Long-term intensive cultivation has caused soil fertility decline and structural degradation in the Songnen Plain, thereby constraining maize root development and yield formation. As a fundamental conservation tillage practice, straw return enhances soil function by incorporating exogenous organic matter and regulating root-shoot physiological processes. However, the mechanism underlying yield improvement through root–photosynthesis–nitrogen synergy remains insufficiently understood. A field experiment was conducted to assess the effects of conventional tillage (CT), straw incorporation (SI), straw mulching (SM), and deep straw incorporation (DF) on maize physiological traits and yield. Compared with CT, DF markedly enhanced root morphology and physiology, increasing the root length, surface area, volume, and root-shoot ratio by 16.46%, 23.87%, 26.64%, and 51.34%, respectively. The root bleeding intensity increased by 23.63%, whereas amino acid and nitrate contents in the bleeding sap increased by 29.20% and 65.93%, respectively, indicating improved root nutrient transport capacity. The enhanced root system positively influenced shoot photosynthesis by increasing the chlorophyll SPAD value by 16.05%, net photosynthetic rate (P_n) by 11.28%, and the activities of RuBP, PEP, nitrate reductase (NR), and glutamine synthetase (GS) by 10.59%, 24.36%, 29.94%, and 12.47%, respectively. These synergistic improvements significantly promoted post-anthesis biomass accumulation and yield formation. DF increased nitrogen and dry matter accumulation at the R3 stage by 26.61% and 15.67%, respectively, and resulted in an average yield increase of 8.34%, which was primarily due to an 11.96% increase in 100-grain weight. Although SI and SM also improved certain physiological indices, their effects were weaker than those of DF. RF analysis identified sap nitrate content (RNO), bleeding intensity (RBI), root length (RL), and root volume (RV) as key yield determinants. PLS-SEM further revealed that straw return enhanced root morphology and bleeding traits (path coefficients: 0.96 and 0.82), which subsequently improved leaf photosynthetic traits (path coefficients: 0.52 and 0.39) and biomass accumulation (path coefficient: 0.71). Collectively, these improvements promoted post-anthesis nitrogen accumulation and dry matter partitioning into grains. These findings elucidated the physiological mechanism by which deep straw incorporation increased maize yield through root system optimization, providing a theoretical basis for conservation tillage optimization in the thin-layer Mollisol region of the Songnen Plain.

Achieving sustainable utilization of black soils in Northeast China hinges on balancing exploitation and conservation. Conventional tillage (CT) degrades soil over time, while no-tillage (NT) conserves soil but often reduces yields. Strip tillage (ST) tills within the seed row zone (ST-IR) while maintains NT with straw mulch between seed rows zone (ST-BR), which appears to integrate the advantages of CT and NT. However, the effects of ST-IR and ST-BR on the soil macropore structures and hydrothermal properties in this region remain unclear. In this study, X-ray computed tomography (X-CT) and time domain reflectometry (TDR) were employed to compare the soil macropore characteristics and hydrothermal conditions across NT, CT, ST-IR, and ST-BR. Results showed that the soil hydrothermal conditions, bulk density (BD), penetration resistance (PR), air capacity (AC), air permeability (AP), and available water capacity (AWC) of ST-IR were similar to those of CT ( P > 0.05). However, the hydrothermal conditions of ST-BR resembled those of NT ( P > 0.05). Furthermore, ST created two distinct macropore structures. ST-IR aligned with CT in macropore size distribution, pore morphology, and connectivity ( P > 0.05), showing high macroporosity and connectivity. The macropores of ST-IR were dominated by irregular, large-volume non-biopores, with higher compactness (CP, 1978), specific surface area (SA, 0.50), and fractal dimension (FD, 2.62), yet lower degree of anisotropy (DA, 0.26). In contrast, ST-BR converged with NT ( P > 0.05), demonstrating significantly lower macroporosity and connectivity than ST-IR and CT ( P < 0.05). The dominant pore type in the ST-BR and NT consisted of tubular biopores, with CP (97), SA (0.11), and FD (2.38) all significantly lower than those in ST-IR and CT ( P < 0.05), while DA (0.42) was significantly higher ( P < 0.05). Overall, ST integrates CT and NT in soil macropore structure and hydrothermal conditions, offering valuable insights into its role in black soil conservation and utilization.

Soil organic carbon (SOC) is a core component of farmland fertility, and its content is significantly influenced by tillage practices. To clarify the effects of alternate tillage on soil organic carbon sequestration and soil aggregate stability, a tillage experiment was initiated in 2017. The study focused on the distribution of soil aggregates across different particle sizes and their organic carbon contents under four tillage treatments: (1) rotary tillage for two consecutive years after initial deep plowing (RT_DP); (2) no-tillage for two consecutive years after initial deep plowing (NT_DP); (3) continuous rotary tillage (RT); and (4) continuous no-tillage (NT). Compared with continuous rotary tillage (RT), RT_DP increased the crop yield by 14.78%, NT decreased the yield by 10.59%, and NT_DP increased the yield by 3.40%. In the topsoil, soil organic carbon (SOC) content increased by 21.57% under RT_DP, 24.47% under NT, and 21.57% under NT_DP. In the subsoil, SOC content increased by 36.91% under RT_DP, 24.80% under NT, and 42.52% under NT_DP. Compared with the RT treatment, practices such as RT_DP increased the SOC content and the proportion of macroaggregates. No significant differences were observed among all treatments in the topsoil. However, in the subsoil, RT_DP significantly increased the SOC content (by 36.91%), SOC content within >0.25 mm aggregates (by 35.75%), and the proportion of >0.25 mm aggregates (by 1.28%), relative to RT. Compared with NT, NT_DP also increased these three indices by 14.2%, 13.38%, and 0.32%, respectively. In the topsoil, the NT_DP treatment resulted in higher mean weight diameter (MWD) stability than the other treatments. In the subsoil, the NT treatment showed the highest MWD and geometric mean diameter (GMD) values, while both RT_DP and NT_DP had significantly higher MWD and GMD than RT. In the deeper soil layer, the NT treatment exhibited the highest aggregate stability. Further analysis indicated that the positive effects of alternate tillage (NT_DP and RT_DP) on aggregate distribution, aggregate stability, and subsoil SOC sequestration were mainly due to improvements in the soil’s nutrient availability, bulk density, porosity, and water content. The optimization of these soil properties further enhanced soil enzyme activity and ultimately promoted the stabilization and accumulation of SOC. In conclusion, incorporating deep plowing into rotational tillage can effectively promote SOC accumulation, especially in the subsoil of maize farmland, and enhance the physical protection of SOC. This study provides a practical tillage strategy for increasing the maize yield and enhancing soil organic carbon sequestration.

Soil respiration is a major pathway of carbon loss from agricultural soils and is substantially influenced by tillage practices. However, the short-term effects of different tillage system transitions on soil respiration and maize yield remain unclear. A field experiment was therefore conducted with five treatments: conventional tillage–conventional tillage (CK), mulching–mulching (CS), conventional tillage–rotary tillage (NR), rotary tillage–rotary tillage (RS), and mulching–rotary tillage (CRS). Soil respiration, maize growth, and yield were monitored throughout the growing season. The results showed that tillage transition significantly altered the soil respiration rate and its component structure. Higher soil respiration increased CO₂ release, raised canopy CO₂ concentration, and accelerated dry matter accumulation. The RS exhibited the highest soil respiration, with a peak rate of 16.83 μmol m⁻² s⁻¹, of which root respiration accounted for 64.16%, and improved soil porosity and promoted aboveground biomass accumulation. The CRS treatment achieved the highest leaf area index, dry matter accumulation, and yield, representing a 51.49% increase over the control, and had the lowest Q₁₀ value (2.97), indicating that respiration under this treatment was more regulated by substrate availability than by temperature. The CS treatment minimized carbon loss while maintaining grain yield. Overall, tillage transitions that improve soil aeration and root activity were generally associated with higher maize yields, but different pathways created distinct trade-offs among respiration, carbon turnover, and harvestable yield. These findings suggest that conservation tillage transitions have considerable potential for balancing yield maintenance with soil respiration regulation, providing useful guidance for sustainable high-yield maize production in semi-arid regions.