Soil aggregate stability is an important factor that impacts ecological restoration and soil erosion. Soil organic carbon (SOC) is also an important factor affecting soil characteristics and quality. The triple-cropping system has the potential to enhance soil aggregate stability by promoting a more diverse and continuous plant cover, which could lead to improved soil structure and resistance to erosion. Over two consecutive years, this study was conducted to explore the impacts of the triple-cropping system on soil aggregate stability, soil carbon pool, and carbon sequestration characteristics in the middle reaches of the Yangtze River. This study set up five planting modes, namely milkvetch–early rice–late rice (CRR, CK), milkvetch–early rice–sweet potato||soybean (CRI), rape–early rice–late rice (RRR), rape–early rice–sweet potato||soybean (RRI) and potato–early rice–late rice (PRR). The contribution of soil aggregates > 2 mm under CRI increased by 20.77%, 6.71%, and 2.19% to the control in winter cropping and early and late rice harvesting periods, respectively. During the winter harvest period, the geometric mean diameter (GMD) and mean weight diameter (MWD) of the CRI treatment were significantly higher than other treatments (p < 0.05), with increases of 7.53–16.28% and 4.67–10.28% respectively. After the late rice harvest, the GMD values of the CRI and PRR treatments were significantly higher than the control treatment by 13.56%, and the MWD values were higher than those of other treatments by 4.24–13.17%, 3.74–12.63% (p < 0.05). Furthermore, CRI also improved the GMD and MWD of soil aggregates, and the stability of soil aggregates was improved by winter milkvetch (treatment of CRI) and paddy-upland multi-crop models (treatment of PRR). RRR treatment was beneficial to the accumulation of soil organic carbon and slowed the loss of soil organic carbon. Irrigation and drought multiple cropping can effectively increase the content of soil active organic carbon, among which the treatment of CRI had the best performance and the most significant effect in increasing the content of soil active organic carbon. After the late rice harvest, the soil’s active organic carbon content in the CRI treatment was the highest, which was significantly different from the control treatment and increased by 35.62% compared with the control (p < 0.05). Compared with before planting, the soil microbial biomass carbon content in each treatment increased by 12.07–27.59% after the late rice harvest. The soil-dissolved organic carbon content in CRI treatment was the highest, which was significantly higher than CK treatment, RRR, and PRR, with an increase of 46.88%, 42.42%, and 30.56%, respectively (p < 0.05). In addition, the accumulation of soil microbial biomass carbon, soil dissolved organic carbon content, and soil easily oxidized organic carbon content was promoted by multi-cropping in rice fields, and the increase from CRI and RRI treatment was more significant. In conclusion, in the triple-cropping area of paddy fields in the middle reaches of the Yangtze River, the milkvetch–early rice–sweet potato||late soybean and rape–early rice–sweet potato||late soybean models are conducive to the optimal management of the soil carbon pool and carbon sequestration. These models can improve the multiple cropping index, reduce costs, and increase revenue.

To investigate the effects of intercropping green manure on the tea plantation ecosystem, this study was conducted using 40-year-old Camellia sinensis cv. “Fuding Dabai” tea plants at the Tea Experimental Base of the Jiangxi Institute of Cash Crops. Four treatments were established: clean tillage (CK), tea intercropped with ryegrass (Lolium perenne, TRG), tea intercropped with rapeseed (Brassica napus, TRP), and tea intercropped with alfalfa (Medicago sativa, TAL). The study systematically evaluated the effects of green manure on tea yield, soil nutrient content, enzyme activity, and microbial community structure. The results showed that intercropping with green manure significantly increased the bud density, hundred-bud weight, and yield of tea in spring, summer, and autumn, with the TAL treatment showing the best overall performance. In terms of soil physicochemical properties, green manure treatments significantly improved soil organic matter, total nitrogen, available nitrogen, available phosphorus, and available potassium contents, with TRP and TAL showing the most pronounced improvements. Enzyme activity analysis indicated that the TRP treatment significantly enhanced the activities of amylase, urease, and invertase. High-throughput sequencing results revealed that green manure treatments significantly increased both the number of bacterial and fungal OTUs (Operational Taxonomic Units) and alpha diversity indices. The TAL and TRP treatments showed superior performance in terms of Shannon, Chao, and ACE indices compared to CK. Principal coordinate analysis (PCoA) indicated that green manure had a greater influence on fungal community structure than on bacterial structure. Correlation analysis demonstrated that dominant microbial taxa were significantly associated with soil nitrogen, phosphorus, and potassium levels, suggesting that green manure modulates microbial community composition by improving soil nutrient status. Intercropping green manure significantly increased tea yield and soil quality compared with clean tillage. Alfalfa intercropping (TAL) increased tea yield by 49.61%, 40.88%, and 43.79% in spring, summer, and autumn, respectively, compared with the control. Soil organic matter and total nitrogen under TAL were 29.02% and 15.67% higher than the control, while rapeseed intercropping (TRP) increased available phosphorus by 186%. TAL and TRP also enhanced microbial diversity, with bacterial Shannon index values 14.11% and 11.25% higher than the control. These results indicate that alfalfa intercropping is the most effective green manure practice for improving tea plantation productivity and soil ecology.

Mixed sowing of green manure in winter is a unique farming mode in southern China, which has the potential to replace or partially replace nitrogen fertilizer. To investigate how mixed sowing of green manure combined with nitrogen reduction regulates soil organic carbon and its fractions, this study was conducted in the 3/4 Chinese milk vetch × 1/4 rapeseed farming mode, without nitrogen fertilizer (CK), 100% N fertilizer (150 kg ha⁻¹, N1MR), 20% N fertilizer reduction (120 kg ha⁻¹, N2MR), 40% N fertilizer reduction (90 kg ha⁻¹, N3MR), and 60% N fertilizer reduction (60 kg ha⁻¹, N4MR). The main results were the N2MR treatment could guarantee stable and increased rice yield. The N1MR and N2MR treatments were more conducive to the accumulation of TOC. The N4MR and N2MR treatments were more conducive to the increase and accumulation of AOC and DOC. The effective spikes were positively correlated with TOC and ROC. The grain number per panicle was positively correlated with DOC. The seed-setting rate was positively correlated with ROC. Overall, mixed sowing of Chinese milk vetch and rapeseed combined with 20% nitrogen reduction ensures a stable yield and increase in rice. Nitrogen reduction by 60% and 20% is beneficial to the increase and accumulation of TOC, AOC, and DOC in soil.

To explore the characteristics of soil microbial community structure diversity for different planting patterns in paddy fields, and to screen out the planting patterns suitable for the promotion of double-cropping rice areas in the middle reaches of the Yangtze River, five typical planting patterns were set up in this study. The five patterns are Chinese milk vetch–early rice–late rice (CRR, CK), Chinese milk vetch–early rice–sweet potato || late soybean (CRI), rapeseed–early rice–late rice (RRR), rapeseed–early rice–sweet potato || late soybean (RRI) and potato–early rice–late rice (PRR). The variation characteristics of soil microbial community structure diversity and the correlation between soil environmental factors and soil microbial community structure diversity under the triple-cropping system in the double-cropping rice area of the middle reaches of the Yangtze River were studied by 16S rRNA high-throughput sequencing and real-time fluorescence quantitative polymerase chain reaction (PCR). The results showed that after two years of experiment, the pH values of each treatment increased, and the rapeseed–early rice–late rice (RRR) model performed better. The soil organic matter and total nitrogen content of the milk vetch–early rice–sweet potato || late soybean (CRI) model was the highest, which increased by 7.89~35.02% and 6.59~26.80% compared with other treatments. The content of soil available phosphorus and available potassium in the potato–early rice–late rice (PRR) model was higher than that in other treatments, which was increased by 29.48% and 126.49% compared with the control. The Chinese milk vetch–early rice–sweet potato || late soybean (CRI) and rapeseed–early rice–sweet potato || late soybean (RRI) models were beneficial to increasing soil nitrate nitrogen and ammonium nitrogen content. Chinese milk vetch–early rice–sweet potato || late soybean (CRI) and rapeseed–early rice–late rice (RRR) patterns were beneficial for improving the microbial diversity index. Proteobacteria, Chloroflexi, and Actinobacteria are the top three dominant phyla in terms of the relative abundance of soil bacteria, and the top three dominant fungi are Ascomycota, Basidiomycota, and Mucor. The Chinese milk vetch–early rice–sweet potato || late soybean (CRI) and rapeseed–early rice–sweet potato || late soybean (RRI) patterns increased the relative abundance of soil Actinobacteria and Ascomycota. The contents of ammonium nitrogen, total organic carbon, nitrate nitrogen, and available phosphorus were the main environmental factors affecting soil microbial community structure. The findings can provide references for screening out the planting patterns suitable for the promotion of double-cropping rice areas in the middle reaches of the Yangtze River.

Continuous fertilization may modify soil nutrient pools and microbial communities in tea plantations, but their joint relationships with nitrogen-cycling genes and tea-leaf composition remain incompletely characterized. Soil properties, tea quality, and shotgun metagenomic profiles were examined after 16 years of four field management regimes: no fertilization (CK), chemical fertilization (CF), organic manure (OM), and combined organic–mineral fertilization (OMN). Relative to CK, OMN had higher soil organic matter (73.30%), total nitrogen (76.12%), total phosphorus (140.45%), alkali-hydrolyzable nitrogen (128.20%), available phosphorus (182.35%), available potassium (93.89%), and nitrate nitrogen (313.86%). OMN also increased tea-shoot free amino acids (29.60%) and catechins (21.96%) relative to CK, whereas caffeine (13.45%) and water-extract content (6.73%) were lower. Microbial richness indices (ACE, Chao1, and observed species) were higher under OMN than CK by 22.46%, 18.24%, and 22.90%, respectively. Community composition differed among treatments (ANOSIM: R = 1, p = 0.001). Of 32,733 annotated nitrogen-cycling genes, 21,874 were shared among treatments, while OMN had the largest treatment-specific gene set (1912). Soil nutrient properties covaried with nitrogen-cycling gene profiles. These endpoint observations indicate distinct soil, microbial, and tea-chemical characteristics under sustained fertilizer regimes; metagenomic gene profiles describe functional potential rather than measured nitrogen-transformation rates.