Effect of nitrogen fertilisation under different land use on the total and labile organic carbon content in a calcareous chernozem under temperate climate

Background and Aims Land management has a significant impact on soil organic carbon (SOC) and its labile fraction, measured as permanganate-oxidizable carbon (POXC). However, the impact of nitrogen (N) fertilisation on these properties is not always consistent. This study investigated the effect of land use and N fertilisation, plant biomass and diversity on SOC and POXC. Methods Samples were taken from a cropland on chernozem soil after 17 and 27 years of ploughing and 20 years after switching to grassland under different N fertilisation (0, 100, 200 and 300 kg ha −1 ). Results Ten years of ploughing reduced both SOC and POXC content, but grassland management reversed the decrement. N fertilisation mitigated SOC decrease by 90% that was 471 kg ha −1 year −1 in the control treatment. Under grassland management N fertilisation reduced SOC restoration rate from 425 (control) to 164 kg ha −1 year −1 (200 kg N ha −1 ). Fertilisation caused inconsistent changes in POXC over the sampling times but average POXC values ​​increased from 352 to 399 mg kg −1 at control and highest N dose, respectively. Under grassland management, the influence of biomass on SOC and POXC outweighed that of biodiversity. The relationship between POXC and SOC has been attenuated with increasing N fertilisation rates. Conclusion Nitrogen fertilisation was effective tool in reducing carbon loss during arable farming but hindered SOC restoration under grassland. SOC was a better indicator of cultivation and N fertilisation than POXC. Land use was more decisive for the POXC level than N fertilisation.