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.     

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。     

Concentrated flow erosion rates as affected by rock fragment cover and initial soil moisture content

Concentrated flow experiments using a small hydraulic flume and a constant flow discharge and bed slope have been conducted in order to investigate the effects of rock fragment cover (Rc) on sediment yield for an initially wet and an initially air-dry loamy topsoil. The experimental results indicate that Rc reduces concentrated flow erosion rates (E) in an exponential way (i.e., E=e^−bRc), which is similar to previously reported relations for other water erosion processes such as interrill erosion and sheet-rill erosion measured on runoff plots. The decay rate (b) of this exponential relationship increased throughout the experiments because of scour-hole development and bed armouring. The concentrated flow erosion rates and b-values also depend on the initial moisture content of the topsoil. Depending on Rc, mean concentrated flow erosion rates were 20% to 65% less on initially wet compared to initially air-dry topsoils. The mean value for b was 0.032 for the initially wet, but only 0.017 for the initially air-dry topsoil, indicating that a rock fragment cover is less efficient in reducing concentrated flow erosion rates when the topsoil is initially air-dry than when it is initially wet. The results help explain the data scatter in reported relationships between Rc and interrill–rill erosion rates. They also indicate that a given surface rock fragment cover will offer more protection to wet topsoils than to dry topsoils, which are very common in Mediterranean environments. Event-based water erosion models should incorporate effects of antecedent soil moisture content as well as those of Rc on concentrated flow erosion rates.     

Structural dynamics of a vegetative soil cover for waste rock dumps

Abstract

Most waste rock dumps of Uranium mining in the Eastern German Ore Mountains near Schlema site are covered with an 80 cm compacted loam sublayer and a vegetated 20 cm top layer by mixing of compost and mineral soil (vol. 50%/vol. 50%). The cover is quite fertile and leads to a considerable reduction of water infiltration into the heaps. However, soil forming processes alter the physical properties of the cover affecting soil hydrology, stability and growth conditions. Within 6 years after placement self-compaction increased dry bulk density of the top soil (10 – 20 cm depth) from 1.15 – 1.35 g cm^?3. As a consequence, the air filled macropores decreased from >20 vol.-% to 8 vol.-%, whereas the water storing medium pores increased by 9 vol.-%. In contrast, dry bulk density of the pre-compacted mineral sublayer remained unchanged at 1.72 g cm^?3. Nevertheless, even in 30 – 60 cm depth, a significant increase in plant available water-holding capacity occurred. Initial soil dynamics are likely to improve the hydrological efficency and stability of the cover system. On the other hand, there is already some evidence for structural cracks and preferential water flow, which counteract the positive effects of self-consolidation and therefore requires further research.     

Effects of a plastic cover on soil moisture change in a Mediterranean climatic regime

Water deficit is a serious problem for most agricultural crops, especially in arid–semiarid regions, and limits sustainable development. Production can be improved by reducing evapotranspiration and loss of infiltrated water by the use of a plastic cover. We monitored soil moisture fortnightly over 1 yr using a neutron probe near four trees in an olive grove (Olea europaea, var. Arbequina), two of which had a plastic cover buried in the topsoil around them. These trees were monitored using three neutron probe access tubes per tree to compare the behaviour of soil moisture over time with two other identically instrumented and nearby trees with no cover. Analysis was based on the resultant moisture profiles. The plastic cover retained moisture and increased soil water residence time. During the dry season, the amount of water retained in the plots was at most 15–20% greater in the mid‐season and at least 5–6% greater at the end of season than in the central part of the plots near the trunk. The plastic cover was effective to ca. 50 cm with maximum water content near the soil surface. During the wet season, the cover did not affect soil water. Soil moisture was greater near the tree trunk as a result of stemflow and throughfall.     

不同碎石含量的土壤降雨入渗和产沙过程初步研究

碎石的存在改变了均质土壤的某些物理特性，降雨入渗和侵蚀产沙过程也因此受到影响，获取相关知识有助于模拟和预测土石混合介质中发生的水土过程。试验在模拟降雨条件下，对4种不同碎石含量(质量含量分别为0%，10%，20%和30%)的土壤入渗和产沙过程进行了室内研究。结果表明，碎石含量为10%时，土壤入渗率最大，当碎石含量超过10%时，入渗率反而降低；4种不同碎石含量的土壤侵蚀产沙高峰期均出现在降雨初期0～20 min，此后土壤侵蚀产沙相对稳定且在不同碎石含量的土壤间差别不大；降雨过程中，10%碎石含量的土壤侵蚀含沙率一直保持稳定较低水平，其他碎石含量的土壤侵蚀含沙率起初很高并在0～10 min内急剧下降，此后与10%碎石含量的土壤侵蚀含沙率接近。     

Effects of tillage and management practices on soil crust morphology under a Mediterranean environment

Soil crust formation can be affected by soil tillage. Alternative soil conservation practices consisting of reduced tillage were tested against traditional tillage, which involves mechanical weeding by frequent ploughing in rainfed vineyard soils in Catalonia, Spain. After 2 years of the experiment (1994–1996), thin sections of the surface crusts were studied to evaluate the effects of the soil management treatments on crust morphology and genesis, using micromorphological observations and pore characterisation with image analysis. Reduced tillage caused thicker and more complex crusts consisting of layers with different degrees of sorting and pore types, compared to traditional tillage. Total porosity of crusts did not differ from that of non-crusted areas, but pores in crusts were less interconnected, more horizontally distributed and more elongated than in the underlying non-crusted material. The soil type, especially structure and texture, affected crust morphology and played an important role in the process of crusting. The results show that reduced tillage may be limited as an alternative management practice when used to reduce crust formation in Mediterranean conditions, due to the difficulty to establish an effective groundcover.     

Heterogeneity in soil hydrological response from different land cover types in southern Spain

This paper reports results from the analysis of the soil hydrological response to simulated rainfall in a cork oak forest in Los Alcornocales Natural Park (SW Spain). Four different soil/vegetation units were selected for the field experiments: [1] cork oak woodland, [2] heathland, [3] grassland, and [4] cork oak/olive tree mixed forest. Rainfall simulations tests were performed on circular plots of 1256.6 cm² at an intensity of 56.5 mm h^− 1 for 30 min.Marked differences in the hydrological behavior of the studied vegetation types were observed after the rainfall simulations. The soils under woodland showed low runoff rates and coefficients. The highest runoff rates were measured on the heath and grass-covered parts of the hillslope. Water repellency of the soil, measured from water drop penetration tests, reduced infiltration (especially under the heathland), and seems to be the cause of fast ponding and runoff generation during the first stages of rainstorms.The mosaic of different patterns of hydrological response to rainfall, such as runoff generation or infiltration, is governed by the spatial distribution of vegetation and its influence on the soil surface.     

土石混合介质导气率变化特征试验

土壤中碎石的存在改变了土壤结构和孔隙分布,进而影响土壤通气性能。该文通过对碎石单粒径土石混合介质导气率变化特征研究,旨在探讨单粒径土石混合介质导气内在机理,为进一步研究复杂的野外土石混合介质的导气特性提供基础。为了研究土石混合介质中碎石对导气率的影响,该文通过试验研究,分析土壤颗粒小于2mm的样本(砂土、砂壤土、黏壤土)、碎石质量分数(10%、20%、30%、40%、50%)和碎石粒径(2～3、>3～5mm)对土石混合介质导气率的影响。结果表明:在土壤颗粒小于2mm的样本条件下,土壤导气率呈砂土>砂壤土>黏壤土;在相同碎石质量分数的土石混合介质中导气率呈砂壤土>砂土>黏壤土;碎石的存在改善黏壤土的导气性能,使黏壤土碎石混合介质的导气率大于黏壤土的导气率;降低了砂壤土和砂土的导气性能,且砂土的降低幅度远大于砂壤土;在砂壤土中碎石粒径2～3mm的导气率大于>3～5mm的导气率;在砂土中碎石质量分数30%之内,碎石粒径>3～5mm的导气率稍大于2～3mm的导气率,在40%则相反,但两种粒径下混合介质导气率差异不是很明显。     

Iron oxides in four Red Mediterranean soils on metarhyolite and metadolerite in Kilkis,Greece

The various iron fractions were quantified by selective dissolution (Fe_d, Fe_o, Fe_t) in four Red Mediterranean soils, developed on metarhyolite and metadolerite. They were similar in all profiles. A strong trend of iron removal from the surface horizon and of its subsequent illuvial translocation to the argillic horizons was observed. In all profiles, Fe_o was not related to the organic matter content indicating the Mediterranean xeric soil environment. The Fe_o/Fe_d ratio and the percentage of crystalline iron oxides (Fe_d-Fe_o) suggested that the pedoenvironment in which the profiles P1, P2 were formed, allowed the high crystallization of iron oxides. As indicated by the Fe_d/Fe_t values, the weathering process was more intense in the metarhyolite-developed soils. In contrast, the metadolerite-developed soils present conditions of poorly crystallized iron oxides and a lower degree of development.     

室内模拟降雨条件下土壤水分入渗及再分布试验

降雨入渗对城市绿化、防洪排涝、农业生产等方面有着重要的意义。采用室内模拟降雨,使用时域反射仪采集相关数据,从土壤含水率变化特征和湿润锋运移特点等方面,研究了在垂向一维条件下不同雨强降雨对水分入渗的影响,探讨在降雨条件下土壤水分的再分布情况,从而确定试验所用砂壤土保水性最优土层范围。结果表明：降雨结束后,土壤水分的再分布主要受土水势控制,随着时间的延长,蒸发作用逐渐占据主导地位;试验所用砂壤土的最佳保水性土层深度为20～35 cm,可为植物的选栽提供参考。     

Impacts of land use/cover change on soil properties in the Mediterranean region of northwestern Jordan

This study was carried out to evaluate the effects of deforestation on physical and chemical properties of soils under native forest in the Mediterranean region of northwestern Jordan. Land use/cover maps of 1953, 1978 and 2002 were interpreted and analysed within GIS to quantify the shift from forest to rainfed cultivation. Six sites were sampled in a non‐changed forest and in cultivated fields, three for each. Different soil properties of texture, bulk density, organic matter, total nitrogen, pH, cation exchange capacity (CEC), phosphorous and potassium were analysed. Results showed that many forests were changed into cultivated lands at a rate more than the reforestation. Subsequently, adverse effects on the studied physical and chemical properties were observed. The most affected properties were particle size distribution, bulk density of surface soil and subsoil. Organic matter and CEC decreased in cultivated soil as compared to the forest soil. Cultivated soils were found to exhibit a significantly lower status in physical and chemical soil properties as compared to forest soils. This general decline in the soil physical and chemical properties, in turn, contributed to soil erosion, reduction of soil fertility and land degradation. There is an urgent need to improve soil quality by developing sustainable land use practices to reduce the rate of soil degradation and to ensure long‐term sustainability of the farming system in the study area and in similar biophysical settings. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of soil rock fragment content on the USLE-K factor estimating and its influencing factors

Rock fragments are an important component of soil, and their presence has a significant impact on soil erosion and sediment yield. In this paper, the effects of rock fragments in the topsoil profile (RFP) and rock fragments on the soil surface (RFS) on the soil erodibility factor (K) were assessed at a global scale. The spatial pattern of the relationship between stoniness and erodibility (R_S-K) and its predominant factors were explored through correlation analysis, pattern analysis, and random forest model analysis. The results were as followings: (1) The existence of RFP increased K by 2.84%. The RFS of the mountain land and desert/Gobi reduced K by 18.7%; therefore, once the RFP and RFS were taken into account in the calculation, K was 6.98% lower. (2) The predominant factors of the effect of RFS and the joint effect of RFP and RFS were elevation and slope gradient. The predominant factors of the effect of RFP were annual average precipitation and annual average temperature. (3) In assessing and mapping soil erosion in large regions, special attention should be given to areas with large rock fragment contents, a relatively high altitude, and the presence of steep slope. If rock fragments were not taken into consideration, the mapping results of soil erosion may be biased. This article made the calculation of K more complete and accurate, thereby improving the accuracy of regional soil erosion estimation. This research was of significance for the investigation of global hydrological effects and simulation of the global soil carbon budget.     

人工模拟降雨条件下花岗岩红壤坡面侵蚀过程与特征分析简

通过室内人工模拟降雨试验,研究降雨强度、坡度及地表覆盖3因素对花岗岩红壤坡面侵蚀过程的影响.结果表明：1）起始产流时间随降雨强度和坡度的增加而有所提前,而地表覆盖能延缓起始产流时间;2）在不同降雨强度和坡度条件下,径流率从产流初期开始都快速增加,7 ～ 10 min后达到稳定,且随着降雨强度和坡度增加,径流率也显著增加;3）随着降雨强度的增大,产沙率明显增大,且降雨强度越大,坡度对产沙率的影响越明显;4）降雨强度和径流总量、产沙总量之间相关性极显著,其相关系数分别为0.892和0.799;5）地表覆盖具有良好的减沙作用,其减沙效益超过90％.     

The effects of applied crop residues on losses of Fe, Mn, Cu and Zn in run-off from a soil prone to crusting

Tillage practices may reduce the organic matter content in near-surface soil horizons causing crust formation. Surface conditions may cause an increase in surface run-off, thus enhancing contaminant transfer of heavy metals or an acceleration in nutrient loss. This study examines the effect of applying crop residues to the surface of tilled soils on heavy metal losses by run-off. Losses in iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) were analysed. Run-off and sediment yield were measured on 1 m² plots using a rainfall simulator with a constant 65 mm/h intensity. Four successive rainfall applications were performed, the first three at 25 mm each and the last at 65 mm. Added corn straw varied between 0 and 4 t/ha in the five studied treatments. After 140 mm cumulative rainfall, total heavy metal losses were as follows: Fe from 137 to 950 mg/L, Mn from 2.3 to 12.83 mg/L, Cu from 0.09 to 0.72 mg/L and Zn from 0.31 to 2.46 mg/L. Dissolved fractions were as follows: Fe from 0.014 to 0.229 mg/L, Mn from 0.034 to 1.45 mg/L, Cu from 0.002 to 0.013 mg/L and Zn from 0.02 to 0.12 mg/L. Total concentrations of the studied elements decreased exponentially due to the effect of corn straw on soil loss. However, dissolved contents of Fe and Cu scarcely varied. Significant positive linear correlations were observed between total heavy metal content and soil and sediment loss by run-off. It is concluded that the addition of straw to a soil of low fertility prevents heavy metal loss.     

降雨类型对褐土横垄坡面土壤侵蚀过程的影响

雨型是影响土壤侵蚀过程的重要因子之一,而影响效应与耕作措施密切相关。目前,雨型对横垄坡面土壤侵蚀过程的影响机制尚不清楚。该文以褐土横垄坡面为研究对象,设计了平均雨强和降雨量相同的4种雨型(增加、减弱、增加-减弱和减弱-增加型),采用可同时调节垄向和坡面坡度的土槽进行模拟降雨,研究各个雨型下不同侵蚀阶段的产流产沙特征。结果表明:雨型间的径流量和侵蚀量在细沟间和细沟侵蚀阶段均差异显著,且差异在细沟阶段体现的更为明显。雨型间径流量的大小顺序为增加-减弱型减弱型减弱-增加型增加型,侵蚀量则为增加-减弱型减弱-增加型减弱型增加型。给定雨强下(30、60或90 mm/h),径流量、径流贡献率和侵蚀量贡献率均随降雨过程中雨强发生时序的延迟而增加,而单位径流侵蚀量呈相反趋势;雨型间给定雨强同一发生时序下的径流量和侵蚀量及其它们对总径流量和总侵蚀量的贡献率均差异显著。4种雨型下,幂函数均能很好的描述细沟间和细沟侵蚀阶段内产沙率与径流率间的关系,且方程中的指数均低于2,但雨型间幂函数方程中的指数存在明显差异。以上研究结果有助于深入理解褐土垄作系统下的土壤侵蚀机理,并为横坡垄作的合理利用提供科学指导。     

Soil degradation and soil surface process intensities on abandoned fields in Mediterranean mountain environments

The Pyrenean and Pre‐Pyrenean mountain areas have been intensively used at least since roman times, but nowadays depopulation has lead to widespread land abandonment without a steering land‐management. Vegetation recovery is weak in most abandoned fields. Soil formation and characteristics are conditioned by this fact, and for this, soils show past degradation processes and are mostly predominant factors for continuing land degradation or restoration. Three study areas were set up along a climatic gradient with increasing summer water deficit in the sub‐humid zone between the Central Pyrenees and Pre‐Pyrenees. Soil survey combined with experiments for the determination of infiltration, runoff and erosion were applied for understanding the degradation history and the future development of the soils. All areas are dominated by Entisols, but also Inceptisols and Alfisols are found, and even soils with hydromorphic features. The soils show signs of heavy erosion. The parental material determines the nutrient supply and the general chemical properties. All sites show a weak water storing capacity, as a result of the removal of fine material by erosion and due to the depletion of soil organic matter. In addition, infiltration capacity and runoff generation are high within the studied areas, averaging between 27 and 37 per cent. The driest area studied shows an ongoing trend to degradation, with high erosion rates combined with a high degradations status of the soil. The other areas are characterised by a patchy pattern of soil degradation and regradation processes. Copyright © 2008 John Wiley & Sons, Ltd.     

Relationships between soil properties and feeding activity of soil fauna in acid forest soils

We investigated the relationships between soil chemical properties, humus form, and feeding activity in eight forest sites in Northrhine‐Westphalia, Germany. The study sites varied in forest type (oak, oak‐hornbeam, spruce, and pine). Three study sites were located under the same climatic conditions, and five study sites were distributed all over Northrhine‐Westphalia. We determined humus form, soil chemical properties, and feeding activity in three replication plots per site. We used the bait‐lamina test to determine feeding activity of soil fauna. Independent of forest type, all study sites were very acid with pH(CaCl₂) values in the Ah horizon between 2.8 and 4.0. The three study sites located under the same climatic conditions showed very homogenous soil chemical properties (pH in Ah: 2.9–3.0), whereas the five other sites varied significantly due to their soil chemical parameters (pH in Ah: 2.8–4.0). All single sites presented feeding activities with a very low spatial heterogeneity. Forest types and climatic conditions were not related to activity of soil fauna. Feeding activity and thickness of the O layer were strongly negatively correlated, whereas the activity was strongly positively correlated to soil pH in the five study sites with a wide range of soil chemical parameters. The three extremely acid forest sites presented significant differences in feeding activities that were not related to soil chemical properties.     

降雨特性和覆盖方式对麦田土壤水分的影响

为探明不同降雨特性和覆盖方式对冬小麦土壤水分的影响,利用人工模拟降雨器,模拟40和60mm/h2种降雨强度,在大田设置地膜覆盖(PM)、秸秆覆盖(覆盖量分别为1500、4500、7500和10500kg/hm2,即SM15、SM45、SM75和SM105),同时设置无覆盖处理作为对照(CK),研究不同降雨强度和覆盖方式对雨后冬小麦0～60cm土层土壤水分分布和降雨土壤蓄积量的影响。结果表明:模拟降雨前各覆盖处理土壤含水率均比CK高,其中0～20cm土层土壤含水率差异显著(P<0.05),而20cm以下各处理土壤水分相差较小,除SM105与CK差异显著外(P<0.05),其他处理与CK差异不显著;同一覆盖处理,60mm/h降雨强度条件下降雨入渗深度和入渗量明显高于40mm/h。在相同雨强条件下,不同覆盖处理可以不同程度的增加耕层土壤含水率,其中秸秆覆盖量越大,效果越明显,而PM效果最差;2种雨强条件下各处理0～60cm土层降雨土壤蓄积量规律表现一致,即SM105>SM75>SM45>SM15>CK>PM,其中SM105和SM75均显著高于CK(P<0.05),PM则显著低于CK(P<0.05);受植株冠层降雨截留的影响,同等降雨条件下,同一覆盖处理拔节前降雨土壤蓄积量大于拔节后的;相比60mm/h降雨强度,40mm/h降雨强度下各处理拔节前、后降雨土壤蓄积量变化幅度较大。     

Exploring the factors influencing the hydrological response of soil after low and high-severity fires with post-fire mulching in Mediterranean forests

Despite ample literature, the influence of the individual soil properties and covers on the hydrological response of burned soils of forests has not clearly identified. A clear understanding of the surface runoff and erosion rates altered by wildfires and prescribed fires is beneficial to identify the most suitable post-fire treatment. This study has carried out a combined analysis of the hydrological response of soil and its driving factors in burned forests of Central-Eastern Spain. The pine stands of these forests were subjected to both prescribed fire and wildfire, and, in the latter case, to post-fire treatment with mulching. Moreover, simple multi-regression models are proposed to predict runoff and erosion in the experimental conditions. In the case of the prescribed burning, the fire had a limited impact on runoff and erosion compared to the unburned areas, due to the limited changes in soil parameters. In contrast, the wildfire increased many-fold the runoff and erosion rates, but the mulching reduced the hydrological response of the burned soils, particularly for the first two-three rainfalls after the fire. The increase in runoff and erosion after the wildfire was associated to the removal of the vegetation cover, soil water repellency, and ash left by fire; the changes in water infiltration played a minor role on runoff and erosion. The multi-regression models developed for the prescribed fire were accurate to predict the post-fire runoff coefficients. However, these models were less reliable for predictions of the mean erosion rates. The predictions of erosion after wildfire and mulching were excellent, while those of runoff were not satisfactory (except for the mean values). These results are useful to better understand the relations among the hydrological effects of fire on one side and the main soil properties and covers on the other side. Moreover, the proposed prediction models are useful to support the planning activities of forest managers and hydrologists towards a more effective conservation of forest soils.