Abstract: Due to the different in soil physicochemical properties, the suitable types of organic materials may vary on red soil with different fertility levels. To precisely guide the classification and selection of appropriate organic materials for red soils of different fertility levels, soil samples were collected from peanut and rapeseed intercropping red soils under long-term rotation. Soil samples were taken at depths of 0-20 and ＞20-40 cm, representing high fertility soil and low fertility soil, respectively. Five treatments were established, including no organic carbon (C0), rapeseed straw carbon (OSC), rice straw carbon (RSC), maize straw carbon (MSC), and pig manure carbon (PMC). The carbon input for each organic material treatment was the same. The samples were subjected to continuous incubation in the dark for 90 days, and the different treatments were analyzed for aggregate composition and soil organic carbon (SOC) and total nitrogen (TN) content. The relationship between the C/N ratio of organic material input and the C/N ratio of aggregate components was analyzed. The results indicate that: (1) Compared with the C0 control, all organic material treatments significantly increased the proportion of ＞2 mm aggregates. In high fertility soils, the proportions of ＞2 mm aggregate components increased by 217.89%, 283.97%, 286.63%, and 210.63% with OSC, RSC, MSC, and PMC treatments, respectively. In low fertility soils, the increases for the above treatments were 72.25%, 84.45%, 72.11%, and 46.47%, respectively. (2) After organic material inputs, the organic carbon content of ＞2, ＞0.25-2, ≥0.053-0.25, and ＜0.053 mm aggregate components all significantly increased. However, there were significant differences in the increase of organic carbon content among aggregate components under different organic material treatments in soils with different fertility levels. For example, in ＞2 mm aggregate components, RSC and MSC treatments showed higher values in high fertility soils, while OSC treatment exhibited higher values in low fertility soils. (3) Adding different organic materials significantly increased the TN content of ＞0.25-2 and ＜0.053 mm aggregate components in both high and low fertility soils, with PMC treatment generally showing the highest trend among treatments. (4) Organic material inputs increased the C/N ratio of aggregate components in both high and low fertility soils, but there were obvious differences between them. For example, in ＞0.25-2 mm aggregate components, OSC, RSC, and MSC treatments showed higher values in high fertility soils, while RSC and MSC treatments exhibited higher values in low fertility soils. Moreover, the trend generally showed that the C/N ratio of soil aggregate components under PMC treatment was significantly lower than that under other organic material treatments. (5) In high fertility soils, increasing the C/N ratio of organic materials significantly increased the C/N ratio of ＞2 and ＞0.25-2 mm aggregate components. In low fertility soils, only the C/N ratio of ＞0.25-2 mm aggregate showed a significant positive correlation with the C/N ratio of organic material inputs. Analysis of the slope of the fitted equations reveals that when the C/N ratio of organic material inputs increased by 1 unit, the increase in the C/N ratio of ＞0.25-2 mm aggregate components was significantly smaller in high fertility soils than in low fertility soils. Compared with pig manure, straw-type organic materials showed better promotion effects on aggregate carbon and nitrogen accumulation. It is suggested to accurately adjust the C/N ratio of organic material inputs according to soil fertility levels to effectively improve the C/N ratio of soil aggregate components.

Key words: type of organic material, soil fertility level, aggregate components, C/N ratio