Abstract
Conversion of native grasslands to agricultural sites has resulted in remarkable changes in soil carbon at depth, but its impact on soil diagnostic horizons is unknown. This study was conducted to radiocarbon date the soil organic carbon (SOC) and quantify pedogenic carbonates in the Russian Chernozem at depth at three sites: a native grassland field (not cultivated for at least 300 years), an adjacent 50-year continuous fallow field in the V.V. Alekhin Central-Chernozem Biosphere State Reserve in the Kursk region of Russia (UNESCO—MAB Biosphere Reserve), and a cropland in the Experimental Station of the Kursk Institute of Agronomy and Soil Erosion Control. All sampled soils were classified as Fine-silty, mixed, frigid Pachic Hapludolls (Haplic Chernozem). The radiocarbon age (14C date, y BP) of SOC was highly variable: in the native grassland field, it varied from post-bomb (A-horizon) to 8011 ± 54 y BP (C-horizon); in the continuous fallow, it varied from 1569 ± 41 y BP (Ap-horizon) to 11,380 ± 180 y BP (C1-horizon); and in the cropland, it varied from 1055 ± 38 y BP (Ap-horizon) to 11,805 ± 68 y BP (Ck-horizon). Cultivation resulted in morphological/diagnostic changes in the soil profile (conversion of A to Ap; conversion of Bw to Bk horizon) over a 50-year period. These changes are supported by radiocarbon dating of SOC and pedogenic carbonate distribution within the soil profile. The proportion of pedogenic carbonates was highly variable: in the native grassland, it was 27% (C-horizon); in the continuous fallow, it varied from 53% (Bk1-horizon) to 72% (C2-horizon); and in the cropland, it varied from 85% (A-horizon) to 10% (Ck-horizon). The radiocarbon age differences with depth among the soils reflect changes in the soil carbon dynamics resulting from cultivation.
Highlights
IntroductionGeosciences 2018, 8, 458 carbon (SIC), and many studies have used radiocarbon dating for determining carbon dynamics [3,4,5,6]
Native and fallow sites were dominated by silty clay loam (SiCL) textural classes compared to cropland, which was dominated by silt loam (SiL) textures (Table 2)
The radiocarbon age of soil organic carbon (SOC) was highly variable: in the native grassland site, it varied from post-bomb to 8011 ± 54 years before present (y BP); in the continuous fallow, it varied from 1569 ± 41 y BP
Summary
Geosciences 2018, 8, 458 carbon (SIC), and many studies have used radiocarbon dating for determining carbon dynamics [3,4,5,6]. Radiocarbon dating was used to compare the 14 C age of humus from different horizons (down to 60 cm depth) of cultivated and non-cultivated Chernozems in the Belgorod region of Russia and concluded that the radiocarbon age of soil organic matter (SOM) increased with cultivation due to a lack of input of fresh plant material compared to non-cultivated sites [7]. Another study used radiocarbon and stable carbon isotopes to quantify the rates of labile and inert organic carbon cycling with depth in Mollisols at a restored prairie within an intensively managed landscape within the Critical Zone Observatory in Illinois, USA [8]. Interpretation of radiocarbon ages of SOM can be a challenging task because SOM is the product of ongoing SOM accumulation and decomposition and does not meet the basic “closed system”
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