Effect of rock fragment cover on interrill soil erosion from bare soils in Western Andalusia, Spain

It is known that rock fragments on the surface of soils can enhance infiltration and protect the soil against rainfall erosion. However, the effect of rock fragments in natural forest soils is less well understood. In this article, we studied the influence of rock fragment cover on run‐off, infiltration and interrill soil erosion under simulated rainfall on natural bare soils in a Spanish dehesa (managed holm oak woodland). We studied 60 plots with different rock fragment cover ranging from 3% to 85% under three simulated rainfall intensities (50, 100 and 150 mm/h). Surface run‐off appeared later and sediment yield values were smaller in soils with greater rock fragment cover. Rock fragment cover also increased infiltration rates. The final infiltration rates were 54–98% at a rainfall intensity of 50 mm/h, 31–88% at 100 mm/h and 20–80% at 150 mm/h. The interrill soil loss rates were decreased by rock fragment cover and increased with rainfall intensity. The soil loss rate was always small (0.02–1 Mg ha/h) when rock fragment cover was 75% or more. Rock fragment cover was related to soil loss rate by an exponential function.     

三峡库区碎石含量对紫色土容重和孔隙特征的影响

土壤容重和孔隙分布特征是土壤重要的基本物理性质,但有关含碎石土壤的物理性质以及碎石含量对土壤结构影响的研究尚不多见。三峡库区紫色土中存在大量的碎石,为了深刻了解和评价土壤中碎石对容重与大孔隙形成的可能作用,通过野外调查、典型土样采集和室内分析实验,探讨了三峡库区典型土地利用类型下土壤中的碎石体积含量以及不同粒径碎石的基本物理性质及其对土壤容重和孔隙特征的影响。结果表明:土壤中碎石的孔隙度和饱和含水率随着碎石粒径的减小而增大,小碎石本身具有一定的持水、供水性能;碎石含量对土壤的总容重、细土容重有显著影响,随着碎石含量的增加,土壤的总容重逐渐增加,而细土容重与碎石含量呈线性负相关关系,土壤中碎石的存在有利于改善土壤的结构;土壤孔隙分布特征与碎石含量密切相关,随着碎石含量的提高,土壤总孔隙度和毛管孔隙度呈减少趋势,而非毛管孔隙度即大孔隙呈增加趋势,碎石的存在有利于改善土壤的透水性能。本研究为山区农用地灌溉与水分管理提供了科学依据。     

Effects of rock fragments on physical degradation of cultivated soils by rainfall

To understand better the role of rock fragments in soil and water conservation processes, the effects of rock fragments in maintaining a favourable soil structure and thus also in preventing physical degradation of tilled soils was studied. Laboratory experiments were conducted to investigate the effects of rock fragment content, rock fragment size, initial soil moisture content of the fine earth and surface rock fragment cover on soil subsidence by rainfall (i.e. change in bulk density by one or more cycles of wetting and drying). A total of 15 rainfall simulations (cumulative rainfall, 192.5 mm; mean intensity, 70 mm h⁻¹) were carried out. Before and after each rainfall application the surface elevation of a 19-cm thick plough layer was measured with a laser microrelief meter. In all experiments, the bulk density of the fine earth increased with applied rainfall volume to reach a maximum value at about 200 mm of cumulative rainfall. From the experimental results it was concluded that the subsidence rate decreased sharply for soils containing more than 0.50 kg kg⁻¹ rock fragments, irrespective of rock fragment size. Fine earth bulk densities were negatively related to rock fragment content beyond a threshold value of 0.30 kg kg⁻¹ for small rock fragments (1.7–2.7 cm) and 0.50 kg kg⁻¹ for large rock fragments (7.7 cm). Initial soil moisture content influenced subsidence only in the initial stage of the experiments, when some swelling occurred in the dry soils. Surface rock fragment cover had no significant effect on subsidence of the plough layer. Therefore, subsidence of the plough layer in these experiments appears to be mainly due to changing soil strength upon drainage rather than the result of direct transfer of kinetic energy from falling drops. The relative increase in porosity of the fine earth as well as the absolute increase in macroporosity with rock fragment content will cause deeper penetration of rainfall into the soil, resulting in water conservation. Therefore, crushing of large rock fragments into smaller ones is to be preferred over removal of rock fragments from the plough layer.     

Simulating infiltration into stony soils with a dual‐porosity model

Soils containing rock fragments are widely distributed in the world. However, literature on the dynamic simulation of water movement in stony soils is scarce. In this paper, a dual‐porosity model was used to simulate water infiltration into soils containing rock fragments. Sensitivity analysis of the dual‐porosity model parameters demonstrates that the increase of rock fragment content clearly decreased infiltration into stony soils. Big stones hampered infiltration more than small stones. Spherical stones accelerated infiltration compared with solid, cylindrical stones and rectangular, slab‐like stones. Numerical analysis was also performed to test and compare a non‐equilibrium dual‐porosity model (NDPM) with an equilibrium dual‐porosity model (EDPM) and an equilibrium single‐pore model (ESPM). Infiltration experiments on disturbed soils were carried out to verify the ability of the NDPM to simulate infiltration into stony soils. Based on hydraulic parameters of soils without rock fragments and mass transfer coefficients obtained independently, the extrapolated cumulative infiltrations calculated by the NDPM were in good agreement with the observed data. Fitted model parameters of the NDPM indicate that rock fragments not only act as a source or sink to affect infiltration but also change the pore structure of the fine earth, apart from reducing the cross‐sectional area for water flow. Though further studies are required to improve the dual‐porosity model, it already describes more characteristics of infiltration into stony soils and explains more phenomena than does the single‐porosity model.     

The soil skeleton, a forgotten pool of carbon and nitrogen in soil

To evaluate the contribution of rock fragments to the soil's total carbon content, the soil of 26 sites, ranging from the Canadian Arctic to the Jordan desert, was analysed for the content of organic C and total N in both fine earth and skeleton fractions. The soils, uncultivated and cultivated, are derived from 11 parent materials: sandstone, mica-schist, granite, gneiss, basaltic pyroclastites, trachyte, dolomite, beach deposits, clay schist, marl and serpentinite. For each soil horizon the contents of fine earth and skeleton were determined by volume. Both fractions were analysed for bulk density, total and organic C and total N. Our results indicate that rock fragments contain amounts of C and N that depend on the nature of the parent material and on its resistance to the weathering processes. The C and N of both fine earth and skeleton were used to calculate the contents of these elements for three depths. At each depth, the skeleton contributes C and N to the soil depending on its abundance. We conclude that the contribution of the rock fragments to the soil C and N cannot be predicted from the soil taxa, but can from the parent material. Calculations that exclude C and N of the skeleton could lead to errors in the estimates of these two elements in soils.     

砾石覆盖对土壤水蚀过程影响的研究进展

 土壤中砾石的存在对水蚀过程有着重要的影响,有关砾石特别是表土砾石覆盖对土壤水蚀影响的研究结果表明,表土砾石对溅蚀分散、细沟间及细沟侵蚀等坡面侵蚀过程有重要影响:1)泥沙溅蚀分散量与砾石覆盖度呈负相关关系;2)砾石覆盖与细沟间侵蚀的关系较为复杂,这取决于表土的结构、砾石的位置和大小以及坡度等因素,当砾石嵌入结皮表土时,二者呈负相关关系,当砾石置于表土之上或嵌入具有结构孔隙的表土时,二者呈正相关关系;3)砾石覆盖对细沟间侵蚀产沙的作用效率与砾石粒径呈负相关关系,砾石置于表土之上的表土产沙量总低于砾石嵌入表土的产沙量;4)表土砾石覆盖能抑制细沟的形成,增加细沟糙度,降低细沟径流速率以及径流的侵蚀速率。鉴于砾石对水蚀过程的重要影响,RUSLE、WEPP和EUORSEM等土壤侵蚀模型预报含砾石土壤流失量时对相关参数做了修正。     

Relationships between rock fragment cover and soil hydrological response in a Mediterranean environment

Rock fragments are a key factor for determining erosion rates, particularly in arid and semiarid environments where vegetation cover is very low. However, the effect of rock fragments in non-cultivated bare soils is still not well understood. Currently, there is a need for quantitative information on the effects of rock fragments on hydrological soil processes, in order to improve soil erosion models. The main objective of the present research was to study the influence of rock fragment cover on run-off and interrill soil erosion under simulated rainfall in Mediterranean bare soils in south-western Spain. Thirty-six rainfall simulation experiments were carried out at an intensity of 26.8 mm h⁻¹ over 60 min under three different classes of rock fragment cover (<50%, 50–60% and >60%). Ponding and run-off flow were delayed in soils with high rock fragment cover. In addition, sediment yield and soil erosion rates were higher in soils with a low rock fragment cover. The relationship between soil loss rate and rock fragment cover was described by an exponential function. After this first set of experiments, rock fragments were removed from sites with the highest cover (>60%) and the rainfall simulation experiments were repeated. The steady-state run-off rate and soil loss increased significantly, showing that run-off and soil erosion were partly conditioned by rock fragment cover. These results have significant implications for erosion modelling and soil conservation practices in areas with the same climate and soil characteristics.     

Modelling cracking stages of saturated soils as they dry and shrink

Cracks that form when clay soils shrink on drying eventually form a network that determines transport properties. I propose and validate a model for (i) analysing the initial cracking stages of shrinking saturated soils, (ii) estimating the minimum dimension of quasi‐brittle cracks capable of developing in such conditions, and (iii) determining relations between the minimum crack dimension and other characteristic dimensions of the soil structure. Shrinkage cracks in soils can be classified on the concept of the minimum quasi‐brittle crack capable of developing at shrinkage. I use the model of developing a shrinkage crack in a semi‐infinite brittle medium with constant relevant properties, desiccating in conditions of shock drying. The model is generalized to the cracking of a saturated clay soil with a limited maximum crack depth. The available data justify the use of constant elastic, strength, diffusivity, and shrinkage properties of clay soil. The critical point of crack development is the existence of the minimum crack capable of developing in the particular conditions. The dimension of the crack is related to the soil properties. The crack goes through stages of delay, jump, stable growth with approximately constant velocity, and then quick decline until it stops. I show that the minimum crack dimension is related to the mean dimension of soil particles, the thickness of an upper intensive‐cracking layer, and the mean spacing of primary cracks at the soil surface.     

石砾参数对土壤水流和溶质运移影响研究进展

土壤水流和溶质运移一直是土壤学研究的热点,溶质运移理论主要应用于地下水污染、污染物运移、土壤重金属污染研究等方面。溶质主要通过优先流和基质流进行运移,影响溶质运移因素很多,主要包括土壤结构、质地、水力传导率、体积质量、初始含水量、根系、石砾等。石砾作为土壤质地中的一个分级单位,与溶质运移关系较为复杂。本文综合介绍了石砾基本内涵以及石砾对土壤水流和溶质运移影响研究进展;系统阐述了石砾内部参数(石砾覆盖度、含量、粒径、空间异质性等)和外部参数(根石结构、干湿冻融、耕作等),指出目前研究主要量化土壤表面及土壤表层石砾参数对水文效应、土壤侵蚀、入渗以及径流的影响,然而石砾参数对溶质运移影响研究不够系统,石砾参数与溶质运移关系研究尚处于初步阶段,对土壤深层石砾研究缺乏;归纳了石砾参数研究技术手段及模型;探讨了目前石砾参数对土壤水流和溶质运移影响研究存在的问题以及今后研究趋势。     

Using soil knowledge for the evaluation of mid‐infrared diffuse reflectance spectroscopy for predicting soil physical and mechanical properties

Mid‐infrared diffuse reflectance spectroscopy can provide rapid, cheap and relatively accurate predictions for a number of soil properties. Most studies have found that it is possible to estimate chemical properties that are related to surface and solid material composition. This paper focuses on prediction of physical and mechanical properties, with emphasis on the elucidation of possible mechanisms of prediction. Soil physical properties that are based on pore‐space relationships such as bulk density, water retention and hydraulic conductivity cannot be predicted well using MIR spectroscopy. Hydraulic conductivity was measured using a tension‐disc permeameter, excluding the macropore effect, but MIR spectroscopy did not give a good prediction. Properties based on the soil solid composition and surfaces such as clay content and shrink‐swell potential can be predicted reasonably well. Macro‐aggregate stability in water can be predicted reasonably as it has a strong correlation with carbon content in the soil. We found that most of the physical and mechanical properties can be related back to the fundamental soil properties such as clay content, carbon content, cation exchange capacity and bulk density. These connections have been explored previously in pedotransfer functions studies. The concept of a spectral soil inference system is reiterated: linking the spectra to basic soil properties and connecting basic soil properties to other functional soil properties via pedotransfer functions.     

Soil Water Relations and Aeration Status of Single Soil Aggregates,Taken from a Gleyic Vertisol

Clayey soils have the potential to swell and to shrink depending on their hydraulic and hydrological status. Thus bulk density values vary in a range of 1.0 to 2.0 g cm^?3 in the case of a gleyic Vertisol, by which also other soil physical properties e.g. the pore size distribution of the bulk soil as well as of the soil aggregates are affected. Intraaggregate airfilled porosities are reduced by shrinkage and are relatively low. Thus it appeared to be difficult to determine the airfilled porosity of the aggregates below pF 1.5. For that reason and because of the influence of pore forms we were not able to get a clear relation of diffusion constant K with airfilled porosity. Regarding soil aeration status, the existence of anoxic microsites in the interior of unsaturated soil aggregates has been proved by microelectrode measurements of oxygen partial pressure and redox potential distribution in single soil aggregates. We verified restrained oxygen supply to the aggregate center as well as reduced redox potentials only for aggregates of the A horizon. There the microbial activity, measured as soil respiration as well as the source for C and N was by a factor 2 to 4 higher than in the subsurface horizons.     

Impact of biochars on swell–shrinkage behavior,mechanical strength,and surface cracking of clayey soil

Swell–shrinkage, cracking and stickiness of expansive clayey soils usually lead to their low yield. Improvement of these poor soil physical properties is a key goal for enhancing the crop productivity of expansive clayey soils. This article presents results of a study on the impact of three biochars produced from wheat straw (SB), woodchips (WCB), and wastewater sludge (WSB) on the swell–shrinkage behavior, mechanical strength, and surface cracking of a clayey soil. The soil was treated with biochars at the rate of 0, 20, 40, and 60 g biochar kg^?1 soil, respectively; and incubated for 180 d in glasshouse. Application of biochars decreased significantly (p < 0.01) the coefficient of linear extensibility (COLE) of the soil, the effect of SB being most prominent. The tensile strength (TS) of the clayey soil was originally 937 kPa, which decreased to 458 kPa, 495 kPa and 659 kPa for 6% SB‐, WCB‐, and WSB‐amended soils, respectively. Shear strength tests indicated that biochars significantly reduced cohesion (c) and increased internal friction angle (θ). Biochar significantly reduced the formation of soil surface cracks, surface area, and length of the cracks. The surface area density of cracks in the 6% biochar‐amended soils decreased by 14% for SB, 17% for WCB, and 19% for WSB, respectively, compared with control. The results suggest that biochar can be used as a soil amendment for improving the poor physical properties of the clayey soil, particularly in terms of reduction in swell–shrinkage, tensile strength and surface area density of cracking.     

Implications of Rock Fragments for Soil Quality Evaluation: Assessing Changes in a Gravelly Irrigated Soil Following No Till Adoption

Stony soils are increasingly being converted to intensive agricultural use, including irrigation. Conservation tillage can be adopted in these soils for soil protection and quality enhancement, but its assessment can be troublesome. Crop yields and the implications of rock fragments for soil quality indicators and for calculating C and N stocks were monitored under conventional and no-tillage in an experimental field recently converted to irrigation, on a soil with 40% rock fragments. Gains of up to 10 Mg C ha^?1 were observed in the tilled layer (0–30 cm) only with two years of irrigation, with no differences between treatments, although the vertical distribution of carbon (C) and nitrogen (N) was affected by the correction of the rock fragment content. The labile organic fraction stood as a sensitive indicator to management changes, even after rock fragment correction. Different methodologies used for rock fragment correction led to overestimations of 20% of organic C stocks.     

土壤中砾石存在对入渗影响研究进展

石质山区的土壤中含有大量砾石,土壤中大量砾石存在会影响土壤物理特性和水力特性,从而对土壤入渗规律造成影响。本文主要介绍了国外土壤中砾石存在对土壤物理特性、水力特性以及入渗规律影响研究的现有研究成果,国外现有研究结果表明,土壤中砾石存在对入渗影响较为复杂,砾石覆盖/含量与入渗量之间既有正相关关系,也有负相关关系。     

含岩屑紫色土水力特性及饱和导水率传递函数研究

紫色土中存在的岩石碎屑会对土壤的水力性质如饱和导水率、水分特征曲线产生显著影响.以两种不同母质发育的土壤(紫色页岩和紫色泥岩)为研究对象,设置0.25～2、2～5、5～10 mm三个岩屑粒径水平,0、30％、50％、70％、100％五个岩屑含量水平,采用压力膜仪法和定水头法分别测定水分特征曲线和土壤饱和导水率.利用BP...     

Effects of rock fragment cover on soil infiltration, interrill runoff and erosion

Considerable attention has been paid recently to the influence of surface rock fragments on hydrological and erosional processes, although much of this research has been done on disturbed soils under laboratory conditions. I have studied the effects of rock fragments on soil infiltration, runoff and erosion under field conditions using simulated rainfall on bare areas of natural soils within typical Mediterranean scrubland characterized by patchily distributed vegetation. Sample areas were chosen where rock fragments cover more than half the surface within unvegetated patches. Twenty experiments were carried out by applying rain at an intensity of 55 mm h^?1 for 60 minutes. This approach shows that rock fragments (i) retard ponding and surface runoff, and (ii) give greater steady‐state infiltration rates and smaller interrill runoff discharges, sediment concentrations and interrill erosion rates. A second set of six experiments was carried out by applying rainfall at an intensity of 55 mm h^?1 for two runs of 60 minutes. The second run was initiated 10 minutes after the first. During this interval, surface rock fragments were removed in order to measure their effects on infiltration, interrill runoff and erosion rates. In this way, I showed that water and soil losses are reduced by the rock fragments. After the removal of rock fragments the steady‐state infiltration rate diminished from 44.5 to 27.5 mm h^?1 and the runoff coefficient, sediment concentration and erosion rates were, respectively, 3, 33 and 39 times greater than they were before the rock fragments were removed.     

Potential role of soil density and clay mineralogy in assessing the suitability of soils for mole drainage

The failure mechanisms causing mole channel deterioration or collapse, which are controlled mainly by the shear, swell/shrink and apparent viscosity properties of soils, are shown to be sensitive to the influence of soil density and clay mineralogy. These two properties have, therefore, a clear potential role in helping to assess the suitability of soils for mole drainage and in helping to define the particular failure mechanisms which are most likely to be active in given situations.     

Micromorphological features of the fine earth and skeletal fractions of soils of West Antarctica in the areas of Russian Antarctic stations

Micromorphological features of the fine earth and skeletal fractions of soils of West Antarctica forming under different conditions of pedogenesis have been studied in the areas of Russian Antarctic stations. The processes of mineral weathering and alteration of rock fragments are more pronounced in the Subantarctic soils with better developed humification and immobilization of iron compounds under conditions of surface overmoistening. The biogenic accumulative processes in the soils of King George Island result in the appearance of initial forms of humic plasma that have not been detected in the Antarctic soils in the areas of the Russkaya and Leningradskaya stations. Humus films on mineral grains are present in the soils of King George Island, and organic plasmic material is present in the ornithogenic soils under penguin guano on Lindsey Island. High-latitude Antarctic soils may contain surface concentrations of organic matter; rock fragments are covered by iron oxides and soluble salts. The formation of amorphous organic plasma takes place in the ornithogenic soils of Lindsey Island. The microprobe analysis indicates the presence of local concentrations of organic matter and pedogenic compounds not only on the surface of rock fragments but also in the fissures inside them. This analysis has also proved the translocation of guano-derived organic substances inside rock fragments through a system of fissures in the soils of Lindsey Island and the development of a network of pores inside rock fragments in the soils of King George Island.     

地表砾石对降雨径流及土壤侵蚀的影响

山区土壤表层常有大量砾石覆盖,地表砾石覆盖会对降雨入渗产生影响,从而影响径流和土壤侵蚀。利用人工降雨试验来评价北京山区普通褐土上不同砾石覆盖度对径流和土壤侵蚀的影响。试验降雨强度为30,67,92mm/h,土盘(1m×0.5m)坡度为20°,砾石覆盖度为0,5%,10%,20%,40%和60%。研究结果表明:对试验土壤,径流量随砾石覆盖度增加呈线性减小。水流流速和土壤侵蚀量随砾石覆盖度的增加呈负指数递减。降雨强度对径流量和土壤侵蚀量与砾石覆盖度之间的关系不存在影响。研究结果可为北京山区的土壤侵蚀预报提供数据基础。     

Properties and regimes of vertisols with gilgai microtopography (a review)

Data on the morphology and spatial distribution of slickensides and cracks, particle-size distribution, the organic carbon content, the content and forms of carbonate concentrations, and physical and physicochemical properties of Vertisols with the gilgai microtopography are systematized. Relatively scarce information on the functioning regimes of gilgai soil complexes (their temperature and moisture conditions, redox potential, vertical and horizontal deformations, and soil density changes) is discussed. Common properties of gilgai soils are the clayey texture of their profiles and the high portion of smectitic minerals specifying the high shrink–swell capacity of the soil material. The most important specificity of soils with the gilgai microtopography is a significant horizontal differentiation of the soil profiles with alternation of bowl-shaped morphostructures with a thick dark layer without carbonates in microlows and diapiric morphostructures composed of the rising material of the lower layers with diverse carbonate concentrations on microhighs. Data on the spatial distribution of soil properties within the gilgai microcatenas can be applied in the studies of the genesis and evolution stages of the gilgai soil complexes.