Effects of Different Crop Rotation Systems on the Contents of Active Carbon and Nitrogen Components in Farmland Soils and Crop Yields in the Southern Foothills of the Daxinganling Mountains

Objective The aims were to provide a scientific basis for selecting suitable rotation systems for the southern foothills of the Greater Xing'anling Mountains.

Methods A two-year field experiment was conducted from 2023 to 2024 at the National Agricultural Experimental Demonstration Base in Zhalite Banner, Xing'an League, Inner Mongolia, at the southern foot of the Daxinganling Mountains. Three cropping systems were compared: continuous maize (MM), maize-soybean rotation (MS), and maize-broomcorn rotation (MB). The contents of total and active components of soil organic carbon (C) and nitrogen (N) at 0 - 20 cm and 20 - 40 cm depths were determined alongside annual crop yields.

Results Compared to continuous maize cropping, in the first year of rotation, the MS rotation showed significantly increasing the contents of inorganic N and microbial biomass N in the 0 - 40 cm layer, the contents of particulate organic C and mineralizable organic C in the 20 - 40 cm layer, as well as the composite index of contents of active C components in the 20 - 40 cm layer (P < 0.05). In contrast, the MB rotation led to a significant decrease in total organic C contents in the 20 - 40 cm layer, the contents of dissolved organic N and microbial biomass N in the 0 - 40 cm layer, as well as the composite index of contents of active N components in the 0 - 40 cm layer (P < 0.05). Maize equivalent yields in both the MS and MB rotation systems decreased significantly (P < 0.05). In the second year of the rotation, the MS rotation significantly increased contents of soil particulate organic C and mineralizable organic C in the 0 - 20 cm layer, as well as the content of dissolved organic N and the composite index of contents of active C components in the 0 - 40 cm layer (P < 0.05). Both (MS and MB) rotation significantly increased the composite index of contents of soil active N components in the 20 - 40 cm layer (P < 0.05), but the soil organic C content in the 0 - 40 cm layer in MB rotation systems was significantly lower than that of the MS rotation systems. Maize yields in both the MS and MB rotation systems increased significantly by 17.18% and 16.55%. This yield increase was significantly and positively correlated with soil dissolved organic C, particulate organic C, inorganic N, and the composite index of contents of active N components (P < 0.05).

Conclusion The maize-soybean (MS) rotation is a superior strategy in this region for increasing soil organic C pools, simultaneously improving soil active nutrient pools and boosting subsequent maize yield. These findings provide strong theoretical and technical support for sustainable agricultural planning and soil fertility management in the region.