This study aimed to elucidate the effects of maize–soybean intercropping patterns on canopy light heterogeneity, light use efficiency, and yield formation in maize rows, and to identify an intercropping configuration suitable for mechanized operations in the black soil region along the foothills of the Greater Khingan Range, so as to enhance regional agricultural productivity.

Field experiments were conducted during 2023-2024 in the black soil region along the eastern foothills of the Greater Khingan Mountains (Arong Banner, Inner Mongolia, China), using maize (Yinongyu 12) and soybean (Dongsheng 19) as test cultivars. The canopy light environment of maize was visualized. Six maize–soybean intercropping configurations were established, including two rows maize–two rows soybean (2M2S), four rows maize–four rows soybean (4M4S), four rows maize–two rows soybean (4M2S), six rows maize–six rows soybean (6M6S), six rows maize–four rows soybean (6M4S), and six rows maize–two rows soybean (6M2S), and differences in canopy structure, light-use characteristics, and yield formation were systematically evaluated.

(1) The 4M4S configuration exhibited the most favorable canopy structural characteristics due to enhanced light penetration in marginal rows and improved light conditions within inner rows, followed by 2M2S. Consequently, light-use efficiency and leaf photosynthetic rate during the tasseling–silking and grain-filling stages were significantly higher under 4M4S and 2M2S than that under the other intercropping treatments. (2) Maize yield under 4M4S did not differ significantly from that under 2M2S, whereas soybean yield was significantly higher under 4M4S, leading to the highest land equivalent ratio (LER), reaching 1.61 and 1.60 over the two years. LER values for the remaining treatments ranged from 1.31-1.56 and 1.28-1.53, respectively. Moreover, owing to better compatibility with agricultural machinery and lower operational costs, 4M4S achieved the highest benefit–cost ratio (6.61), exceeding those of other treatments by 7.39%-32.28%.

The upper canopy layer (L160 and L200) was identified as a key functional zone regulating photosynthesis in intercropped maize, with pronounced gradient differentiation in the relationships among canopy structure, photosynthetic performance, and yield across spatial row positions, where marginal rows exhibited the strongest advantage. Mantel analysis further revealed a strong coupling between light environmental structure and photosynthetic efficiency, forming a continuous pathway of “light acquisition–photosynthetic conversion–yield formation”. Owing to enhanced marginal effects and improved light distribution within inner rows, maize yield under the 4M4S configuration did not differ significantly from that under the conventional 2M2S pattern, whereas soybean yield was significantly increased (P<0.05), resulting in the highest land equivalent ratio and a greater benefit–cost ratio. Therefore, in the black soil region along the eastern foothills of the Greater Khingan Mountains, the 4M4S intercropping system represented an effective strategy to simultaneously enhance productivity and economic returns while facilitating fully mechanized cultivation and promoting sustainable agroecosystem development.

Soil organic carbon pool activity and stability are important indicators that directly reflect soil quality. This study aimed to explore the effects of long-term crop rotation system on soil organic carbon, active organic carbon and soil carbon pool management index, so as to provide the scientific management of soil carbon pool and rational crop layout in black soil areas.

The experiment started in 2016, and 7 treatments were set up: potato continuous cropping (P-P), maize continuous cropping (M-M), soybean continuous cropping (S-S), soybean-maize rotation (S-M), soybean-potato rotation (S-P), maize-maize-potato rotation (M-M-P), and soybean-maize-potato rotation (S-M-P). P-P was used as a control. The characteristics of soil organic carbon (SOC), readily oxidizable carbon (ROC), inert organic carbon (IOC) and soil carbon pool management index (CPMI) in 0-60 cm soil layer at the harvest stage in 2022 and 2023 were analyzed systematically.

Compared with the P-P treatment, in 2022 and 2023: (1) SOC content under S-M-P and S-M treatment in 0-10 cm soil layer increased significantly by 10.22%-12.49% and 20.67%-36.75%, respectively. The M-M-P treatment of 10-20 cm soil layer significantly increased by 16.65% and 33.76%, respectively. SOC content under S-M-P and M-M-P treatments in 20-40 cm soil layer was significantly increased by 28.74%-36.78% and 48.78%-53.67%, respectively. In 2023, the S-M-P in 40-60 cm soil layer was significantly increased by 14.90% (P<0.05). (2) ROC₃₃₃ content in 0-10 cm soil layer under S-M and M-M-P treatment was significantly increased by 20.09%-20.41% and 34.94%-39.69%, respectively. ROC₃₃₃ of all rotation treatments in 10-20 cm soil layer increased significantly by 13.16%-26.32% and 28.98%-52.63%, respectively (P<0.05). (3) ROC₁₆₇ content in S-P, S-M and S-M-P treatments in 0-10 cm soil layer was significantly increased by 21.11%-35.46% and 42.33%-44.85%, respectively (P<0.05). (4) ROC_33.3 content in 0-10 cm soil layer under S-M-P treatment was significantly increased by 18.04% and 19.02%, respectively (P <0.05). (5) IOC of S-M-P treatment in 0-10 cm soil layer was significantly increased by 13.30% and 14.84%; M-M-P, S-M-P and S-M treatments in 20-40 cm soil layer significantly increased by 20.38%-52.51% and 59.56%-69.54%, respectively (P<0.05). (6) CPMI in 0-10 cm soil layer was significantly increased by 24.07%-28.13% and 41.46%-42.57% under S-M and M-M-P treatments, respectively. All rotation treatments in 10-20 cm soil layer were significantly increased by 17.34%-31.49% and 36.97%-61.11%, respectively (P<0.05).

In conclusion, maize-soybean, soy-maize-potato and maize-maize-potato rotation treatments were beneficial to improve soil carbon pool activity and increase soil carbon stability. Leguminous crop rotation could not only increase the activity of organic carbon pool but also maintain its stability, which was conducive to the stability of soil carbon pool balance in black soil.

Soil-related indicators were measured during the mature period of maize in 2020 and 2021. The purpose of this study was to investigate the effects of tillage methods with straw returning on soil labile organic carbon and carbon pool management index of black soil farmland at the southern foot of the Daxing’an mountains based on four consecutive years of tillage experiment.

Seven treatments were set up in the tillage positioning experiment, including deep tillage with straw returning (DTS), deep loosening and shallow with straw returning (DSS), subsoiling tillage with straw returning (STS), heavy harrowing straw returning (SHS), rotary tillage with straw returning (RTS), and no-tillage straw returning (NTS), with shallow tillage without straw returning (CK). 0-60 cm surface soil was collected. The contents of labile organic carbon (R₃₃₃), medium labile organic carbon (R₁₆₇) and high labile organic carbon(R₃₃) were determined by potassium permanganate solution with different concentrations (0.333, 0.167 and 0.033 mol·L^-1), and the effects of different tillage methods on soil labile organic carbon content and carbon pool management index were studied.

(1) Compared with CK, the R₃₃₃ content in 0-10 cm soil layer treated by DSS, DTS, NTS, RTS and STS significantly increased by 9.0% to 63.7% in two years, respectively. DSS was the highest, followed by DTS and NTS. R₃₃₃ in 10-60 cm soil layer, DTS, DSS and NTS significantly increased by 30.8%-134.5%, 14.1%-97.8% and 18.9%-63.0%, respectively (P<0.05). (2) Compared with CK, the medium labile organic carbon (R₁₆₇) of 0-10 cm soil layer under different tillage methods was significantly increased (P<0.05). The DSS treatment of R₁₆₇ content was the highest, with an increase of 37.3%- 101.0%, and the DTS treatment of 10-60 cm soil layer was the highest, with an increase of 44.8%-72.9%, showing DTS>DSS>NTS treatment. (3) Compared with CK, the R₃₃ content in 0-10 cm soil layer was significantly increased by 13.8%-55.6% under DSS treatment (P<0.05). In 10-20 cm soil layer, R₃₃ content of DTS, DSS, STS, RTS and NTS treatment was significantly increased by 3.6%-29.3% (P<0.05), with DTS being the highest, followed by DSS. In 20-60 cm soil layer, R₃₃ under DTS, DSS and STS treatment was significantly increased (P<0.05), and the proportion was 68.1%-20.0%. (4) The inert organic carbon (IOC) of 0-10 cm soil layer under straw returning was significantly increased by 4.7%-21.8% (P<0.05). In 20-60 cm soil layer, DTS and DSS significantly increased by 5.3%-156.6% and 4.2%-138.8% compared with other treatments (P<0.05). (5) Compared with CK, DTS treatment significantly increased carbon pool activity and carbon pool activity index in 0-20 cm soil layer (P<0.05), and increased by 7.7%-44.8% and 7.7%-45.0%, and significantly increased by DTS, DSS, STS and RTS soil layer carbon pool index (P<0.05). DTS, DSS and NTS treatment significantly increased the carbon pool management index of 0-60 cm soil layer by 21.9%-140.9%, 4.9%-103.7%, 13.3%-62.0% (P<0.05). (6) In 0-60 cm soil layer, R₃₃₃, R₁₆₇, R₃₃ and IOC were positively correlated with organic carbon content, carbon pool activity index, bulk density and geometric mean diameter, but negatively correlated with total soil porosity (P<0.01). Increasing the content of active organic carbon could improve soil physical structure and enhanced aggregate stability. The IOC was positively correlated with maize yield and dry matter mass (P<0.01).

Comprehensive analysis shows that both deep tillage with straw returning (DTS) and deep loosening and shallow with straw returning (DDS) can increase soil labile organic carbon and inert organic carbon to a certain extent, and effectively improve the organic carbon pool of farmland.