Soil organic carbon content and stock change after half a century of intensive cultivation in a chernozem area

Abstract

Soil organic carbon (SOC) is a significant soil parameter controlling soil quality and productivity and also playing an essential role in the global carbon cycle. Assessment of long-term SOC content and stocks changes is only possible by comparing historical and present data. The Czech Republic holds a national database of agricultural soils completed during the 1960s, which we used to assess SOC changes. SOC content and stock changes were detected after more than 50 years of intensive cultivation in a rolling chernozem landscape prone to soil erosion by re-sampling soil profiles from the 1960s and assessing these changes in relation to local topography. Each re-sampled soil profile was classified based on its position within the terrain, into one of three distinct slope positions namely shoulder slope (SH), backslope (BS), and foot slope (FS) which refers to a predisposition to soil erosion (SH, BS) or deposition (FS). Despite previous studies reporting SOC content decline over the past several decades, our results showed an increase in SOC content in all slope positions, being the most pronounced at FS position. However, median value for the SOC stock significantly decreased at SH positions primarily due to intensive erosion (decreased by 2.82 kg·m−2). At the FS positions, the median value for the SOC stock increased but not significantly (increased by 5.51 kg·m−2). Changes in the SOC stock were primarily driven by changes in the topsoil depth, which significantly decreased at the SH positions by 22 cm; the opposite result was found for the FS position. The local topography as a driver of SOC stock changes was further supported by the significant correlation between SOC stock changes and topographical attributes (predominantly with Multiresolution Valley Bottom Flatness index, Topographic position index or Topographic wetness index) showing increasing SOC stocks in terrain depressions or valley bottoms due to soil accumulation. We concluded that soil erosion is a dominant process in our study area, explaining the long-term changes in SOC stock.