Rotary and subsoiling tillage rotations influence soil carbon and nitrogen sequestration and crop yield

Long-term single tillage causes serious deterioration of land quality and reduction of crop yield. Tillage rotation can alleviate the problems caused by long-term single tillage. However, the effects of different tillage rotations are still very limited. A tillage rotation experiment was conducted in the North China Plain to evaluate the impacts of tillage rotation on soil organic carbon (SOC), soil total nitrogen (STN) and crop yield. There were eight treatments with two main factors: tillage practice (four types: rotary tillage (R, 2002–2017), subsoiling tillage (S, 2002–2017), rotary to subsoiling tillage (RS, 2015–2017) and subsoiling to rotary tillage (SR, 2015–2017)) and straw management (two types: straw return (F) and straw removal (0)). RSF treatment yielded the highest SOC, at 12.53 g/kg. RSF significantly increased SOC by 41.4% compared to RF, while SRF significantly reduced SOC by 11.1% compared to SF. In addition, RSF significantly increased STN content by 21.7% compared with that under RF. Compared with SF, SRF promoted the uniform distribution of soil nitrogen in the 0–20 cm soil layer. Among the treatments, the RSF treatment yielded the highest SOC stock (SOC_S) and STN stock (STN_S), which were 67.68 t/ha and 6.63 t/ha, respectively. Compared with RF treatment, RSF treatment greatly increased SOC_S, by 31.7%. Both tillage rotation treatments increased STN_S by 13.3% under RSF compared to RF, and by 2.3% under SRF compared to SF. In 2016, the annual yield was highest under RSF treatment at 19.80 t/ha. In 2017, the annual yield was highest under SF treatment at 21.37 t/ha, and next highest under RSF at 20.94 t/ha. In summary, long-term rotary tillage followed by subsoiling tillage combined with straw return (RSF) can significantly increase SOC, STN and crop yield. The rotation of rotary tillage to subsoiling tillage combined with the straw return is an effective measure for improving soil quality and increasing crop yields in the North China Plain.