Internal Force Mechanism of Pisha Sandstone as a Soil Amendment to Improve Sandy Soil Structural Stability in Mu Us Sandy Land

Soil aggregate stability and carbon–nitrogen content are critical indicators for assessing the vegetation restoration effects. Salix cupularis plays a vital role in rehabilitating desertified alpine meadows on the eastern Qinghai–Tibet Plateau. However, research remains limited about how afforestation influences the soil aggregate stability and associated carbon and nitrogen dynamics. In this study, sandy land (0 years) served as the control, and the spatial time replacement method was used to examine changes in the soil water-stable aggregate composition, stability, organic carbon (OC) and total nitrogen (TN) contents, and density at a 0–60 cm depth after 5 and 10 years of afforestation restoration (Salix cupularis). Ecological restoration significantly enhanced the proportion of macroaggregates (>0.25 mm) in the topsoil (0–20 cm), and improved aggregate stability. After 10 years of restoration, macroaggregates increased by 45.04% and 51.32%, respectively. The average weight diameter and geometric mean diameter of the aggregates increased by 51.32% and 59.53%, respectively. Following restoration, there was a gradual increase in the OC and TN contents in the soil, with the highest increase observed in the 0–10 cm layer (266.67% and 391.67%). The OC and TN of the aggregates also displayed a similar trend. Correlation analysis results indicated a significant positive relationship between the soil OC and TN contents and density, OC content in aggregates of various diameters, and the stability of these aggregates. The Pearson’s correlation coefficient for OC in aggregates > 1 mm was the highest. Compared with 5 years, 10 years of recovery were more conducive to the formation of macroaggregates, enhancement in aggregate stability, and the accumulation of OC and TN. Therefore, vegetation restoration on the Zoige Plateau can significantly enhance the soil water-stable aggregate composition and stability and can also increase the soil and OC and TN contents and density, thereby enhancing the soil ecological quality. This study provides fundamental data and theoretical support for rehabilitating desertified grasslands on the eastern Qinghai–Tibet Plateau.

Reasonable application of organic-inorganic soil conditioners can effectively improve the structure and fertility of reclaimed soil in abandoned homestead. Aggregate stability is an important indicator to evaluate soil structure and fertility, and is largely influenced by soil internal forces (van der Waals attractive force, electrostatic repulsive force, hydration repulsive force) and particle surface properties. However, there are few studies on the influence of different soil conditioners on the reclaimed soil internal forces and its relationship with the aggregate stability. Therefore, we selected six different treatments of organic fertilizer (TO), fly ash (TF), maturing agent (TM), maturing agent + organic fertilizer (TMO), fly ash + organic fertilizer (TFO) and control (CK) to conduct a 5-year field experiment to study the effects of reclaimed soil particle interaction forces and surface characteristics on aggregate stability under the treatment of different soil conditioners. The results showed that with the application of soil conditioners, the soil organic matter (SOM), specific surface area (SSA), surface charge (σ0), cation exchange capacity (CEC), aggregate mean weight diameter (MWD) and Hamaker constant increased gradually, while the pH value decreased slightly. In particular, the MWD under the treatments of TFO and TMO increased by 150.3% and 65.6% respectively compared with that under the CK treatment. With the increasing application of soil conditioners, the electrostatic repulsive force and van der Waals attractive force between reclaimed soil particles increased constantly, but the net resultant force between particles decreased and the net attractive force increased continuously, thus improving the aggregate stability. Therefore, there is a significant negative correlation between the net resultant force among reclaimed soil particles and MWD and CEC. In addition, 10−2 mol L-1 is the critical concentration that affects the reclaimed soil internal force, and the organic-inorganic treatments of TFO and TMO can improve the net resultant force better. In a word, the particle interaction forces are important factors affecting the reclaimed soil structural stability, and this study provides a scientific reference for the rational selection of soil conditioners and its interaction force mechanism in the reclaimed soil improvement.

The coupling effects of soil organic matter and particle interaction forces on soil aggregate stability

Importance of soil interparticle forces and organic matter for aggregate stability in a temperate soil and a subtropical soil

Biochar and compost are important organic amendments which act as cementing agents and increase the aggregate stability in the sandy soils. The main idea of this study was to investigate the impact of date palm waste biochar, compost and their mixture on soil aggregate stability at the rate of 1, 2, 3 and 4%. The objectives were to evaluate the changes in indicators of aggregates stability to water due to biochar, compost, and biochar-compost addition and to study the impact of biochar and compost on sandy soil erodibility. Water stable aggregates (WSA), macroaggregates (WSA>0.25), mean weight diameter (MWD), geometric mean diameter (GMD) and erodibility factor (Kerodibility) were measured and evaluated. The results showed that the indicators of WSA, WSA>0.25, MWD, GMD and Kerodibility were 76.35, 15.94%, 0.19, 0.39 mm and 0.09 for control (unamended soil), respectively. The WSA, WSA>0.25, MWD, GMD and Kerodibility were enhanced with different rates of biochar and compost. However, biochar exhibited a significant improvement in aggregate stability and their effect was slightly better than compost. Accordingly, biochar increased WSA (24.6-31%), WSA>0.25 (69.9-164.2%), MWD (57.5-121.6%), GMD (24-44.2%), and decreased Kerodibility (18.8-31.1%). Compost increased WSA (7.8-45.3%), WSA>0.25 (11.1-45.3%), MWD (9.7-36.5%), GMD (5.1-17.5%) and deceased Kerodibility (4.7-14.5%) compared with unamended soil. Therefore, the amendment materials reduced the soil erosion and led to increased aggregation stability against erodibility. The results of this study can be helpful in predicting the behavior of biochar and compost amendments towards aggregate stability in loamy sand soils.

土壤团聚体物理保护是促进有机碳积累主要机制之一。以黄土高原子午岭林区天然次生林植被演替群落为对象，研究从农田、草地（白羊草，Bothriochloa ischaemum）、灌木林（沙棘，Hippophae rhamnoides）、先锋林（山杨，Populus davidiana）到顶级林（辽东栎，Quercus liaotungensis）5个植被演替阶段0-20 cm土壤团聚体稳定性和团聚体有机碳的动态变化，并分析团聚体有机碳的影响因素。结果表明：土壤团聚体稳定性随着植被演替显著提高（P<0.05），顶级林的团聚体稳定性最高；土壤有机碳含量和各粒径土壤团聚体（> 2 mm、2-0.25 mm、0.25-0.053 mm、<0.053 mm）有机碳含量均随着植被演替而增加。除草地0.25-0.053 mm团聚体有机碳含量最高外，其他演替阶段均为0.25-2 mm粒径最高。根系生物量、凋落物生物量、微生物生物量碳、团聚体稳定性均与团聚体有机碳含量呈显著正相关关系（P<0.05）。总体而言，长期植被演替有助于团聚体稳定性和团聚体有机碳累积。;Vegetation restoration plays an important role in soil structure and nutrients. The effects of vegetation restoration on the aggregate stability and soil carbon storage have been widely studied, but the distribution of aggregate associated organic carbon and the effects of plants on aggregate associated organic carbon in the secondary forest succession are still unclear. This paper studied the stability of soil aggregates and the changes of soil aggregate-associated organic carbon under the succession sequence of the secondary forests in Ziwuling forest region of the Loess Plateau, China. We discussed the dynamics of aggregate-associated organic carbon and its influencing factors following the secondary forest succession. In the field investigation, five vegetation succession stages were selected:farmland (CL), grassland (GL), shrub (S), pioneer forest (PF), and climax forest (CF). Soil samples in 0-20 cm were collected and the aggregates were separated by wet sieving. The stability of aggregates was characterized by mean weight diameter (MWD), geometric mean diameter (GMD), and percentage of water stable aggregates (WAS). The organic carbon, root biomass, litter biomass and microbial biomass carbon (MBC) of soil and aggregates were measured. The dynamics of soil aggregate-associated organic carbon and its influencing factors were analyzed. The results showed that soil organic carbon contents increased with vegetation succession, which showed that CF>PF>S>CL, and the organic carbon contents of aggregates increased more significantly from grassland to pioneer arbor stage. The succession of vegetation communities significantly increased the content of soil organic carbon. The stability of soil aggregate increased significantly with vegetation succession (P<0.05). The stability of soil aggregate in climax forest was the highest, and the contents of macroaggregate>0.25 mm in pioneer forest and climax forest were higher than that in farmland. The organic carbon contents of soil aggregates with different particle sizes increased with vegetation succession, and the organic carbon content of 2-0.25 mm was the highest in each succession stage. The stability of aggregates was positively correlated with the soil organic carbon. Root biomass, litter biomass and the MBC were significantly positively correlated with aggregate-associated organic carbon content. The main factors affecting soil organic carbon contents of aggregates were different in different particle sizes. Except the stages of vegetation succession, soil total organic carbon, litter biomass and soil aggregate stability were the main factors affecting the organic carbon content in the macroaggregates (> 0.25 mm), middle aggregates (0.25-0.053 mm), and microaggregates (<0.053 mm). The study suggests that vegetation succession plays an important role in the stability of aggregates and the fixation of organic carbon in aggregates.

Maintenance of soil organic carbon (SOC) is important for sustainable use of soil resources due to the multiple effects of SOC on soil nutrient status and soil structural stability. The objective of this study was to identify the changes in soil aggregate distribution and stability, SOC, and nitrogen (N) concentrations after cropland was converted to perennial alfalfa (Medicago sativa L. Algonguin) grassland for 6 years in the marginal oasis of the middle of Hexi Corridor region, northwest China. Significant changes in the size distribution of dry-sieving aggregates and water-stable aggregates, SOC, and N concentrations occurred after the conversion from crop to alfalfa. SOC and N stocks increased by 20.2% and 18.5%, respectively, and the estimated C and N sequestration rates were 0.4 Mg C ha(-1) year(-1) and 0.04 Mg N ha(-1) year(-1) following the conversion. The large aggregate (>5 mm) was the most abundant dry aggregate size fraction in both crop and alfalfa soils, and significant difference in the distribution of dry aggregates between the two land use types occurred only in the >5 mm aggregate fraction. The percentage of water-stable macroaggregates (>2, 2-0.25 mm) and aggregate stability (mean weight diameter of water-stable aggregates, WMWD) were significantly higher in alfalfa soils than in crop soils. There was a significant linear relationship between total SOC concentration and aggregate parameters (mean weight diameter) for alfalfa soils, indicating that aggregate stability was closely associated with increased SOC concentration following the conversion of crops to alfalfa. The SOC and N concentrations and the C/N ratio were greatest in the >2 mm water-stable aggregates and the smallest in the 0.25-0.05 mm aggregates in crop and alfalfa soils. For the same aggregate, SOC and N concentrations in aggregate fractions increased with increasing total SOC and N concentrations. The result showed that the conversion of annual crops to alfalfa in the marginal land with coarse-texture soils can significantly increase SOC and N stocks, and improve soil structure.

The Maowusu Desert is still suffering from serious ecological and environmental security issues such as wind erosion and desertification, influenced by both natural and human factors. The amendment of aeolian sandy soil with soft rock material presents an effective erosion control strategy, leveraging the complementary structural and compositional properties of both materials to enhance soil stability and rehabilitate degraded environments. However, there are few studies that investigate the effect of soil surface electrochemical properties and particle interaction forces on the structural stability of compound soils with soft rock and sandy soil. This decade-long field study quantified the electrochemical properties and interparticle forces and their synergistic effects on structural stability across five soft rock-to-aeolian sandy soil blend volume ratios (0:1, 1:5, 1:2, 1:1, 1:0) within the 0–30 cm soil profile. The results showed that the soil organic matter (SOM), specific surface area (SSA), and cation exchange capacity (CEC) significantly increased with the incorporation of soft rock material. For five different proportions, with the addition of soft rock and the extension of planting years, the content of SOM increased from 5.65 g·kg−1 to 11.36 g·kg−1, the CEC varied from 4.68 cmol kg−1 to 17.91 cmol kg−1, while the σ0 importantly decreased from 1.8 to 0.47 c m−2 (p &lt; 0.05). For the interaction force at 2.4 nm between soil particles, the absolute value of van der Waals attractive force increased from 0.10 atm to 0.38 atm, and the net force decreased from 0.09 atm to −0.30 atm after the incorporation ratios of soft rock from 0:1 to 1:1. There was a significant negative correlation between the resultant net force between the particles of compound soil and the SSA and CEC. These results indicate that the addition of soft rock material positively improves the surface electrochemical properties and internal forces between aeolian sandy soil particles, further enhancing its structural stability. This study establishes a foundational theoretical framework for advancing our mechanistic understanding of aeolian sand stabilization and ecosystem rehabilitation in the Mu Us Desert.

Soil aggregates are important indicators of soil quality and sustainable land utilization, and impact the retention abilities of water and fertilizers and the release of nutrients in soil. This study aimed to understand the effects of two land use types (an orchard and farmland) on the distribution, stability, and organic carbon content of soil aggregates, and provides a theoretical basis for the optimal management of the soil carbon pool in the Weibei Dryland of the Loess Plateau. We examined the soils from an orchard and from farmland by simultaneous sampling and wet sieving; the proportions of large macroaggregates (>2 mm), small macroaggregates (0.25-2 mm), microaggregates (0.053-0.25 mm), and silt and clay (<0.053 mm) were then determined; the content of organic carbon in each aggregate fraction at soil depths of 0-40 cm were also measured, and the total organic carbon content of all aggregates fractions was determined for each soil. The results showed that the type of agricultural land use had a significant effect on the distribution and stability of soil aggregates in the 0-20 cm soil layer, with the relative proportions of the different sized aggregates (>2, 0.25-2, 0.053-0.25, and<0.053 mm) being 12.9%, 51.3%, 28.8%, and 7.0% in the orchards, respectively, and 8.3%, 49.7%, 33.6%, and 8.4% on the farmland, respectively. The proportion of macro-aggregates (>0.25 mm) was significantly higher in the orchard soils than in the farmland soils. Mean weight diameter (MWD) and geometric mean diameter (GMD) are important indicators of the soil aggregate stability; the MWD and GWD of the farmland soils were significantly lower than the orchard soils in the 0-40 cm depth zone (P<0.05). The effects of different land use types on the organic carbon content of soil aggregates was most marked in the 0-10 cm layer. Compared with farmland, the organic carbon content in the large aggregates, intermediate aggregates, micro-aggregates, and the silt and clay fraction of orchard soils were relatively increased by 56.0% (P<0.05), 57.1% (P<0.05), 40.8% (P>0.05), and 13.0% (P>0.05), respectively. Organic carbon storage in each aggregate class (excluding the<0.053 mm fraction) in the orchard soils was higher than in the farmland soils. In the orchard soils, the proportion of soil macro-aggregates (>0.25 mm) and the associated organic carbon content was elevated, damage to aggregates was reduced, and the organic carbon stability was enhanced. In general, the soil aggregate stability and organic carbon content of orchard soils were higher than for the farmland soils. Orchards appear to enhance the physical stability of aggregates with respect to soil organic carbon, contribute to soil organic carbon accumulation, and thus promote soil carbon sequestration.

Application of various methodological approaches for assessment of soil micromorphology due to VESTA program applicable to prediction of the soil structures formation

Soil dispersion is an important process that should be considered in irrigation and ferti-irrigation of agricultural soils. Triplicate topsoil samples from five different locations in southeastern Nigeria were characterized and examined for aggregate stability and clay dispersion potential by leaching with different NaCl concentrations. The results showed that the soils were mainly sandy clay loam (SCL), slightly acid to neutral pH and low in soil organic carbon (SOC), total nitrogen, and exchangeable cations. The soils had lower proportions of &gt; 1.00 mm water-stable aggregates (WSA) compared to the higher proportions of &lt; 1.00 mm WSA. Percent aggregate stability (AS) of the soils averaged 36.25 % and was significantly positively correlated with SOC (r = 0.55*) and Na+ content (r = 0.58*). Furthermore, Na+ correlated positively with the 1.00-2.00 mm WSA (r = 0.67*), but negatively with the &lt; 0.25 mm WSA fraction (r = -0.68**), while the opposite was true for the correlation of clay and these WSA fractions (r = -0.57*; 0.60*, respectively), indicating the minor role of clay in aggregate formation. The soils were less dispersible in water than in NaCl solutions, resulting in a higher clay content, which increased with increasing NaCl concentration. However, the clay dispersion ratio of the soils was moderately low and showed a decreasing trend with increasing NaCl concentration, and indicating the NaCl dispersion potential at the lowest 25 S m-1. Thus, the clay dispersion potential of Na+ at ≤ 50 S m-1 relates to the reduced stability of &lt; 0.25 mm microaggregates, while the clay flocculation potential of Na+ at ≥ 75 S m-1 accounts for the 1.00-2.00 mm macro aggregation and aggregate stability of the soils. Therefore, the structural stability of SCL soils in the humid tropics depends on SOC and Na+ content, including the dispersive and flocculative influence of Na+ on clay minerals.

Sandy soils are characterized by rapid water loss, low nutrient availability, poor vegetation establishment, and high susceptibility to wind erosion. Although Pisha sandstone has been recognized as an effective amendment to improve the physical stability of sandy soils, its role in enhancing soil fertility and biological functioning-particularly when combined with microbial inoculants-remains poorly understood. This gap limits the development of integrated restoration strategies for desertified regions. To address it, a randomized field experiment was conducted in the Hobq Desert, China. Pisha sandstone was incorporated into native sandy soil at five volumetric ratios (0%, 30%, 50%, 80%, and 100%), with or without microbial inoculants. Indicators measured included soil organic carbon, available nitrogen and phosphorus, microbial populations (bacteria, fungi, actinomycetes), enzyme activities (urease, invertase, acid phosphatase), and licorice growth. Results showed that Pisha sandstone significantly improved soil nutrients and enzyme activities, with the greatest effect at the 50% mixing ratio. Microbial inoculation further enhanced these improvements, producing 1.5- to 2.0-fold increases in microbial populations and enzyme activities relative to uninoculated controls. The best licorice growth occurred in the 50% sandstone plus inoculant treatment, corresponding to the highest fertility and microbial activity. Correlation analysis revealed strong positive relationships among soil organic carbon, available nutrients, microbial densities, enzyme activities, and plant growth. These findings demonstrate that the co-application of Pisha sandstone and microbial inoculants effectively enhances the fertility and biological functioning of sandy soils, filling a key knowledge gap and offering a practical strategy for ecological restoration.

Influence of cover crops on soil aggregate stability, size distribution and related factors in a no-till field

In order to explore the effects of continuous annual crop rotation and fallow on aggregate stability and organic carbon content in red soil, the red soil in sloping farmland was taken as the research object, and the water-stable aggregates and organic carbon content were determined using the wet sieve method and potassium dichromate-concentrated sulfuric acid external heating method, respectively. The changes in soil aggregate stability and organic carbon content under the four treatments of maize-vetch-maize rotation (M-V-M), maize-pea-maize rotation (M-P-M), maize-fallow-maize (M-F-M), and annual fallow (F-F-F) from 2020 to 2022 and the relationships between them were analyzed. The results showed that in 2021 and 2022, the contents of > 2 mm aggregates treated with F-F-F, M-V-M, and M-P-M were significantly increased by 67.01%-100.92%, 29.71%-33.67%, and 29.68%-38.07%, respectively, compared with that treated with M-F-M. In 2021 and 2022, the stability parameters of F-F-F and M-V-M were significantly higher than those of M-F-M (P < 0.05). The content of > 2 mm aggregates, geometric mean diameter (GMD), and mean weight diameter (MWD) under the M-V-M treatment and R0.25 (> 0.25 mm aggregate contents), MWD and > 2 mm aggregate contents under the F-F-F treatment increased with the increase in fallow years, whereas the content of 1-2 mm and < 0.25 mm under the F-F-F treatment decreased with the increase in fallow years. Both green manure rotation and fallow treatment could increase the SOC content, and the SOC content of F-F-F and M-V-M treatment increased with the extension in age. Correlation analysis showed that SOC content was significantly positively correlated with R0.25 and GMD under all treatments. R0.25 and GMD under the F-F-F treatment and GMD and MWD under M-V-M were significantly positively correlated with SOC content. The results showed that continuous annual crop rotation and fallow was beneficial to improve the content of soil macro-aggregates, aggregate stability, and SOC content, which could provide theoretical basis for the implementation of reasonable continuous annual crop rotation and fallow patterns and soil erosion control in red soil areas of sloping farmland in southern China.

In order to explore the effect of reconstructing soil quality change after adding Pisha sandstone rich in clay mineral materials to improve sandy soil in the Mu Us Sandy Land. Long-term field monitoring experiments were conducted to study the characteristic changes of the reconstructed soil carbon and nitrogen content and corn yield with different proportions of Pisha sandstone and sand. The results showed that after 9 years of experiment, compared with the original sandy soil, in T1, T2, and T3 treatments the reconstructed soil organic matter content increased by 10, 12, and 11 times, total nitrogen content increased by 5.5, 5.4, and 3.9 times, and corn yield increased by 43.9, 105.9, and 58.5%. Especially, the corn yield of T2 and T3 treatment is greater than or equal to the corn yield of local high-yield fields. In summary, the reconstructed soil quality in different proportions has developed toward a good trend after long-term planting. T2 and T3 treatments have the best effects on reconstructing soil carbon and nitrogen accumulation reconstruction and corn yield increase. T2 and T3 treatments are recommended as the best scientific ratio for improving sandy soil with Pisha sandstone in Mu Us Sandy Land. This method has important reference and guidance for ecological remediation of desertification and degraded land.