Soil aggregate stability (AS) is a critical indicator of soil physical quality, yet its long-term drivers in vulnerable silty soils remain inadequately quantified. This study analyzed the determinants of AS over 25 years (1999–2023) in a long-term field experiment on a temperate silty Luvisol, comparing four cropping systems: conventional (CON), low-input (LI), organic (ORG), and conservation agriculture (CA). Aggregate stability was assessed biennially using Le Bissonnais tests targeting distinct disaggregation mechanisms, alongside soil organic carbon (SOC), quantitative management indicators (intensity of crop sequence, grass-to-legume ratio, crop diversity and carbon biomass, and nitrogen inputs), and climatic variables. Mean AS remained low in frequently tilled systems (CON, ORG), reflecting the legacy of mechanical disturbance. In contrast, CA achieved a stable, high-AS state after approximately six years, which persisted. Intermittent tillage in LI prevented long-term recovery, underscoring a non-linear response to disturbance frequency. While SOC accumulation was associated with improved aggregate stability, it was insufficient to explain AS dynamics on its own. Long-term aggregate stability was primarily associated with cumulative indicators of crop diversity and below-ground biomass, whereas short-term variations responded more strongly to recent management factors such as crop sequence composition, nitrogen inputs, and rooting continuity. Precipitation exhibited dual effects, with recent rainfall promoting aggregate disruption, particularly in the Slaking test, whereas antecedent moisture conditions were generally associated with increased aggregate stability. Among the tests evaluated, Micro-cracking proved particularly sensitive to management and environmental drivers. The study demonstrates that sustained reduction of mechanical disturbance is the primary prerequisite for restoring aggregate stability in silty agroecosystems. Complementary management practices become effective determinants of soil structure only once mechanical constraints are alleviated. These findings provide a hierarchical framework for prioritizing soil management strategies to enhance the physical health and resilience of cultivated silty soils.
The use of conventional plastic mulch films is a common agricultural practice that can lead to persistent plastic film fragments entering soil systems. To prevent the accumulation of these fragments, soil-biodegradable mulch films are marketed as alternatives. Unlike conventional plastic mulch, soil-biodegradable mulch films are ploughed into the soil after use, where they biodegrade over time. This study aims to elucidate the effects of soil-biodegradable mulch film fragments—following six months of application on the soil surface—ploughed into soil on surface runoff, soil erosion, and lateral mulch film fragment loss during simulated rainfall events. Our results showed a significant increase in runoff coefficient for the pre-wetted (wet run) simulations in soils with soil-biodegradable mulch film fragments compared to soils without them, while differences in sediment delivery were insignificant. In the delivered sediments, large mulch film fragments (> 2 mm) were depleted, whereas small fragments (< 2 mm) were transported approximately proportionally to the topsoil of the plots. Overall, our results indicate that film fragments can affect surface runoff on arable land, and generally, soil erosion is a pathway of soil-biodegradable mulch film fragments transport into adjacent ecosystems, which is especially effective in the case of small film fragments (< 2 mm) available from topsoil.
Cadmium (Cd) contamination in agricultural soils threatens global food safety. Organic fertilizers (OFs) are renewable soil amendments with considerable potential for regulating Cd bioavailability. However, how abiotic reactions interact with microbially mediated processes under different OF properties and soil conditions remains insufficiently understood. This review focuses on OF sources and composition, their effects on soil physicochemical and biological properties, and the pathways that modulate Cd bioavailability. Key advances include: (1) OFs abiotically immobilize Cd via adsorption, ion exchange, complexation, and precipitation. Indirectly, they alter Cd partitioning by elevating soil pH and cation exchange capacity (CEC), modulating redox potential (Eh), and improving aggregate stability. (2) OF composition influences microbial activity by controlling carbon and nutrient availability, thereby affecting extracellular polymeric substance production, sulfate reduction, phosphate mobilization, carbonate precipitation, and Fe cycling. These microbial processes further modify Cd partitioning through changes in Cd binding, mineral formation, and mineral dissolution. (3) Cd regulation by OFs is dynamic and bidirectional. Continuous feedbacks among soil pH, Eh, dissolved organic matter, and microbial activity can either sustain Cd retention or increase the risk of Cd remobilization during progressive OF decomposition. Overall, this review proposes an integrated framework linking source-dependent OF chemical “fingerprints” to abiotic–microbial interactions governing Cd retention and remobilization in soils. This framework provides a mechanistic basis for selecting and applying OFs to reduce Cd bioavailability while accounting for potential remobilization risks in contaminated agricultural soils.
Red soils in subtropical regions are highly susceptible to structural degradation, resulting in poor water retention and restricted water transport. Although tillage strongly influences soil hydraulic properties, the pore-scale mechanisms governing these responses after long-term management remain poorly understood. Here, we investigated how 11 years of no-tillage (NT), rotary tillage (RT), and deep ploughing (DP) reshaped pore architecture and regulated soil hydraulic behavior across a 0–40 cm red soil profile by integrating soil physical measurements, van Genuchten modeling, X-ray computed tomography (CT), and multivariate analyses. Relative to conventional rotary tillage (RT), DP reduced bulk density by 16.8% and increased saturated hydraulic conductivity (Ks) by 138.9–1248.2% and air permeability (Ka) by 25.9–167.0% within the 0–30 cm cultivated layer through enhanced macroporosity and pore connectivity. In contrast, NT maintained higher Ks and Ka in the 20–40 cm subsoil, reflecting the preservation of continuous biopore networks under long-term minimal disturbance. RT preferentially promoted mesopore (200–500 μm) development, resulting in the highest saturated water content, field moisture capacity, and plant-available water. Random forest analysis identified global pore connectivity (Γ), pore anisotropy (An) and pore size distribution, rather than total porosity, as the dominant predictors of hydraulic behavior. Correlation, principal component, and redundancy analyses consistently showed that macropores (>500 μm) primarily controlled water transmission, whereas meso- and micropores (60–200 and 200–500 μm) governed water retention. Structural equation modeling demonstrated that tillage regulated hydraulic function indirectly through pore architecture, with pore conductivity promoting hydraulic conductivity (standardized path coefficient: 0.38) and pore storage enhancing hydraulic storage (0.45), while revealing a strong antagonistic trade-off (-0.93) between conductivity and water storage. These findings establish pore architecture as the mechanistic link between long-term tillage and soil hydraulic function, providing a scientific basis for optimizing tillage strategies to improve water use efficiency and drought resilience in red soil agroecosystems.
Vegetation restoration commonly increases soil organic carbon (SOC) and macroaggregate abundance. However, it remains unclear whether macroaggregate-centered SOC recovery is coupled with greater incorporation of restoration-derived C into finer aggregate fractions or remains largely confined to macroaggregates. Here, we compared active cropland with two woody vegetation types restored for 24 years, forestland and shrubland, in the hilly-gully region of the Loess Plateau. We quantified plant inputs, soil properties, aggregate structure, SOC pools, δ13C signatures, new/old C allocation, and Δδ13C-based isotopic distances at 0–10 and 10–20 cm. Vegetation restoration enriched macroaggregates and increased bulk-soil SOC storage by 75.5–79.3% in the 0–10 cm layer and by 24.3–24.6% in the 10–20 cm layer. Macroaggregates dominated restored SOC storage, contributing 67.3–71.8% in topsoil and 64.0–64.7% in subsoil, compared with 58.4% and 58.8% in cropland, respectively. Newly derived C accounted for 52.9–74.8% of restored topsoil SOC and was preferentially retained in macroaggregates, whereas finer fractions showed proportionally greater old-C enrichment. In the 0–10 cm layer, macroaggregate-silt + clay isotopic distance was significantly greater in both restored vegetation types than in cropland, whereas macroaggregate-microaggregate and microaggregate-silt + clay distances did not differ significantly among vegetation types. The 10–20 cm pattern was less consistent, with a significant macroaggregate-silt + clay difference detected only between cropland and shrubland. Thus, after 24 years of restoration, newly accumulated C remained concentrated mainly in macroaggregates, without a corresponding strengthening of its association with finer fractions. These findings distinguish where restoration-derived C is stored from how strongly it is associated with finer, potentially more persistent fractions.
