Physical Crusts Research Articles

Surface instability driven by wetting-drying cycles hinders the colonization by biocrusts in Tabernas Desert

AbstractCatchment asymmetry in the Tabernas Desert suggests a relatively greater instability in the sunnier hillslope in a very early stage of catchment development due to abiotic factors, which would hinder the biocrust colonization. In the absence of erosion, such a difference in stability between opposite hillslopes could be due to differences in wetting-drying cycles. To verify this, as biocrust types assumed as successional stages are associated with different microhabitats, the surface movements of three types of physical crusts (Structural, Depositional and Island) and four biocrust types, representative of different stages of succession (Incipient, Cyanobacteria, Squamarina and Lepraria), were analyzed based on the distances calculated between markers placed on a grid on the soil surface. Two sample groups were analyzed: in situ samples, with four plots per crust type, and ex situ, with four unaltered samples per crust type extracted from the field site to control the effect of slope angle, orientation, trampling by animals, etc. Physical crusts showed greater surface instability compared to biocrusts, and this instability was influenced by the amount and frequency of precipitation. Biocrusts were more stable and elastic to surface movements, often recovering their initial position, and this stability increased throughout succession. Furthermore, the results showed that reducing instability (when sediment deposition ceases) favors colonization. Our results support the hypothesis that, in absence of erosive events, larger surface instability due to wetting-drying cycles hinders biocrust colonization on the relatively sunnier hillslopes with physical crusts; however, it is unknown where (or when) biocrust can develop.

Biological soil crusts significantly improve soil fertility and change soil microbiomes in Qinghai-Tibetan alpine grasslands.

Biological soil crusts (BSCs), a vital component of ecosystems, are pivotal in carbon sequestration, nutrient enrichment, and microbial diversity conservation. However, their impact on soil microbiomes in alpine regions remains largely unexplored. Therefore, this study aimed to determine the influence of BSCs on alpine grassland soil microbiomes, by collecting 24 pairs of soils covered by biological and physical crusts along a transect on the Qinghai-Tibetan Plateau. We found that BSCs significantly increased the contents of soil moisture, organic carbon, total nitrogen, and many available nutrients. They also substantially altered the soil microbiomes. Specifically, BSCs significantly increased the relative abundance of Cyanobacteria, Verrucomicrobiota, and Ascomycota, while decreasing the proportions of Gemmatimonadota, Firmicutes, Nitrospirae, Mortierellomycota, and Glomeromycota. By contrast, microbial abundance and α-diversity demonstrated low sensitivity to BSCs across most study sites. Under the BSCs, the assembly of prokaryotic communities was more affected by homogeneous selection and drift, but less affected by dispersal limitation. Conversely, soil fungal community assembly mechanisms showed an inverse trend. Overall, this study provides a comprehensive understanding of the effects of BSCs on soil properties and microbial communities, offering vital insights into the ecological roles of BSCs.

Variation in preferential flow features induced by desiccation cracks in physical crusts

Studies have shown that preferential flow induced by cracks establishes multiple features such as morphology in different soil profiles. However, there has been little experimental evidence of the contribution of physical crust towards crack features and preferential flow. Essentially, this investigation focused on physical crusts (structural and deposition crust) of Lou soil, a loam and silt loam-textured soil, to demarcate the formation of cracks and preferential flow under artificial rainfall. The crack initiation and propagation processes were defined as the formation of primary cracks in the initial phase and narrow cracks around primary cracks, respectively. The cylindrical soil containers and cubical stainless-steel boxes were employed to trace preferential flow in the horizontal and vertical profile, respectively. The cracks in structural and deposition crusts were dominated by initiation and propagation cracks, respectively. The area, length, and width of the cracks in the structural crusts (5.7 cm2, 815, and 1.44 mm) were notably larger than deposition crusts (1.7 cm2, 604, and 0.96 mm). The maximum dyed depths of the structural and deposition crusts reached 35, 45, and 65 mm, and 35, 55, and 75 mm under the infiltration amounts of 10, 30, and 50 mm, respectively. The uniform infiltration depth, length index and PF-fr of structural crusts were in the ranges of 6.7 ∼ 25.5 mm, 19 ∼ 46 %, and 83 ∼ 111 %, respectively. Corresponding values for deposition crusts were 7.2 ∼ 26.2 mm, 10 ∼ 46 %, and 87 ∼ 103 %, respectively. The preferential flow in the soil profiles with structural crusts was superior to deposition crust. An assessment of the potential function of the physical crust for preferential flow is a supplement to study the effect of soil surface morphology on hydrological process.

Soil physicochemical properties and crusts regulate the soil infiltration capacity after land-use conversions from farmlands in semiarid areas

Large scale land-use conversions played important role in regulating the process of soil infiltration, and thus changing soil moisture recharge. However, how the soil properties influence infiltration after farmland conversions remain unclear in the semiarid areas. This study used a double-ring infiltrometer to conduct infiltration experiments in soil surface and subsurface among land-uses on the Loess Plateau, to explore the mechanism of soil physicochemical properties and crusts on infiltration. The results showed that the revegetation lands effectively improved infiltration properties, while no significant differences were observed between the orchards and the farmlands. The loose soil structure, stable aggregates, higher organic matter and root mass density improved while soil crusts impeded infiltration capacity after farmland conversions. The impeding effect of the biocrusts presented throughout the infiltration process while physical crusts impeded infiltration only at the initial stage. Soil physical properties (i.e., bulk density, porosity, macroaggregate, texture, moisture), biochemical properties (i.e., soil organic matter, roots) and crusts were major factors in the variation of the surface (0–20 cm) infiltration properties, while subsurface (20–40 cm) infiltration were mainly influenced by soil physical properties. The deeper soils had a greater impact on steady infiltration rate than initial infiltration rate. Due to the plough pan in agricultural lands, the subsurface soil (20–40 cm) had a strong effect (42.1%) on the steady infiltration rate of the surface (0–20 cm) soil, even close to the surface (0–20 cm) soils (49.8%). These findings improve the comprehensive understanding of the soil hydrological processes after farmlands conversions in semiarid areas.

Variation in sprinkler irrigation droplet impact angle on the physical crusting properties of soils

The angle at which a droplet impacts determines its shearing and compaction effects on soil, which in turn affects the formation and properties of the physical soil crust. To investigate the effect of the droplet impact angle on soil physical crusting, this study considered droplet quantity, quality, and velocity and proposes an energy-weighted method for calculation of the equivalent droplet impact angle. Droplet information was acquired using a spraying platform with a controllable droplet impact angle and two-dimensional video disdrometer (2DVD). Six groups (38.10°, 49.43°, 58.77°, 68.88°, 76.81° and 84.10°) of droplet impact angles were established to obtain the parameters of the soil physical crust characteristics at different droplet impact angles by indoor soil tank tests. The results show that: 1) the stable values of crack length density (CLD), crust thickness (Ct), soil bulk density (BD), cohesion force (Cf), and internal friction angle (IfA) are strongly positively correlated with droplet impact angle; 2) the stable value of the crack area ratio (CAR) is strongly negatively correlated with the droplet impact angle, with maximum and minimum values of 6.94% and 5.57%, respectively; 3) the content of macro aggregates (MAA) tends to increase and then decrease with the increase in droplet impact angle, and the content of MAA has a maximum value of 50.2% at the impact angle of 68.88°. The content of micro aggregates (MIA) tends to decrease and then increase with the increase in the drop impact angle, with a minimum value of MIA of 20.4% at the impact angle of 58.77°; 4) the maximum soil bulk density of 1.99 g·cm−3 at an impact angle of 84.10° is significantly greater than the initial soil bulk density (1.35 g·cm−3); 5) the energy-weighted equivalent droplet impact angle takes into account the effects of both large and small droplets and characterises the overall impact angle of the sprayed droplet from an energy perspective. The results of this study provide new ideas for determining suitable sprinkler irrigation parameters to reduce soil erosion and promote the sustainable development of irrigated agriculture.

Effects of straw incorporation on soil erosion resistance along a land degradation gradient in the black soil region of China

Soil erosion resistance (reflected by rill erodibility and critical shear stress) is a useful parameter for evaluating soil erosion subjected to concentrated flow. The changes in soil properties and root trait induced by straw incorporation and land degradation likely affect soil erosion resistance considerably. Nevertheless, few studies have been conducted to quantify the effects of straw incorporation on soil erosion resistance of degraded croplands in the black soil region. In this study, a large hydraulic flume (5.0 m in length and 0.4 m in width) was utilized to quantify the impacts of straw incorporation on soil erosion resistance of four croplands with different degradation degrees (non-degradation, light degradation, moderate degradation and strong degradation) and further to determine the related influencing mechanisms in Northeast China. The results showed that straw incorporation reduced rill erodibility by 44.9%, 41.2%, 27.1% and −11.4% for non-degradation, light degradation, moderate degradation and strong degradation croplands, respectively. Land degradation degree had much stronger influence on soil erosion resistance than that of straw incorporation and regulated the roles of straw incorporation in mitigating erosion. Rill erodibility was significantly and negatively correlated with clay content, organic matter content, aggregate stability, soil cohesion, physical crust thickness and root mass density, whereas positively correlated with silt content. The increase in soil organic matter and clay content was the key to improve soil erosion resistance and prevent land degradation. Straw incorporation was suggested in non-degradation, light degradation and moderate degradation croplands, but vegetation restoration was recommended in strong degraded cropland. The results are helpful to understand the mechanism of straw incorporation to improve soil erosion resistance and make reasonable agricultural management strategies in semi humid region.

Effects of physical crust on soil detachment by overland flow in the Loess Plateau region of China

Physical soil crust (PSC), a key component of surface soil structure, exists extensively in loess areas. PSC is considered to have a significant effect on soil detachment processes. However, the long-term effects and the corresponding mechanisms of PSC on soil detachment by overland flow are still not well understood, especially in natural environments. To investigate temporal variation in soil erosion resistance and the underlying factors during PSC formation, an 8 × 8-m soil plot was exposed to natural conditions in the Loess Plateau over a 524-day period spanning two rainy seasons and a winter between them. A flume test was conducted to determine soil detachment capacity (Dc) under six designed flow shear stress levels (5.66–22.11 Pa) using crusted (SC) and non-crusted (NSC) soil samples at different PSC development stages. Subsequently, two soil erosion resistance parameters, rill erodibility (Kr) and critical shear stress (τc), were calculated. Over time, in the SC and NSC treatments, Kr decreased from 0.516 to 0.120 s m−1 and 0.521 to 0.223 s m−1, respectively, while τc increased from 0.49 to 4.42 Pa and 0.26–2.46 Pa, respectively. Variation in soil erosion resistance was rapid in the first one to two months, and then slowed down, with slight fluctuations afterwards. In the SC treatment, Kr was 42% lower and τc was 67% greater than those in the NSC treatment. Soil properties changed greatly for both treatments. SCT increased from 0 to 7.09 mm in the SC treatment. Coh increased from 2.91 to 9.04 kPa and 3.01–4.78 kPa in SC and NSC treatments, respectively. Both soil erosion resistance parameters could be well predicted by SCT and Coh in the SC treatment (R2 ≥ 0.82), while their best predictor was Coh in the NSC treatment (R2 ≥ 0.90). The results demonstrate that PSC formation enhances soil erosion resistance in the soil detachment process in the loess region under natural conditions. Our study revealed the important role and complexity of PSC in the process of soil erosion, and provided theoretical and data support for accurate understanding and prediction of soil erosion.

Runoff and soil loss in biocrusts and physical crusts from the Tabernas Desert (southeast Spain) according to rainfall intensity.

Biological soil crusts (biocrusts) influence hydrological and erosive processes in drylands, and their effects increase with hypothetic successional development. Runoff and raindrops, both dependent on rain intensity, are among the main causes of erosion in these areas. However, little is known about the existence of soil loss nonlinearity in relation to rain intensity and crust types; this nonlinearity could control biocrust succession and dynamics. The assumption of biocrust types as successional stages, which allow space-for-time sampling, makes it advisable to include all the successional stages when exploring possible nonlinearity. We considered seven types of crusts, three physical and four biological. We created four rainfall intensity levels in controlled laboratory conditions: 18, 60, 120, and 240 mm/h. In all but the last, we conducted the experiments at two levels of antecedent soil moisture. Generalized Lineal Models enabled us to test for differences. These analyses confirmed previous knowledge regarding the significant effect of rainfall intensity, crust type and antecedent soil moisture and their interactions on runoff and soil loss, despite the small sample size of the sample units. For example, runoff, and particularly soil loss, decreased along succession. Moreover, some results were novel: the runoff coefficient increased only up to 120 mm/h of rain intensity. A decoupling between runoff and soil loss occurred at high intensities. Soil loss increased as rainfall intensity increased only up to 60 mm/h, and then it decreased, mainly due to physical crusts, because of the formation of a water sheet on the surface due to the incoming rainwater exceeding the drainage capacity. Although soil loss was greater in the incipient cyanobacteria than in the most developed lichen biocrust (Lepraria community), the protection provided by any biocrust against soil loss was great compared to the physical crust, and almost as strong at all rain intensities. Soil loss increased with antecedent soil moisture only in physical crusts. Biocrusts resisted the rain splash even at a rainfall intensity of 240 mm/h.

Infiltration properties affected by slope position on cropped hillslopes

Soil infiltration properties (SIPs) and their spatial variability are essential for simulating hydrologic and erosion processes. Intensive water erosion likely leads to large spatial heterogeneity of soil particle distribution, thus the large spatial variability of general soil properties, such as SIPs. Nevertheless, little is known about the spatial variabilities of SIPs along long, gentle hillslopes and their dominant controlling factors. This study was conducted to investigate SIPs under different slope positions under agricultural management and to identify dominant SIP-related factors in the Black-soil region of Northeast China. Soil infiltration properties were determined at five slope positions (i.e. upper, middle-upper, middle, middle-lower, and lower) on two approximate 5 % hillslopes using a disc infiltrometer under three pressure heads (-3, −1.5, and 0 cm). Results showed that the initial infiltration rate (IIR), steady infiltration rate (SIR), and saturated hydraulic conductivity (KS) varied from 0.11 to 0.47 mm min−1, 0.04 to 0.30 mm min−1, and 0.04 to 0.29 mm min−1, respectively. Soil infiltration properties generally increased initially, then decreased from the upper to the lower position along the hillslope. The middle-slope position had the numeric maximum SIPs, and SIPs were significantly greater than those of the upper and lower slope positions. Compared to the middle-slope position, IIR, SIR, and Ks of the upper and lower slope positions were lower by 50.9, 61.1, 63.6 and 33.8, 32.3, 34.6 %, respectively. Initial infiltration rate, SIR, and Ks were positively correlated with sand content (r = 0.60, 0.69, 0.69; p < 0.01), total porosity (r = 0.67, 0.71, 0.71, respectively; p < 0.01), saturated soil water content (r = 0.62, 0.70, 0.71, respectively; p < 0.01), and gravel content (r = 0.48, 0.66, 0.70, respectively; p ≤ 0.01), but were negatively correlated with silt (r = -0.50, −0.49, −0.49, respectively; p ≤ 0.01) and clay (r = -0.50, −0.64, −0.63, respectively; p ≤ 0.01) contents, bulk density (r = -0.67, −0.70, −0.70, respectively; p < 0.01), and physical crust thickness (r = -0.63, −0.73, −0.73, respectively; p < 0.01) across positions of the two hillslopes. The result of redundancy analysis indicated that physical crust thickness, bulk density, and water-stable aggregate and clay contents were the dominant factors attributed to the variation in SIPs under different slope positions, and collectively they explained 74.6 % of the total variation of SIPs. Physical crust thickness alone explained the largest proportion (49.9 %) of the variation of SIPs. Results will be helpful for improving precision of hydrologic and erosion processes modeling and sustainable soil management on long, gentle hillslopes in the agricultural region of Northeast China.

Use of multifractal parameters to determine soil particle size distribution and erodibility of a physical soil crust in the Loess Plateau, China

Understanding the knowledge of multifractal analysis on particle size distribution (PSD) of soil physical crusts is indispensable for progressing soil surface erosion mode. In this study, hoeing tillage (20 cm long × 15 cm wide × 5 cm deep) were conducted to simulate classic tillage mode in Yangling, China to obtain physical crusts under artificial rainfall (60 mm h−1 intensity with three durations (5, 15, and 30 min)). We defined crusts formed in ridges as structural crust (Cst), formed by infiltration of runoff in hoes as sediment-containing depositional crust (Cscd), and formed by the extraction of runoff as sediment-free depositional crust (Csfd). Soil stratification methods were used to explore physical crust particle sorting. Results represented that the sand content of Cst, Cscd, and Csfd decreased, whereas clay and silt contents increased after rainfall compared to undisturbed soil. There was no significant difference between Cscd and Csfd under short rainfall duration. Three crust types became gradually concentrated in areas with higher density with increasing rainfall duration according to six common parameters in the generalised dimension spectrum (D0, D1, D2, D1/D0, Dv(D-10–D0), and Ds(D0–D10)). Multifractal singularity spectrum (α0, Av, Fv) showed that PSD was most symmetrical in Csfd, followed by Cscd and Cst. Erodibility index KEPIC was largest for Cst, followed by Csfd then Cscd. The relationship between KEPIC and multifractal parameters were significant. Spatial difference caused by tillage activities and rainfall events determine the heterogeneous formation mode, particle size distribution and erodibility of physical crust.

Biocrust Amendments to Topsoils Facilitate Biocrust Restoration in a Post-mining Arid Environment.

Soil cryptogamic biocrusts provide many ecological functions in arid zone ecosystems, though their natural reestablishment in disturbed areas is slow. Accelerating reestablishment of biocrusts may facilitate the establishment of vascular plant communities within the timeframes of restoration targets (typically 5–15 years). One technique is to inoculate the soil surface using slurries of biocrust material harvested from another site. However, this is destructive to donor sites, and hence the potential to dilute slurries will govern the feasibility of this practice at large spatial scales. We conducted a replicated experiment on a disturbed mine site to test the individual and combined effects of two strategies for accelerating soil cryptogamic biocrust reestablishment: (1) slurry inoculation using biocrust material harvested from native vegetation; and (2) the use of psyllium husk powder as a source of mucilage to bind the soil surface, and to potentially provide a more cohesive substrate for biocrust development. The experiment comprised 90 experimental plots across six treatments, including different dilutions of the biocrust slurries and treatments with and without psyllium. Over 20 months, the reestablishing crust was dominated by cyanobacteria (including Tolypothrix distorta and Oculatella atacamensis), and these established more rapidly in the inoculated treatments than in the control treatments. The inoculated treatments also maintained this cover of cyanobacteria better through prolonged adverse conditions. The dilute biocrust slurry, at 1:100 of the biocrust in the remnant vegetation, performed as well as the 1:10 slurry, suggesting that strong dilution of biocrust slurry may improve the feasibility of using this technique at larger spatial scales. Psyllium husk powder did not improve biocrust development but helped to maintain a soil physical crust through hot, dry, and windy conditions, and so the potential longer-term advantages of psyllium need to be tested.

Response of Sheet Erosion to the Characteristics of Physical Soil Crusts for Loessial Soils

The influences and quantifications of soil crust traits on the infiltration, hydrodynamic of runoff, and erosion rate of sheet erosion under the combined effects of raindrop impact and sheet flow scouring need further study. Loessial soil from the Loess Plateau was tested to produce different antecedent crusts under simulated rainfall intensities (0.5, 1.0, 1.5, 2.0, and 2.5 mm/min, typical storm intensity in the area), and then the effects of antecedent crusts on sheet erosion processes were quantified at a rainfall intensity of 1.5 mm/min. The results showed that the bulk density and hardness of antecedent crusts were higher than those of soil. Particle sizes of crusts were smaller than those of soil at light rain intensity but larger under heavy rain intensity. The bulk density, hardness, and particle size D50 of the antecedent crust were all positively correlated with rainfall intensity, being well described by linear equations (R2 &amp;gt; 0.87), while the thickness was negatively linearly correlated with rainfall intensity (R2 = 0.88). Although the existence of antecedent crusts could decrease the infiltration and increase the runoff, resulting in the high flow velocity and stream power, antecedent crusts could still effectively reduce sheet erosion. The reductions in the average infiltration rate and average erosion rate and the increases of average flow velocity and stream power all increased with the increment of bulk density of antecedent crust. Relationships could be all well described by linear positive correlations (R2 &amp;gt; 0.79). When the bulk density of crust was enhanced by 27∼29%, the flow velocity and stream power could be increased by 8∼29% and 15∼70%, and the sheet erosion could be reduced by 61∼73%. The existence of crust could effectively reduce sheet erosion. These results could help understand the mechanism of the erosion process in the presence of physical crusts.

Water repellent characteristics of physical and biological crusts and their effects on water infiltration

Soil crust is a normal natural phenomenon with different water hydrophilicity and repellency due to different formation mechanism, thus affecting soil hydraulic characteristics and hydrological cycle. In this study, we measured water repellent characteristics of physical and biological crusts under different vegetations in the field using water drop penetration time (WDPT). The surface morphology of crusts was observed using scanning electron microscopy, and the infiltration characteristics of crusts and their non-crust soils (control) was evaluated with micro-infiltration device. The results showed that: 1) The average WDPT of physical crusts and the control soils was 3.3 s and 0.9 s, respectively, indicating that both were hydrophilic. The average WDPT of biological crusts ranged from 20.9 s to 140.9 s, which was 2.8 to 19 times that of control, and that under Diospyros lotus and Robinia pseudoacacia was 134.5 s and 140.9 s, respectively. 2) Compared with the control, the cumulative infiltration amount, average infiltration rate and moisture absorption force of physical crusts decreased by 0-4.3%, 3.5%-5.1%, and 27.2%-90.1%, respectively, while those of biological crusts decreased by 0-25%, 1.4%-28.2% and 36.0%-84.9%, respectively. 3) Regardless of the presence of crusts or not, there were "hockey-stick-like" curves by using Philip model to fit infiltration data. Before the WRCT point in the "hockey-stick-like" curve, the point source infiltration was mainly horizontal diffusion. After the WRCT point, the infiltration was mainly vertical diffusion. The presence of soil crust prolonged the formation time of the turning point. In all, physical crusts formed by inorganic mineral particles blocking the surface soil did not affect water repellency, while biological crusts that reflected the effects of hydrophobic organic compounds on soil structure enhanced its water repellency. Both physical crusts and biological crusts decreased the cumulative infiltration amount and average infiltration rate of soil. Compared with the control, physical crusts mainly affected soil hygroscopicity, but with limited effects on the steady infiltration rate. Biological crust decreased soil hygroscopicity and increased steady infiltration rate.

Aggregate stability in rainfall‐induced soil physical crusts on the Loess Plateau, Northwest China

AbstractComprehensive insights into the aggregate stability of physical crusts enhance the understanding of erosional processes and transport mechanisms. This study evaluated the erosion resistance and aggregate stability in structural and sedimentary crusts of a Lou soil induced by simulated rainfall. A runoff plot (200 cm long × 100 cm wide × 50 cm high) with a slope of 5° was set up to simulate contour tillage (20 cm in ridges, 30 cm in furrows). A single rainfall intensity (60 mm h−1) was applied over six durations (5, 10, 15, 20, 25, and 30 min) to obtain structural and sedimentary crusts. With an increase in rainfall duration, bulk density of structural and sedimentary crusts increased from 1.26 g cm−3 (soil before rainfall) to 1.56 and 1.58 g cm−3, respectively. Macroaggregate contents in structural crust changed slightly (from 7.5 to 7.4%); however, a marked increase (from 9.0 to 18.6%) was observed in sedimentary crust with increased rainfall duration. The mean weight diameter and geometric mean diameter (i.e., the inverse of erodibility factor) in structural crusts were lower than sedimentary crusts developed from all rainfall conditions. The aggregate stability index of structural and sedimentary crusts initially increased from 2.12 and 2.07 with the increase in rainfall duration, respectively, and then leveled off at 2.42 and 2.48. Soil aggregate stability of sedimentary crust, which conferred greater resistance against external erosive forces, was stronger than that of structural crust.

The Effect of Sea Salt with Low Sodium Content on Dough Rheological Properties and Bread Quality

The aim of this study was to analyze the effects of the addition of sea salt with low sodium content (SS) in a refined wheat flour at the levels of 0.3%, 0.6%, 0.9% 1.2% and 1.5% on the rheological properties of the dough during mixing, extension, pasting and fermentation and the bread quality in terms of bread physical properties, crumb and crust color, texture and sensory characteristics. According to the data we obtained, the SS presented a strengthening effect on the dough network by increasing its stability, dough development time, energy and resistance. Moreover, the SS addition resulted in an increase in dough extensibility, to a delay of the gelatinization process and an increase of the falling number value. The bakery products obtained with the SS were of a higher quality compared to the control sample, presenting better physical and textural characteristics, a darker color and being more appreciated by consumers with the increased level of SS addition in the wheat flour. According to the sodium content from the bread recipe, the bread samples obtained may be classified as products with a very low sodium content of up to a 0.6% SS addition in the wheat flour or with a low sodium content if at least 0.9% SS is contained in the bread recipe.

Variations in the disintegration rate of physical crusts induced by artificial rainfall in different alcohol concentrations

Disintegration is closely correlated with geological disasters and soil erosion. However, quantitative studies on the disintegration processes of physical crust controlling the soil surface erosion are limited. Therefore, we disintegration process in structural and sedimentary crusts induced by artificial rainfall on a typical cropland soil from the Loess Plateau, China. The physical crusts were immersed for 200 s at different alcohol concentrations applied for delaying disintegration process to obtain disintegration rate (DR). The content of organic matter and the sand percentage in the structural and sedimentary crusts decreased with increasing rainfall duration, while the bulk density, silt and clay percentages increased. The initial DR values ranged from −0.01 to 1.82 in structural crusts and from −0.01 to 1.47 in sedimentary crusts under different alcohol concentrations. DR decreased by [86.5%, 91.3%] in structural crusts and by [86.3%, 88.2%] in sedimentary crusts during the whole disintegration period. For both structural and sedimentary crust, the DR was the lowest when the rainfall lasted for 30 min, and finally stabilized at 0.19 and 0.18, respectively, at the disintegration time of 80 s. Notably, the 50% alcohol concentration slowed the disintegration process most efficiently. The structural crust had a lower erosion resistance than the sedimentary crust due to the lower DR. These results provide a theoretical method for evaluating disintegration process and timely information revealing the erosion resistance mechanism of physical crusts.

Pore characteristics of physical crust samples from two typical erodible soils in southern China

AbstractPhysical soil crusts will form on most soils during and after rainfall, which has important impacts on hydrological and erosion processes by affecting soil pore structure. However, the soil pore characteristics of physical crusts of two typical erodible soils (quaternary red clay [QRC] and granite red soil [GRS]) in southern China are still unclear due to the limitations of objective and accurate quantitative methods. We scanned physical crusted (structural crust [SC] and depositional crust [DC]) soil samples from the QRC and GRS at various slopes using X‐ray computed tomography, and extracted and analysed soil pore characteristics using two‐ and three‐dimensional indexes. The averages of the two‐dimensional pore indexes, that is, pore number, porosity, circularity, and equivalent diameter across the four soil sample types were 116–205, 4.83%–8.31%, 0.83–0.87, and 0.19–0.28 mm, respectively, indicating the characteristics of a large number of small pores with nearly circular shape. The mean values of pore number and circularity were significantly smaller for the structural crust samples than the depositional crust samples, and the porosity and equivalent diameter were significantly larger for the structural crust samples than the depositional crust samples. The three‐dimensional pore indexes also differed among the four soil sample types, where the mean fractal dimension and surface area values for QRC were 2.62 and 1959.77 mm2, respectively, which were significantly larger than those for GRS (2.52 and 1457.97 mm2). The pore number and circularity decreased, the equivalent diameter increased, and the surface area and connectivity density increased initially and then decreased with the slope, mainly due to differences in the run‐off and sediment process, and crust formation process on slopes with different gradients. The results provide a scientific basis for the objective quantification of physical soil crusts to facilitate further studies on physical crusts affect run‐off and sediment processes.Highlights CT method was first used to quantify pore structure of crusted soil samples in southern China. The crusted soil pores had a feature of a large number of small pores with nearly circular shape. The two‐ and three‐dimensional soil pore indexes were differed among the four soil sample types. The slope had a negligible influence on soil pore structure.

Soil Particle Size Distribution and Erodibility of the Physical Crust Using Multifractal Parameters in the Loess Plateau, China

Soil Particle Size Distribution and Erodibility of the Physical Crust Using Multifractal Parameters in the Loess Plateau, China

Variation in soil detachment capacity of structural and sedimentary crusts induced by simulated rainfall formed on ridge and furrow

The response of erosion to soil physical crusts (i.e., structural and sedimentary crusts) has been extensively investigated. Yet few studies have quantified the effects of physical crusts on their detachment capacity (Dc). Accordingly, we investigated the variation in Dc of physical crusts as induced by simulated rainfall. The runoff plot (2.0 m long × 1.0 m wide × 0.5 m high) was set to a slope of 5° and filled with Lou soil (Haplic Luvisol) using horizontal tillage with ridges (1.0 m long × 0.2 m wide × 0.1 m high) and cm furrows (1.0 m long × 0.3 m wide × 0.1 m deep). Simulated rainfall was applied at a single intensity (60 mm h−1) for seven durations (0, 5, 10, 15, 20, 25, and 30 min) to obtain structural (at ridges) and sedimentary (at furrows) crusts. Crust samples were collected to obtain Dc, by scouring them for 2 min at a constant inflow discharge (0.8 L min−1) on a hydraulic flume (15° slope). For both structural and sedimentary crusts, with increasing rainfall duration, the measured bulk density (BD), crust thickness (Ct), micro-aggregate content (MIA), and disintegration index (DI) increased, whereas the macro-aggregate content (MAA) decreased. Dc of 0 min and structural crust formed within 5 min of rainfall decreased with a longer scouring time. By contrast, Dc of the other crust types initially rose with an extended scouring time but then plateaued after ∼ 60 s. Dc of sedimentary crusts were significantly lower than that of structural crusts. Notably, crusts formed by rainfall at 30 min had greatest detachment reduction benefit. Dc was inversely related to BD, Ct, MIA and DI, whereas increased with increasing MAA. This research provides a timely reference for the effect of physical crust on concentrated flow in arid and semi-arid areas.

Seasonal variation in soil erosion resistance to overland flow in gully-filled farmland on the Loess Plateau, China

Large areas of farmland have been established in China’s Loess Plateau region by backfilling forest and grasslands in gullies with topsoil from hillslopes. High amounts of plant litter are incorporated into the topsoil during such processes; however, their effects on soil erosion resistance under natural conditions are not fully understood. Therefore, the present study investigated seasonal variation in soil erosion resistance to overland flow and the underlying factors in the gully-filled farmland. Two typical plant litter species were selected in this study, i.e., Artemisia sacrorum Ledeb. (ASL) and Bothriochloa ischaemum (L.) Keng. (BIL). Overland water flow was tested under six shear stress levels (5.66–22.11 Pa) in natural soil samples incorporated with plant litter and without plant litter to determine soil erosion resistance parameters (rill erodibility Kr and critical shear stress τc). The study was conducted over 524 days (through May 6, 2017, to October 11, 2018), covering two rainy seasons and one winter. Soil properties changed significantly over time, with physical crust thickness and cohesion increasing from 0 to 10.7 mm and 2.9–13.4 kPa, respectively. In contrast, the mass density of incorporated plant litter decreased from 0.7 to 0.2 kg m−2. Soil erosion resistance increased with time, which showed that Kr decreased (from 0.516 to 0.021 s m−1) and τc increased (from 0.49 to 7.98 Pa). Compared with the initial state of new farmland (Kr = 0.507 s m−1,τc= 0.48 Pa), Kr decreased by 77–96% and τc increased 8–14 times at the end of the study. Plant litter incorporation markedly enhanced soil erosion resistance in a time- and species-dependent manner. Compared with the bare soil without plant litter, the Kr values of ASL and BIL treatments were 3–64% and 2–83% lower, and their τc values were 0–81% and 0–55% higher, respectively. Kr was significantly and positively correlated with cumulative precipitation, cumulative rainfall kinetic energy, soil cohesion, and physical soil crust thickness, while τc was negatively correlated with the influencing factors. Further, both Kr and τc could be well predicted by physical soil crust thickness and cohesion (R2 = 0.79 and 0.87, p < 0.01, n = 27). According to the results, seasonal patterns of soil erosion resistance in the gully-filled farmland established under plant litter incorporation were mainly controlled by rainfall and physical soil crust structure. This study provides a reference resource for soil erosion prediction in farmland ecosystems on the Loess Plateau.