Long-term agricultural management and erosion change soil organic matter chemistry and association with minerals

Xiang Wang; Nicolas A Jelinski; Brandy Toner; Kyungsoo Yoo

doi:10.1016/j.scitotenv.2018.08.110

Long-term agricultural management and erosion change soil organic matter chemistry and association with minerals

Sci Total Environ. 2019 Jan 15:648:1500-1510. doi: 10.1016/j.scitotenv.2018.08.110. Epub 2018 Aug 9.

Authors

Xiang Wang¹, Nicolas A Jelinski¹, Brandy Toner¹, Kyungsoo Yoo²

Affiliations

¹ Department of Soil, Water, and Climate, University of Minnesota-Twin Cities, Saint Paul, MN 55108, USA.
² Department of Soil, Water, and Climate, University of Minnesota-Twin Cities, Saint Paul, MN 55108, USA. Electronic address: kyoo@umn.edu.

PMID: 30340295
DOI: 10.1016/j.scitotenv.2018.08.110

Abstract

The interaction of soil organic matter (SOM) and minerals is a critical mechanism for retaining SOM in soil and protecting soil fertility and long-term agricultural sustainability. The chemical speciation of carbon (C) and nitrogen (N) in mineral-associated SOM can be sensitive to both anthropogenic management practices and landscape positions, but these two aspects are rarely examined in tandem. Here we examined the effects of long-term (>100 years) agricultural management and erosion on mineral-associated SOM along grassland and agricultural hillslope transect. The mineral-associated SOM was obtained using particle size and density fractionation approaches. Chemical speciation of C and N in mineral-associated SOM was characterized using micro X-ray absorption near-edge fine structure (XANES) spectroscopy. The extent of SOM coverage and contribution of iron oxyhydroxides (Fe oxides) to the total specific mineral surface area (SSA) were determined using the BET-N₂ adsorption method of soil samples under three conditions: untreated, SOM removal, and Fe oxides removal. The amount of SSA covered by SOM (SSA_SOM-covered) was lower by 61% and 37% in cultivated eroding and depositional topsoils, respectively, compared with the corresponding grassland. Depositional soils had higher SSA_SOM-covered than eroding positions. In the cultivated hillslopes, aromatic and phenolic C species were more abundant in depositional soils than in the eroding topsoils, indicating that deposition and burial of eroded or in-situ plant-derived phenolic C protected them from further transformation. Our results, therefore, highlight the importance of anthropogenic activities in the interaction of SOM and minerals, including C speciation changes, which may exert a considerable influence on SOM retention in soils.

Keywords: Cultivation; Erosion; Mineral-associated soil organic matter; Specific mineral surface area; XANES.