Assessing the effect of arable management practices on carbon storage and -fractions after 24 years in Boreal conditions

Samenvatting

Soil organic matter (SOM) is beneficial for soil functions and crucial for ensuring sustainable agriculture. Understanding how agricultural management and soil properties impact on SOM throughout the soil profile would aid in preserving and increasing soil carbon (C) stocks. We sampled a 24 year-old cultivation field experiment on a heavy clay soil with organic and conventional cropping systems, and an adjacent unmanaged meadow to 70 cm soil depth and assessed the total carbon stocks and their distribution into mineral-associated (MAOM) and particulate (POM) organic matter. Throughout the soil profile, >83% of the soil C was in the MAOM fraction. The distribution of C between MAOM and POM was not strongly affected by soil management within a studied soil depth. Largest C stocks (169 t ha-1) together with the largest plant root biomass was found in the unmanaged meadow, which highlights the importance of deep-rooting plants in sequestering C into the soil. We also determined the contribution of clay, and aluminum and iron oxides in explaining the amount of total C, MAOM-C and POM-C. Whereas aluminum and iron oxides correlated with C in all the studied soil layers, clay was not associated to any of the C fractions below the 20 cm depth, suggesting that estimating the C accumulation potential of the deeper soil should not be based on the soil texture alone. Results indicate that aluminum and iron oxides can be important in transporting and stabilizing of C in the soil profile.