C and N in the labile fractions obtained the higher values than in the stabilized fractions. Forest lands had the highest amounts of organic C and N among all fractions whereas agricultural lands showed highest values for inorganic C content of soils in different fractions.

KEYWORDS:

• Calcareous soils
• soil organic carbon
• resistant organic carbon (rSOM)
• particulate organic matter (POM)
• sand and stable aggregates  (S+SA)

Acknowledgments

The authors would like to thank the technical staff of the Institute of Crop Science at the University of Hohenheim for providing excellent support as well as their data services. The corresponding author would like to appreciate the Ministry of Science, Research and Technology in Iran for providing the expenses during research in Germany.

Disclosure statement

No potential conflict of interest was reported by the authors.