Properties Of Soil Aggregates Research Articles

Long-term rice cultivation enhances root development and yields by improving the structural properties of soil aggregates in saline–alkaline environments

Rice cultivation has the ability to improve saline soils. However, the effects of long-term rice cultivation on saline soil chemistry, salt ions, root characteristics, and aggregate formation remain unclear. In this study, the impact of different planting durations (1, 3, 5, 8, and 10 years) on the spatial and temporal transport of soil salts, soil chemical properties, distribution and stability of aggregates, root characteristics, and yields, were assessed. Long-term rice cultivation reduced soil pH, exchangeable sodium percentage (ESP), and EC in the 0-60cm soil layer compared to 1Y (5.45%, 61.57%, and 81.87% reduction in topsoil (0-20cm) and 8.54%, 72.82%, and 71.94 in subsoil (20-60cm), respectively). However, the soil organic matter (OM), alkaline nitrogen (AN), phosphorus (AP), and potassium (AK) increased (217.09%, 90.18%, 89.23%, and 179.18% increase in topsoil and 223.72%, 81.24%, 174.28%, and 172.57% increase in subsoil, respectively). Additionally, the Cl-, K+, and Na+ in the soil gradually leached downward with the increase in the duration of rice cultivation (55.87%、36.08%、59.80%). Simultaneously, the increased duration markedly elevated the soil macroaggregate content (11.43%-20.04% by dry-sieving and 53.48%-288.09% by wet-sieving), clayey grain content (59.17%-198.33%), and soil aggregate stability, especially for 8Y and 10Y. The improved soil structure and root characteristic under long-term rice cultivation conditions increased the yield (28.89-54.81%). Partial least squares path model displayed that rice cultivation affected the aggregate stability, root characteristics, and rice yield via the corresponding chemical properties (pH, EC, and ESP), nutrient contents (AN, AP, AK, and SOM), and salt ion contents (Cl-, K+, and Na+). These findings are critical to understanding aggregate formation in saline soils.

Grass species and mycorrhizal fungi improved aggregate stability of compacted and vegetated soils

Abstract Aim Compaction of slope soils can substantially hinder root penetration of grass cover, which may be alleviated through the colonisation of arbuscular mycorrhizal (AM) fungi and aggregate stabilisation. We investigated aggregate stabilisation and breakdown mechanisms in compacted dense mycorrhizal soils. Methods A pot-culture experiment with seven treatments (five replicates per treatment) was implemented. In a local decomposed granitic soil, we inoculated two grass species (Chrysopogon ziaanioides and Cynodon dactylon) with AM fungi. We used loose soil to grow C. dactylon to compare it with compacted dense soil, as well as pots without a plant and/or fungal inoculation for comparison. After 20 weeks of cultivation, we measured root and AM fungal characteristics, soil organic matter and aggregate properties by dry sieving, wet sieving and Le Bissonnais methods. Results Compaction led to the formation of macro-aggregates (> 0.25 mm) but had a negative influence on the aggregate stability. The fungal inoculation increased polysaccharide production and aggregate stability in the compacted soil vegetated with C. dactylon. The inoculated C. ziaanioides showed a similar level of aggregate stability as the inoculated C. dactylon, but the uninoculated group demonstrated higher aggregate stability compared with the inoculated group owing to root decomposition. The aggregate stability against various breakdown mechanisms was related to the established aggregate hierarchy and qualitative organic matter inputs. Conclusion Soil organic matter supplied by grass species together with the mediation of AM fungal hyphae played a crucial role in the systemic enhancement of aggregate stability in the compacted soil.

Characteristics and mechanisms of phosphorus adsorption-desorption in soil aggregates during cut slope restoration

Soil phosphorus (P) effectiveness and sustainability play a crucial role in influencing the ecological restoration process of cut slopes. However, the P adsorption-desorption characteristics of soil aggregates during the ecological restoration of cut slopes remain unclear. We selected three roadside slopes that have undergone ecological restoration for 7, 11, and 14 years, respectively, in Songpan County on the eastern Tibetan Plateau in China. We determined the characteristic parameters of P adsorption-desorption in soil aggregates using isothermal adsorption-desorption experiments. X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were conducted to characterize the mineral and functional group properties of soil aggregates. The results showed that the P adsorption-desorption capacity of soil aggregates increased with the restoration years. Microaggregates (<0.25 mm) were higher adsorption-desorption capacity than that of macroaggregates (>0.25 mm). Soil organic matter (SOM), available phosphorus (AP), free iron oxide (FeDCB), and free aluminum oxide (AlDCB) were the driving factor of P adsorption. In addition, total phosphorus (TP), AP, pH, SOM, FeDCB, and AlDCB played key roles in P desorption. SOM, AP, and AlDCB affected indirectly FeDCB, while SOM and TP affected indirectly pH, consequently affecting adsorption-desorption. Calcite was involved in P adsorption by soil aggregates. The ligand exchange between the hydroxyl group in montmorillonite and P in the aqueous phase may the key adsorption-desorption process. The current study provides a scientific basis for promoting the effectiveness and sustainability of soil P in cut slope restoration.

Root Influences Rhizosphere Hydraulic Properties through Soil Organic Carbon and Microbial Activity.

Processes of water retention and movement and the hydraulic conductivity are altered in the rhizosphere. The aim of this study was to investigate the physical-hydric properties of soil aggregates in the rhizosphere of annual ryegrass (Lolium multiflorum) cropped in a Kandiudalfic Eutrudox, taking into account aspects related to soil aggregate stability. Soil aggregates from rhizosphere soil (RZS) and soil between plant rows (SBP) were used to determine soil water retention curves (SWRCs) and saturated hydraulic conductivity (Ksat). In addition, properties related to soil aggregate stability, such as water-dispersible clay, soil organic carbon (SOC), and microbial activity, were also assessed. The higher microbial activity observed in the RZS was facilitated by increased SOC and microbial activity, resulting in improved soil aggregation (less water-dispersible clay). For nearly all measured matric potentials, RZS had a higher water content than SBP. This was attributed to the stability of aggregates, increase in SOC content, and the root exudates, which improved soil water retention. The increase in total porosity in RZS was associated with improved soil aggregation, which prevents deterioration of the soil pore space and results in higher Ksat and hydraulic conductivity as a function of the effective relative saturation in RZS compared to SBP.

Long-Term Organic Cultivation in Greenhouses Enhances Vegetable Yield and Soil Carbon Accumulation through the Promotion of Soil Aggregation

The long-term use of fertilizers and pesticides in conventional cultivation has resulted in a decrease in soil productivity and vegetable yields in greenhouses. However, there is little research exploring the changes in soil organic carbon and the microbial community mediated by soil aggregates, or their impacts on soil productivity. This study investigated the properties of soil aggregates, including the levels of organic carbon fractions, microbial community, and enzyme activity with the three aggregate classes: microaggregates (&lt;0.25 mm), small macroaggregates (2–0.25 mm) and large macroaggregates (&gt;2 mm) under conventional cultivation (CC), integrated cultivation (IC), and organic cultivation (OC) in greenhouses. The results showed that (1) OC and IC promoted the formation of small macroaggregates and enhanced aggregate stability compared to CC; (2) SOC in the three size fractions of OC increased by 92.06–98.99% compared to CC; EOC increased by 98.47–117.59%; POC increased by 138.59–208.70%; MBC increased by 104.71–230.61%; and DOC increased by 21.93–40.90%, respectively; (3) organic cultivation significantly increased enzyme activity in all three particle-size aggregates and increased the relative abundance of bacteria in microaggregates as well as the relative abundance of fungi in small macroaggregates. Structural equation model (SEM) analysis revealed that organic farming practices fostered the development of smaller macroaggregates, elevated microbial and enzyme activities within soil aggregates, and facilitated the conversion of soil nutrients and carbon sequestration. Therefore, long-term organic cultivation increases soil carbon content and vegetable yield in greenhouses by increasing the proportion of small aggregates. In conclusion, long-term organic cultivation in greenhouses improves soil structure, increase soil fertility and vegetable yield, and has a positive impact on the environment. Organic cultivation increases soil fertility and contributes to maintaining ecological balance and protecting the environment in greenhouses.

Evaluation of Wastewater Treatment Properties of Artificial Soil Aggregates by Materials Analysis After Wastewater Treatment

Evaluation of Wastewater Treatment Properties of Artificial Soil Aggregates by Materials Analysis After Wastewater Treatment

Applying Hydrochar Affects Soil Carbon Dynamics by Altering the Characteristics of Soil Aggregates and Microbes

Hydrochar as a carbon-based fertiliser is hypothesised to permanently improve soils by modifying soil carbon quality through the regulation of soil organic carbon dynamics, aggregation properties and microbial diversity. However, the interactions between soil organic carbon (SOC) molecular structure, soil aggregates and soil microbial communities as a result of hydrochar application have not been fully elucidated. In this study, the use of hydrochar derived from duck farm biomass waste for a maize cultivation experiment verified that hydrochar had a promoting effect on maize growth, effectively increasing the nutrient supply to the soil. The application of hydrochar increased the soil organic carbon content by 78 to 253 per cent, which was dominated by CHON-type lignin, carbohydrates and condensed aromatic structural compounds. Meanwhile, hydrochar had a significant effect on both soil aromatic structures and oxygenated functional groups, forming more soil macroaggregates. In addition, hydrochar had a positive effect on soil bacterial abundance. This study suggests that the key mechanism by which hydrochar regulates soil carbon dynamics is mainly through the stabilising effect of hydrochar on macroaggregates while increasing the abundance of carbon-related microscopic bacteria. These results will help to elucidate the potential effects of aqueous carbon on the biogeochemical cycling of carbon in soils.

Enhancement of soil aggregation and physical properties through fungal amendments under varying moisture conditions.

Soil structure and aggregation are crucial for soil functionality, particularly under drought conditions. Saprobic soil fungi, known for their resilience in low moisture conditions, are recognized for their influence on soil aggregate dynamics. In this study, we explored the potential of fungal amendments to enhance soil aggregation and hydrological properties across different moisture regimes. We used a selection of 29 fungal isolates, recovered from soils treated under drought conditions and varying in colony density and growth rate, for single-strain inoculation into sterilized soil microcosms under either low or high moisture (≤-0.96 and -0.03 MPa, respectively). After 8 weeks, we assessed soil aggregate formation and stability, along with soil properties such as soil water content, water hydrophobicity, sorptivity, total fungal biomass and water potential. Our findings indicate that fungal inoculation altered soil hydrological properties and improved soil aggregation, with effects varying based on the fungal strains and soil moisture levels. We found a positive correlation between fungal biomass and enhanced soil aggregate formation and stabilization, achieved by connecting soil particles via hyphae and modifying soil aggregate sorptivity. The improvement in soil water potential was observed only when the initial moisture level was not critical for fungal activity. Overall, our results highlight the potential of using fungal inoculation to improve the structure of agricultural soil under drought conditions, thereby introducing new possibilities for soil management in the context of climate change.

Influence of crop rotation, irrigation, fertilization, and tillage on the aggregate property and soil wind erosion potential in the floodplain of the Yellow River

The floodplain of the Yellow River (FPYR) is threatened by severe soil erosion. Soils are often susceptible to wind erosion owing to their coarse-textures and weak aggregation, yet studies are yet to describe the ability of soils to resist wind erosion in this region. Accordingly, this study aimed to quantify how soil wind erosion potential is affected by soil aggregate properties, such as dry aggregate geometric mean diameter (GMD), aggregate geometric standard deviation (GSD), aggregate stability, and soil bulk density, and to assess the effects of soil type, crop rotation, irrigation, fertilization, and tillage treatments on these aggregate properties in the main wind erosion area across the FPYR. Significant differences in GMD and aggregate stability were found between crop rotation treatments, whereas crop rotation marginally affected the soil bulk density. Further, the impact of management practices on aggregate properties differed for each soil type. The soil aggregate erodible fraction (EF) in the FPYR ranged from 1.14 to 82.73% across sites, with a mean of 26.14% across soil types and management practices, which was lower than that previously reported in other wind erosion regions. We incorporated these measured EFs into the Revised Wind Erosion Equation (RWEQ) to evaluate the wind erosion risk of the FPYR. The results indicated that the central FPYR was more susceptible to wind erosion than the other regions, although the total wind erosion potential in the FPYR was small. Adoption of soil conservation practices could help minimize wind erosion and improve atmospheric quality in the region.

Size- and concentration-dependent effects of microplastics on soil aggregate formation and properties

Plastics fragment and threaten soil ecosystems. Degradation of soil structure is one of the risks. Despite this, data on impacts of different sized microplastics (MPs) on soil aggregates is lacking. This study systematically investigated the effects of pristine polyethylene powders of different sizes (< 35, < 125, < 500 µm) and concentrations (0, 0.1, 1.0, 10 wt%) on aggregate formation and their properties for two contrasting soils (woodland soil, WS; agricultural soil, AS). 75 day wet-dry cycles produced newly-formed aggregates in all treatments. MP size and concentration impacted the incorporation of MPs in aggregates and this varied with aggregate size; the size distribution of aggregates also varied with MP size and concentration. Aggregates produced in soil containing 10 wt% < 35 µm MPs had significantly lower MWDs (mean weight diameters) than controls. The wettability of aggregates (> 4 mm) reduced with increasing MP exposure concentration and decreasing MP exposure size. MP incorporation decreased the water stability of aggregates (1–2 mm) in WS but increased it in AS. The particle density of aggregates (> 4 mm) significantly decreased with increasing MP concentration, whereas MP size had no effect. As MPs breakdown, fragment and become smaller over time, their potential risk to the aggregated structure of soil increases.

Magnetically treated water drip irrigation combined with carboxymethyl cellulose (CMC) application: A regulating strategy for enhancing the jujube yield and quality in southern Xinjiang of China

Developing effective regulation strategies for improving the efficiency of irrigation water and fertilizers, and preventing further expansion of desertification in southern Xinjiang, China, is crucial. Magnetically treated water (MTW) has been shown to have a positive effect on plant growth. The carboxymethyl cellulose (CMC) has been widely used as an efficient soil amendment to improve soil aggregation and hydraulic properties. This study aimed to explore the optimal mode of combining MTW drip irrigation and CMC application for high-quality jujube production. Conventional freshwater irrigation was set up in both 2021 and 2022 (control group, CK). CMC treatments under MTW drip irrigation included C0 (0), C150 (150 kg/ha), C250 (250 kg/ha), C350 (350 kg/ha), and C450 (450 kg/ha) in 2021, and C0 (0), C150 (150 kg/ha), C300 (300 kg/ha), C450 (450 kg/ha), and C600 (600 kg/ha) in 2022. The results showed that CMC significantly increased soil porosity, water-holding capacity, and decreased soil bulk density and soil saturated hydraulic conductivity. CMC contributed 2.88 % to 27.96 % of large aggregates (>0.25 mm), significantly improving soil aggregate stability. Water and fertilizer (N, P, K) productivity increased by 4.5 % to 11.0 % and 1.9 % to 11.3 %, respectively. Jujube yield increased by 2.75 % to 15.98 %, and MTW increased jujube yield by 3.10 % compared to the CK. The recommended optimal CMC application rate was approximately 430 kg/ha. This mode provides a reliable theoretical reference for jujube industry development and soil desertification improvement in southern Xinjiang, China.

Assessment of soil aggregate pore structure after 8 years of cultivation from the parent material of a Mollisol

Soil erosion exposes the underlying parent material (PM) to the surface and an appropriate soil restoration approach is required to maintain soil quality. However, the current knowledge on soil restoration (e.g., improvement of soil aggregate structure) is mainly obtained from studies on well-developed soils. It remains unclear how aggregate pore structure of soils can be improved following different agricultural practices during the early stage of pedogenesis. The present study quantified the effects of 8 years of different agricultural practices (land use types, mineral fertilizers, and different amounts of organic inputs) on the aggregate stability, aggregate pore morphology, and surface properties of a topsoil (0–20 cm) and compared the findings with those of a prior PM and a long-cultivated Mollisol (MO). The results showed that clay content and the specific surface area of soil aggregates decreased, while soil organic carbon, aggregate stability, and surface fragment structure increased for all treatments as compared to those for the PM. Mineral fertilization alone did not increase aggregate stability; however, the combination of mineral and organic fertilization increased aggregate stability by 117%. Compared to the PM, the treated soils showed an increase in porosity as determined by synchrotron radiation X-ray micro-computed tomography (SR-µCT). Compared to naturally restored grasslands, the soil under crop rotation with tillage showed a decrease in pore roundness by 15%; however, supplementation with a large amount of organic input during cultivation increased pore roundness. The principal component analysis using all the indicators showed that the soil structure after 8-year cultivation was not comparable to that of the well-developed MO. Our results revealed the development of PM structure under various agricultural practices and highlighted the co-interaction effects of mineral fertilizers and organic inputs on the properties of soil aggregates during the early stage of pedogenesis.

Stoichiometric characteristics drive the soil aggregate stability after 5 years of vegetation restoration in China

Soil stoichiometric characteristics and aggregate stability are affected by vegetation restoration in degraded land. Yet, it is not known that how the aggregate stability is related to soil stoichiometric characteristics under different vegetation restorations. A 5-year in situ experiment was conducted to investigate the effects of vegetation restoration on the composition, stability and stoichiometric properties of soil aggregates. In the northwest part of Beijing, Bromus inermis Leyss. and Medicago sativa L. were planted in a typical area of desertification, and natural restoration was used as control. Boosted regression trees (BRTs) were applied to partition the factors that control aggregate stability. The results showed that the mean weight diameter (MWD) of soil water-stable aggregates under natural restoration (CK) and Medicago sativa L. sowing treatments (AF) was significantly higher than that under the restoration of the Bromus inermis Leyss. sowing treatments (SB). Compared with CK, AF significantly increased the geometric mean diameter (GMD) water stable aggregates, while SB showed the opposite result. AF significantly increased the proportion of soil aggregates &amp;gt;2 mm compared with CK. AF could improve the stability of soil aggregates by increasing the proportion of large aggregates. For the stoichiometric characteristics of the aggregates, AF increased significantly the value of C/P in 0.053−0.125 mm particle size aggregates in all soil layers. The MBC/MBN ratio aggregates at depths of 0–10 cm and 10–20 cm was also significantly increased in the treatment of AF. The BRTs indicated that stoichiometric ratio is the main factor driving the stability of soil aggregates rather than microbial community characteristics and soil nutrients. The C/P is the main driving factor affecting the MWD, in which the overall stoichiometric influence accounts for 46%, followed by the microbial influence of 36%. For the GMD, MBC/MBN is the main driving factor, and the stoichiometric influence accounts for 94%. Our findings indicate that AF is beneficial to the stability of deep soil aggregates, and their stoichiometric characteristics of soil are the key factors affecting the stability of soil aggregates.

Soil aggregate size mediates the impact of different fertilization patterns on the diazotrophic community of mine soils

The development of the mining industry has led to significant environmental pollution around mining sites, affecting the nitrogen (N) cycle and associated microorganisms and disrupting the structure of soil aggregates. In this study, mine soil incubation experiments were conducted under the application of two types of N fertilizer (urea (U) and ammonium chloride (AC)) and nine different fertilization patterns, and the effects of the different N fertilization patterns on soil aggregate properties and diazotrophic community structure were compared. The results showed that carbon (C), phosphorus (P) and N were mainly enriched in megaaggregates (2–4 mm) and macroaggregates (0.25–2 mm). N fertilizer addition decreased the bioavailable heavy metal (HM) content of soil aggregates to different degrees. In addition, N fertilization resulted in significantly higher activities of cellulase, invertase, amylase, urease, protease and phosphatase in microaggregates (<0.25 mm) than in mega- and macroaggregates (p < 0.05). Among the nine fertilization patterns, AC application was performed at a low frequency and high concentration. In most cases, U application resulted in a higher nifH gene abundance than AC application. Specifically, nifH gene abundance in microaggregates in the four U treatments ranged from 9.75 × 106 to 16.63 × 106 gene copies g−1 dry soil, which was significantly higher than that in the control (p < 0.05). Proteobacteria was the major diazotrophic phylum, accounting for 52.9 % to 79.1 %, 46.4 % to 80.3 % and 49.1 % to 81.2 % in mega-, macro- and microaggregates, respectively, followed by Firmicutes and Actinobacteria. The application of N fertilizers had different impacts on soil physicochemical properties, which in turn indirectly affected the abundance and community composition of soil diazotrophs. Among the aggregate properties, microbial nitrogen (MBN) was an important variable that explained the variation in diazotrophic communities (p < 0.05). Our results suggest that the addition of N fertilizer affects the physicochemical properties and the structure and functions of diazotrophic community in soil aggregates.

Effects of polyethylene microplastics on properties, enzyme activities, and the succession of microbial community in Mollisol: At the aggregate level

Soil, as a heterogeneous body, is composed of different-sized aggregates. There is limited data available on the potential role of microplastics (MPs) in microbial properties at the soil aggregate level. In this study, changes in microbial construction and diversity in farmland bulk soil and aggregates induced by polyethylene MPs (PE-MPs) were investigated at a dose of 0.5% (w/w) through 16s rDNA sequencing and enzyme activity measurements of different particle size aggregates in incubated soil. The presence of low-dose PE-MPs increased the proportion of >1 mm soil aggregates fraction, and decreased soil available nitrogen and available phosphorus in bulk soils. Furthermore, low-dose PE-MPs increased bacterial richness and diversity in 1–0.5 and < 0.25 mm fractions and decreased operational taxonomic unit, abundance-based coverage estimator, and Chao1 indices in bulk soil and >1 mm fractions. The levels of predicted functional genes taking part in the biodegradation and metabolism of exogenous substances also increased. At the phylum level, PE-MPs changed the proportion of Proteobacteria and Actinobacteria. The variations in soil aggregate properties were significantly correlated with the bacterial communities’ composition and diversity. This study deepens our perception of the soil microenvironment, microbial community composition, and diversity in response to PE-MPs.

Increased humic materials explain aggregate-protected carbon and nitrogen accumulation in biochar-amended tropical soils

Humic materials make important contributions to soil organic carbon (SOC) and nitrogen (TN) accumulation. However, information on the correlation between humic substances and the accumulation of aggregate-protected C and N in response to biochar application to soils under tropical agroecosystems is limited. Therefore, a replicated field trial was conducted to elucidate the effects of biochar on soil aggregate properties and humic materials, and how these humic compounds affect aggregate-protected SOC and TN in a humid tropical agroecosystem. The treatments included no biochar/ control (CT), 15-Mg biochar ha-1 (BC-15), 30-Mg biochar ha–1 (BC-30), and 30-Mg biochar ha-1 + phosphate fertilizer (BC-30+P). The BC-30 and BC-30+P treatments significantly increased the contents of humic materials (humic and fulvic acids) as compared to the CT. There was a significant increase in the mean weight diameter of soil aggregates by 3- and 4-fold in the BC-30 and BC-30+P treated soils, respectively. Similarly, the application of the BC-30 and BC-30+P treatments yielded significant increases in the soil structural coefficient by 3- and 4-fold, respectively, relative to the CT. A 10% decline in soil bulk density was observed with biochar applied at 30-Mg ha-1. Significant increases in SOC and TN accumulation were observed in the macroaggregates of the biochar-amended soils. An inverse relationship between the degree of polymerization and aggregate-protected C and N was observed, implying that low molecular weight aliphatic compounds favor SOC and TN accumulation with biochar amendments. The important soil property that contributed to SOC and TN accumulation in aggregates was FA, which could be used as an early and sensitive indicator to notice early changes in aggregate-protected C and N accumulation in soils of the humid tropics.

The Impacts of the Hydrological Regime on the Soil Aggregate Size Distribution and Stability in the Riparian Zone of the Three Gorges Reservoir, China

The impoundment of the Three Gorges Reservoir (TGR) has greatly altered the hydrological regime and thus formed a distinctive riparian zone with anti-seasonal inundation and exposure, which may affect the soil aggregate properties in this riparian zone. Yet, the soil aggregate size distribution and stability influenced by the hydrological regime along the step-impounded elevation have rarely been documented. This study aimed to elucidate how the hydrological regime of the TGR affected the aggregate size distribution and stability in the riparian zone. Based on the step-impounded elevation, topsoil samples were collected from four elevation-dependent transects in a middle section of the TGR. Dry-sieving and wet-sieving methods were employed. The results showed that, with a decrease in the elevation gradient, the mass percentage of the &gt;5 mm aggregates significantly decreased, while the proportions of the other size classes presented an increasing trend. Additionally, the mean weight diameter (MWD), geometric mean diameter (GMD), aggregate stability rate (ASR), and percentage of aggregate destruction (PAD) of the fractal dimension showed a successive decrease with a decrease in the elevation gradient, whereas PADMWD, PADGMD, PADASR, and the fractal dimension demonstrated a reverse trend. It can thus be deduced that the hydrological regime of the TGR significantly modified the aggregate size distribution and dramatically reduced the aggregate stability, which may provide a crucial basis for assessing the soil erosion in similar riparian zones.

Linking Rhizosphere Soil Aggregates with Belowground and Aboveground Plant Traits

Rhizosphere soil ecosystems are represented by the diversity of different soil aggregate-size classes, such as large macroaggregates, small macroaggregates, mesoaggregates, and microaggregates. Though these aggregate-size classes represent distinct biological, chemical, and physical properties, little is known about their dynamics and relationships with belowground and aboveground plant traits. In this study, we examined the relationships of various soil aggregate-size classes and their organic carbon contents with many aboveground and belowground soybean plant traits. Our study revealed several novel and interesting relationships between soil structural properties and plant traits. Notably, small macroaggregates represented a major portion of the rhizosphere soil ecosystem of soybean plants while organic carbon contents decreased with decreasing size of soil aggregates. Only microaggregates showed a significant relationship with root architectural traits, such as length and surface area. Among all soil aggregate size classes, the abundance of small macroaggregates and the organic carbon contents of microaggregates were better correlated with plant traits. In general, organic carbon contents of different soil aggregate-size classes showed positive correlations with leaf trichome density (defense traits) and major macronutrients, such as root P, K, and S contents; while there were mostly negative correlations with some micronutrient (Ca, Mn, Zn, Cu, B, and Mg) contents of roots and shoots. However, the abundance of small macroaggregates mostly positively correlated with the mineral contents of plant roots and shoots. Collectively, the positive and negative correlations of organic carbon contents of different soil aggregate-size classes with trichomes (defense) and physiological traits (micro-mineral contents) suggest their significance in plant nutrition and defense. Though our results suggest the relationships of soil aggregate properties with aboveground and belowground traits, further research is needed to discern the role of soil structural traits in mediating plant growth, development, defense, and physiology.

Soil-Available Nutrients Associated with Soil Chemical and Aggregate Properties following Vegetation Restoration in Western Sichuan, China

The status and drivers of soil-available nutrients in plant-recovered soils are not fully understood, limiting our ability to explore the role of soil-available nutrients in soil geochemical cycling and ecosystem sustainability. Here, we combined the spatial distribution of soil-available nutrients and chemical and aggregate properties from six soil types (subalpine meadow soil, meadow soil, dark brown soil, brown soil, yellow-brown soil, and cinnamon soil) and three horizons (a leaching horizon, sediment horizon, and parent material horizon) to study the status and drivers of soil-available nutrients. Our findings reveal that the soil-available nitrogen (AN) ranged from 72.33 to 169.67 mg/kg, the soil-available phosphorus (AP) ranged from 1.77 to 75.90 mg/kg, and the soil-available potassium (AK) ranged from 46.43 to 88.55 mg/kg in the six soil types. The subalpine meadow soil and the dark brown soil had the highest soil AN, with means of 169.67 and 139.35 mg/kg, respectively. The brown soil had the highest soil AP, with a mean of 75.9 mg/kg, and the dark brown soil and the brown soil had the highest soil AK, with means of 83.49 and 88.55 mg/kg, respectively. The results show that the soil types and soil depths had a significant impact on the status of AN, AP, and AK (p &lt; 0.05). Moreover, a higher cation exchange capacity (CEC), the macro-aggregate contents (with 2–1 mm and 1–0.5 mm particle sizes) of the non-water-stable aggregates, and the macro-aggregate content and stability (2–1 mm particle size and geometric mean diameter (GMD) of the water-stable aggregates were deemed to facilitate soil-available nitrogen because of the positive correlations (p &lt; 0.05). Lower exchangeable cations (ECs) and the micro-aggregate content (≤0.1 mm particle size) of the water-stable aggregates and higher soil cations helped in the accumulation of soil-available phosphorus and soil-available potassium, respectively. Moreover, the regulation of the soil chemical and aggregate properties was found to vary with soil type and horizon in a correlation analysis. Together, our results provide insights into the importance of chemical and aggregate properties in regulating soil nutrient availability across soil types, as well as providing strong support for the inclusion of soil resource utilization in regional forest restoration and management.

Improvements in soil physical properties after long-term manure addition depend on soil and crop type

Manure application and crop rotation are common agricultural practices that can alter soil physical properties and affect soil functions. In this study, we assessed the effect of long-term manure fertilization (24 to 126 years) and crop type on soil hydraulic, aggregate and pore structural properties. Samples were collected from three long-term experiments (LTEs) in Sweden (silty clay, SiC), Germany (silt loam, SiL) and Denmark (sandy loam, SL). Measurements included water retention, air permeability and gas diffusivity measured at five matric potentials −3, −5, −10, −30 and −50 kPa, saturated hydraulic conductivity (Ksat), bulk density (ρb), and water-stable aggregates (WSA). The treatments at the three LTEs included various manure rates and crop sequences (winter wheat, maize, spring barley, and grass/clover). Results showed that long-term manure addition reduced ρb by an average of 3–6% for all three sites, and improved soil water retention, plant available water and WSA for most investigated plots. However, increasing manure rates for the SiL and SL sites did not result in further improvements in soil water retention, ρb and water-stable aggregates. The effect of manure on soil pore size distribution, gas transport, and Ksat varied with soil and crop type. Manure increased the porosity of pores < 30 µm in the two fine-textured sites and increased the porosity of pores > 30 µm for wheat and maize plots in the SL site. Manure improved gas transport and Ksat in the wheat plots and decreased these properties in the barley plots regardless of soil texture. The maize plots in the SL site had well developed pore structure, while the pore structure in the SiL site was relatively poor. Grass plots had poorer gas transport than maize plots in the SL site despite the manure addition. The study shows that improvements in soil physical and chemical properties arising from manure application largely depend on the crops grown and the soil texture.