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Herbaceous plants influence soil hydraulic conductivity by changing soil macropore structure through their root systems, but the effects of different root types on macropore structure have yet to be clarified. In this study, soil column experiments were conducted to investigate temporal variations in soil macropores and saturated hydraulic conductivity, as influenced by herbaceous plants with fibrous roots (Cynodon dactylon) and taproots (Medicago sativa L.). Computed tomography (CT) scanning was used to quantify soil macropore indices, and the saturated hydraulic conductivity (Ks) was measured from April to November after 3, 5, and 7 months of sowing. The results showed that both soil macropore indices and Ks increased with grass growth. The taproots had macroporosity (MP), macropore diameter (MD), and global connectivity (Γ) values that were 1.94, 2.76, and 2.45 times higher than fibrous roots, which are more efficient at increasing the number of soil macropores (PN). This resulted in higher Ks values for the fibrous roots during the experimental period than for the taproot herbs. For both plants, the top 5 cm of soil had a higher macropore index and Ks values than the bottom layer. The Ks for fibrous roots was most closely related to PN. On the other hand, Ks for the taproot soil column was most closely related to MP and MD. Based on a combination of soil macropore indices, functions were established to predict Ks values for fibrous root and taproot herbaceous plants. [ABSTRACT FROM AUTHOR]

The protection and management of the wetland should consider the changes in hydrological connectivity (HC) caused by the structural modifications of the soil macropores. The main purpose of our work is to clarify and quantify the influence of the soil macropores volume on the vertical soil hydrodynamic process mechanically and statistically by taking the form of a case study in Yellow River Delta (YRD), and further reveal the vertical hydrological connectivity in this area. Based on X-ray computed tomography and constant head permeability test, the results showed a highly spatial heterogeneity of the soil structure in the YRD, hydraulic parameter (K s ) was negatively correlated with bulk density and positively with soil macropore volume, soil aeration and maximum water capacity. Using Hydrus 1-D software and the Green–Ampt model, we estimated the characteristics of the hydrodynamic process in the soil without macropores, then evaluated the effect of the soil macropore on soil hydrodynamic process by comparing the experimental results with the simulation results. We found that increasing soil microporosity improved the convenience of water movement, which would enhance the HC of the region. The results will further help to reveal the eco-hydrological process at a vertical scale in soil and provide a theoretical guide for wetland conservation and restoration. [ABSTRACT FROM AUTHOR]

This study examined the relationship between the decline in sugarcane productivity and the distribution of macropores and depth of root penetration in sugarcane plantations in Takalar during one planting period (October 2021-September 2022). There were five observation points (P1, P2, P3, P4, and P5) in one hectare of land to measure the distribution of soil macropores using methylene blue solution. Cross-sections of the soil were made to observe the presence of plant roots at a depth of 0-40 cm with a width of 60 cm. In each plot, disturbed soil samples were collected to measure soil texture, soil organic matter (SOM), nitrogen (N), phosphorus (P), and potassium (K) contents. Other measurement parameters were the infiltration rate and plant productivity. The results indicated that SOM and NPK levels at the research location were deficient, serving as the first indicators of problematic soil. Macropore observations revealed that macropores were distributed only at a less than 10 cm soil depth. This distribution limited the penetration of plant roots to a depth of 0-40 cm. The root length density (RLD) value indicated the absence of roots at depths of 30-40 cm in plots P2 and P3. The field findings explained why sugarcane production in Takalar only achieved 50%, around 40 t ha-1 from the first ratoon sugarcane harvest, instead of the expected 70-80 t ha-1.

Soil hydrology seriously affects the prevention of desertification in karst areas. However, water infiltration in the different soil layers of secondary forests and artificial forests in karst areas remains uncertain. This lack of clarity is also the factor that constrains local vegetation restoration. Therefore, monitoring and simulating the priority transport of soil moisture will help us understand the shallow soil moisture transport patterns after artificial vegetation restoration in the local area, providing a reference for more scientific restoration of the ecological environment and enhancement of carbon storage in karst areas. The integration of soil physical property assessments, computed tomography (CT) scanning, dye tracing studies, and HYDRUS-2D modeling was utilized to evaluate and contrast the attributes of soil macropores and the phenomenon of preferential flow across various forestland categories. This approach allowed for a comprehensive analysis of how the soil structure and water movement are influenced by different forest ecosystems and infiltration head simulations (5 mm, 15 mm, 35 mm, and 55 mm) to elucidate the dynamics of water movement across diverse soil types within karst regions, to identify the causes of water leakage due to preferential flow in secondary forests, and to understand the mechanisms of water conservation and reduction in artificial forests adopting a multifaceted approach. This study demonstrated that (1) the soil hydrological capacity of a plantation forest was 20% higher than a natural forest, which may be promoted by the clay content and distribution. (2) Afforestation-enhanced soils in karst regions demonstrate a significant capacity to mitigate the loss of clay particles during episodes of preferential flow and then improve the soil erosion resistance by about 5 times, which can effectively control desertification in karst area. (3) The uniform distribution of macropores in plantation forest soil was conducive to prevent water leakage more effectively than the secondary forest but was incapable of hindering the occurrence of preferential flow. The secondary forest had a very developed preferential flow phenomenon, and soil clay deposition occurred with an increase in depth. (4) Moreover, the results for preferential flow showed that the matrix flow depth did not increase with the increase in water quantity. Short-term and high-intensity heavy rainfall events facilitated the occurrence of preferential flow. Infiltration along the horizontal and vertical directions occurred simultaneously. These results could facilitate a further understanding of the contribution of the plantation to soil amelioration and the prevention of desertification in karst areas, and provide some suggestions for the sustainable development of forestry in karst areas where plantation restoration is an important ingredient. [ABSTRACT FROM AUTHOR]

Different types of soil macropores respond differently to various tillage practices, owing to disparities in origin, scale, morphology, and function, consequently exerting distinct effects on soil structure. This study aimed to investigate the response mechanisms of three different soil pore types (total macropores, non-biopores, and biopores) to two distinct tillage practices: smash-ridging tillage (T) and no-tillage (NT) in sugarcane fields. The parameters characterizing soil pore treatments in two and three dimensions were obtained using X-ray computed tomography scanning technology. ImageJ and MATLAB software were employed to analyze the data and separate soil macropores into biopores and non-biopores categories. The results showed that non-biopores predominated in two-dimensional cross-sectional areas in NT treatment, whereas biopores were more dominant in T treatment. Biopores in T treatment had a higher proportion of two-dimensional pores compared to NT treatment. A three-dimensional analysis indicated that total macropores had larger mean diameters (MD) and macroporosity, with more continuous tubular pores in T treatment than that in NT treatment. However, NT treatment had more numerous non-biopores with broader spatial distribution and complex morphology. Additionally, biopores in T treatment had larger MD and branching length density (LD). These vertically developed biopores, along with high macropore connectivity and under smash-ridging tillage, could improve soil water and pore conductivity. Therefore, smash-ridging tillage was more beneficial for sugarcane growth compared to no-tillage in Guangxi of China. [ABSTRACT FROM AUTHOR]

This study examined the relationship between the decline in sugarcane productivity and the distribution of macropores and depth of root penetration in sugarcane plantations in Takalar during one planting period (October 2021-September 2022). There were five observation points (P1, P2, P3, P4, and P5) in one hectare of land to measure the distribution of soil macropores using methylene blue solution. Cross-sections of the soil were made to observe the presence of plant roots at a depth of 0-40 cm with a width of 60 cm. In each plot, disturbed soil samples were collected to measure soil texture, soil organic matter (SOM), nitrogen (N), phosphorus (P), and potassium (K) contents. Other measurement parameters were the infiltration rate and plant productivity. The results indicated that SOM and NPK levels at the research location were deficient, serving as the first indicators of problematic soil. Macropore observations revealed that macropores were distributed only at a less than 10 cm soil depth. This distribution limited the penetration of plant roots to a depth of 0-40 cm. The root length density (RLD) value indicated the absence of roots at depths of 30-40 cm in plots P2 and P3. The field findings explained why sugarcane production in Takalar only achieved 50%, around 40 t ha-1 from the first ratoon sugarcane harvest, instead of the expected 70-80 t ha-1. [ABSTRACT FROM AUTHOR]

Repeated broiler litter application on agricultural lands can cause nutrient enrichment of subsurface effluent, especially with the existence of preferential flow through soil macropores. Previous studies quantifying soil macropores have not attempted to establish a connection of soil macropore characteristics with the subsurface nutrient (nitrogen [N] and phosphorus [P]) losses, across different topographical locations in the field. This study investigated the effect of broiler litter application and preferential flow on subsurface nutrient transport (N and P) at different topographical positions (upslope, midslope, and downslope) in a no‐till pasture field located in Alabama, USA. Twelve intact soil columns (150 mm id and 500 mm length) were used, and the nutrient leaching measurements from laboratory experiments were linked to soil macropore characteristics quantified using X‐ray computed tomography image analysis and solute transport modeling. Treatments included surface broadcast broiler litter (5 Mg ha−1, on dry basis) and unamended control. Leachates were analyzed for dissolved reactive P (DRP), total P (TP), and nitrate + nitrite‐N (NO3− + NO2−–N). The bromide breakthrough curves provided evidence of preferential flow in all columns. Litter application significantly increased leachate P concentrations, and average TP and DRP concentrations were significantly higher in the leachate from upslope columns compared to those at downslope location. The NO3−–N concentrations in leachate exceeded the US EPA drinking water standard of 10 mg L−1 in all the treatment columns. The highest flow‐weighted mean concentrations of TP and DRP, at 2.7 and 2.5 mg L−1, respectively, were recorded in the upslope columns. Soil physicochemical properties and nutrient leaching losses varied substantially across topographical positions, indicating a need for variable litter application rates to reduce P build‐up and subsequent leaching in vulnerable locations within the field. The relevance of the effect of topographic position on nutrient leaching found in this study should be further tested by investigating a wider range of slopes and soil types in pastures. Core Ideas: Phosphorus and nitrogen concentrations in the leachate varied as a function of slope position.Breakthrough curves and X‐ray computed tomography (CT) analysis provided evidence of preferential flow.Solute transport was well‐fitted by the two‐region physical nonequilibrium model.Broiler litter application significantly increased phosphorus leaching under saturated conditions. [ABSTRACT FROM AUTHOR]

Rare earth resources in the weathered crust elution-deposited rare earth ore (WCEDRE-ore) are mainly recovered by in situ leaching process. A new understanding of the engineering properties modification of WCEDRE-ore as well as the occurring microscopic mechanism was presented when leaching using ammonium sulfate agent occurred. The soil–water chemical reactions in leaching had a significant impact on engineering properties (such as permeability and strength) of WCEDRE-ore, which determined the success or failure of in situ leaching process. To reveal the internal processes and effects of ammonium sulfate leaching on WCEDRE-ore, indoor tests including leaching tests, chemical analyses, triaxial tests and nuclear magnetic resonance (NMR) tests were conducted. The results show that: (1) Under the action of ion exchange and seepage, the dispersion, deposition and clogging of fine particles occurred repeatedly and alternately along the seepage direction. (2) During the leaching process, the total porosity of the ore samples rarely changed, but the migration of fine particles leads to the transformation of micropores, mesopores and macropores in weathered-ore soil samples as well as the change of pore connectivity. As a result, the permeability coefficient of the tested soil samples decreased significantly at the beginning of test and then rose slightly. (3) Increased salt content during the leaching process enhanced soil cementation and structure until the end of ion exchange. However, owing to the loose pore structure in the upper part of sample and the dense pore structure in the lower part of the tested specimen generated by particle migration, the strength of soil sample was weakened, which was conducive to the occurrence of shear failure in the upper part of sample. [ABSTRACT FROM AUTHOR]

In recent years, the problematic circumstances of the constant cropping problem in facility crops have become increasingly serious. Compared to chemical disinfection, soil steam disinfestation offers the benefits of environmental protection and being pollution-free, which can effectively reduce the problem of constant cropping in crops. However, during the steam disinfection procedure, a large quantity of liquid water is formed due to the condensation of high-temperature steam, which causes soil pore blockage, seriously affecting the mass and heat transfer efficacy of steam and, thus, affecting the disinfection efficiency. Therefore, to solve this problem, this paper proposes the use of hot air dehumidification to remove excess water from soil pores and achieve the goal of dredging the pores. However, further exploration is needed on how to efficiently remove excess water from different pore structures through hot air applications. Therefore, this paper first used CFD simulation technology to simulate and analyze the hot air flow field, mass, and heat transfer in soil aggregates of different sizes (<2 mm to >8 mm). Then, based on the soil hot air heating experimental platform, research was conducted on the mass and heat transfer mechanism of hot air under diverse soil pore conditions. The results show that as the soil particle size increases from <2 mm to >8 mm, the number of soil macropores also increases, which makes the soil prone to the formation of macropore thermal currents, and the efficiency of hot air heating for dehumidification first increases and then decreases. Among them, the 4–6 mm treatment has the best dehumidification effect through hot air heating, with a deep soil temperature of up to 90 °C and a water content reduction of 6%. The 4–6 mm treatment has a high-temperature heating and dehumidification area of 15–20 cm deep. The above results lay the theoretical foundations for the parameters of hot air heating and dehumidification operations, as well as the placement of the hot air pipe. This paper aims to combine hot air dehumidification technology, for the removal of excess water from soil, and dredging soil pores, ultimately achieving the goal of improving soil steam disinfection efficiency. [ABSTRACT FROM AUTHOR]

Traditional correlation analyses based on whole-rock data have limitations in discerning pore development determinants in shale oil reservoir, given the complex lithology of shale formations and intricate interdependencies (multicollinearity) among geological variables. In this study, mercury injection capillary pressure and digital analysis of scanning electron microscopy were employed to examine the macropore structures of both whole rocks and their constituent lithologies for the Upper Triassic Chang-7 shale of the Ordos Basin. Variations were observed among clay shale (shale primarily consisting of clay-sized mineral grains), massive siltstone and silty laminae within the Chang-7 shale. Through the combination of correlation analysis and scanning electron microscope digital technique, it was demonstrated that total organic carbon content primarily controls the level of macropore development, while lithology primarily governs macropore types and structures. Although quartz and pyrite exhibit correlations with macropore volume, they do not emerge as primary factors; instead, they appear interconnected to total organic carbon. Due to detrital mineral framework preservation during compaction, larger macropores are more developed in massive siltstones and silty laminae than in clay shale. Additionally, silty laminae, situated closer to the source rock and influenced by organic acids, exhibit a higher abundance of larger dissolution pores, potentially favoring shale oil development. This study overcomes traditional method constraints, disentangling multi-correlations, and providing new insights into shale macropore development mechanisms, potentially advancing shale oil exploration and production. [ABSTRACT FROM AUTHOR]

Direct information about the soil structure can be obtained with X‐ray computed microtomography, and the imaged macropore networks can be used as geometries in the lattice Boltzmann flow simulations. This method has not been widely applied for near‐saturated flows due to methodological issues related to diffuse‐interface two‐phase flow simulations in samples with limited resolution. Here, a simple pore‐scale lattice Boltzmann approach to simulate steady‐state water flow in partially saturated soil macropore networks that circumvents these problems is presented. The actual simulation is preceded by the determination of water–air distribution, for example, by using morphological operations. Flow through the water‐filled part of the pore space is done by using no‐slip conditions at water–solid boundaries and slip conditions at water–air interfaces. The method was tested by simulating film flow over a solid surface, and the numerical results are shown to agree with the analytical expression available for this flow geometry. The method is further tested, and its use is demonstrated with real tomographic reconstructions of clay soil samples. Core Ideas: Lattice Boltzmann method was used to simulate near‐saturated flow in the imaged soil macropore system.The approach uses static water–air distribution in soil macropores that were determined by a morphological model.Slip boundary condition at water–air interfaces was realized with a bounce‐back rule from a moving boundary.The approach reduces the computational costs for simulating water flow in pore networks at near‐saturated condition. [ABSTRACT FROM AUTHOR]

Earthworm incubation combined with organic fertilization is promoted as an amended measure to improve soil properties in the ecological restoration of various degraded soils. However, the impacts of earthworms on the soil aggregate size under different organic fertilization in salt‐affected soils have not yet been fully revealed. This hinders our ability to develop policies by which to alleviate soil salinization. In this study, under mesocosm experiments, we investigate the effects of earthworm (Aporrectodea trapezoides) and organic fertilization on the soil aggregate size after 16 weeks of incubation. The soil treated with clover residues showed lower earthworm survival rates and biomass compared to that treated with sheep manure. However, the soil macropores and large macroaggregate were higher in the soils treated with clover residue when earthworms were present. In addition, earthworm burrowing activities form pathways toward food patches improve the characteristics of soil macropores, and the properties of the residue itself play a decisive role. Moreover, whether earthworms are present or not significantly influences the soil macroporosity, macropore number, and soil electrical conductivity. This demonstrates that earthworms exhibit a key feature of soil physical functioning in salt‐affected soil. In conclusion, we propose that the application of earthworms with organic residues in salt‐affected soils is a priority in producing and maintaining favorable soil structure. [ABSTRACT FROM AUTHOR]

Oil pollution is widespread in frozen regions around the world, and the mechanical properties of clay are highly susceptible to prolonged freeze–thaw cycles and diesel pollution. In order to study the properties of diesel-contaminated clay at the influence of freeze–thaw cycles, the laboratory tests are performed here, based on which the mechanical properties of diesel-contaminated soil under freeze–thaw cycles are studied. Additionally, the effects of freeze–thaw cycles and contents of diesel on the microstructure of clay are studied by scanning electron microscopy. The results show that the shear strength and strength parameters of soil samples decrease with the increase of diesel content and freeze–thaw cycles. Moreover, the scanning electron microscopy (SEM) results show that the freeze–thaw cycle and the increase in diesel content increase the number of large pores and decrease the number of small pores. The soil particles coagulate and form larger pores after the soil sample undergoes freeze–thaw and diesel pollution. The appearance of macropores leads to soil compaction worse and soil strength decrease. Based on the poromechanics, the diesel-contaminated soil is considered as porous material, and a constitutive model with consideration of the influence of freeze–thaw cycles and diesel content is established. The model can model the test results and the main features of diesel-contaminated soil can be duplicated relatively well. Therefore, the study can provide some help in understanding diesel-contaminated engineering under freeze–thaw cycles in cold regions. [ABSTRACT FROM AUTHOR]

Understanding and quantification of the spatial variation and the primary factors that affect soil macropore distribution is helpful to restore soil water and productivity of cultivated land. However, the information of spatial distribution and influencing factors of soil macropores in coal mining subsided areas is still scare. We investigated the soil physicochemical properties and computed tomography (CT)-measured pore parameters at different slope positions and slope aspects (shady slope and sunny slope), and quantified the contribution of influencing factors of soil pore using the model of principal component analysis with multiple linear regression (PCA-MLR). The results showed that pH, electrical conductivity and total P had significant difference between two slope aspects, and the contents of quartz, feldspar, calcite, clay, organic matter and Na ion exhibited significant difference among three slope positions. The number of soil macropores (64.23 ± 50.38), macroporosity (4.09 ± 5.36%), roundness rate (0.85 ± 0.03), and connectivity density (1.04 ± 0.63 cm-3) showed obvious spatial variations in the subsided area. The soil macroporosity on the shady slope was significantly higher than that on the sunny slope. The number of macropores and macroporosity at the top slope position were significantly higher than those at the middle and bottom slope positions. The PCA-MLR model estimated that the factors of soil particle composition and organic matter contributed 43% and 24%, respectively, to the distribution of soil macroporosity. In conclusion, coal mining subsidence had directly and indirectly significant impacts on the spatial distribution of soil macropores. The findings of this study are critical for developing strategies for the conservation of soil water through regulation of soil macropore conditions in mining subsided areas. [ABSTRACT FROM AUTHOR]

Purpose: Soil macropores affect the proportion of rainfall infiltration and regulate the amount of water available to the plants on a field scale. However, the distribution of soil macropores and the effect on hydrologic and ecological regimes have been underestimated at a continental scale. The aim of this study was to investigate the relationships between soil properties and climatic factors on soil macropores and assess the eco-hydrological effect of soil macropores. Materials and methods: We hypothesized that the spatial distribution of soil macropores was controlled by soil properties and climatic factors at the continental scale. Using a spatial error-egression method, the soil effective porosity (EP) and residual effective porosity (REP) across China were calculated. The effects of soil macropores on soil physicochemical properties and climate factors were analyzed by the random forest model. The effect of macropores on soil water content (SWC) and normalized difference vegetation index (NDVI) was also analyzed. Results and discussion: The EP ranged from 0.06 to 0.35 cm3 cm−3 and was significantly related with soil chemical index, particularly, negatively correlated with cation exchange capacity (CEC) and total nitrogen (TN), but positively correlated with pH. There was a negative relationship between REP and mean annual precipitation in drylands. In humid regions, there was a positive relationship between REP and mean annual precipitation. Random forest model showed in humid region mean annual precipitation was more important than the annual temperature difference in explaining REP, but the results were reversed in drylands. The SWC and NDVI had different correlations with REP in drylands and humid regions. Conclusion: Soils with better quality had lower EP at the continental scale. Soil macropores were related simultaneously to precipitation and temperature conditions. Importantly, soil macropores were not conducive to soil water conservation and vegetation development in drylands. [ABSTRACT FROM AUTHOR]

Microbially induced calcite precipitation (MICP) stands as an environmentally friendly and promising technique for enhancing the performance of soil. Bacteria catalyze the hydrolysis of urea, prompting calcium ions to react with carbonate ions, ultimately forming calcium carbonate precipitation as a cement within soil grains. However, studies of using MICP to enhance granite residual soil (GRS) that is recognized as a problematic soil because of its wide grain size distribution are relatively rare. In this present study, bio-cemented GRS samples were prepared through grouting with Sporosarcina pasteurii as the colony and a mixture of urea and calcium chloride as the cementation solution. The effect of cementation–solution concentrations on the mechanical properties of the bio-cemented samples was analyzed through unconfined compression and triaxial shear tests. Furthermore, X-ray computerized tomography, scanning electron microscopy, and X-ray diffraction experiments were performed to reveal the mechanism of MICP from a microscopic perspective. The experimental results indicate that an optimal concentration of 2 mol/L achieved the highest level of cementation, resulting in an impressive 47.15% increase in the unconfined compressive strength of the GRS samples. The triaxial shear strength and stress paths of bio-cemented samples were affected by the cementation level. The variation of porosity indicated that CaCO3 precipitation improves soil densification by filling the macropores among the soil grains. The CaCO3 precipitates from the MICP treatment predominantly exist in the form of calcite crystals, serving to fill, wrap, and cement within the soil structure, thereby enhancing the cohesive and frictional forces exerted by the bio-cemented grains. [ABSTRACT FROM AUTHOR]

The soil on the slope may experience more severe erosion as a result of the surface cracks caused by desiccation. Xanthan gum (XG) was introduced to reduce the soil's tendency to erode and crack in order to increase the stability of slope soil. In this study, the microstructure and behaviors of sand-admixed soil (0%–70% sand content) with various XG contents (0.05%–0.25% by the mass of dry soil) were investigated using the desiccation cracking tests, erosion tests, and scanning electron microscope (SEM) technique. The findings showed that soil water evaporation, crack resistance, and erosion resistance are significantly influenced by sand and XG content. The initial evaporation rate increased by 15.6%, the drying time decreased by 11 h, and the surface crack ratio dropped by 11.9% as the sand content rose from 0% to 70%. The initial evaporation rate of the clay decreased by 11.1% with a 0.25% XG content, while the residual water content increased by nearly six times and there were no soil cracks. Additionally, the sand-admixed soil would not crack and the erosion significantly decreased with 0.15% XG content, demonstrating that this level of XG is the most efficient and cost-effective for controlling both cracking and erosion. Because soil contains macropores, it was discovered that higher sand content accelerates water evaporation, lowers matric suction, increases friction and fracture toughness, which prevents crack formation. Because of its potent water adsorption and pore clogging properties, the addition of XG reduced water evaporation and improved the soil's ability to hold water. Besides, due to the inter-particle bonds and formed network structure, biopolymer treatment effectively improved soil cohesion and conferred cracking resistance. The generation of preferential flow and the occurrence of infiltration, which promote the soil's antierosion ability, were also prevented by the presence of XG. [ABSTRACT FROM AUTHOR]

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The ecological environment in southwestern China is fragile. Due to the significant preferential flow in vertical and horizontal directions and poor water conservation ability, vegetation degradation still exists under conditions of abundant rainfall. Therefore, the pore connectivity and infiltration characteristics in shallow soil under typical local vegetation need to be studied. A calculation model for the vertical connectivity of soil macropores was independently constructed, and differences in soil macropore structures and the degree of vertical connectivity in typical vegetation types (natural secondary forest, natural grassland, Yunnan pine plantation, eucalyptus plantation, cypress plantation, mulberry bushes) were investigated by CT scanning technology of undisturbed soil columns. The results showed that the vertical connectivity of large pores in the shallow soil of the region can be quantitatively described by X-ray tomography, and the total surface area and cumulative curvature of macropores in natural grassland soil were two or three times that in artificial vegetation. The concentration area of macropores in the soil of artificial forestland was closer to the surface, and the tendency of macropore preferred path decreased by 76.18% around 30 cm depth in the soil. The vertical connection of soil macropores in artificial forests was significantly lower than that of natural secondary forestlands (33.03%) and natural grasslands (36.75%). The restoration of the plantation improved surface soil pore structure, and the vertical connectivity of soil is nearly 20% less than that of natural vegetation types (natural secondary forestland, natural grassland), which reduced water outflow rate by nearly 44% and electrolyte content by nearly 14% at a depth of 30 cm. This study provided data and research directions for the study of hydrological processes in local forest vegetation and technical support for solving the problems of soil water loss and forestland water conservation in southwestern China. [ABSTRACT FROM AUTHOR]

Aims: The influence of the moss layer on soil structure and soil water retention is not well understood. Therefore, this study aims to investigate the changes in soil structure and soil water retention under moss layer and to reveal the influencing factors of these changes. Methods: 3D networks of moss layer and soil macropores were quantified using CT scanning and image analysis techniques, and soil water retention characteristics were explored through soil water retention curves (SWRCs) and VG model. Results: The length densities of the soil macropores under the thin moss and thick moss layers were approximately 2.7 and 1.6 times higher than that under no moss cover. The soil water retention under the thin and thick moss layers were greater than those under no moss cover, with the highest plant-available water capacity under the thin moss layer. The maximum water-holding capacity of the moss layer was significantly positively correlated with the field water-holding capacity of the soil and negatively correlated with the equivalent diameter of the macropores, while the storage capacity of the moss layer was significantly and negatively correlated with the maximum effective water content of the soil. The field capacity (FC) and permanent wilting point (PWP) were significantly and positively correlated with the soil organic matter. Conclusions: The effect of the moss layer on water retention may be mainly realized by influencing the pore distribution and organic matter accumulation. The moss layer had a positive ecohydrological effect on soil water retention and even water conservation in forest soils. [ABSTRACT FROM AUTHOR]

Exogenous silicon is widely applied to soils to alleviate the soil cadmium contamination. The effect of silicon on the translocation and transformation of cadmium in plants and soils has been thoroughly studied, but the influence of silicon on soil water movement has rarely been reported. Hence, an experiment is conducted to investigate the influence and mechanism of silicon (0, 200, 400 kg/hm²), cadmium (0, 2.5 and 5 mg/kg) and their reactions on the soil water characteristic curve (SWCC). The group of soil with no addition of silicon and cadmium (0 kg/hm², 0 mg/kg) is denoted as CK for comparison. The SWCCs of soils are measured by pressure plate extractor, and pH, zeta potential. Field Emission Scanning Electron Microscopy (FESEM) are performed for the soil samples. After that, three models including Brooks-Core (BC) model, Van Genuchten (VG) model, and Dual-porosity (DP) model are used to fit the experiment data. The results show that ➀ in comparison with the CK, cadmium has no influence on the SWCCs, the right-skewed SWCCs of soils with silicon application indicate that more water is held in soils, whereas the left-skewed SWCCs of cadmium-contaminated soils with silicon application indicate a reduction in the water holding capacity of soils within the suction range of 710~1 200 kPa. ➁ Compared to CK, cadmium has no influence on the soil pore distribution. Silicon application in both no cadmium-contaminated and cadmium-contaminated soils increase the proportion of soil macropores (equivalent pore size of 0.002 14~0.002 50 mm), whereas there is no influence on the small pores (equivalent pore size of 0.000 49~0.002 14 mm). ➂ The images of FESEM illustrate that there is no difference between the CK and the cadmium-contaminated soils, whereas the soil particles are more clustered after silicon application in comparison with CK. ➃ Silicon application can significantly increase the pH value and the absolute value of soil zeta potential. The high absolute value of soil zeta potential is of benefit to disperse the soil colloidal particles, which goes against the formation of soil micro-aggregates. However, the silicic acid gel is formed after silicon application can promote the cementation of soil micro-aggregates and thus increase the proportion of large pores in the soil and improved soil water holding in the low suction range. van der Waals force might be weakened due to the formation of silicon-cadmium complex after the application of silicon in cadmium-contaminated soil, which reduces water holding ability of soils within the high suction range. ➄ Compared with BC model and VG model, DP model can better describe the influence of silicon and cadmium on soil water characteristic curve, and the influence of silicon application on soil hydraulic characteristics can be quantitatively expressed by adjusting saturated and residual water content of soil water characteristic curve. [ABSTRACT FROM AUTHOR]

Wetting and drying (WD) cycles have a strong influence on the structure of soil, especially on the pore distribution, which can significantly affect soil quality and crop growth. Most studies have conducted the controlled cycles effects on soil pores at the laboratory. However, the effects of natural wetting and drying cycles (NWD) on the pore characteristics of soil are still not well understood. This study was to quantify and compare the modifications in computed tomography (CT)-measured macropore parameters induced by cycles under two experimental conditions of NWD at the field and WD at the laboratory. Intact soil cores, 15 cm in diameter and about 20 cm in height, were taken from Calcic Cambisol at cultivated land and scanned using X-ray computed tomography. Two conditions of NWD and WD cycles had obviously different influence on soil macropores, and NWD cycles may have a stronger influence than WD cycles. Soil depths had an obvious effect on soil macropore features during the cycles. Our results suggest that the decrease in soil macropore number, macroporosity, fractal dimension and connectivity density under NWD cycles is adverse to soil water retention, soil quality and crop production. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Northwest A & F University - Natural Science Edition is the property of Editorial Department of Journal of Northwest A&F University (Natural Science Edition) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil salinity and sodicity caused by saline water irrigation are widely observed globally. Clay dispersion and swelling are influenced by sodium (Na+) concentration and electrical conductivity (EC) of soil solution. Specifically, soil potassium (K+) also significantly affects soil structural stability, but which concern was rarely addressed in previous studies or irrigation practices. A soil column experiment was carried out to examine the effects of saline water with different relative concentrations of K+ to Na+, including K+/Na+ of 0:1 (K0Na1), 1:1 (K1Na1), 1:0 (K1Na0) at a constant EC (4 dS m-1), and deionized water as the control (CK), on soil physicochemical properties. The results indicated that at the constant EC of 4 dS m-1, the infiltration rate and water content were significantly (P < 0.05) affected by K+/Na+ values, K0Na1, K1Na1 and K1Na0 significantly (P < 0.05) reduced saturated hydraulic conductivity by 43.62 %, 29.04 % and 18.06 % respectively compared with CK. The volumetric water content was significantly (P < 0.05) higher in K0Na1 than CK at both 15 and 30 cm soil depths. K1Na1 and K1Na0 significantly (P < 0.05) reduced the desalination time and required leaching volume. K0Na1 and K1Na1 reached the desalination standard after the fifth and second infiltration, respectively, as K1Na0 did not exceed the bulk electrical conductivity required for desalination prerequisite throughout the whole infiltration cycle at 15 cm soil layer. Furthermore, due to the transformation of macropores into micropores spurred by clay dispersion, soil total porosity in K0Na1 dramatically decreased compared with CK, and K1Na0 even increased the proportion of soil macropores. The higher relative concentration of K+ to Na+ in applied water was more conducive to soil aggregate stability, alleviating the risk of macropores reduction caused by sodicity. [ABSTRACT FROM AUTHOR]

Macropores such as crab burrows are a common feature of salt marsh sediment and are recognized as an important factor influencing pore‐water flow in salt marshes. In this study, we examined the effect of macropores on saline water evaporation and pore‐water salinity based on laboratory experiments and numerical simulations. Soil columns with and without an artificial macropore were packed with clay‐loam and were set with different hydraulic heads fixed at the bottom. The results showed that increase in pore‐water salinity significantly reduced evaporation rates. The preferential flow induced by macropores recharged the soil surrounding macropores and maintained higher evaporation rates in comparison with homogeneous soil without macropores. As macropores induced lateral flow, the pore‐water salinity in shallow soil around the macropores was reduced but that in the area away from the macropores was increased. These impacts were more remarkable on the soil layers with higher hydraulic heads. A sensitivity analysis showed that with a higher initial pore‐water salinity, the macropore's impact on soil evaporation rates was more remarkable for both clay‐loam and silt‐loam. These results revealed the effect of macropores on soil evaporation processes and soil conditions, and also shed light on associated biogeochemical processes in salt marshes. Key Points: Macropores increased evaporation from marsh soil with high hydraulic headsMacropores altered pore‐water flow and salinity distributionsMacropores' impacts were more remarkable on soil with high hydraulic heads [ABSTRACT FROM AUTHOR]

Solute transport behaviour can indicate the efficiency of eco‐hydrological responses. However, this behaviour has not been consider for use in assessing the health of wetland ecosystems. We assessed solute transport behaviour in degraded wetland soils using 72 undisturbed soil columns located in Robinia pseudoacacia (tree) and Tamarix chinensis (bush) communities. Soil column tracer experiments were conducted under the same initial and boundary conditions using Brilliant Blue FCF as a conservative tracer. Solute transport behaviour at a soil column scale was described by four measures: steady infiltration rate of effluents, concentration of effluents, dye staining patterns and cumulative effluents leaching. Numerical modelling by the dual‐permeability model in HYDRUS‐1D was used to simulate the proportion of cumulative effluents leaching from soil macropores. These data showed that steady infiltration rate of effluents at the tree site decreased with increasing soil depth (5.742, 0.716, 0.657, and 0.458 ml/min) but at the bush site first increased and then subsequently decreased with increasing soil depth (0.336, 0.548, 0.974 and 0.379 ml/min). The concentration of effluents at the tree site (0.583, 0.149, 0.147 and 0.067 g/L) and the bush site (0.281, 0.109, 0.161 and 0.053 g/L) decreased nonlinearly with increasing soil depth. Dye staining patterns were significantly different between different soil locations. The largest dark blue staining domains were from 0 to 10 cm soil depths at the tree site and 20–40 cm depths at the bush site. The proportion of cumulative effluents leaching from soil macropores ranged from 37.6% to 61.1% at the tree site and ranged from 0% to 99.9% at the bush site. Understanding the solute transport behaviour in the Yellow River Delta is the first step towards the restoration of degraded wetlands. [ABSTRACT FROM AUTHOR]

A complex soil-water transformation can be found under undulating topographical conditions in low mountain and hilly areas. It is also easy to cause the distribution of soil macropores and heavy preferential flow under the dry and wet alternative environment. This study aims to explore the characteristics of soil preferential flow patterns in the Jiangning District, Nanjing City, Jiangsu Province, China. A typical low mountain and hilly region was then selected as the study area. Three land use patterns were selected as the study objects, including the typical paddy field, dry land, and forest land. The outdoor dry tracer technology combined with indoor image processing was used to quantitatively analyze the differences in soil dye area ratio, dye path, and preferential flow type at different sites (inner field, transition zone, and ridge). The results showed that the stained area ratio (SAR) of land use types decreased with the increase of soil depth. Specifically, the average SAR of paddy fields was higher than that of dry land and forest land, particularly in the depth of 20-40 cm. There was also a significantly different average SAR of the three field sites. The overall performance was higher in the field than that in the transition zone and ridge. The number of staining paths (SPN) of different sites in various land use types first increased and then decreased with the increase of the soil depth. The average SPN of the whole profile was the highest in the forest land and its average SPN of each point was at most in the inner field, while the value in the paddy field and dry land was the opposite. The staining path width (SPW) of the 0-10 cm soil layer in the inner field and transition zone under different land use modes was in the range of 4-40 mm and more than 40 mm, whereas, the SPW of less than 10 cm was in the range of 4-40 mm. The water flow types are homogeneous flow or heterogeneous finger flow in 0~15 cm soil layer of the inner field and transition zone, and the highly interacting macropore flow is below 15 cm soil layer. The water flow types of ridges were highly interacting with macropore flow. The correlation analysis showed that the SPN and the proportion of SPW< 4 mm showed a positive correlation under different land use patterns, where the largest was found in the paddy field, followed by the dry land and forest land. Different sites showed a negative correlation with the SAR and SPW, indicating the maximum of SAR and SPW in the field, followed by the transition area, and the minimum of the ridge. Nevertheless, the proportion of SPW<4 mm was irrelated to the depth of the soil layer. The rest indicators decreased with the increase in the depth of the soil layer. The path of water leakage showed that the vertical and lateral leakage of paddy field ridges developed significantly. The ridge of dry land only developed the vertical seepage. There was a significant development of vertical leakage in the forest land ridge, instead of the lateral leakage. Some recommendations were proposed to improve the utilization efficiency of water and fertilizer for the reduced loss of water and soil. Specifically, the crack development can be controlled the soil moisture and reduced under the alternation of dry and wet conditions in the paddy field. The plough bottom was broken in the dry land. The weeds can be regularly removed inside and outside the ridge of the dry land and forest land. Particularly, animal holes can also be reduced in the typical low mountain and hilly areas in south China. [ABSTRACT FROM AUTHOR]

The current study aims to ascertain the reservoir characteristics of the Tariki Sandstone Member of the Otaraoa Formation, Taranaki Basin, New Zealand. This study was carried out by integrating the comprehensive petrophysical evaluation, sedimentological and petrographic studies, as well as well log analysis by using data from six wells. The porosity-permeability relationship is used to divide the samples of the Tariki Sandstone Member into reservoir and non-reservoir facies. A thorough petrophysical analysis shows that the maximum porosity values fluctuate between 16.6% and 22.1%, while permeability ranges from 102 mD to 574 mD, which indicates fair to good reservoir quality. Moreover, the Tariki sandstone represents six hydraulic flow units with a high reservoir quality index and flow zone indicator representing good reservoir characteristics. The pore size varies between nano and megapores with dominant macropores. Based on the sedimentological and petrographic analysis, the Tariki Sandstone Member is classified as a combination of subarkose, arkose, and lithic arkose with fine to medium and moderately to moderately well-sorted grains. The main diagenetic factor affecting the reservoir quality is cementation, which occupied all the pores with calcite. On the bright side, the secondary pores are developed due to the dissolution of calcite cement and few grains. The well log analysis demonstrates the presence of low clay volume ranging from 0.3% to 3.1%, fair to good effective porosity values between 13.6% and 15.9%, net pay thickness from 18.29 m to 91.44 m, and hydrocarbon saturation from 56% to 77.9%. The findings from this study revealed that the Tariki Sandstone Member possesses fair to good reservoir quality and hydrocarbon potential, which indicate submarine fans as appealing hydrocarbon reservoirs. This study can be used in similar depositional environments elsewhere in the world. [ABSTRACT FROM AUTHOR]

Understanding the relationship between root systems, soil macropore networks, and soil hydraulic properties is important to better assess ecosystem health. In this study, treatments were performed in forested wetland soils with different vegetation densities, i.e., large (LWa) and small communities (LWb) of reed (Phragmites australis (Cav.) Trin. ex Steud.). At each plot, three undisturbed PVC cylinders (10 cm in diameter and 50 cm in height) were obtained, and X-ray microtomography (μCT) scanning was used to determine the root and macropore architectures. Results showed that the values of total root length and total root volume at LWa were significantly larger than those at LWb (p < 0.05). Imaged macroporosity, macropore volume, macropore length density, macropore node density, macropore branch density, mean macropore surface area, mean macropore diameter, and mean macropore volume at LWa were significantly larger than those at LWb (p < 0.05), whereas mean macropore length, mean macropore branch length, and mean macropore tortuosity at LWb were larger than those at LWa. Total root length and total root volume were positively correlated with soil saturated hydraulic conductivity. Imaged macroporosity, macropore volume, macropore length density, macropore node density, macropore branch density, mean macropore surface area, mean macropore diameter, and mean macropore volume were positively correlated with soil saturated hydraulic conductivity, whereas mean macropore length, mean macropore branch length, and mean macropore tortuosity were negatively correlated with soil saturated hydraulic conductivity. In conclusion, root systems and soil macropore networks constitute a complex synthesis inside soil environments, and together affect soil hydrological responses. [ABSTRACT FROM AUTHOR]

Understanding the influence of soil microstructure on light non-aqueous phase liquids (LNAPLs) behavior is critical for predicting the formation of residual LNAPLs under spill condition. However, the roles of soil particle and pore on LNAPLs migration and residue remains unclear. Here, the experiment simulated an LNAPLs (diesel) spill that was performed in fourteen types of soils, and the key factors affecting diesel behavior are revealed. There were significant differences between fourteen types of soils, with regard to the soil particle, soil pore, and diesel migration and residue. After 72 h of leakage, the migration distance of diesel ranged from 3.42 cm to 8.82 cm in the soils. Except for sandy soil, diesel was mainly distributed in the 0–3 cm soil layer, and the residual amounts were 7.85–26.66 g/kg. It was further confirmed from microstructure that the consistency of soil particle and volume of soil macropores (0.05–7.5 μm) are important for diesel residue in the 0–1 cm soil layer and migration distance. The large soil particles corresponding to 90% of volume fraction and volume of soil mesopores (<0.05 μm) are key factors affecting diesel residue in the 1–3 cm soil layer. The result helps to further comprehend the formation mechanism of residual LNAPLs in the soil. [ABSTRACT FROM AUTHOR]

The effects of long-term fertilization on the macropore microstructure of vertisol were studied. In this study, soil pore structure was assessed using intact soil columns (7.4 cm diameter, 20 cm height), which were sampled from five long term fertilization treatments established in 1981, including no fertilizer (CK), inorganic fertilizer (NPK), a single application of organic fertilizer (M), a combination of inorganic fertilizer and organic manure with isonitrogen (MNPK), and a combination of inorganic fertilizer and organic manure with high nitrogen levels (HMNPK). Each column was scanned with X-ray microtomography (μCT) and quantified using image analysis. The results showed that there were macropores in the soil aggregate structure and between the aggregates in each treatment, in particular, the M treatment had the largest number of pores. The order of fractal dimension and anisotropy from large to small was HMNPK>M>MNPK>NPK> CK and MNPK>CK>M>NPK>HMNPK, respectively. Compared with CK, the organic manure treatments (M, MNPK, and HMNPK) increased the number of macropores by 41.5%, 33.3%, and 26.8%, while the porosity increased by seven, six, and ten percentage points, respectively. The fluctuations in the pore size distribution of HMNPK treatment were the most intense, with the first and second peaks appearing at 395~577 μm and 1 545~1 701 μm, respectively. Principal component analysis showed that pores <126 μm in size were mainly affected by particle content, 126~500 μm pores were affected by bulk density, and 500~2 500 μm pores were affected by multiple factors, including sand content, clay content, connectivity, and fractal dimension. Overall, this study demonstrates that long-term application of organic and inorganic fertilizers can significantly improve the morphology and quantity of macropores in vertisol, especially HMNPK treatment, while NPK alone caused no significant improvement. Fractal dimension and connectivity could be used as a quantitative evaluation index for improving the pore structure of vertisol. [ABSTRACT FROM AUTHOR]

The establishment of large-scale forest plantations in the arid and semi-arid area of the Qilian Mountains in China has effectively protected water and soil resources and enhanced carbon sequestration capacity of forest ecosystems. However, the effects of different management practices in these plantations on soil water holding capacity (SWHC) and soil water availability (SWA) are uncertain in this fragile ecosystem. Here, we investigated the effects of no thinning (NT), light thinning (LT, 20% thinning intensity), and heavy thinning (HT, 40% thinning intensity) on SWHC and SWA in different soil depths of a forest plantation, and compared them to those in a natural Picea crassifolia forest (NF). Our results revealed that at low soil water suction stage, SWHC in the plantations (LT, HT, and NT) was greater in the topsoil layer (0-40 cm) than that in the NF site, while SWHC in the subsoil layer (40-80 cm) in NF was significantly greater than that in the thinning stands. At medium and highwater suction stage, SWHC in LT and NF stands was greater than that in HT and NT. Soil water characteristic curves fitted by VG model showed that the relative change in soil water content in LT topsoil layer was the smallest and SWHC was greatest. Changes in soil physicochemical properties included higher bulk density and lower total porosity, which reduced the number of macropores in the soil and affected SWHC. The bulk density, total porosity, silt content, and field capacity were the main factors jointly affecting SWA. High planting density was the main reason for the low SWA and SWHC in NT, but this can be alleviated by stand thinning. Overall, 20% thinning intensity (light intensity thinning) may be an effective forest management practice to optimize SWHC and SWA in P. crassifolia plantations to alleviate soil water deficits. [ABSTRACT FROM AUTHOR]

Pore structure is a key determinant of soil functioning, and both root growth and activity of soil fauna are modified by and interact with pore structure in multiple ways. Cover cropping is a rapidly growing popular strategy for improving agricultural sustainability, including improvements in pore structure. However, since cover crop species encompass a variety of contrasting root architectures, they can have disparate effects on formation of soil pores and their characteristics, thus on the pore structure formation. Moreover, utilization of the existing pore systems and its modification by new root growth, in conjunction with soil fauna activity, can also vary by cover crop species, affecting the dynamics of biopores (creation and demolition). The objectives of this study were (i) to quantify the influence of 5 cover crop species on formation and size distribution of soil macropores (>36pm 0); (ii) to explore the changes in the originally developed pore architecture after an additional season of cover crop growth; and (iii) to assess the relative contributions of plant roots and soil fauna to fate and modifications of biopores. Intact soil cores were taken from 5 to 10 cm depth after one season of cover crop growth, followed by X-ray computed micro-tomography (CT) characterization, and then, the cores were reburied for a second root growing period of cover crops to explore subsequent changes in pore characteristics with the second CT scanning. Our data suggest that interactions of soil fauna and roots with pore structure changed over time. While in the first season, large biopores were created at the expense of small pores, in the second year these biopores were reused or destroyed by the creation of new ones through earthworm activities and large root growth. In addition, the creation of large biopores (>0.5mm) increased total macroporosity. During the second root growing period, these large sized macropores, however, are reduced in size again through the action of soil fauna smaller than earthworms, suggesting a highly dynamic equilibrium. Different effects of cover crops on pore structure mainly arise from their differences in root volume, mean diameter as well as their reuse of existing macropores. [ABSTRACT FROM AUTHOR]

In regards to soil macropores, the solute loss carried by overland flow is a very complex process. In this study, a fuzzy neural network (FNN) model was used to analyze the solute loss on slopes, taking into account the soil macropores. An artificial rainfall simulation experiment was conducted in indoor experimental tanks, and the verification of the model was based on the results. The characteristic scale of the macropores, the rainfall intensity and duration, the slope and the adsorption coefficient of ions, were chosen as the input variables to the Sugeno FNN model. The cumulative solute loss quantity on the slope was adopted as the output variable of the Sugeno FNN model. There were three membership functions, and the type of membership function was gbellmf (generalized bell membership function). The hybrid learning algorithm, which combines the back propagation algorithm with a least square method, was applied to train and optimize the network parameters, and the optimal network parameters were determined. The simulation results showed that the simulated values were consistent with the measured values. [ABSTRACT FROM AUTHOR]

The soil water behavior of sandy soils was studied under semiarid conditions in the Shendong mining area (China). The soil water content (θ) was measured under different depths and topographies using an HH2 moisture meter. The infiltration process was studied using a Guelph soil permeameter. A set of hydrodynamic variables was calculated in the laboratory. The θ of the first 20 cm was the lowest and increased with depth. The content of soil water increased from the top slope to the bottom slope. The infiltration experiments showed that the steady state infiltration rate was >40 mm h−1 in most cases. Owing to the higher contents of sand and soil macropores at the top of the slope and the top 0–20 cm of surface soil, the initial infiltration rate and steady infiltration rate were higher. The average available water capacity was 18.28%, which was consistent with the predominance of a sandy textural fraction. The results of a soil water retention curve and a rainfall simulation experiment showed that there was a low soil water retention capacity throughout the whole profile. This study contributes to the understanding of several aspects of the soil water behavior of sandy soils and provides key information for environmental management and land reclamation under semiarid conditions in the Shendong mining area. [ABSTRACT FROM AUTHOR]

Identification of water flow through non‐root soil macropores and along roots using X‐ray computed tomography (CT) is still challenging because of limited methods to quantify roots and pore structures. This study selected shrub‐encroached grassland consisting of a mosaic of shrub patches and interspace grass patches and the original grassland as a control treatment. Twelve intact soil columns (0–30 cm deep) were excavated, which included four replicates each from the soils under the original grassland, the shrub patches and interspace grass patches. Three‐dimensional networks of soil macropores and roots were quantified using CT scanning and image analysis techniques, and active flow pathways were identified through KI tracing experiment using CT scanning. The results showed that the tracer depths of soils under the shrub patches and interspace grass patches were deeper than those of the original grassland, which was attributed to the well‐developed root system. The tracer volume density was significantly and positively correlated with soil macropore node density and root volume density (p < 0.05), and significantly and negatively correlated with root mean angle (p < 0.05). Soils under the shrub patches had lower tracer volume density than that under the interspace grass patches, which was attributed to the horizontal‐oriented roots under the shrub patches. The relative contribution of water flow along roots was larger than that through non‐root soil macropores 35 min after dye application. This provided direct evidence that shrub roots were the main pathway of macropore flow resulting in water flow into deep soil layers in the shrub‐encroached grassland. Highlights: The tracer depths of shrub‐encroached grassland were deep due to well‐developed root system.Shrub patches had low tracer volume density due to the horizontal‐oriented roots.The contribution of water flow along roots was larger than that through non‐root soil macropores.Shrub roots were the main pathway of water flow. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Irrigation & Drainage is the property of Journal of Irrigation & Drainage Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil infiltration at a watershed scale is important for understanding and predicting the hydrological process in soil-water-plant systems. This study investigated the effects of land use (LU) conversion on the infiltration rate in the Ouriyori watershed. To that end, in situ infiltration was carried out over the watershed under thirty-six pairs of adjacent cropland-fallow plots using the hood infiltrometer. Saturated hydraulic conductivity (Ks), soil properties, and soil classes were further compared. Results showed a high variability of Ks following the LU classes with a coefficient of variation greater than 60%. After data log transformation, the mean values of Ks showed high infiltration and ranged between 2.59 and 2.42 cm d−1, respectively, for fallow land and cropland. Thus, Ks was relatively lower in cropland compared to fallow land. Hence, the low infiltration recorded in croplands indicated the degradative impacts of unceasing tillage operations for crop production without crop residue incorporation into the soil during tillage. There was no significant difference in bulk density and soil texture in both types of land use. Considering soil classes, the highest infiltration rate was found in Ferric Luvisol and the lowest rate in Dystric Gleysol, meaning that the high infiltration observed in Ferric Luvisol was due to the abundance of soil macropores. Change in natural vegetation to croplands induced a low infiltration rate and macropore connectivity. Moreover, fallow lands tend to provide water storage capacity through the improvement of mesopores, while soil compaction through agricultural activities reduces soil porosity and therefore soil infiltration. In addition, the paired Student's t-test performed on the transformed data was statistically significant, indicating a difference between Ks under cropland and Ks under fallow land. To improve soil and water conservation for crop production as well as for sustainable rural populations' livelihoods in the watershed, occasional fallowing may be observed to dampen infiltration hindering soil surface conditions. [ABSTRACT FROM AUTHOR]

Copyright of Forest Research is the property of Forest Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Purpose: Preferential flow via soil macropores can have a large effect on water quality. Hence, it is important to quantify soil macropore characteristics to better understand preferential flow behavior in soils. Currently, little information exists on the changes in soil macroporosity in response to topographical position within a field and how macropore characteristics change temporally. The objective of this study was to use X-ray computed tomography (CT) and image analysis to quantify temporal and spatial variability in 3D soil macropore structure in a 0.40 ha pasture field. Methods: A total of 36 undisturbed soil columns, 150 mm in diameter and 500 mm in length, were collected during May and September of 2019 from a pasture field located in Alabama, USA. The image analysis was performed to quantify spatial and temporal variability in soil macropore characteristics. Results and discussion: The macropore characteristics varied significantly between different topographical positions and sampling seasons, especially at the surface layer (0–100 mm) depth. The soil macropores at the downslope position were sparsely distributed in the surface soil layer. This was attributed to a relatively higher degree of grazing-induced compaction due to higher soil moisture as compared to the upslope and midslope locations. In contrast, dense macropore networks were observed at the downslope positions for depths greater than 250 mm. Conclusions: The results of this study show that macropore characteristics varied as a function of topography and time. Except macropore diameter, all other macropore characteristics showed an increasing trend from season 1 (spring) to season 2 (fall). The regeneration of macropores was mainly attributed to the wetting and drying cycles that promoted formation of smaller macropores (0.70–1 mm) at the surface soil, thereby reducing the average macropore diameter. Significant differences in the macropore characteristics were observed mostly in the surface layer (0–100 mm). [ABSTRACT FROM AUTHOR]

The characteristics of soil macropores and water infiltration are closely connected to the growth of plant roots and their root zone environment. However, it is unclear how the root zone environment of oasis farmlands regulates the development of soil macropores and water flow in hyper‐arid regions. The objective of this study was to investigate soil macropores and their effect on water flow under irrigated oasis farmlands using a combination of X‐ray computed tomography (CT) and dye tracer. It was hypothesized that the integration of CT and dye tracer could clearly reveal preferential flow through biopores and large pores of oasis soils. A helical medical CT scanner was used to quantify more information about soil macropores in the root zone, along with an in situ single‐ring dye infiltration experiment to reveal water flow in three different oasis farmlands (piedmont oasis farmland, marginal oasis farmland, and old oasis farmland). Soil macroporosity was 0.44% under crop rows, while soil macroporosity in the interrows was only 0.30% across the oasis farmlands. Biopores contributed 73% of the volume of the total macropores under crop rows. The stable infiltration rate in the interrows was 0.3 mm min−1, which was significantly (p < 0.05) less than that under crop rows (0.7 mm min−1). Water flow under crop rows were mainly transported in biopores and large pores. The contribution of macropores to preferential flow under crop rows was 4.8 times larger than interrows. The integration of CT and dye tracer was a more holistic technique, which adequately revealed that oases had preferential flow affected by biopores and large pores, resulting in higher solute and contaminant transport. Key Points: Soil macropores and preferential flow affected by crop roots were investigated in hyper‐arid regions.The integration of CT and dye tracer adequately identified preferential flowpaths of oasis soils.Biopores were larger under crop rows than interrows.Preferential flow transported in biopores and large soil pores under crop rows. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bioenergy sorghum has high biomass yield potential, drought resilience, good nitrogen use efficiency, and a root system that contributes to the accumulation of soil organic carbon. In this study, field grown bioenergy sorghum root systems were analyzed during the growing season to characterize their depth, biomass, morphology, anatomy, and gene expression profiles. Bioenergy sorghum roots grew continuously during a 155‐day growing season producing ~175 nodal roots, accumulating ~7 Mg of dry biomass per hectare, and reaching >2 m deep in the soil profile. Nodal roots within 20 cm of the stem were 1–5 mm in diameter, whereas roots deeper in soil profiles were enriched in lateral roots with small diameters (~30–500 µm) enabling growth through soil macropores. In older field‐grown plants, roots with intact endodermal, vascular and inner root tissues were surrounded by degraded or aerenchyma‐filled epidermal and cortical cell layers. Transcriptome analysis of nodal, surface, and deep roots identified >2,500 differentially expressed genes involved in root growth, transport, adaptation, defense, and AMF–root interaction. Deep roots (180–240 cm) differentially expressed genes that regulate lateral root growth. Surface roots (0–20 cm) located mid‐row differentially expressed genes involved in nitrate transport, whereas ammonium transport genes were expressed in surface and deep roots and genes involved in phosphate transport were expressed in nodal, surface, and deep roots. Overall, bioenergy sorghum's long growing season enables root systems to grow deeper and accumulate more biomass than annual grain crops such as maize, attributes that could help restore annual cropland soil organic carbon levels and improve soil productivity. Deep roots active in nutrient transport are positioned to take‐up fertilizer leached deep into soil profiles mitigating potential nutrient run‐off. Bioenergy sorghum's large and deep root system is a key to sustainable production of biofuels, biopower, and bioproducts on annual cropland. [ABSTRACT FROM AUTHOR]

The focus of this paper was directed towards investigating the influence of multiple freeze–thaw (FT) cycles on the mechanical behaviors of an expansive soil under a wide range of confining stresses (σc) from 0 to 300 kPa. Consolidated undrained (CU) shear tests with pore pressure measurement (σc = 10–300 kPa) and unconfined compression (UC) tests (σc = 0 kPa) were conducted on FT impact specimens to derive the shearing stress–strain relationships and the associated mechanical properties including (i) failure strength (qu), elastic modulus (Eu), effective and apparent cohesion (c′ and c), and effective and apparent friction angle (ϕ′ and ϕ) obtained from CU tests and (ii) qu and reloading modulus (E1%) and stress (Su1%) at 1% strain obtained from UC tests. Besides, the influence of FT cycles on the soil structure was investigated using mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) tests. Testing results show that FT cycles mainly influence the soil's macropores with diameters between 5 and 250 μ. Cracks develop during FT cycles and result in slight swelling which contributes to an increase in the global volume of the soil specimens. There is a significant reduction in the investigated mechanical properties after FT cycles. They typically achieve equilibrium after about six cycles. The shearing stress–strain curves transit from strain-softening to strain-hardening as the confining stress increases. A simple empirical model is developed to well describe the strain-softening behavior of the stress–strain curves under low confining stresses. [ABSTRACT FROM AUTHOR]

From 9 March 2016 to 12 November 2018 we conducted an intensive experimental field campaign, the WormEx I Experiment, to quantitatively assess the seasonality of the earthworm macropores and their effect on the soil hydrological properties in a temperate mountain range. Six 1-m2 plots were selected in two shallow soils in Valle Camonica (Central Italian Alps) at an elevation of 274 and 935 m a.s.l., in order to count the earthworm macropores. Two plots were amended with calcium trioxocarbonate to stimulate the digging activity. In this work we present results regarding the seasonality of earthworm macropores, its correlation with the antecedent meteorological conditions and the effectiveness of calcium trioxocarbonate. Earthworm activity showed a marked seasonality with Winter hibernation and medium or great digging activity during all the other seasons. A relevant peak of Summer and Autumn macropores was detected in the site at 935 m a.s.l.. The castings number resulted very well positively correlated to the antecedent air temperature in both sites. It resulted correlated to the antecedent precipitation, with increasing Pearson's coefficient at increasing time window in the range from 1 day to 8 weeks. Also, it resulted very well positively correlated to the antecedent average soil water content in a range from 1 to 4 days. Finally, the calcium trioxocarbonate proved to be effective at stimulating the earthworm digging activity. [ABSTRACT FROM AUTHOR]

The existence of soil macropores is a common phenomenon. Due to the existence of soil macropores, the amount of solute loss carried by water is deeply modified, which affects watershed hydrologic response. In this study, a new improved BP (Back Propagation) neural network method, usingLevenberg-Marquand training algorithm, was used to analyze the solute loss on slopes taking into account the soil macropores. The rainfall intensity, duration, the slope, the characteristic scale of macropores and the adsorption coefficient of ions, are used as the variables of network input layer. The network middle layer is used as hidden layer, the number of hidden nodes is five, and a tangent transfer function is used as its neurons transfer function. The cumulative solute loss on the slope is used as the variable of network output layer.A linear transfer function is used as its neurons transfer function. Artificial rainfall simulation experiments are conducted in indoor experimental tanks in order to verify this model. The error analysis and the performance comparison between the proposed method and traditional gradient descent method are done. The results showthat the convergence rate and the prediction accuracy of the proposed method are obviously higher than that of traditional gradient descent method. In addition, using the experimental data, the influence of soil macropores on slope solute loss has been further confirmed before the simulation. [ABSTRACT FROM AUTHOR]

In this review, we explore the concept, approach, and future research of hydrological connectivity and its assessment at multiscales, because according to the literature, an integrated review upon hydrological connectivity is lack. Systematic studies illustrate the effects of (i) human activities (i.e., dam construction, groundwater extraction, water flow regulation and diversion, and land management) and (ii) natural factors (i.e., climate, soil characteristics, vegetation, and topography) on hydrological connectivity. Approaches (i.e., soil water content patterns, runoff patterns and processes, numerical models, and index of hydrological connectivity) applied to evaluate hydrological connectivity are examined in detail. Lastly, hydrological connectivity at multiscales is indicated. This review concludes with a discussion of potential research trends that can improve understanding of hydrological connectivity. Reported records showed that few studies were published on hydrological connectivity from 1980 to 2003, whereas the evolution of these studies is temporally promising since 2003. We cannot define a standard concept of hydrological connectivity that works in all environments. We desire to show different concepts of hydrological connectivity in different environments. The degree and nature of hydrological connectivity are not static due to the influences of human activities and changes of natural factors. The index of hydrological connectivity and numerical models are the most significant approaches to assess the changes in hydrological connectivity. This study showed that considering hydrological connectivity in social-economical-ecological-hydrological frameworks can prevent its negative effects on surface or subsurface water quantity and quality and is beneficial for sound water sources management. [ABSTRACT FROM AUTHOR]

Aims: Cracks and biopores in compacted soil such as plough pans could aid deep rooting, mitigating constraints to seasonal upland use of paddy fields for rice production. This research investigated how soil macropores through a simulated plough pan affects root growth of contrasting deep and shallow rooting rice genotypes. Methods: Deep rooting Black Gora and shallow rooting IR64 rice varieties were grown in packed cores of unsaturated soil in a controlled greenhouse. Simulated biopores and cracks (macropores) were inserted through the plough pan to form treatments with no macropores, biopores, cracks, and combined cracks and biopores. Different root parameters such as root length density (RLD), root volume, root diameter, number of root tips and branches were measured. The number of roots was calculated manually, including the number of roots growing through macropores in the plough pan layer. Results: Plough pans with macropores had 25–32% more roots than with no macropores. RLD was 55% greater in the plough pan layer if cracks were present compared to biopores. Conversely, RLD was 26% less in subsoil if the plough pan had cracks compared to biopores. Different root parameters were greatly influenced by the presence of macropores in the plough pan, and deep-rooted Black Gora produced 81% greater RLD, 30% more root numbers and 103% more branching than the shallow rooted rice genotype IR64 within the plough pan layer. Conclusions: Macropores greatly improve rice root growth through plough pans for a deep rooting but not a shallow rooting rice variety. Whereas cracks produce a greater number of roots in the plough pan, biopores result in greater root branching and root numbers deeper in subsoil. [ABSTRACT FROM AUTHOR]