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1.
Wischmeier's soil erodibility factor K calculated for 10 surface soils in the Hornos area, S. Spain, is compared with 3 aspects of aggregate stability. A significant correlation is found with the percentage of particles < 100 μm after aggregate breakdown, which is used as a measure of the vulnerability of the soil to erosion by overland flow. No significant correlation exists with the number of water drops required to cause breakdown of the aggregates nor with the mean size of the shattered aggregates, both being aspects of the resistance of aggregates to splash erosion. Of the micromorphological and analytical soil properties explaining aggregate stability, only the clay and silt content and the number of closed voids are significantly correlated with the factor K. The aggregate stability of the investigated soils is mainly determined by soil properties inherited from the parent material; the stabilizing effect of pedological features is small.  相似文献   

2.
The objective of this work was to describe a method for isolating meaningful and measurable soil organic matter (SOM) pools that differ in the mechanisms by which they are protected from decomposition. The proposed method is appropriate for soil C stabilization and sequestration studies. Unlike previous fractionation schemes, this procedure allows free SOM located between aggregates (unprotected C pool) and SOM occluded within both macroaggregates and microaggregates (C weakly and strongly protected by physical mechanisms, respectively) to be recovered separately, freed from the soil mineral matrix and the mineral‐associated SOM pool (C pool protected by chemical mechanisms) and thus well suited to advanced chemical characterization by 13C‐NMR. Briefly, free SOM is isolated by an initial density separation. Stable macroaggregates are broken up into stable microaggregates and intra‐macroaggregate SOM, which is then separated by density. Finally, intra‐microaggregate SOM is isolated from mineral‐associated SOM by a third density separation after ultrasonic disruption. The SOM dissolved during the fractionation procedure is also recovered. Results obtained on soil samples with contrasting textures suggested that clay content induces a decrease of the proportion of free organic C and an increase of mineral‐associated organic C content. Free SOM is characterized by a marked presence of undecayed organic material and biologically labile substances, such as carbohydrates and proteins. In contrast, SOM occluded within aggregates, especially within microaggregates, represents a more decomposed fraction, relatively enriched in unsubstituted‐aliphatic material, most probably lipid biopolymers.  相似文献   

3.
Aggregate stability, one of the main factors controlling soil erodibility, varies over time. Knowledge of its variation would help to identify better soil management practices. In 10 soils from central Greece devoted to cereal cropping, seasonal wet aggregate stability (WAS) fluctuations were investigated over a period of two successive years. The wet‐sieving technique of air‐dried aggregates was used for WAS determinations, according to a test resulting in an instability index calculation. Over the first year, when typical Mediterranean climatic conditions dominated, WAS varied according to a nearly cyclic pattern, from a low in winter or early‐spring months to a high in summer months. The instability index varied from a high between 123–152% of annual average to a low between 58–83% of annual average. Total monthly rainfall (TR) and mean monthly air temperature (MAT) strongly correlated with seasonal WAS. Their ratio (TR/MAT, ombrothermic ratio) has been proved to be a good predictor of structural stability throughout the year, for most of the soils studied. Possible mechanisms deteriorating aggregation seemed to be raindrop impact, repeated soil drying and wetting and repeated soil freezing and thawing, while possible mechanisms promoting aggregation seemed to be soil drying and warming and biological activity. Over the second year, severe climatic inconsistencies complicated the seasonal pattern of WAS response. From January to March, WAS unexpectedly increased, obtaining its maximum value for most of the soils in March, then it varied inconsistently until October and thereafter decreased, obtaining its minimum value in December for all soils. The instability index varied from a high between 130–196% of annual average to a low between 61–83% of annual average. Uneven seasonal distribution of climatic characteristics and extreme events decisively modified the typical for Mediterranean conditions seasonal WAS variation pattern. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

4.
The paper examines the relationships between soil aggregate stability, selected soil properties and land use in central Spain. Aggregate stability indices derived from three procedures were found to be significantly (p > 0.01) correlated with each other as well as with clay content, organic carbon and a range of water-soluble salts. Soils with a higher clay content have a lower aggregate stability. It appears that the presence of expandable clays has a major negative influence, although this impact is strongly modified by recent land-use history and contemporary land-management practices. Agricultural land, abandoned in the 1940s, was subsequently invaded by Cistus matorral or planted with Pinus. The most stable aggregates occur under matorral and may represent a lag of more resistant aggregates surviving past land-use-related erosional processes. Comparisons with aggregates under Pinus however suggest that hydrophobic substances from the Cistus may have increased aggregate stability. Aggregates from areas remaining in cultivation are the least resistant although the stability envelope overlaps with areas under Pinus. These differences may be related to cultivation practices whereby clay-rich subsurface horizons characterized by higher proportions of expandable clays are drawn to the surface, and to enhancement of aggregate stability under forest by fungal hyphae.  相似文献   

5.
Hysteresis is a common feature exhibited in hydraulic properties of an unsaturated soil. The movement of wetting front and the hysteresis effect are important factors which impact the shear strength of the unsaturated soil and the mechanics of shallow landslides. These failures are mainly triggered by the deepening of the wetting front accompanied by a decrease in matric suction induced by infiltration. This research establishes a method for determining a stability analysis of unsaturated infinite soil slopes, integrating the influence of infiltration and the water retention curve hysteresis. Furthermore, the present stability analysis method including the infiltration model and the advanced Mohr–Coulomb failure criterion calculates the variations of the safety factor (FS) in accordance with different slope angle, depth and hydrological processes. The experimentally measured data on the effect of hysteresis are also carried out for comparison. Numerical analyses, employing both wetting and drying hydraulic behaviour of unsaturated soil, are performed to study the difference in soil‐water content as observed in the experiments. The simulating approximations also fully responded to the experimental data of sand box. The results suggest that the hysteresis behaviour affect the distribution of soil‐water content within the slope indeed. The hysteresis made the FS values a remarkable recovery during the period of non‐rainfall in a rainfall event. The appropriate hydraulic properties of soil (i.e. wetting or drying) should be used in accordance with the processes that unsaturated soil actually experience. This method will enable us to acquire more accurate matric suction head and the unsaturated soil‐shear strength as it changes with the hysteretic flow, in order to calculate into the stability analysis of shallow landslides. An advanced understanding of the process mechanism afforded by this method is critical to realizing a reliable and appropriate design for slope stabilization. It also offers some immediate reference information to the disaster reduction department of the government. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

6.
Wind erosion depends on the ease with which particles can be detached from the soil surface, but suitable tests to characterize this property are not available. Two possible methods to determine surface soil strength in the field were therefore compared on a range of artificially ‘crusted’ surfaces. These were made by spraying or tension wetting aggregates (10–2, 2–0.5 and <0.5 mm) from a structurally unstable sandy loam, followed by drying. Each test involved measuring the force exerted on a probe driven at a steady rate into the surface, using either a flat-tipped 0.6 mm diameter penetrometer or a flat-ended cylindrical punch with inner and outer diameters of 5 and 6 mm, respectively. Both probes showed that crusts could be produced reproducibly. Depending on the probe and aggregate size, penetration mainly occurred either as a result of aggregates being deflected out of the pathway of the probe or by genuine rupture of aggregates or of the crusted surface. The penetrometer, because it was comparable to the size of sand grains, gave results that can be used to characterize surface erodibility to saltating particles. The punch gave results that would be unsuitable for this purpose, as would other strength tests that are on too large a scale. Penetrometer results were analyzed to calculate the energy required for penetration. It was thus possible to demonstrate that only the spray-wetted fine aggregates had a surface that could undergo large-scale rupture by saltating sand grains. For all other surfaces, saltating particles would be unable to supply sufficient energy to rupture aggregates or the crusted surface. Erosion could only occur by a slower process of abrasion in which smaller particles or aggregates are chipped away from the surface. However, it is shown that saltating particles could rupture the interaggregate bonding in the 2–0.5 mm aggregate surfaces, thus permitting creep. An alternative and potentially simpler way of characterizing surface erodibility by using a surface modulus of elasticity is also discussed. Our results demonstrate that the small diameter penetrometer is a promising technique for characterizing erodibility of aggregated and crusted surfaces. © 1997 by John Wiley & Sons, Ltd.  相似文献   

7.
This paper describes laboratory testing of 148 samples collected from Southern Alberta for erosion by wash and splash. Rainfall intensity was held constant during these tests. Soil aggregation was the most significant variable explaining soil loss. The significance of other soil properties, such as organic carbon and clay content is variable, depending on the interrelationships among aggregate stability, organic content, and clay content of particular soils. Variations in erodibility of the major soils examined are explained by the resistance of aggregates to compaction and dispersion. Splash detachment and wash transport are the dominant erosion mechanisms in inter-rill areas.  相似文献   

8.
This work was undertaken for two main purposes. One was to examine spatial and temporal variability in surface water repellency under field conditions in sandy loam forest soils of NW Spain, and its relationship to weather and soil moisture conditions. The other purpose was to get further inside in the dynamics of soil water repellency by studying a wetting–drying cycle under controlled laboratory conditions. Both for the field and laboratory study, water repellency was determined using the Water Drop Penetration Time test. Soil water repellency under field conditions was found to exhibit a seasonal pattern, i.e. it peaked during the summer and was absent between November and May. The time required for repellency to become re‐established during the spring was shorter under eucalyptus than under pine. Spatial variability peaked at an early stage of soil drying and was minimal during the wet period when soils were hydrophilic as well as at the end of the summer, when repellency was strongest. Spatial and temporal variability in water repellency was found to be negatively correlated with soil moisture and, to a lesser extent, with antecedent rainfall. The moisture range of the so‐called transition zone (below which the soil is hydrophobic and also above which it is hydrophobic) differed for the pine (21–50%) and eucalyptus plantations (17–36%). The lower and upper bounds of the transition zone agreed well with the soil moisture contents at the permanent wilting point and at field capacity, respectively. The laboratory results with samples in the wetting phase confirmed those of the field tests. Water repellency increased slightly during the drying phase, but not so much as in the field. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

9.
Laboratory experiments were used to investigate the influence of simulated cracks and roots on soil water repellency (SWR) dynamics with and without basal drainage impedance in wetting–drying cycles. Observations and measurements were taken following water application equivalent to 9.2‐mm rainfall and then periodically during 80 h of drying. In total, 180 experiments were carried out using 60 samples of three homogeneous, reconstituted soils with different organic matter contents and textures, but of similar initial severity of SWR [18% molarity of an ethanol droplet (MED)]. Water flowing down the cracks and roots left the soil matrix largely dry and water repellent except for vertical zones adjacent to them and a shallow surface layer. A hydrophilic shallow basal layer was produced in experiments where basal drainage was impeded. During drying, changes in SWR were largely confined to the zones that had been wetted. Soil that had remained dry retained the initial severity of SWR, while wetted soil re‐established either the same or slightly lower severity of SWR. In organic‐rich soil, the scale of recovery to pre‐wetting MED levels was much higher, perhaps associated with temporarily raised levels (up to 36% MED) of SWR recorded during drying of these soils. With all three soils, the re‐establishment of the original SWR level was less widespread for surface than subsurface soil and with impeded than unimpeded basal drainage. Key findings are that as follows: (1) with unimpeded basal drainage, the soils remained at pre‐wetting repellency levels except for a wettable thin surface layer and zones close to roots and cracks, (2) basal drainage impedance produced hydrophilic basal and surface layers, (3) thorough wetting delayed a return to water‐repellent conditions on drying, and (4) temporarily enhanced SWR occurred in organic‐rich soils at intermediate moisture levels during drying. Hydrological implications are discussed, and the roles of cracks and roots are placed into context with other influences on preferential flow and SWR under field conditions. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

10.
In this study our main objective was to quantify water interrill erosion in the sloping lands of Southeast Asia, one of the most bio‐geochemically active regions of the world. Investigations were performed on a typical hillslope of Northern Laos subjected to slash and burn agriculture practiced as shifting cultivation. Situations with different periods of the shifting cultivation cycle (secondary forest, upland rice cultivation following a four‐year fallow period and three‐year continuous upland rice cultivation) and soil orders (Ultisols, Alfisols, Inceptisols) were selected. One metre square micro‐plots were installed to quantify the soil material removed by either detachment of entire soil aggregate or aggregate destruction, and the detached material transported by thin sheet flow, the main mechanisms of interrill erosion. In addition, laboratory tests were carried out to quantify the aggregate destruction in the process of water erosion by slaking, dispersion and mechanical breakdown. The average runoff coefficient (R) evaluated throughout the 2002 rainy season was 30·1 per cent and the interrill erosion was 1413 g m?2 yr?1 for sediments and 68 g C m?2 yr?1 for soil organic carbon, which was relatively high. Among the mechanisms of interrill water erosion, aggregate destruction was low and mostly caused by mechanical breakdown due to raindrops, thus leading to the conclusion that detachment and further transport by the shallow runoff of macro‐aggregates predominates. R ranged from 23·1 to 35·8 per cent. It decreased with the proportion of mosses on the soil surface and soil surface coverage, and increased with increasing proportion of structural crust, thus confirming previous results. Water erosion varied from 621 to 2433 g m?2 yr?1 for sediments and from 31 to 146 g C m?2 yr?1 for soil organic carbon, and significantly increased with increasing clay content of the surface horizon, probably due to the formation of easily detachable and transportable sand‐size aggregates, and proportion of macro‐aggregates not embedded in the soil matrix and prone to transport. In addition, water erosion decreased with increasing proportion of structural crusts, probably due to their higher hardness, and when cultivation follows a fallow period rather than after a long period of cultivation due to the greater occurrence of algae on the soil surface, which affords physical protection and greater aggregate stability through binding and gluing. This study based on simultaneous field and laboratory investigations allowed successful identification and quantification of the main erosion mechanisms and controlling factors of interrill erosion, which will give arguments to further set up optimal strategies for sustainable use of the sloping lands of Southeast Asia. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

11.
Rainsplash is an important component of interrill erosion. To date, few studies have critically examined the linkages between aggregate entrainment by splash and associated nutrient flux. An Oxisol was used in laboratory rainfall experiments with two different antecedent moisture contents (AMC) and ten different rainfall energy flux densities (EFD). Splash and soil organic carbon (SOC) flux increased with increased EFD regardless of initial AMC. Aggregates were not transported in proportion to their content in the original soil matrix, those of 2000–4000 μm and <105 μm were found to be the most resistant to splash. Energy required to detach 1 gC varied from a median of 1870 J for the 2000–4000 μm fraction to 120 J for the 425–850 μm fraction. Temporal variation in cumulative splash flux and carbon flux for various combinations of AMC and EFD indicated distinct patterns. Under dry AMC, splash increased during 1 h duration storms and this was explained by increased aggregate breakdown by air-slaking, decreased soil strength and increased erodibility as soil moisture increased. Wet soil runs exhibited the opposite pattern of decreased flux with time, probably indicating a complex response to limited aggregate availability, increased seal development by raindrop compaction, and transient water layer effects in drop impact craters. The formulation of mass-based SOC enrichment ratios (ER) clearly indicated preferential detachment and transport of splashed aggregates between 250 and 2000 μm. A reliance of chemical transport models on concentration-based ER values can be misleading, because it is the balance between nutrient concentration and sediment quantity that is important for soil quality and non-point source modelling.  相似文献   

12.
The effect of peat on crust strength was investigated using ten soils with organic matter levels ranging from 1-50 to 18-23 per cent. As peat content increased, the crust strength reduced. This occurred in spite of the inability of peat to increase the stability of soil aggregates. Peat reduced crust strength by acting as a mulch on the soil surface, thereby reducing breakdown of soil aggregates. Peat also formed a source of weakness on the soil, reducing crust formation. Using a factorial experiment involving a further seven soils with different levels of peat treatment, exposed to four rainfall durations and with two aggregate sizes, crust strength was described in terms of the direct effects and the interactions of these factors. Most of the crust strength values reduced with increasing peat content. For each soil, crust strength increased significantly with increasing rainfall duration. Crust strength was greater for the smaller aggregate size. The most significant interactions affecting crust strength were between soil and aggregate size, rainfall duration and aggregate size, and soil and rainfall duration in that order. These interactions were used to describe the effect of organic matter in form of peat on crust strength. For each soil and aggregate size, polynomial relationships were established to relate crust strength to total kinetic energy of rainfall.  相似文献   

13.
R. M. Bajracharya  R. Lal 《水文研究》1998,12(12):1927-1938
Sealing and crusting of soil surfaces have dramatic effects on water infiltration into and runoff from soils, thereby greatly influencing erosion processes. This study focused on the effect of the initial stage of crusting on inter-rill erosion processes for a crust-prone Alfisol sampled from south-central India. Soil aggregates ranging from 2·4 to 8 mm collected from ploughed (PL) and naturally vegetated (NV) treatments were subjected to rainfall simulation under laboratory conditions. Runoff from PL soil aggregates was 2–2·5 times higher, while percolation was 20–100% lower, than for NV aggregates. Soil wash and splash losses were 0·5–3 times greater for PL than for NV soil. Runoff and inter-rill erosion were significantly higher during the wet simulation run compared with the dry run. The results indicated that NV soil aggregates were more resistant to breakdown from raindrop impact and slaking, and subject to less rapid sealing, than PL soil. Total soil loss was influenced most by initial aggregate stability and the extent of seal development. Splash and wash losses of soil both increased as a result of surface sealing regardless of soil condition for short (30–60 min) rainfall durations. High drying rates resulted in the highest crust bulk densities. Increased crust strength for PL soil compared with NV soil reflected the greater susceptibility of cultivated soil to surface sealing and crusting. © 1998 John Wiley & Sons, Ltd.  相似文献   

14.
Wildfires are a cause of soil water repellency (hydrophobicity), which reduces infiltration whilst increasing erosion and flooding from post-fire rainfall. Post-fire soil water repellency degrades over time, often in response to repeated wetting and drying of the soil. However, in mountainous fire-prone forests such as those in the Western USA, the fire season often terminates in a cold and wet winter, during which soils not only wet and dry, but also freeze and thaw. Little is known about the effect of repeated freezing and thawing of soil on the breakdown of post-fire hydrophobicity. This study characterized the changes in hydrophobicity of Sierra Nevada mountain soils exposed to different combinations of wet–dry and freeze–thaw cycling. Following each cycle, hydrophobicity was measured using the Molarity of Ethanol test. Hydrophobicity declined similarly across all experiments that included a wetting cycle. Repeated freezing and thawing of dry soil did not degrade soil water repellency, but freeze–thaw cycles decreased hydrophobicity in wet soils. Total soil organic matter content was not different between soils of contrasting hydrophobicity. Macroscopic changes such as fissures and cracks were observed to form as soil hydrophobicity decayed. Microscopic changes revealed by scanning electron microscope imagery suggest different levels of soil aggregation occurred in samples with distinct hydrophobicities, although the size of aggregates was not clearly correlated to the change in water repellency due to wet–dry and freeze–thaw cycling. A 9-year climate and soil moisture record from Providence Critical Zone Observatory was combined with the laboratory results to estimate that hydrophobicity would persist an average of 144 days post-fire at this well-characterized, typical mid-elevation Sierra Nevada site. Most of the breakdown in soil water repellency (79%) under these climate conditions would be attributable to freeze–thaw cycling, underscoring the importance of this process in soil recovery from fire in the Sierra Nevada.  相似文献   

15.
Particles eroded from hillslopes and exported to rivers are recognized to be composite particles of high internal complexity. Their architecture and composition are known to influence their transport behaviour within the water column relative to discrete particles. To‐date, hillslope erosion studies consider aggregates to be stable once they are detached from the soil matrix. However, lowland rivers and estuaries studies often suggest that particle structure and dynamics are controlled by flocculation within the water column. In order to improve the understanding of particle dynamics along the continuum from hillslopes to the lowland river environment, soil particle behaviour was tested under controlled laboratory conditions. Seven flume erosion and deposition experiments, designed to simulate a natural erosive event, and five shear cell experiments were performed using three contrasting materials: two of them were poorly developed and as such can not be considered as soils, whilst the third one was a calcareous brown soil. These experiments revealed that soil aggregates were prone to disaggregation within the water column and that flocculation may affect their size distribution during transport. Large differences in effective particle size were found between soil types during the rising limb of the bed shear stress sequence. Indeed, at the maximum applied bed shear stress, the aggregated particles median diameter was found to be three times larger for the well‐developed soil than for the two others. Differences were smaller in the falling limb, suggesting that soil aggregates underwent structural changes. However, characterization of particles strength parameters showed that these changes did not fully turn soil aggregates into flocs, but rather into hybrid soil aggregate–floc particles. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

16.
The fate of 14C‐labeled sulfamethoxazole and acetyl‐sulfamethoxazole in soil has been investigated with special respect to possible entry routes of human and veterinary pharmaceuticals into soil environments. Therefore, the stability of the test substances was monitored first in sewage sludge and bovine manure. Within the incubation period of 72 d, 1% at maximum of the initially applied radiotracers was released as 14C‐carbon dioxide while ?75% was transferred to non‐extractable residues that were operationally defined by the ethyl acetate extraction. Test‐sludge and test‐manure samples with defined aged residues were prepared and, supplementary to standard solutions, applied to silty‐clay soil samples. After standard and test‐sludge application, soil/water distribution coefficients of Kd < 5 L kg–1 were determined revealing both test substances as potential leachers. In contrast, the sorption of sulfamethoxazole increased after test‐manure application (Kd > 10 L kg–1). In the long‐term degradability tests, the metabolic fate of both test substances was characterized by the continuous decrease of extractable residues, resulting in disappearance times of DT90 ? 33 d, and the increase of non‐extractable residues. Mineralization reached 11% at maximum. Thereby, the dynamics of these processes differed whether the test substances were applied via standard, test‐sludge or test‐manure application. This fact emphasized the relevance of entry route specific matrix effects on the fate of both test substances in soil.  相似文献   

17.
Previous studies have shown that water retention curve (WRC) and the hydraulic conductivity vary because of changes of the void ratio or porosity of soil. However, limited documents pointed out the change of hydraulic properties of soil when compacted to different porosities while considering both of the drying and wetting processes of the WRC. This information is sometimes necessary for research like finger flow analysis or the occurrence of wetting and drying cycles as what would be seen in the field. Therefore, this study aims to examine the change of WRC characteristics with varied porosity considering both of the drying and wetting path in WRC by conducting a sand box experiment. Results show that the same type of sand compacted to various porosities have different hydraulic parameters. Hydraulic conductivities generally decrease with reduced porosities; shape parameter α of the van Genuchten equation (1980) linearly decreases with declining porosity and shape parameter n in a reversal manner for the sands of interest whether in the drying process or wetting process. The unsaturated properties of sand are further characterized by inspecting the variations of moisture content, matric suction and vertical displacement of soil body subject to periodic changes of the water level by another sand box experiment. The outcomes suggest that the saturated water content and residual water content are changing during the wetting–drying process, which can be an implication of the changed properties of WRC. The characteristics of volumetric deformation might be varied as well because of the observation of the dissimilar patterns of the changing vertical displacements among each wetting–drying process. Infiltration patterns of the sands also are identified through numerical modelling by introducing a constant infiltration flux from the surface followed by a no‐influx condition. Results indicate that less water accumulates in the sand near the surface for the sand compacted to higher porosity, but water can move deeper. Hydraulic conductivity is found as the prime factor dominating the evolvement of wetting fronts. However, shape parameters of water retention curves also affect the infiltration pattern to some extent. In addition, different sands with similar porosities can have quite different infiltrating characteristics. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

18.
Two methods for sampling aggregates in the soil surface under simulated rain were compared using two soil types. Results showed that aggregate size distributions obtained by spatula sampling were not significantly different from those obtained using rings buried in the soil surface, provided both were sampled to the same depth. The effect of transporting samples over a distance of 60 km was non-significant when samples were placed in bottles half-filled with rainwater and transported in an upright position. The per cent aggregates > 0.125 mm was found to be the most suitable index of aggregate stability for both soils.  相似文献   

19.
Soil surface crusting, a common phenomenon on cultivated soils, has major implications for agriculture and the environment because of its effects on soil hydrological properties, erosion and crop establishment. The objectives of this study were to evaluate land use controls on crust formation and the hydraulic response of soils to crust development for a Patancheru series soil (clayey skeletal, mixed, isohyperthermic Udic Rhodustalf) in south‐central India. Soil aggregates, obtained from cultivated (PL) and naturally vegetated fallow (NV) land, were packed into sample trays and subjected to laboratory rain simulation to form crusts. Thin sections and visual observation indicated that crust development reached a more advanced stage in the PL case compared with NV following 90 min of rain at 40–80 mm h−1 intensity. This was reflected in a thicker crust layer with fewer voids in the former and a less smooth surface with partially disintegrated aggregates in the latter. The hydraulic response of the soil surface with the progression of crust development indicated a more permeable and less dense crust formed on NV than on PL soil. The results suggested that NV soil aggregates were more stable and that crust formation is more gradual for stable aggregates compared with the less stable PL aggregates. A structural crust‐type formed on the Patancheru soil by means of parallel subprocesses involving translocation and illuviation of aggregate disruption by products, and raindrop compaction and particle rearrangement. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

20.
The enrichment of organic matter in interrill sediment is well documented; however, the respective roles of soil organic matter (SOM) and interrill erosion processes for the enrichment are unclear. In this study, organic matter content of sediment generated on two silts with almost identical textures, but different organic matter contents and aggregations, was tested. Artificial rainfall was applied to the soils in wet, dry and crusted initial conditions to determine the effects of soil moisture and rainfall and drying history on organic matter enrichment in interrill sediment. While erosional response of the soils varied significantly, organic matter enrichment of sediment was not sensitive to initial soil conditions. However, enrichment was higher on the silt with a lower organic matter content and lower interrill erodibility. The results show that enrichment of organic matter in interrill sediment is not directly related to either SOM content or soil interrill erodibility, but is dominated by interrill erosion processes. As a consequence of the complex interaction between soil, organic matter and interrill erosion processes, erodibility of organic matter should be treated as a separate variable in erosion models. Further research on aggregate breakdown, in particular the content and fate of the organic matter in the soil fragments, is required. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

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