Crop yield and soil carbon responses to tillage method changes in North China

•Effects of 10 years conservation tillage plus 4 years deep tillage experiments were investigated in North China.•Crop yield and soil carbon were significant changed by conservation tillage conversion to deep tillage.•Deep tillage increased crop yields by 35, 24 and 24% compared with no tillage, rotary tillage and harrow tillage.•Deep tillage altered SOC pools by −1.5, 15.6 and 13.2 Mg ha−1 compared with no tillage, rotary tillage and harrow tillage.

Subsoil compaction at 15–30 cm depths due to the increase of bulk density or decrease in porosity after long-term no tillage or reduced tillage (e.g. rotary tillage or harrow tillage) is of growing concern. Deep tillage is generally regarded as an important method to reduce subsoil compaction due to long-term conservation tillage and thereby improve crop production and soil conditions. We compared the responses of crop yield and soil carbon (C) among 10-year no tillage (NT), rotary tillage (RT), and harrow tillage (HT) treatments, and their conversions to deep tillage (DT) for 4 years involving NT-DT, RT-DT and HT-DT treatments. The soil organic carbon (SOC) pool under the NT treatment was 29 and 91% higher than the SOC pools of the HT and RT treatments, respectively, whereas the NT annual yield decreased by 0.6 Mg ha−1 yr−1 over 10 years. The NT-DT, RT-DT and HT-DT treatments increased crop yield by 35, 24 and 24% and altered the SOC pool by −1.5, 15.6 and 13.2 Mg ha−1 over the 4 years of deep tillage compared with the corresponding values for NT, RT, and HT, respectively. Therefore, conversion to DT after long-term NT, RT, and HT use can benefit crop yield and play an important role in improving soil carbon sequestration following the long-term adoption of RT and HT systems in North China.