Abstract
Soil organic matter (SOM) is unevenly distributed in arable fields in undulated landscapes, but the chemical composition resulting from their turnover, transport and deposition processes is insufficiently known. Therefore, we aimed at disclosing the molecular-chemical composition of SOM in four different catenae at shoulderslope, backslope and footslope positions in arable fields in the Baltic Sea catchment, Europe. The backslope positions always had the lowest organic C-contents (Corg) (1.6…11.8 g·kg−1) and C-stocks (3.8…8.5 kg·m−2) compared to the shoulderslopes and footslopes (1.7…17.7 g·Corg·kg−1, 5.4…15 kg·Corg·m−2). In the SOM-poor backslope positions, the organic matter was characterized by relatively high proportions of carbohydrates, phenols + lignin monomers, alkylaromatic compounds, N-compounds and amides, indicating intensive microbial decomposition. By contrast, the footslopes had the largest Corg-contents (9.3…16.5 g·kg−1) and C-stocks (8.9…15 kg·m−2) in the catenae and particular enrichments in lipids, lignin dimers, sterols and free fatty acids. These relatively stabile SOM compound classes are interpreted as leftovers from erosive downslope transport and concurrent microbial decomposition, e.g., they are pronounced at backslope positions, followed by restricted microbial decomposition. This heterogeneous SOM distribution calls for an adapted soil management that reduces erosion and places amendments to field areas, such as the shoulderslope and backslope.
Highlights
Interlinked processes, such as soil compaction and structure deterioration, soil erosion and re-distribution, together with soil organic matter (SOM) loss and biological degradation, are areas of major concern in Europe [1,2]
Hypothesis 1, that SOM at the shoulder- and backslope positions is affected by erosive losses, is partly confirmed by the C-stocks and differences in chemical composition
C-stocks (Table 2) and the most pronounced differences in chemical SOM composition compared to the upper shoulderslope as well as the lower footslope positions
Summary
Interlinked processes, such as soil compaction and structure deterioration, soil erosion and re-distribution, together with soil organic matter (SOM) loss and biological degradation, are areas of major concern in Europe [1,2]. In undulated landscapes under intensive crop production, erosion sedimentation dynamics result in a redistribution of humus- and nutrient-rich, potentially fertile, soil constituents at the field scale [3]. 2019, 3, 42 these processes, the top and upper slope positions are usually depleted, whereas the depressional areas are enriched in SOM [4,5]. Former (pre-erosion) surface (1) SOM=f(Il, Isub,Teda, S, Ll,tur,e). Soil Syst. 2019, 3, 42 these processes, the top and upper slope positions are usually depleted, whereas the depressional areas are enriched in SOM [4,5].
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