Water-stable Aggregate Stability Research Articles

Effects of Varied Tillage Practices on Soil Quality in the Experimental Field of Red-Soil Sloping Farmland in Southern China

Red-soil sloping farmland in southern China plays a crucial role in the local economy and food production. However, improper tillage practices have resulted in topsoil degradation and deteriorating soil quality. This study investigated changes in soil physico-chemical properties under four tillage methods—cross-slope ridge tillage (RT), down-slope ridge tillage (DT), plastic mulching (PM), and conventional tillage (CT)—on red-soil sloping farmland. The study applied the Soil Management Assessment Framework (SMAF) to assess the influence of these tillage practices on soil quality. Results indicated that PM can increase the total porosity of the soil, reduce soil bulk density, and simultaneously decrease soil surface-water evaporation, significantly improving the soil’s water-retention capacity. RT improved soil aggregate formation and stability, leading to increased macro-aggregate content, mean weight diameter, and soil water-stable aggregate stability rates. PM and RT effectively preserved soil nutrients like total nitrogen and organic matter, although PM lowered soil pH, potentially causing acidification. RT demonstrated the highest soil quality, with PM following. Crop growth positively impacted soil macro-aggregate content and stability, showing continuous improvement in soil structure and quality (p < 0.05). Priority should be given to RT in red-soil sloping farmland, followed by PM and CT, while avoiding DT if possible. This research furnishes valuable scientific substantiation for the selection of optimal tillage practices in the preservation of soil quality on red-soil slopes.

Spatial Distribution and Relationship between Slope Micro-Topography Changes and Soil Aggregate Stability under Rainfall Conditions

Natural rainfall affects the stability of soil aggregates by the kinetic energy of the rain changing the morphological characteristics of slope micro-topographic factors. Although the relationship between the stability of soil aggregates and micro-topography is not very significant at the slope scale, there are also rules to be found. This study aims to explore the relationship between slope micro-topography and aggregate stability, and to observe the spatial distribution of aggregate stability after water erosion. In this study, a digital elevation model of slope micro-topography was established by using a three-dimensional laser scanner to observe the slope erosion changes after rainfall events and clarify the spatial changes of soil aggregate stability and its relationship with slope micro-topography by combining geostatistics and generalized additive model (GAM). The results showed that the area of serious water erosion in the lower part of the slope accounted for 38.67% of the slope, and the micro-topography index of the slope changed obviously after rainfall, with the slope increasing by 3.1%, the surface roughness increasing by 5.34%, the surface cutting degree increasing by 26.67%, and the plane curvature decreasing by 61.7%. In addition, the GAM model was used to fit the multivariate variables. The results revealed that the slope and surface roughness were the key factors affecting the stability of water-stable aggregate. The slope and surface roughness were negatively correlated with the stability of water-stable aggregates.

Contribution of soil aggregate particle size to organic carbon and the effect of land use on its distribution in a typical small watershed on Loess Plateau, China

Soil organic carbon (SOC) is an important pool in the global carbon cycle, playing a vital role in moderating atmospheric CO2 concentrations. Soil is the largest carbon pool in terrestrial ecosystems and, as the basic unit of soil structure, soil aggregates are key to protecting soil carbon pools. However, the influence of soil aggregate particle size, SOC distribution, and the contribution of different particle sizes to SOC is still unclear, particularly under different land use types. In this study, soil samples were collected from five land use types (slope farmland (SF), forest (FL), grassland (GL), shrubland (SL), and terraced field (TF)) in a typical small watershed in the Loess Plateau, China. We analyzed the soil aggregate particle size, composition, and stability after dry and wet sieving, SOC content of different particle sizes in aggregates, and the effects of different aggregate particle sizes and land use on the distribution of SOC. The results showed that, the surface soil (0 ∼ 20 cm) water-stable aggregates were relatively stable, particularly under FL, the mean weight diameter (MWD) value was 2.16 mm. Deep soil (40 ∼ 60 cm) non-water stable aggregates were more stable, and GL was optimal, the MWD value was 3.94 mm. SOC and total nitrogen (TN) were significantly correlated with water-stable aggregate stability indicators (p < 0.01). The SOC content in the small aggregates (0.25 ∼ 2 mm) was the highest and lowest in the microaggregates (<0.25 mm) under different land use. The carbon/nitrogen (C/N) ratio of microaggregates was significantly higher in SF (the C/N ratio was 23.17) and GL (the C/N ratio was 31.04) than in other land uses (p < 0.01) in the 20–40 cm soil layer. In surface soil, small aggregates contributed>50% to SOC in SF and TF. In deep soil, small aggregates under all five land uses made the largest contribution rate to SOC at 57%. These findings indicate that carbon sequestration in the study area can be improved by a combination of appropriate soil management with ecological construction to increase the content of small aggregates, strengthen the fixation and protection of SOC, and reduce carbon emissions in the soil.

Analysis of Slope Stability with Different Vegetation Types under the Influence of Rainfall

Rainfall-prone shallow landslides account for one-fifth of the global land area, and rainfall is critical to the mechanics and hydrology of shallow slopes. In typical geological disaster-prone areas, the hydrodynamic responses of slopes with different vegetation types under rainfall conditions require further study. The purpose of this study was to analyze the hydraulic stability of soils with different vegetation types under rainfall conditions and their effects on slope stability. Thus, the soil–water characteristic curves and water-stable aggregate characteristics of soils with three vegetation types were analyzed. A two-dimensional finite element model was used to simulate the slope stability of extreme rainfall environments with different rainfall durations. The results showed that the matric suction of soil with trees was less affected by rainfall with a better stability of water-stable aggregates than that of soil with shrubs and grass. The plastic strain cloud map showed that the maximum plastic strain occurred at the toe of the slope. In addition, the potential slip depth of slopes with trees was smaller than that of slopes with shrubs and grass. Under the two rainfall durations, the factor of safety (FoS) of slopes with trees changed by 0.06, whereas that of slopes with shrubs and grass changed by 0.1. The findings of this study provide valuable insights into changes in the stability of slopes with different vegetation types under varying rainfall conditions. It is of great significance to provide a scientific basis for the application of ecological measures in the prevention and control of mountain disasters and guide the implementation of appropriate land management measures.

Soil health assessment for different tillage and cropping systems to determine sustainable management practices in a humid region

Various soil indicators can be chosen for soil health assessment. The important indicators representing overall soil health need to be carefully selected to reduce the cost and time involved in sampling and testing, which can be achieved by establishing a minimum data set (MDS). The objective of this paper was to identify the indicators that are important for assessing soil health in northeast Mississippi and establish an MDS. Values for chemical, physical and biological indicators obtained from three treatments (no-fertilized control, no-organic fertilizer and poultry litter) in five different field experiments were used to screen MDS. The methodology followed a combination of principal component analysis (PCA), cluster analysis and expert’s opinion (EO) method. Results showed that the correlation between the MDS and total data set (TDS) was high (R2 =0.94). The chosen MDS included four chemical indicators (pH, organic carbon, total nitrogen and Mehlich-3 phosphorus), three physical indicators (bulk density, water-stable aggregate stability, available water capacity), and two soil biological indicators (dehydrogenase activity, heterotrophic plate count). When the selected chemical MDS was applied to all treatments of the five experiments, the MDS and TDS data fitted well (R2 =0.81), indicating that the soil indicators included in the MDS were the most important for soil health in this study. In conclusion, an MDS for soil health assessment was established for the experiments in northeast Mississippi. The results can provide fundamental guidance for researchers, growers, and stakeholders to evaluate soil health and optimize soil management.

Soil depth determine the ecological stoichiometry of soil aggregates after returning ancient rice terraces to forest

Soil carbon-nitrogen-phosphorus (CNP) ecological stoichiometry is an effective means of reflecting soil nutrient status, transformations, and limitations, but the effect of returning ancient rice terraces to forest on soil CNP stoichiometry is still unclear at the aggregate scale in the subtropical hilly areas of southern China. This study explored how the CNP content and stoichiometry of soil water-stable aggregates responded after returning ancient rice terraces to forest in the soil layer depth of 0–60 cm in subtropical hilly areas. The results showed that the stability, soil organic carbon (SOC), total nitrogen (TN), C/P, and N/P ratios of soil aggregates decreased significantly with soil depth in ancient rice terraces, Chinese fir (Cunninghamia lanceolata), and moso bamboo (Phyllostachys pubescens). The proportion of macroaggregates decreased gradually and the proportion of microaggregates increased significantly after the soil depth increased. Returning ancient rice terraces to Chinese fir was more conducive to increasing the SOC, TN, C/P, and N/P ratios of soil aggregates, which may be related to plant litter biomass. Eta squared analysis showed that soil depth had a greater impact on soil aggregate stability (34 %, 38 %, and 46 %), CNP content (34 %–45 %), and stoichiometry (34 %–57 %) than land use types and their interactions. These findings indicated that returning ancient rice terraces to Chinese fir and moso bamboo can significantly alter soil water-stable aggregate stability, CNP content, and stoichiometry, and soil depth plays an extremely important role in changing them. Future research should focus on the ecological impacts of soil depth on agroforestry ecosystems.

Effects of large-grained activated humic acid fertilizer on soil aggregates and organic carbon in apple orchard soil

The new large-grained activated humic acid fertilizer (LAF) can significantly reduce the amount of chemical fertilizer application and stable fruit yield. Understanding its impacts on soil aggregates and organic carbon is an important basis for revealing its role in driving soil structure of apple orchard. There were four LAF treatments: LAF1 (full fertilization, fertilization period and mass ratio (the same below), germination stage: fruit expansion stage: maturity stage=3:4:3), LAF2 (full fertilization, germination stage: fruit expansion stage: maturity stage=2:3:5), LAF3 (fertilizer application reduction by 1/4, germination stage: fruit expansion stage: maturity stage=2:3:5), LAF4 (fertilizer application reduction by 1/3, germination stage: fruit expansion stage: maturity stage=2:3:5); with no fertilization as control (CK). In a four-year pot experiment, we examined the composition, stabi-lity and organic carbon content of soil aggregates under different fertilization treatments. The results showed that: 1) compared with CK, each treatment of LAF increased the content of &gt;2 mm and 2-0.25 mm aggregate by 53.4%-77.5% and 12.3%-17.0%, respectively. The application of LAF significantly increased the content of soil water stable aggregates, and such effects were positively related with application amount. The content of soil water stable aggregate was the highest in the LAF1 treatment. 2) There was no significant difference in aggregate content of each particle size among LAF treatments, with the proportion of aggregate content of 2-0.25 mm particle size being the highest. 3) Compared with CK, all LAF treatments significantly increased the average weight diameter (MWD) and geometric mean diameter (GMD), and reduced the fractal dimension (D). LAF1 treatment had the highest MWD and GMD values, and had the strongest effect on the stability of soil aggregates. 4) Except for LAF4 treatment, the content of soil organic carbon in other LAF treatments was significantly higher than that in CK, and the content of soil organic carbon in LAF2 treatment was the highest. All LAF treatments increased the organic carbon content of soil aggregates with each particle size. LAF1, LAF2, and LAF3 treatments significantly increased the organic carbon of aggregates with particle size &gt;2 mm. Particle size &gt;2 mm had the highest contribution to the total organic carbon. The contribution rate of water stable large aggregate organic carbon to total organic carbon of LAF treatment was significantly higher than that of CK, which was all higher than 66.0%, and that of LAF1 treatment was the highest. In conclusion, the application of LAF enhanced the formation and stability of water stable aggregates and increased organic carbon content of aggregates in apple orchard soil, with the best performance of the full application. The application of LAF could be used as an effective measure to improve soil structure and fertility in apple orchard.

Effects of saline-water furrow irrigation on the stability of soil water-stable aggregates in cotton field

It is of great importance to explore the effects of saline-water furrow irrigation on soil water-stable aggregates for safe and efficient utilization of saline water resources. We conducted a long-term cotton experiment with six levels of saline-water furrow irrigation (1, 2, 4, 6, 8, 10 g·L-1) since 2006 and analyzed the variations of soil salinity and water-stable aggregates in the 10th and 15th years under saline irrigation. The results showed that soil salinity in the 0-30 cm layer at the ditch increased with increasing salinity level of irrigation water. There were significant differences between the 6, 8, 10 g·L-1 and 1 g·L-1 treatments. Soil salinity in each treatment increased gradually with increasing soil depth. Saline-water furrow irrigation tended to reduce the stability of soil water-stable aggregates. When the salinity level of the irrigation water was ≥6 g·L-1, the mass fraction of macroaggregates (&gt;0.25 mm), the mean weight diameter and geometric mean diameter of water-stable aggregates significantly decreased. In contrast, the fractal dimension and mean weight specific surface area increased significantly. The stability of soil water-stable aggregates decreased with soil depth in all treatments. Under the condition of saline-water furrow irrigation for several years, there was no accumulation of soil salinity and instability of water-stable aggregates in the 0-30 cm soil layer at the ditch with each passing year. With the irrigation scheduling of this study, saline-water furrow irrigation with salinity ≤4 g·L-1 did not affect soil salinity and water-stable aggregate stability of cotton field in this area.

Effect of Long-Term Fertilization on Aggregate Size Distribution and Nutrient Accumulation in Aeolian Sandy Soil.

Soil aggregates are the material basis of soil structure and important carriers of nutrients. Long-term application of organic and inorganic fertilizers can affect the composition of soil aggregates to varying degrees, which in turn affects the distribution and storage of soil nutrients. We report the results of a 15-year long-term field-based test of aeolian sandy soil and used the wet sieve method to analyze the stability of water-stable aggregates, as well as the distribution characteristics of nutrients in different particle size aggregates. Our results show that long-term application of organic fertilizer (M3) and combined organic–inorganic treatments (NPK1-M1, NPK1-M2, and NPK1-M3) help to increase the amount of organic carbon, inorganic carbon, and cation exchange in the macro-aggregates, and the improvement rates are 92–103%, 8–28%, and 74–85%, respectively. The organic content of the fertilizers also promotes the formation of macro-aggregates, and the stability of aggregates increase from 0.24 to 0.45. In contrast, the application of inorganic fertilizers (NPK1, NPK2, and NPK3) has no marked effect on the formation and stability of macro-aggregates; the application of inorganic fertilizers can merely maintain the organic carbon content of the soil. Correlation analysis shows that the application of organic fertilizers and chemical (inorganic) fertilizers containing phosphorus and potassium can markedly increase the content and reserves of available phosphorus and potassium across all aggregate sizes, and there is a significant positive correlation between these parameters and the amount of applied fertilizer (p < 0.05). Aggregates of various sizes in aeolian sandy soils in arid areas have the potential for greater nutrient storage. Therefore, organic fertilizers can be used in the agricultural production process to improve soil structure and fertility.

Distribution and stability of water-stable aggregates as affected by long-term cattle manure application to saline-sodic soil in the black soil region of northeastern China

Distribution and stability of water-stable aggregates as affected by long-term cattle manure application to saline-sodic soil in the black soil region of northeastern China

Effects of different nitrogen application rates on soil water stable aggregates and N2O emission in winter wheat field.

Excessive nitrogen application would deteriorate soil structure and increase greenhouse gas emission. We set up six treatments, i.e., N0, N120, N180, N240, N300and N360(nitrogen application rates of 0, 120, 180, 240, 300 and 360 kg·hm-2, all straws returned into the field in situ) in the nitrogen fertilizer experimental site to investigate the effects of different nitrogen application rates on soil N2O emission, soil water-filled porosity (WFPS), soil temperature, nitrate and ammonium contents, composition and stability of water stable aggregates in winter wheat filed in 2018-2020. The results showed that there was a significant positive correlation between soil N2O emission and nitrogen application rate. There was no correlation between WFPS and nitrogen application rate. Soil temperature in the 0-10 cm layer decreased significantly with the increases of nitrogen application rates. There was a significant positive correlation between nitrate and ammonium contents and nitrogen application rate. With the increases of nitrogen application rates, the content of water stable aggregates with diameter &gt;2 mm decreased, while that of water-stable aggregates with diameter &lt;0.5 mm increased. The particle size of soil water-stable aggregates also decreased gradually. There was a significant negative correlation between nitrogen application rate with mean weight diameter (MWD) and geometric mean diameter, while no correlation with fractal dimension. The fitting equation between MWD and N2O emission flux was y=3928.3e-2.171x (R2=0.55, P&lt;0.001), indicating that N2O emission increased markedly as MWD decreasing. The increases in nitrogen application rate reduced soil temperature in the 0-10 cm layer, increased nitrate and ammonium contents, decreased the average particle size of soil water stable aggregates, and the stability of soil aggregates, and increased soil N2O emission.

Exogenous Glomalin-Related Soil Proteins Differentially Regulate Soil Properties in Trifoliate Orange

Glomalin-related soil protein (GRSP) is a specific glycoprotein secreted into the soil by hyphae and spores of arbuscular mycorrhizal fungi that have many potential functions. It is not clear whether exogenous GRSP has an effect on plant growth and soil properties or whether the effects are related to the type of GRSP used. In this study, trifoliate orange (Poncirus trifoliata L. Raf.) seedlings were used to analyze the effects of easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) at a quarter-, half-, and full-strength concentration on shoot and root biomass as well as soil properties The results showed that, at different strengths, exogenous EE-GRSR significantly increased shoot and root biomass compared to the control, which displayed the most significant effects from the half-strength EE-GRSP. In contrast, DE-GRSP, at various strengths, significantly reduced shoot and root biomass. Furthermore, the application of exogenous EE-GRSP stimulated soil water-stable aggregate (WSA) content at 2–4 mm and 0.5–1 mm sizes, while DE-GRSP strongly reduced WSA content at the 2–4 mm, 1–2 mm, 0.5–1 mm, and 0.25–0.5 mm sizes, consequently leading to an increase or decrease in the WSA stability, according to the mean weight diameter. However, exogenous EE-GRSP decreased soil pH and DE-GRSP increased it, which was related to WSA stability. Exogenous EE-GRSP almost significantly increased soil acidic, neutral, and alkaline phosphatase activity at different strengths, while exogenous DE-GRSP, also at different strengths, significantly inhibited soil acidic phosphatase activity. The application of both exogenous EE-GRSP and DE-GRSP increased the organic carbon content of the soil. This study concluded that exogenous GRSP exerted differential effects on plant biomass and soil properties, and EE-GRSP can be considered as a soil stimulant for use in citrus plants. To our knowledge, this is the first report on the negative effects of exogenous DE-GRSP on plant biomass and soil properties.

Freeze-thaw cycles aggravated the negative effects of moss-biocrusts on hydraulic conductivity in sandy land

Moss-biocrusts (BCs) play an essential role in soil stabilization, but it reduces soil hydraulic conductivity, hindering precipitation convert to soil water. Freeze-thaw cycles (FTCs) is a natural phenomenon, which can alter soil properties, causing widespread concern. However, few studies have focused on the effects of FTCs on hydraulic conductivity in BCs, which may alter the negative effects of BCs on hydraulic conductivity. We conducted an in-situ FTCs simulated experiment in BCs and bare sand (BS), to analyze the response of particle-size composition, water-stable aggregates and water repellency (WR) to FTCs, and their effects on saturated hydraulic conductivity (Ks). The results showed that the existence of BCs had affected water-stable aggregates, particle-size composition, WR and Ks. Compared with BS, the percentage of clay-size particle content increased by 44% and 60% in BCs layer and its underlying soil, respectively. The stability of water-stable aggregates was 19% higher in BCs than the measured stability in BS. Ks of BS was 2.4 times higher than that of BCs, and the increasing percentage of water-stable aggregates larger than 5 mm would reduce Ks in sandy land. FTCs had the significant effects on water-stable aggregates, WR and Ks. WR and Ks of BCs were decreased 57% and 25% after FTCs, respectively. Moreover, after FTCs, the percentage of soil water-stable aggregates > 5 mm reduced 19%, while 1–5 mm increased 18%. WR and sand content were significantly and negatively correlated with Ks, while clay content and the percentage of soil water-stable aggregates > 5 mm were significantly and positively correlated with Ks in BCs. Our results indicated that BCs and FTCs had a significant and negative effects on Ks. FTCs further decreased the hydraulic conductivity, which was not conductive to the supply of meltwater to soil water reservoir in the period of winter and early spring.

Changes of Soil Water–Stable Aggregates after Rice–Crawfish Rotation in Low-lying Paddy Fields: A Case Study in Jianghan Plain of China

ABSTRACT Crawfish aquaculture in low-lying paddy fields is implemented after middle-season rice is harvested, namely, Rice–crawfish rotation (RCR), and has been practiced for almost 30 years in Jianghan plain of China. However, little information is available on the effects RCR has on soil aggregates and water stability. Some soil properties were obtained by field sampling and analysis including mean weight diameter of soil aggregate (MWD), geometric mean diameter (GMD), fractal dimension (FD), and agglomerate with particle size more than 0.25 mm (R0.25) after RCR was implemented in low-lying paddy fields. Soil samples were taken from paddy fields that are used separately for RCR and mid-season rice monoculture (CK), and the depth of sampling on a soil profile is 0–20, 20–40, and 40–60 cm from the top to below. RCR’s duration in different paddy fields is 1, 7, 13, 18, and 23 years, marked as RC1, RC7, RC13, RC18, and RC23, respectively. The results showed that in the 0–60 cm soil layer, the water-stable aggregates of soil in the paddy field for RCR were mainly composed of large aggregates (particle size more than 5 mm) and micro-aggregates (particle size less than 0.25 mm), and with the increase of RCR’s duration, aggregate content is increased for large aggregates and declined for micro-aggregates; at the same time, the RCR for long term increases the mean weight diameter, geometric mean diameter and R0.25 of each soil layer, reduces the Fractal dimension, where there is a significant positive correlation (P < 0.05) between mean weight diameter (geometric mean diameter) and R0.25, a significant negative correlation (P < 0.05) between mean weight diameter (geometric mean diameter) and fractal dimension; the content of aggregate (<0.25 mm) is significantly negatively correlated with mean weight diameter (P < 0.05), geometric mean diameter, R0.25, respectively, and positive correlative with fractal dimension. Therefore, it was determined that RCR for long-term production is conducive to form soil water-stable large aggregates, correspondingly, to reduce micro-aggregates and improve the stability of water-stable aggregates.

Soil water-stable aggregates and microbial community under long-term tillage in black soil of Northern China.

Long-term frequent tillage would cause black soil degradation and serious soil erosion as soil microbial communities and soil structure are extremely sensitive to tillage process. However, there is no unified conclusion on the relationship between the distribution of soil water-stable aggregates (WSAs), and microbial community construction and diversity under long-term tillage in black soil during different seasons. In this study, we used wet-sieving method to evaluate the composition and stability of soil WSAs and employed Illumina MiSeq high-throughput sequencing technology to study the diversity, taxonomic composition and co-occurrence network properties of microbial community, comparing outcomes between uncultivated soil and long-term cultivated soil for 60 years in Keshan farm of Heilongjiang Province. The results showed that after long-term tillage, the proportion of larger than 1 mm WSAs reduced by 34.17-51.37%, and the stability of WSAs, soil pH, organic matter (OM), total nitrogen (TN) contents decreased significantly in all seasons (P < 0.05), while soil available phosphorus (AP) and available potassium (AK) contents increased remarkably (P < 0.05). The diversity of bacteria increased, while that of fungi decreased. Soil fungal communities were more susceptible to long-term tillage than bacterial and archaeal communities. Actinobacteria mainly exist in large WSAs (˃1 mm), and when their relative abundance is high, it is beneficial to improve the water-stability of black soil; while Proteobacteria and Gemmatimonadetes may exist in small WSAs (˂1 mm), whose high relative abundance will weaken the water-stability of black soil. The experimental results provide a scientific theoretical basis for sustainable utilization of black soil.

Effects of biochar on waterlogging and the associated change in micro-ecological environment of maize rhizosphere soil in saline-alkali land

Saline-alkali soils of northern China are prone to waterlogging after degradation caused by overuse. The effects of biochar (40 t/ha) were tested relative to the physico-chemical properties of maize rhizosphere soil, the composition and function of the soil bacterial community, and its response to sudden waterlogging. Biochar treatment decreased the pH and bulk density of the soil and increased soil organic carbon (SOC), available nitrogen (AN), and available phosphorus (AP). The relative abundance of bacteria (Proteobacteria, Actinobacteria, Bacteroidetes, and Nitrospirae) also increased, along with the activities of soil enzymes, such as dehydrogenase, β-glucosidase, and alkaline phosphomonoester. The response of soil microbial enzymes to biochar addition was induced by changes in the soil physical properties (pH, soil moisture content, and soil respiration (BR)). Changes in the bacterial community structure were driven by soil nutrients and physical characteristics (AN, AP, SOC, pH, moisture, water-stable aggregate stability rate, BR, and bulk density). After waterlogging, soil with biochar demonstrated high water permeability and improved soil respiration. The relative abundance of soil bacteria and enzyme activities remained higher in the biochar plot than in the no-biochar plot. Biochar maintained the growth and vitality of maize roots in unfavorable environmental conditions, thus ensuring high yields.

Physicochemical determinants in stabilizing soil aggregates along a hydrological stress gradient on reservoir riparian habitats: Implications to soil restoration

Stability of soil aggregates, playing a significant role in soil quality, has been greatly impacted by wetting-drying cycles. Yet, determinants in stabilizing soil aggregate structure have been rarely clarified under the hydrological stress. Therefore, under the hydrological stress, this study evaluated the relative importance of soil physicochemical properties in stabilizing soil aggregates on the water level fluctuating zones of the Three Gorges Reservoir riparian at China's Yangtze River. Water stable aggregates of soils (large macroaggregates: > 2 mm, small macroaggregates: 0.25–2 mm, microaggregates: 0.053–0.25 mm, silt- and clay-sized aggregates: 0–0.053 mm) were measured by wet sieving, and soil aggregate stability was evaluated as mean weight diameter (MWD), geometric mean diameter (GMD) and fractal dimension (D) of soil aggregate and soil erodibility parameter (K). Physicochemical properties of the riparian soils were analyzed as total carbon, nitrogen, organic matter, phosphorus and potassium content, C/N ratio, soil mechanical composition, pH, bulk density and moisture content. The results indicated that soil total carbon, nitrogen, organic matter, phosphorus and potassium were highly concentrated in the areas under strong hydrological stress; the pH was mainly alkalinity, pH value and bulk density both decreased along the incremental stress gradient. The findings revealed that the proportion and stability of water stable aggregates were affected by hydrological stress, and stability indices were interpreted by pH, C/N ratio, potassium and silt contents. Aggregates showed the highest and lowest stability under intermediate and strong stress, respectively, however, no significant difference was found between weak and none stress. Finally, our results suggested that the riparian ecosystem may have the ability of autogenic restoration for soil stability. Under intermediate hydrological stress level, autogenic restoration with less human intervention would be recommended for stabilizing the riparian soil. However, under strong hydrological stress, anthropogenic restoration is still needed to stabilize soil structure and reduce soil erosion in the reservoir riparian habitats.

Changes in soil properties and erodibility of gully heads induced by vegetation restoration on the Loess Plateau, China

Soil erosion on the Loess Plateau of China is effectively controlled due to the implementation of several ecological restoration projects that improve soil properties and reduce soil erodibility. However, few studies have examined the effects of vegetation restoration on soil properties and erodibility of gully head in the gully regions of the Loess Plateau. The objectives of this study were to quantify the effects of vegetation restoration on soil properties and erodibility in this region. Specifically, a control site in a slope cropland and 9 sites in 3 restored land-use types (5 sites in grassland, 3 in woodland and 1 in shrubland) in the Nanxiaohegou watershed of a typical gully region on the Loess Plateau were selected, and soil and root samples were collected to assess soil properties and root characteristics. Soil erodibility factor was calculated by the Erosion Productivity Impact Calculator method. Our results revealed that vegetation restoration increased soil sand content, soil saturated hydraulic conductivity, organic matter content and mean weight diameter of water-stable aggregate but decreased soil silt and clay contents and soil disintegration rate. A significant difference in soil erodibility was observed among different vegetation restoration patterns or land-use types. Compared with cropland, soil erodibility decreased in the restored lands by 3.99% to 21.43%. The restoration patterns of Cleistogenes caespitosa K. and Artemisia sacrorum L. in the grassland showed the lowest soil erodibility and can be considered as the optimal vegetation restoration pattern for improving soil anti-erodibility of the gully heads. Additionally, the negative linear change in soil erodibility for grassland with restoration time was faster than those of woodland and shrubland. Soil erodibility was significantly correlated with soil particle size distribution, soil disintegration rate, soil saturated hydraulic conductivity, water-stable aggregate stability, organic matter content and root characteristics (including root average diameter, root length density, root surface density and root biomass density), but it showed no association with soil bulk density and soil total porosity. These findings indicate that although vegetation destruction is a short-term process, returning the soil erodibility of cropland to the level of grassland, woodland and shrubland is a long-term process (8–50 years).

Characteristics of soil stability and carbon sequestration under water storage and drainage model

This research was conducted to investigate the influence of saline alkali soil on soil physical properties, stability and organic carbon storage under water storage and drainage, and to provide scientific basis for improving soil quality in Fuping County of Shaanxi Province, China. Saline alkali soil model test was conducted and the process was assessed with two different methods: i) traditional drainage and ecological water storage, measure and analyze 0-30 cm soil bulk density, porosity, field water capacity, mean mass diameter (MWD), geological mean diameter (GMD), stability of water stable aggregate (WASR), aggregate destruction rate (PAD), fractal dimension (D) and; ii) organic carbon storage, comprehensively analyze the relationship between stability index and soil organic carbon. The results show that: (1) compared with traditional drainage treatment, water treatment may effectively reduce the soil bulk density by 1.3%-4.2%, and improve soil porosity and field capacity at the same time; (2) under dry and wet screen treatment, soil stability, the water storing treatment is higher than the drainage treatment. Performance trend of soil MWD and GMD increases with the increase of soil depth. The stability of soil water stable aggregates increased 14.5%-53.4%. The average aggregate destruction rate was 3.2% lower than that of the drainage treatment and the difference is obvious (P< 0.05). (3) Soil organic carbon content and organic carbon storage in 0-30 cm soil layer could be increased effectively by water storage. Both of them were 13.4%-27.9% and 9.9%-18.8% higher than the drainage treatment. (4) There is a negative correlation among average aggregate destruction rate, fractal dimension and soil organic carbon storage. The correlation coefficient is, respectively, R2=0.86 and R2=0.94, and the difference is obvious (P<0.05). To sum up, the water storage treatment can effectively improve the soil quality, improve soil stability and soil organic carbon storage, which can be a good control of saline alkali soil.

Mycorrhizal hyphal disruption induces changes in plant growth, glomalin-related soil protein and soil aggregation of trifoliate orange in a core system

By breaking up soil, tillage often disrupts mycorrhizal extraradical mycelium (ERM). In a core having four windows covered with 37-μm mesh in a perspex box, trifoliate orange (Poncirus trifoliata) seedlings were colonized with an arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae. The core was rotated weekly at 180° around vertical axes, in order to simulate ERM disruption. After 13 such rotations, root mycorrhizal colonization, soil hyphal length inside and outside the core, and plant biomass were substantially reduced. On the other hand, mycorrhizal inoculation without disruption of ERM (static core) was associated with significant increase in biomass production, compared with disruption of ERM (rotating core). Disruption of ERM (rotating core) inhibited the production of easily-extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP) inside the core under mycorrhization, due to breakdown of ERM. Mycorrhization markedly increased soil organic carbon content, distribution of water-stable aggregate (WSA) at 0.5–4mm size and mean weight diameter (MWD), whereas core rotation showed a negative effect on MWD and the percentage of WSA within 1–4mm size under mycorrhization and within 0.25–2mm size under non-mycorrhization. It was proposed that soil tillage, in terms of the core rotation, strongly disrupted ERM network, which adversely influenced EE-GRSP and T-GRSP production and plant growth under mycorrhization, subsequently weakening the GRSP functioning on WSA stability.