Jiangxi Institute of Red Soil

ABSTRACT The availability of soil phosphorus (AP) is profoundly affected by multi‐factors, such as soil properties, fertilization, and land‐use. Those multi‐factor coupling interactions are widely spread and particularly important in field ecosystems in the subtropical and tropical regions. However, there is still a large knowledge gap in those comprehensive effects, especially the long‐term effect. To explore the coupling interactions of fertilization, land use, and soil properties in AP, several treatments of long‐term experiments (> 30 years) in red soil were carried out, including two types of land use (upland and paddy soil), five fertilizations, and differential soil properties. The addition of manure increased the total phosphorus (∆TP), the change of available phosphorus (∆AP), and phosphorus activation coefficients (PAC) of both upland and paddy soils. The P application increased ∆TP and PAC of paddy soil while made no difference in PAC of upland soil. The random forest modeling showed that P balance, organic carbon, pH, iron‐aluminum oxides, and acid phosphatase activity (ACP) were the critical factors in regulating the variation of PAC. Moreover, pH and amorphous iron‐aluminum oxides were the most important for upland and paddy soil, respectively. The partial least squares path model indicated that P balance and organic carbon directly affected PAC and indirectly affected PAC by regulating the iron‐aluminum oxides and ACP. In addition, the pH indirectly increases PAC by influencing iron‐aluminum oxides and ACP. Therefore, the long‐term input of P is key for an increase of AP and TP in red soil areas, especially the combination of chemical P and manure. Furthermore, the rise of soil PAC in upland was higher than that in paddy soil under the same fertilizations. Overall, this study provides a framework for understanding the mechanism and driving factors of P dynamics in agricultural ecosystems with red soils.

ABSTRACT Soil pore structure plays a fundamental role in particulate organic matter (POM) dynamics by regulating water and air exchange within the soil matrix. However, the effects of long‐term fertilization on POM distribution, pore characteristics, and their interrelationships may differ between upland and paddy soils. In this study, we examined two long‐term fertilization field experiments conducted in contrasting agroecosystems in Jiangxi, China: a 38‐year upland field and a 43‐year paddy field. Four fertilization regimes were compared: no fertilizer (control), inorganic fertilizer (NPK), double‐rate inorganic fertilizer (2NPK), and inorganic fertilizer combined with pig manure (NPKM). X‐ray computed tomography (CT) was used to quantify soil pore structure and POM, and a random forest model was trained on a manually classified dataset of 1322 POM fragments to operationalize the decomposition degree, distinguishing fresh (e.g., exhibiting low blobness, plateness) from decomposed (e.g., exhibiting high sphericity, compactness) morphologies based on four morphological features. The NPKM treatment significantly increased fresh and decomposed POM volume density by 2.05% (7.51 mm 3 cm −3 ) and 47.7% (2.01 mm 3 cm −3 ) in upland soil, and 253% (15.2 mm 3 cm −3 ) and 103% (1.47 mm 3 cm −3 ) in paddy soil, respectively. NPKM also enhanced air permeability ( K a ), image‐based porosity, connected porosity, > 300 μm porosity, and surface area density in both soils. POM in upland soil is rapidly aerobically decomposed and physically fragmented within dynamic pore networks, while in paddy soil, it is preserved by anaerobic conditions that suppress microbial activity. Overall, our findings demonstrate that combined organic–inorganic fertilization promotes both POM accumulation and the development of pore structure in upland and paddy soils, with distinct mechanisms operating under different land‐use systems.

Manure fertilization can enhance the activity of soil enzymes involved in cellulose degradation, thereby generating positive legacy effects on soil organic carbon sequestration when crop residue incorporation is implemented. However, it remains unclear how manure fertilization regulates the cellobiohydrolase (CBH)-producing microbial community and the linkages between this regulation and the enhanced soil CBH activity. This study investigated the relationship between soil cellulose degradation potential, CBH activity, chemical properties, and the cbhI -harboring fungal community in an upland Ultisol subjected to four long-term fertilization treatments (no fertilization, mineral fertilization, swine manure fertilization, and mineral plus swine manure fertilization). The soil cellulose degradation potential and CBH activity in the manure treatment increased by 108 % and 233 % compared to the no-fertilization control, respectively. Those in the mineral plus manure treatment increased by 107 % and 108 % compared to the mineral treatment, respectively. Manure fertilization significantly increased the abundance of cbhI -harboring fungal community and altered its composition, while exerting no significant influence on its diversity. Sordariomycetes and Leotiomycetes were dominant and indictor taxa within the functional fungal community under manure fertilization. The co-occurrence networks within the cbhI -harboring fungal community showed greater complexity and stability across the manure-amended soils compared to the non-manure-amended soils. Soil CBH activity was closely associated with the abundance and composition of cbhI -harboring fungal community, both of which were strongly influenced by soil pH and nutrient content and stoichiometric ratios. The structural equation modeling revealed that the shifts in the functional fungal community outcompeted soil pH in influencing soil CBH activity. The findings of this study collectively suggest that the enhanced soil CBH activity following long-term application of swine manure is primarily attributed to the proliferation of r-strategist cbhI -harboring fungi, which is driven by the improvement in soil nutrient status. • Swine manure boosted soil cellulose degradation potential via enhanced CBH activity. • Swine manure increased cbhI fungal abundance and altered their community composition. • Swine manure enhanced co-occurrence network complexity of cbhI fungal community. • Soil nutrient content and stoichiometry drove cbhI fungal abundance and composition. • Shifts in cbhI fungal community closely linked to enhanced CBH activity.

Analyzing the effects of long-term fertilization treatments on dryland red soil fertility and identifying optimal fertilization regimes for soil amelioration are of great significance for enhancing soil fertility and crop yield. Based on a 37-year fertilization experiment (1986-2023) in Jiangxi Province, we examined the impacts of six treatments, no fertilization (CK), nitrogen-only (N), chemical fertilizer (NPK), double-dose chemical fertilizer (2NPK), organic manure (OM), and combined chemical-organic fertilization (NPKM) on soil physical, chemical, and biological properties, maize yield, and comprehensively assessed soil fertility using the integrated fertility index (IFI). The results showed that long-term organic fertilization (OM and NPKM) significantly increased soil pH, macroaggregate content, soil organic matter, total nitrogen, total phosphorus, available nutrients, and activities of catalase, sucrase, glucosidase cellulase, urease, and acid phosphatase. Long-term chemical fertilization (NPK and 2NPK) showed weak improvements in these parameters, while long-term application of nitrogen-only (N) reduced soil pH, organic matter, total nitrogen, total phosphorus, available nutrients content, and the activities of catalase, sucrase, and glucosidase. NPK, 2NPK, OM and NPKM treatments significantly increased maize yield relative to CK by 847.6%, 712.7%, 716.3%, and 1162.7% respectively. Maize yield exhibited significant positive correlations with soil macroaggregates, pH, total nitrogen, total phosphorus, alkali-hydrolyzable nitrogen, available phosphorus contents, and activities of all the tested enzymes. The IFI values derived from both minimum and full datasets consistently ranked: NPKM>OM>2NPK>NPK>CK>N, with a significant positive correlation between datasets. Thus, long-term combined chemical-organic fertilization optimally could enhance dryland red soil fertility and maize yield. Alkali-hydrolyzable nitrogen, total phosphorus, pH, and catalase were key indicators for evaluating soil fertility.