Enhancing the structural stability of Pisha sandstone soil is an important measure to manage local soil erosion. However, Pisha sandstone soil is a challenging research hotspot because of its poor permeability, strong soil filtration effect, and inability to be effectively permeated by treatment solutions. In this study, by adjusting the soil water content to improve the spatial structure of the soil body and by conducting unconfined compressive strength and calcium ion conversion rate tests, we investigated the effect of spatial distribution differences in microbial-induced calcium carbonate deposition on the mechanical properties of Pisha sandstone-improved soil in terms of the amounts of clay dissolved and calcium carbonate produced. The results demonstrate that improving the soil particle structure promotes the uniform distribution of calcium carbonate crystals in the sand. After microbial-induced carbonate precipitation (MICP) treatment, the bacteria adsorbed onto the surface of the Pisha sandstone particles and formed dense calcium carbonate crystals at the contact points of the particles, which effectively enhanced the structural stability of the sand particles, thereby improving the mechanical properties of the microbial-cured soils. The failure mode of the specimen evolved from bottom shear failure to overall tensile failure. In addition, the release of structural water molecules in the clay minerals promoted the surface diffusion of calcium ions and accelerated the nucleation and crystal growth of the mineralization products. In general, the rational use of soil structural properties and the synergistic mineralization of MICP and clay minerals provide a new method for erosion control in Pisha sandstone areas.

Background and aims The changes in soil physical properties caused by root exudates depend largely on the chemical composition of root exudates. Our aim was to explore the effects of non-specific root exudates on the physical properties of soil change. Methods Five sugar compounds, five amino acid compounds, and five organic acid compounds were selected and added to loess as three single addition treatments (amino acids, organic acids, and sugars) and four combined addition treatments (amino acids + organic acids, amino acids + sugars, organic acids + sugars, and amino acids + organic acids + sugars). Soil water repellency, aggregate stability, and shear resistance tests were performed on the loess. Results The treatments sugars, amino acids, and amino acids + sugars significantly increased soil water repellency. In addition, organic acids + sugars maximised mean weight diameter (MWD), geometric mean diameter (GMD) and the content of > 0.25 mm water-stable aggregates (R0.25), and minimised the percentage of aggregates destroyed (PAD) in the addition treatments. All treatments except for amino acids significantly increased soil shear strength and cohesion of the loess. Amino acids, amino acids + sugars, and amino acids + organic acids + sugars significantly increased the internal friction angle. Conclusion The single addition treatments had a higher effect on soil hydraulic properties, while the combined addition treatments had a higher effect on soil mechanical properties. Sugars and amino acids substantially increased soil hydraulic stability. Sugars combined with other compounds, especially with organic acids, significantly improved soil mechanical stability.

The relationships between soil aggregates, aggregate-associated carbon (C), and soil compaction indices in pomegranate orchards of varying ages (0-30 years) in Assiut, Egypt, were investigated. Soil bulk density (Bd) and organic carbon (OC) content increased with orchard age in both the surface (0.00-0.20 m) and subsurface (0.20-0.40 m) layers 0.20-0.40 m). The percentage of macroaggregates (R-0.25) and their OC content in the aggregate fraction > 0.250 mm increased as the pomegranate orchard ages increased in the surface layer (0.00-0.20 m). Older pomegranate orchards show improved soil structure, indicated by higher mean weight diameter (MWD) and geometric mean diameter (GMD), alongside reduced fractal dimension (D) and erodibility (K). As orchard ages increased, maximum bulk density (BMax) decreased due to an increase in OC, while the degree of compactness (DC) increased, reaching a maximum at both soil layers for the 30 Y orchards. Soil organic carbon and aggregate-associated C significantly influenced BMax, which led to reducing the soil compaction risk. Multivariate analyses identified the >2 mm aggregate fraction as the most critical factor influencing the DC, soil compaction, and K indices in pomegranate orchards. The OC content in the >2 mm aggregates negatively correlated with BMax, DC, and K but was positively associated with MWD and GMD. Moreover, DC and Bd decreased with higher proportions of >2 mm aggregates, whereas DC increased with a higher fraction of 2-0.250 mm aggregation. These findings highlight the role of aggregate size fractions and their associated C in enhancing soil structure stability, mitigating compaction, and reducing erosion risks in pomegranate orchards.

Although it has been recognized that soil structure formation affects soil organic carbon (SOC) sequestration, experimental data elucidating the relation between mechanical properties of soil structure and soil organic matter (SOM) stability are lacking. This study assesses the link between aggregate stability and SOM stability in lowland and hilly land soils of Central Europe. Overall, 39 topsoil samples were taken. Besides determining basic properties and nutrient availability, stability of soil aggregates was quantified using wet sieving (WS) and rainfall simulation (RS) procedures. The samples were analyzed by thermogravimetry and differential scanning calorimetry (TG-DSC). Besides significant correlations with basic soil properties and contents of selected nutrients, the aggregate stability data were linked to thermal processes, such as water desorption and SOM degradation. The RS values were significantly correlated (r > 0.7, p < 0.001) with the rate of water desorption (T < 200 degrees C) and SOM degradation (200 - 570 degrees C). Observed correlation pattern, with multiple maxima, suggests that aggregate stability is supported by clay and several SOM fractions, each showing different thermal stability. Significant correlations observed bellow 200 degrees C indicate that properties controlling soil specific surface area (SOM and clay) are important also for the aggregate stability. The 78 % of the variance observed in aggregate stability testing was explained by multilinear regression using weight loss rates recorded at selected temperatures (80, 130, 248, 401 and 455 degrees C) as predictors. We observed different relations between exothermic energy values, soil aggregate stability and thermal stability of SOM (SOC). Exothermic heat flux normalized with respect to SOC mass (energy density) indicates presence of stable organic fraction, as it showed correlation also with clay, which has positive effect on SOC stabilization. This is in line with the positive correlation between SOC energy density and aggregate stability. On contrary, normalizing the heat with respect to SOM mass indicates the content of labile organic components, as the correlations with clay or aggregate stability were insignificant. The TG-DSC data revealed that hilly land soils are depleted in fresh organic material, which is due to their genesis and the erosion intensified by tillage.

In response to the current serious problem of soil cadmium (Cd) contamination in agricultural land, phytoremediation technology is a green and environmentally friendly application prospect; however, its remediation efficiency is currently limited. An enhanced phytoremediation technique was constructed using the biodegradable chelator aspartate diethoxysuccinic acid (AES) combined with the plant growth regulator gibberellic acid (GA3) to enhance the formation of maize. This technique has been proven to have a superior remediation effect. However, the safety of the restoration technique is of particular importance. The remediation process not only removes the contaminants, but also ensures that the original structure and stability of the soil is not damaged. In this regard, the constructed enhanced phytoremediation technique was further investigated in this study using soil columns. In combination with microscopic tests, such as X-ray diffraction and scanning electron microscopy, this study investigated the effects of the remediation process on the distribution characteristics of Cd in soil aggregates, and the structure and stability of soil aggregates. This was conducted by analyzing, as follows: plant growth conditions; the morphology, structure and mineral composition of soil aggregates in different soil layers; and the changes in these characteristics. The results demonstrated that the enhanced phytoremediation technique constructed in this study has a negligible impact on the morphology and mineral composition of soil aggregates, while exerting a limited influence on soil structure stability. This indicates that the technique can facilitate the safe utilization of remediated contaminated soil.

Most climate models predict that the timing, magnitude, and duration of snow cover will change over much of the Northern Hemisphere. Because snow cover effectively buffers soil against changes in air temperature, fluctuations in snowpack could alter freeze-thaw cycling, resulting in shifts in macroaggregate stability and subsequent detachment. Moreover, vegetation type could modify these effects; however, these interactions remain unexplored. In this study, we experimentally manipulated snow cover in an agricultural field and in an adjacent 13-year-old restored prairie to assess changes to soil aggregation and detachment over a three-winter period (November-April 2014-17). Treatments consisted of complete snow removal, natural snow cover, and a sustained snowpack simulated via straw insulation. Averaged over the course of the study, snow removal resulted in a 5% and 15% over-winter reduction in wet-aggregate stability (WAS) and mean weight diameter (MWD), respectively. Conversely, natural snow cover and straw insulation resulted in a 3% and 15% over-winter increase in WAS and MWD, respectively. However, over-winter changes to WAS and MWD did not persist but instead appeared to return to a set point by the end of each growing season regardless of vegetation type. In addition, we found an offset in WAS; it was approximately 11% higher in the prairie than in the agricultural field, likely due to increased root and microbial activity in the prairie. No similar offset was observed in MWD between vegetation types. These responses in soil aggregation did not result in significant springtime changes to soil critical shear stress, measured as a proxy for soil detachment potential. The results of this study suggest that future investigations into over-winter soil processes should consider vegetation type, temporal soil aggregation dynamics, and more detailed quantification of freeze-thaw cycling.

Throughout most of the northern hemisphere, snow cover decreased in almost every winter month from 1967 to 2012. Because snow is an effective insulator, snow cover loss has likely enhanced soil freezing and the frequency of soil freeze-thaw cycles, which can disrupt soil nitrogen dynamics including the production of nitrous oxide (N2O). We used replicated automated gas flux chambers deployed in an annual cropping system in the upper Midwest US for three winters (December-March, 2011-2013) to examine the effects of snow removal and additions on N2O fluxes. Diminished snow cover resulted in increased N2O emissions each year; over the entire experiment, cumulative emissions in plots with snow removed were 69% higher than in ambient snow control plots and 95% higher than in plots that received additional snow (P < 0.001). Higher emissions coincided with a greater number of freeze-thaw cycles that broke up soil macroaggregates (250-8000 A mu m) and significantly increased soil inorganic nitrogen pools. We conclude that winters with less snow cover can be expected to accelerate N2O fluxes from agricultural soils subject to wintertime freezing.