Straw return is a common cultivation to improve soil fertility and realize sustainable agricultural development. However, the effect of returning interval on the corn straw humification process in northeast China is little known. In this study, a four-year field trial was conducted to investigate the characteristics of soil carbon sequestration under the annual deep straw return (T1), the biennial deep straw return (T2), and the non-straw return (T3) in Jilin Province, China. In order to precisely evaluate the soil organic carbon density (SOCD), each soil horizon was divided differently according to the actual situation, rather than a fixed thickness. The results show that both the annual and the biennial deep straw return had a significantly positive influence on the content of soil organic carbon (SOC), humic acid, fulvic acid, and humin in the plough pan (straw-applied horizon), compared to the no-straw return. SOC of the cambic horizon and the C horizon in annual straw return was 28.78%, 47.44% higher than the biennial straw return, but it was 27.58% lower in the plough pan. The SOCD in the plough pan in the biennial straw return was higher than the annual straw return, but their difference in the entire soil profile was not significant. However, the conversion rate of straw carbon to SOC was 18.42% in the annual straw return and 21.05% in the biennial straw return. The straw return amount was not a key factor affecting the SOC sequestration in the cold area; it was restricted by the comprehensive effects of the cold weather, the intensity of soil disturbance, C/V and the initial SOC content. In conclusion, the biennial deep straw return was a better management tool, as it generally had an identical quality and quantity of soil organic carbon and a higher straw conversion rate relative to the annual deep straw return.

The interaction between secondary phyllosilicate minerals and straw is crucial for preserving soil organic carbon (SOC) and fertility. However, the specific mechanism through which these minerals affect straw decomposition and its products in northeast China’s black soil remains unclear. In this study, montmorillonite, illite, and vermiculite were mixed with quartz sand and maize straw, inoculated with microbes, and incubated to analyze the effects of different secondary phyllosilicate minerals on the degradation of organic components in maize straw and the formation of soil humus. The results showed that montmorillonite significantly facilitated the decomposition of maize straw hemicellulose and lignin, which decreased by 95.85% and 76.38%, respectively. Conversely, vermiculite decelerated hemicellulose and lignin degradation. Regarding soil organic acids, lactic acid and malic acid were predominant, with the highest content being found after the montmorillonite treatment. Montmorillonite was the most effective in enhancing extractable humic-like substances, which increased by 71.68%. Montmorillonite increased the content of G0 (water dispersion group), G1 (sodium ion dispersion group), and G2 (sodium grinding dispersion group) complexes. The addition of secondary phyllosilicate minerals increased the organic carbon (OC) content in the G0, G1, and G2 samples, with montmorillonite demonstrating the most pronounced effect. Secondary phyllosilicate minerals increased the abundance of fungi, particularly Ascomycota, with the highest abundance being found after the montmorillonite treatment. In conclusion, our results indicated that montmorillonite facilitated the decomposition of lignocellulose in maize straw, enhanced the accumulation of humus, and promoted the formation of organic–mineral complexes. These findings provide valuable insights into the interaction between secondary phyllosilicate minerals and maize straw and have important implications for improving the quality of black soil in northeast China.

Long-term organic inputs increase soil organic carbon (SOC) in black soil; however, it remains uncertain if straw and manure enhance SOC via separate microbial necromass carbon (MNC) routes. Therefore, a 12-year field experiment was conducted to explore this mechanism. Treatments included inorganic fertilizer, partial substitution of inorganic fertilizer with straw, and partial substitution of inorganic fertilizer with manure, along with a no-fertilizer control. According to the results, compared with inorganic fertilizer alone, treatments involving both organic manure and straw returned markedly raised the levels of SOC, MNC, bacterial necromass carbon (BNC), and fungal necromass carbon (FNC). Notably, compared to the CK treatment, N75S showed a greater contribution of MNC to SOC (MNC/SOC), but in both N75M and M, the MNC/SOC was lower than in CK. The CAZyme genes related to hemicellulose, lignin, chitin, and peptidoglycan differed among treatments. Elevated gene abundances for plant-derived lignin and hemicellulose decomposition were observed under M and N75M, whereas they reduced the genes responsible for peptidoglycan and glucan. However, under N75S, there was a notable rise in the number of genes responsible for hemicellulose and lignin, as well as an increase in genes that degrade chitin and peptidoglycans. In conclusion, this finding demonstrates that long-term straw return tends to promote SOC stabilization primarily through the microbial necromass pathway, while the application of manure over the long term tends to increase the total SOC primarily through the input of exogenous organic carbon.

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.