Straw residue incorporation promotes soil organic carbon accumulation and enhances the effect of subsoiling on plant growth

Subsoiling tillage (SubT) is an effective strategy for improving soil structure in the agricultural management. However, little is known about the response of soil organic carbon (SOC) accumulation and plant nutrient uptake to SubT and subsoiling with straw residue incorporation (SubTS). We conducted a one-year field experiment in the Mollisol region of northeastern China, including three treatments: (1) conventional tillage (ConT); (2) SubT; (3) SubTS. Soil samples were collected from topsoil (0–20 cm) and subsoil (20–35 cm) to determine contents of SOC fractions, soil nutrients and soil microbial community structure. Crop biomass components and plant nutrient concentration as well as uptake were determined at maturity. SubTS increased particulate and mineral-associated organic carbon (POC and MAOC) contents and soil microbial biomass in the whole soil profile relative to ConT during days 30–150, and significantly (P < 0.05) for subsoil (averagely by 18.8 %, 13.2 % and 76.7 %, respectively). However, SubT was only conducive to POC and MAOC formation and soil microbial activities in the topsoil but not for the subsoil during days 60–150. Nonetheless, SubT and especially SubTS substantially increased harvest index and plant nutrient uptake. Moreover, the stronger relationships among SOC pool, aggregate stability, soil microorganisms and soil nutrients were observed in the subsoil than those in the topsoil. These results demonstrated that soil structure improvement and exogenous organic materials input performed pivotal functions in SOC accumulation, soil nutrients preservation and plant nutrition absorption. Accordingly, SubTS was recommended as a sustainable agriculture practice to promote SOC accumulation and plant growth in Northeast China.