Subsoiling and plowing rotation increase soil C and N storage and crop yield on a semiarid Loess Plateau

Subsoiling loose subsoil, plowing loose topsoil, burying crop residue, the take turns used of subsoiling and plowing in years seem to be good methods to achieve the goal of regulating topsoil and subsoil structure and improving soil fertility and crop yield. However, the evaluation of the long-term effects of a subsoiling and plowing yearly rotation in a crop residue retention cropping system is lacking. Therefore, a 12-year (2007-2019) experiment was established to evaluate the influence of a subsoiling and plowing rotation with residue retention on water-stable aggregates (WSA), soil organic carbon (SOC), total nitrogen (TN) storage, and crop yield in a winter wheat-spring maize rotation field. Tillage treatment was 1-year subsoiling and 1-year plowing rotation (ST/CT), and continuous subsoiling (ST) and plowing (CT) were used as controls. During the 12-year experiment, the ST/CT rotation reduced the mean C input of winter wheat (5.4%) and spring maize (1.7%) at harvest compared with the ST treatment but significantly improved the mean C input of winter wheat (6.2%) and spring maize (10.9%) at harvest compared with the CT treatment. After 12 years of the experiment (2019), the ST/CT rotation significantly increased water-stable macroaggregates (6.6% and 7.7%) at 0-40 cm compared with the ST and CT treatments, respectively. In addition, the ST/CT rotation had a lower SOC (0.11 Mg.ha(-1)) and N (0.16 Mg & BULL;ha? 1) storage at the 0-10 cm soil depth than the ST treatment. However, the ST/CT rotation had a higher SOC (0.51 and 2.77 Mg.a(-1)) and N storage (0.11 and 0.18 Mg.ha(-1)) at the 10-20 and 20-40 cm soil depths than the ST treatment. When compared to the CT treatment, the ST/CT rotation significantly improved SOC and N storage at 0-10 cm (4.24 and 0.18 Mg & BULL;ha? 1), 10-20 cm (0.50 and 0.14 Mg & BULL;ha? 1), and 20-40 cm (2.66 and 0.22 Mg & BULL;ha? 1), respectively. Additionally, the ST/CT rotation also significantly enhanced the yield of winter wheat (5.6% and 10.5%) and spring maize (8.4% and 12.7%) compared with the ST and CT treatments, respectively. Different tillage significantly influenced the yield stability and sustainability of winter wheat, but no marked differences were observed in spring maize. In addition, a nonlinear relationship indicated that maximal SOC storage-responsive C input levels ranged from 3580 kg.ha(-1) to 6007 kg.ha(-1) for winter wheat and spring maize. ST/CT rotation can increase SOC storage before C saturation to reach maximized yield. To improve and sustain nutrient storage and crop production in winter wheat-fallow-spring maize rotation fields, ST/CT rotation seems to be a more suitable tillage practice.