The characterization of straw decomposition and the resulting carbon (C) and nitrogen (N) release is crucial for understanding the effects of different straw returning methods on the immobilization and cycling of soil organic carbon (SOC) and soil total nitrogen (STN). In 2017–2018, a field micro-plot experiment was carried out in northeastern China to investigate the effects of different straw returning approaches on straw decomposition, C release, N release, SOC, STN, and the soil C–N ratio. Six straw returning treatments were applied: straw mixed with soil (SM) and straw buried in the soil (SB) at soil depths of 10 (O), 30 (T), and 50 cm (F). The results indicate that the straw decomposition proportion (SD), C release, and N release in SM + O were higher than that in SM + T and SM + F. Moreover, SOC and STN concentrations and the soil C–N ratio were significantly enhanced by SM/B + O in the 0–20 cm soil layers, SM/B + T in the 20–30 cm soil layer, and SM/B + F in the 40–60 cm soil layers. In the 0–50 cm soil profile, the highest SOC stocks were obtained using SB + T. The STN stocks were also significantly affected by the straw returning depth, but the effect was inconsistent between the two years. SD had a positive relationship with SOC and STN in the 0–20 cm soil layers; conversely, they were negatively related in the 30–60 cm soil layers. The results of this study suggest that straw buried in the soil to a depth not exceeding 30 cm might be an optimal straw returning approach in northeastern China.

Returning crop straw to soil can potentially improve soil health and crop production, facilitating sustainable agriculture. However, the effects of straw incorporation with various tillage management techniques combined with nitrogen (N) regimes on crop root growth, and water and N utility are not well understood. In this study, rotary tillage (RTS) and plow tillage (PTS) for straw incorporation combined with N regimes (CK, no N applied; LN, 112 kg N ha⁻¹; MN, 187 kg N ha⁻¹; and HN, 262 kg N ha⁻¹) were used to determine their effects on soil water and mineral N availability, root distribution, crop N uptake, grain yield, and water use efficiency (WUE) of maize in northeast China. The results demonstrate that higher levels of pre-sowing soil-water storage and field evapotranspiration (ET), and lower levels of WUE and pre-sowing soil mineral N storage (Nmin-PS) at a depth of 0–60 cm were obtained with the RTS treatments as compared to the PTS treatments. N addition improved Nmin-PS and post-harvest soil mineral N storage (Nmin-PH) at a depth of 60–100 cm in 2016, and increased WUE compared to CK. RTS treatments enhanced root weight density (RWD) at a depth of 0–60 cm in 2016–2017, root length density (RLD), ratio of root length density (RLDR), and ratio of root weight density (RWDR) at a depth of 30–60 cm in 2016, and RLD at a depth of 0–30 cm in 2017. N addition promoted RLD and RWD at a depth of 0–10 cm in 2016–2017. RTS treatments reduced pre-silking shoot N uptake (NPS) and grain yield. Shoot N uptake and grain yield were enhanced in response to increasing levels of N; however, the grain yield did not show further significant improvements when the amount of N applied was over 187 kg N ha⁻¹ (except for RTS in 2016). Overall, tillage with straw incorporation management and N levels markedly affected the soil physicochemical properties (such as ET, Nmin-PS, and Nmin-PH). This influenced grain yield indirectly by further mediating root traits (RLD, RWD, RLDR, and RWDR) with consequences for the NPS and post-silking shoot N uptake (NPOS) of maize, which were found to have greatest direct and positive impact on maize grain yield.