Influence of Land Use and Parent Material on the Organic Carbon Content and Stocks in Drained Soddy-Podzolic Soils, Tver Region

The results of baseline evaluation of soil organic carbon (SOC) contents and stocks, soil bulk density, and their spatial variability and vertical distribution patterns within the upper 40-cm-thick layer of agrosoddy-podzolic soils developed from glacial till (Albic Gleyic Retisols (Episiltic, Anoloamic, Aric, Ochric)) and agrosoddy podzols developed from sands (Albic Podzols (Arenic, Aric, Ochric)) are considered. Thirteen monitoring plots (30 × 30 m) have been established on drained (closed drainage) arable land, hayfield, and unmanaged fallow land of the experimental site of the All-Russia Research Institute of Reclaimed Lands (VNIIMZ) in Tver oblast, European Russia. The spatial variability of the SOC content within the plots exceeds the reproducibility of SOC determination by the dry combustion method by 5–10 times. The standard deviation of the SOC stocks nonlinearly increases with increasing thickness of the assessed layer from 1–5 t/ha for a layer of 0–5 cm to 10–20 t/ha for a layer of 0–40 cm. Differentiated soil sampling from thin layers within the upper 40-cm-thick layer demonstrated a uniform vertical distribution of SOC in the plow layer of the arable land; differences between SOC stocks in the layers of 0–10 and 10–20 cm are statistically insignificant. In the Retisols of the five-year-old hayfield with perennial grasses and of the 5- to 20-year-old unmanages fallow lands, a sod layer of 3–10 cm in thickness is formed, and the SOC content displays an accumulative distribution with a maximum in the surface layer. However, the SOC stocks in the upper and lower parts of the former plow horizon do not display statistically significant differences. Similar regularities have been found for the sandy Podzols against the background of generally lower contents and stocks of SOC.