Changes in soil organic carbon fractions in response to different tillage practices under a wheat-maize double cropping system

To understand the turnover of soil organic carbon (SOC) and the improvement of soil quality in response to tillage practices, it is important to identify changes in labile SOC fractions, for example, permanganate oxidizable organic carbon (POxC) and particulate organic carbon (POC). Five tillage treatments were initially undertaken in a winter wheat (Triticum aestivum L., mid-October to early-June)-summer maize (Zea mays L., mid-June to early-October) system in the North China Plain in 2008 with changes being examined in 2012-2013. These treatments included plough tillage with residue removed, plough tillage with residue incorporation, no tillage with residue mulching, subsoiling with residue incorporation, and rotary tillage (tillage with a rotary tiller) with residue incorporation for the winter wheat season; summer maize was only managed with the NTM treatment. The greatest POxC and POC concentrations at the 0-5-cm depth were observed under RTR and NTM treatments (p<.05), respectively. Both STR and RTR recorded larger POxC and POC concentrations at the 5-10-cm depth (p<.05). Both POxC and POC concentrations for STR treatment were significantly higher than those under RTR, NTM, and PT0 treatments in the 20-50-cm soil profile. The POC concentrations in each soil layer of 0-30-cm showed a significant response to residue amount, temperature, and precipitation; and POxC concentrations did not record similar responses. Therefore, subsoiling with residue incorporation could be a potential tillage practice to manage labile SOC pool in top soil (0-50-cm) in the North China Plain region.