Soil acidification is a significant form of agricultural soil degradation, which is accelerated by irrational fertilizer application. Sweetpotato and wheat rotation has emerged as an important rotation system and an effective strategy to optimize nutrient cycling and enhance soil fertility in hilly areas, which is also a good option to improve soil acidification and raise soil quality. Studying the effects of different fertilization regimes on soil acidification provides crucial data for managing it effectively. An eight-year field experiment explored seven fertilizer treatments: without fertilization (CK), phosphorus (P) and potassium (K) fertilization (PK), nitrogen (N) and K fertilization (NK), NP fertilization (NP), NP with K chloride fertilization (NPK1), NP with K sulfate fertilization (NPK2), and NPK combined with organic fertilization (NPKM). This study focused on the soil acidity, buffering capacity, and related indicators. After eight years of continuous fertilization in the sweetpotato–wheat rotation, all the treatments accelerated the soil acidification. Notably, N fertilization reduced the soil pH by 1.30–1.84, whereas N-deficient soil showed minimal change. Organic fertilizer addition resulted in the slowest pH reduction among the N treatments. Both N-deficient (PK) and organic fertilizer addition (NPKM) significantly increased the soil cation exchange capacity (CEC) by 8.83% and 6.55%, respectively, compared to CK. Similar trends were observed for the soil-buffering capacity (pHBC). NPK2 increased the soil K⁺ content more effectively than NPK1. NPKM reduced the sodium and magnesium content compared to CK, with the highest magnesium content among the treatments at 1.60 cmol·kg⁻¹. Regression tree analysis identified the N input and soil magnesium and calcium content as the primary factors influencing the pHBC changes. Structural equation modeling showed that the soil pH is mainly influenced by the soil ammonium N content and pHBC, with coefficients of −0.28 and 0.29, respectively. Changes in the soil pH in the sweetpotato–wheat rotation were primarily associated with the pHBC and N input, where the CEC content emerged as the main factor, modulated by magnesium and calcium. Long-term organic fertilization enhances the soil pHBC and CEC, slowing the magnesium reduction and mitigating soil acidification in agricultural settings.

The long-term excessive use of chemical fertilizers may result in soil degradation, but manure and straw application is considered to be an effective approach for alleviating this problem. The aim of this study is to examine the long-term impacts of different fertilization patterns on soil quality variables in a wheat–sweet potato rotation system. Four treatments were conducted in a field trial for a duration of twelve years, including (1) no fertilizer (control, CK); (2) application of mineral fertilizers (NPK) alone; (3) NPK with crop straw return (NPKs); (4) combined use of NPK and farmyard manure (NPKm). Thirteen physical, chemical, and biological soil parameters were measured. The results showed that the NPKm and NPKs significantly improved the proportion of macroaggregates (>0.25 mm) by 24.7% and 21.9% compared to the NPK alone, respectively. The proportion of microaggregates (0.053–0.25 mm) under the NPKm was 47.4% significantly higher than the NPKs. Additionally, the NPKm resulted in a 22.2% and 19.6% increase in the SOC content than the NPK and NPKs, respectively. In terms of soil-available K, the NPKs resulted in levels that were 42.1% and 49.6% higher than the NPKm and NPK alone, respectively. Long-term fertilization significantly decreased soil pH by 0.95–1.85 units compared to the control, whereas manure application could alleviate soil acidification, as shown when the pH increased by 10.6–18.7%. The NPKm and NPKs resulted in significantly increased soil pHs by 10.6% and 18.7% compared to the NPK alone, respectively. In addition, the NPKm and NPKs increased N-acetyl-β-D-glucosaminidase activity by 52.6% and 60.3% compared to the NPK alone. Determined by the minimum data set method, the NPKm treatment exhibited the highest soil quality index, followed by the NPKs and NPK. Our findings suggested that the combined use of chemical fertilizers with organic amendments proved beneficial for enhancing soil quality.

Organic amendments can mitigate soil acidification and degradation, yet their long-term effects on soil microbiome, functions, and crop productivity remain underexplored in latosolic red soils. This study aimed to elucidate how different fertilization regimes reshape soil microbial communities and predicted functions, and how these changes link to sweet potato productivity after 15 years. Soil and plant samples were collected from a 15-year field experiment on latosolic red soil under five treatments: no fertilizer (CK), chemical fertilizer alone (NPK), and chemical fertilizer combined with commercial manure (NPK + CM), pig manure (NPK + PM), or rice straw (NPK + RS). Soil properties, bacterial and fungal communities, and predicted functions (FAPROTAX, FUNGuild) were analyzed. The results showed that long-term NPK alone significantly acidified soil (pH decreased by 1.49 units), whereas NPK + PM increased pH by 1.38 units relative to NPK, and also increased soil organic carbon, available nutrients, and sweet potato yield (by 31% compared with NPK). Soil pH was strongly associated with reshaping the microbial community. NPK + PM enriched beneficial phyla (e.g., Myxococcota, Nitrospirota, Latescibacterota, Entotheonellaeota, and Mortierellomycota) and enhanced predicted chemoheterotrophic, predatory or exoparasitic, and saprotrophic functions. Variance partitioning showed that nutrients, key microbial taxa, and predicted functions jointly explained productivity variation (adjusted R² = 0.9386). Thus, chemical fertilizer combined with pig manure is an effective strategy to mitigate soil acidification and improve sweet potato productivity by regulating soil nutrient-microbiome interactions. Our findings support reshaping the microbiome via organic amendments for sustainable agriculture in acidic soils.