Long‐term development of organic carbon contents in arable soil of North Rhine–Westphalia, Germany, 1979–2015

Europe currently faces a decline in soil organic carbon (SOC) content under arable cropping irrespective of improved management practices. In this study we used more than 32 000 SOC data from the entire North Rhine–Westphalia (NRW) area to elucidate the temporal development and current state of SOC content in arable soil from 1979 to 2015 and, in addition, to identify potential causal factors of changes in SOC content. The dataset comprised 7401 data points for 1979–2003 from FIS StoBo, the branched information system on soil contamination in NRW, and 24 930 data points for 2007–2015 from the Agricultural Investigation and Research Institute NRW (LUFA NRW); all data considered refer to soil sampled at 0–30 cm. We found that topsoil carbon contents in arable soil increased over the entire NRW area during the 1980s (from 1.87% in 1979 to 2.82% in 1987), and that this increase was followed by an exponential decrease from 1988 to 2015 (1.42% SOC in 2015) without a new equilibrium being reached. Livestock‐poor regions showed a more rapid gain and a more rapid loss of SOC contents than regions with large livestock densities. The data correlated with changes in grassland area, which was reduced in NRW by about 360 000 ha mainly between 1970 and 1990; that is, recently ploughed grassland probably contributed to increasing averages of SOC contents in arable land during this period, but not thereafter. We conclude that past changes in land use controlled the evolution in SOC from 1979 to 2015, and there is little opportunity for changed management practices to prevent ongoing loss of SOC from the topsoil. HIGHLIGHTS: The SOC contents in arable soil in North Rhine–Westphalia (NRW) show temporal trend. The SOC contents increased during the 1980s, but decreased thereafter. Data from the entire NRW area indicate that new SOC equilibria have not yet been reached. Past changes in land use still control current SOC evolution.