Nitrogen (N) fertilizer application is one of the causes of soil acidification at tea plantations. However, the effect of N fertilizer application on the soil acidification characteristics of tea plantations with different acidities remains unclear. In this study, field experiments were conducted to investigate the effects of different nitrogen fertilizer application rates on the pH, pH buffer capacity (pHBC), exchangeable total acidity (ETA), exchangeable base cations (EBCs), and cation exchange capacity (CEC) in the topsoil of non-acidified (NA), mildly acidified (MA), and heavily acidified (HA) tea plantations. The results showed that the exchangeable Al³⁺ (E-Al) and CEC were HA > MA > NA in all tea plantations, whereas the EBCs and base saturation percentage (BSP) were HA < MA < NA. In the tea plantations with pH > 4.0, the pH, EBCs, and BSP showed decreasing trends with increasing N fertilizer application, whereas E-Al showed an increasing trend. In the tea plantations with pH < 4.0, the soil pH showed a small increasing trend with the increase in N fertilizer application, whereas the soil exchangeable H⁺ (E-H), E-Al, and CEC showed decreasing trends. Meanwhile, in the pH range of 4–6, the soil acid–base buffer curve rose sharply, and an excessive application of N fertilizer (N900) significantly reduced the pHBC. In addition, a stepwise regression analysis showed that the BSP, EBCs, and exchangeable Mg²⁺ (E-Mg) had significant direct effects on the soil pH, whereas the CEC and N application had significant direct effects on the soil pHBC. In conclusion, a decrease in the BSP and an increase in E-Al were the main mechanisms of acidification at tea plantations, whereas a decrease in the BSP caused by the application of N fertilizer was the main cause of exacerbated soil acidification in non-acidified tea plantations.

Current research has long focused on soil organic carbon and soil aggregates stability. However, the effects of different long-term fertilization on the composition of yellow soil aggregates and the characteristics of the occurrence of organic carbon in the karst region of Southwest China are still unclear. Based on a 25-year long-term located experiment on yellow soil, soil samples from the 0–20 cm soil layer were collected and treated with different fertilizers (CK: unfertilized control; NPK: chemical fertilizer; 1/4 M + 3/4 NP: 25% chemical fertilizer replaced by 25% organic fertilizer; 1/2 M + 1/2 NP: 50% chemical fertilizer replaced by organic fertilizer; and M: organic fertilizer). In water-stable aggregates, soil aggregates stability, total organic carbon (TOC), easily oxidized organic carbon (EOC), carbon preservation capacity (CPC), and carbon pool management index (CPMI) were analyzed. The findings demonstrated that the order of the average weight diameter (MWD), geometric mean diameter (GWD), and macro-aggregate content (R_0.25) of stable water aggregates was M > CK > 1/2M +1/2NP > 1/4M +3/4NP> NPK. The MWD, GWD, and R_0.25 of NPK treatment significantly decreased by 32.6%, 43.2%, and 7.0 percentage points, respectively, compared to CK treatment. The order of TOC and EOC content in aggregates of different particle sizes was M > 1/2M +1/2NP > 1/4M +3/4NP> CK > NPK, and it increased as the rate of organic fertilizer increased. In macro-aggregates and bulk soil, the CPC of TOC (TOPC) and EOC (EOPC), as well as CPMI, were arranged as M > 1/2M +1/2NP > 1/4M +3/4NP> CK > NPK, but the opposite was true for micro-aggregates. In bulk soil treated with organic fertilizer, the TOPC, EOPC, and CPMI significantly increased by 27.4%–53.8%, 29.7%–78.1%, 29.7–82.2 percentage points, respectively, compared to NPK treatment. Redundancy analysis and stepwise regression analysis show that TOC was the main physical and chemical factor affecting the aggregates stability, and the TOPC in micro-aggregates has the most direct impact. In conclusion, the primary cause of the decrease in SOC caused by the long-term application of chemical fertilizer was the loss of organic carbon in macro-aggregates. An essential method to increase soil nutrient supply and improve yellow soil productivity was to apply an organic fertilizer to increase aggregates stability, storage and activity of SOC in macro-aggregates.

Reducing greenhouse gas emissions from rice fields is essential to respond to the national “dual-carbon” strategy, achieve green agricultural development, and ensure food security. The substitution of organic fertilizers for chemical fertilizers is an important means to achieve zero growth and has a positive impact on crop yield and soil nutrients; however, the impact on the greenhouse effect is inconsistent. The effects of organic fertilizers on soil greenhouse gas emissions vary depending on factors such as soil, geography, ecological environment, and human management. However, previous research has shown that the combined application of organic fertilizer can increase soil carbon storage and increase crop yield, and may be an effective fertilization measure to reduce greenhouse gas emissions from yellow paddy fields. To clarify the effects of different ratios of organic fertilizer on the greenhouse gas emission characteristics of Guizhou yellow paddy soil, CH₄, CO₂, and N₂O emissions from rice fields were monitored by static opaque chamber-gas chromatography, and the effects of different fertilization treatments on the cumulative greenhouse gas emissions and global warming potential (GWP) were investigated. Results showed that organic fertilizer application increased CH₄ emissions from rice fields, and the effect increased with increasing organic fertilizer application. The peak period was from the heading stage to the filling and ripening stage, and there was almost no emission during the fallow period. Compared with the balanced application of chemical fertilizer (NPK), the treatment with organic fertilizer alone (M) significantly increased CO₂ emissions, but the replacement of 1/2 chemical fertilizer nitrogen with 1/2 organic fertilizer (1/2 M + 1/2 N-PK) and the replacement of 1/4 chemical fertilizer nitrogen with 1/4 organic fertilizer (1/4 M + 3/4 N-PK) did not significantly increase CO₂ emissions; emissions were 5% lower in the 1/2 M + 1/2 N-PK treatment than in the NPK treatment. Compared with the NPK treatment, the application of organic fertilizer alone significantly reduced N₂O emissions by 32.16%, while the 1/2 M + 1/2 N-PK and 1/4 M + 3/4 N-PK treatments increased N₂O emissions by 6.31% and 16.02%, respectively. However, there were no significant differences between the organic–inorganic combined treatments and NPK. During the flooding period, N₂O emissions were relatively low, but the emissions increased rapidly after field drying. The application of organic fertilizer increased the GWP of rice fields. Compared with the NPK treatment, the M treatment increased GWP by 47.07%, 1/2 M + 1/2 N-PK increased GWP by 10.16%, and the 1/4 M + 3/4 N-PK treatment increased GWP by 2.93%. Except for the M treatment, the differences between treatments were not significant. Our results concluded that replacement of chemical fertilizers with organic fertilizers at a ratio of 1/4 to 1/2 did not significantly increase greenhouse gas emissions in rice fields, besides, it mitigate the greenhouse effect and increase soil carbon sequestration and yield in rice fields.

To compare the differences in the soil microbial community structure in yellow soil paddy fields after the long-term application of chemical fertilizer, the role and mechanism of chemical fertilizer in maintaining soil microbial diversity were analyzed, and a theoretical basis for fertilization management in farmlands was provided. In this study, long-term experiments were conducted at the Scientific Observation and Experimental Station of the Arable Land Conservation and Agricultural Environment (Guizhou), Ministry of Agriculture and Rural Affairs. Soil samples were collected from five treatments: fertilizer N, P, and K (NPK); fertilizer P and K (PK); fertilizer N and K (NK); fertilizer N and P (NP); and no fertilizer (CK). High-throughput sequencing technology was used to analyze the microbial composition and diversity of the colonies, and the influencing factors are discussed. An analysis of the soil bacterial α diversity indices under the different fertilization treatments revealed that the long-term application of NPK fertilizers had less of an effect on the soil bacterial α diversity indices than did the CK. The long-term application of chemical fertilizers significantly reduced the soil bacterial Chao1, Shannon, and Simpson indices, while there was no significant difference in the bacterial Pielou e index among the treatments. The long-term application of chemical fertilizers significantly increased the soil fungal Chao1 index, but the effects on the other indices were not significant (p < 0.05). An analysis of the bacterial and fungal species under different fertilization treatments showed found that compared with CK, the long-term application of chemical fertilizer increased the relative abundance of Proteobacteria to varying degrees while reducing the relative abundance of Chloroflexi. The impact of other phyla was relatively small, and the difference in the relative abundance of fungi was not significant (p < 0.05). Principal component analysis revealed that, at the genus level, the bacterial and fungal community structures in the CK and NK treatments were relatively independent, while those in the NPK, PK, and NP treatments were similar. Random forest analysis revealed that OM, TP, and TK are the dominant factors that affect soil bacteria α diversity. The dominant factors affecting fungi α diversity are pH, OM, and AK. Redundancy analysis indicated that AK and TP were the main factors affecting bacterial community structure, while AP, AK, and pH were the main factors affecting fungal community structure. The conclusion drawn from this study is that the long-term application of nitrogen, phosphorus, and potassium fertilizer; phosphorus and potassium fertilizer; and nitrogen and phosphorus fertilizer can improve soil fertility, alter the soil environment, enhance microbial diversity, and improve the microbial community structure in yellow soil paddy fields, promoting soil ecosystem stability and health.

Phosphorus (P) in soil is important in the process by which soil microbial communities regulate soil enzyme activity. We aim to explore how short-term P fertilization affects the composition and functionality of the soil fungal community, offering insights into the complex responses of soil fungi to fertilization. Soil samples from a long-term experiment with no P fertilization were collected for pot experiments. The pot experiment included four treatments: non-P fertilizer (NK), chemical P fertilizer (NPK), 1/2 organic fertilizer + 1/2 chemical fertilizer (MNP), and organic fertilizer (M). High-throughput sequencing was employed to analyze the composition, diversity, and functionality of soil fungal communities. Results showed that short-term P addition significantly increased the soil fungal Shannon and Pielou e indices, with increases of 34.48%~59.00% and 29.79%~53.19%, respectively. Ascomycota and Basidiomycota were the most abundant fungal phyla, whereas Cladosporium and Emericellopsis were the most abundant genera. The main factors affecting soil fungal community composition were total nitrogen (TN) and organic matter (OM). A linear discriminant analysis effect size (LEfSe) analysis indicated that Mortierellomycota were significantly enriched under the NPK treatment. A FUNGuild analysis revealed that, compared to the NK treatment, the relative abundance of Animal Pathogen–Endophyte–Lichen Parasite–Plant Pathogen–Wood Saprotroph was reduced by 67.54%, 46.93%, and 44.10% under NPK, MNP, and M treatments, respectively. The relative abundance of Plant Pathogen was less than 1% in the NPK and the MNP treatments. These results indicate that short-term P addition increased soil nutrient levels and soil fungal community diversity. Chemical P fertilizer significantly improved the fungal community structure in yellow paddy soils, enhancing beneficial fungi and suppressing pathogens.

This study aimed to compare bacterial community structure differences in yellow paddy soil under long-term chemical/organic fertilisation and fertiliser conversion to guide farmland fertilisation strategies in yellow loam areas. Treatments included (1) continuous application of chemical fertilisers for 27 years (CF-CF); (2) application of chemical fertiliser continuously for 24 years and then application of organic fertiliser for 3 years (CF-OF); (3) continuous application of organic fertiliser for 27 years (OF-OF); and (4) application of organic fertiliser continuously for 24 years and then application of chemical fertiliser for 3 years (OF-CF). The results show that long-term fertilisation alters genus-level bacterial taxa, while fertilisation mode changes significantly increase taxa quantities at both phylum and genus levels. Different fertilisation treatments affect the relative abundance of bacteria; the relative abundance of Firmicutes in OF-OF is significantly greater than that in CF-CF, while Gemmatimonadota and Patescibacteria show the opposite trend. Compared to CF-CF, CF-OF increases the relative abundance of Firmicutes and decreases that of Cyanobacteria, whereas OF-CF increases the relative abundance of Firmicutes compared to OF-OF. Notably, Patescibacteria is significantly enriched in CF-CF, while Cyanobacteria and Bacteroidota are significantly enriched in CF-OF, and Firmicutes and Myxomycophyta are significantly enriched in the OF-OF treatment. The bacterial community composition of CF-CF and CF-OF is similar, while the bacterial community composition of OF-OF and OF-CF is similar. In bacterial assembly processes, OF-CF improves the heterogeneous selection process and reduces the homogeneous dispersal process compared to OF-OF. The bacterial assembly process of OF-CF gradually becomes similar to that of CF-CF and CF-OF. Further analyses indicate that fertilisation influences the soil bacterial community composition by affecting total nitrogen, organic matter, available phosphorus, and pH. Overall, long-term different fertilisation predominates bacterial community distribution, while short-term changes in fertilisation mode have a smaller but significant effect on bacterial community distribution, influencing the quantity and relative abundance of bacterial taxa; the application of organic fertilisers is more beneficial for the even distribution of bacteria.