Tillage-induced changes in the distribution of soil organic matter and the soil aggregate stability under a former short rotation coppice

No-till, perennial cropping in short rotation coppice (SRC) can increase the contents of soil organic carbon (SOC) in arable soils. The return to annual crops will involve an intense tillage, which was hypothesised to accelerate the mineralisation. The impact of tillage on the contents of SOC and of total nitrogen (Nt) and the aggregate stability was investigated at a SRC with 17 years old stools of willows and poplar (Salix and Populus spp.), a tilled former SRC (TFC) and a continuously annually tilled arable soil (TS) at an Eutric Cambisol in Northern Germany in 2010. The contents of SOC and Nt in the topsoil (0-30 cm soil depth) decreased in the following order: SOC: SRC (9.1 ± 1.21 mg g−1) > TFC (8.2 ± 0.41 mg g−1) > TS (6.4 ± 0.0 mg g−1) and Nt: SRC (0.94 ± 0.03 mg g−1) > TFC (0.86 ± 0.08 mg g−1) > TS (0.78 ± 0.07 mg g−1). SOC was relatively homogeneously distributed in the topsoil under TFC and TS, but concentrated close to the surface under SRC. The C/N ratio was significantly larger under SRC (9.7 ± 0.40) and TFC (9.5 ± 0.36) than under TS (8.2 ± 0.55). The ratio of water-stable soil aggregates in the size of 2.00-3.15 mm decreased in the following order: SRC (60 ± 16%) > TFC (10 ± 5%) > TS (3 ± 1%). Overall the study indicated that tillage of former SRC leads to a fast redistribution of SOC in the topsoil combined with a loss of aggregate stability. The pool size of SOC in the topsoil (SRC 36.7 ± 4.7 Mg ha−1; TFC 38.1 ± 2.4 Mg ha−1) remained unchanged after the first year of returned tillage and did not confirm an accelerated mineralisation in the short term. SRC and TFC exceed TS by about 6-8 Mg ha−1 SOC (TS 30.2 ± 0.0 Mg ha−1 SOC).