Effect of water quality and amendments on the hydraulic properties and erosion from several mediterranean soils

The response of six sandy-loam soils from Portugal and Israel to leaching with sodic and saline water and to simulated rain was studied. The dominant clay mineral in the soils from Portugal was kaolinite, whereas smectite predominates in the soils from Israel. The permeability of the soils depended on the soil texture: it decreased with an increase in the silt and clay content. The response of the soils to sodicity depended on the electrolyte concentration; salt concentrations exceeding 10 mmol_c·L⁻¹ was enough to prevent the deleterious effect of exchangeable sodium (≤20%). When leaching with distilled water (stimulating rain water), the presence of primary minerals and lime determine the susceptibility of the soils to sodicity. The calcareous loess from Israel was the least susceptibility to sodicity.The six soils were susceptible to sealing, high runoff and erosion when exposed to rain. The soil surface was particularly vulnerable to sealing due to both the mechanical impact of raindrops and the low concentration of electrolytes in the rainwater. Seal formation was due to two mechanisms:

• 1.(i) physical disruption of aggregates at the soil surface which depended on the impact energy of raindrops and the inherent aggregate stability; and
• 2.(ii) chemical dispersion which depended on the mineralogy of the clay, the ESP, and the electrolyte concentration.

When the impact of the drops was prevented, or when the anionic polymer was sprayed at the soil surface, physical breakdown of the aggregates was reduced and runoff and erosion were slight. When the electrolyte concentration was high, the chemical dispersion was small and runoff and erosion decreased, compard with the control. The smectite soils from Israel were more susceptible to sealing than the kaolinitic soils from Portugal.     

Polysaccharide and salt effects on infiltration and soil erosion. A rainfall simulation study

Seals forming at the soil surface during rainstorms reduce water penetration and increase runoff in many arid and semi-arid regions. The effect of surface application of an anionic polysaccharide (designated F-Ac), synthesized by the filamentous cyanobacterium Anabaenopsis circularis PCC 6720, on infiltration rate (IR), runoff and erosion of three soils during simulated rainstorms, was studied. The interaction between F-Ac and electrolyte concentration at the soil surface was studied by using distilled water (DW) or tap water (TW) or by spreading phosphogypsum (PG) on the soil surface. F-Ac added at the rate of 3.4 kg ha⁻¹ together with PG at the rate of 5 t ha⁻¹ was the most efficient treatment in improving infiltration and reducing runoff and erosion. This treatment reduced runoff, from the three soils studied, from 65–80% in the control to 14–24%. Soil loss was reduced from 3.6–4.5 Mg ha⁻¹ in the control to 0.5–1.3 Mg ha⁻¹ in the treated soils. DW treatment, singly and in combination with F-Ac, was quite inefficient in preventing seal formation and in reducing runoff and soil loss. Adding F-Ac with TW maintained final IR and runoff levels intermediate between those of F-Ac with PG and those of F-Ac with DW. Electrolytes in the soil surface which flocculated soil clay, enhanced the beneficial effect of F-Ac on aggregate stability and thus greatly reduced water and soil losses. The efficacy of F-Ac as a stabilizing agent (i.e., soil conditioner) wore out during three consecutive storms of 60 mm each.     

Surface seal micromorphology as affected by fluidized bed combustion bottom-ash

Amendments that alter clay dispersion and aggregate disintegration also change soil porosity and sealing. Soils selected for this study had increased (Mollisol, Oxisol, and Vertisol), decreased (Oxisol), or non-affected (Oxisol and Ultisol) water infiltration when fluidized bed combustor bottom-ash (FBCBA) was surface applied to decrease dispersion. Soil was sieved to pass 8-mm, packed into small erosion pans, prewetted by capillarity, and subjected to 110 mm h⁻¹ simulated rain until steady state infiltration. Image analysis was used to quantify crust morphology, porosity and characteristics of the seal and the unsealed soil below it. A conspicuous feature was a structural crust at the surface with a continuous dense layer of lesser porosity and smaller pores than uncrusted soil. The seal showed no evidence of a “washed-in” zone of illuvial clay in the control treatment, although dispersed clay was observed in the percolating water for some soils. Where FBCBA was effective in increasing water infiltration, an increase in total porosity attributed to planar pores was observed. A sandy loam Oxisol was the least prone to sealing. For this soil, a considerable amount of dispersed clay was observed in the control, while FBCBA rapidly flocculated clay and formed an illuvial clay layer, lowering infiltration. A layer of eluvial silt and fine sand was observed at the surface of soils where considerable dispersion occurred on non-treated soils. Differences in steady-state infiltration could not be explained by the variation in total porosity or pore shape. Spatial variability, pore continuity, and expansion/contraction of clays obscure any relationship with an averaged infiltration even on a small plot.     

The analysis of spectroscopical data to map soil types and soil crusts of Mediterranean eroded soils

A study was carried out to investigate the potential use of imaging spectroscopy for mapping erosion hazard in Mediterranean areas. In the study area in southern France five soil types are recognized showing different vulnerability towards erosion. Samples were taken to the laboratory and exposed to artificial rainfall to stimulate crust formation. In the laboratory the spectroscopical behaviour of the soils with and without crusts was measured in the near and shortwave infrared in very narrow bands.Correspondence analysis was used to analyze the soil physical data and the soil spectra. This multivariate analysis method was useful to select spectral bands on which to focus to discriminate between the different soil types. Two important soil types having different vulnerability towards erosion, were discriminated by absorption features of iron and calcite. Crusting of the soils was not recognized by spectral absorption features, but generally crusts caused an increase of albedo of approximately 12%. This increase of albedo might be used to assess the presence of crusts.It was concluded that some main soil types can be discriminated by spectral absorption features and that imaging spectroscopy might have a good potential for surveying the hazard of physical soil degradation in Mediterranean areas.     

团粒结构对黄绵土溅蚀速率和结皮形成的影响研究

为弄清团粒结构在土壤结皮形成过程所起的作用,笔者通过人工模拟降雨溅蚀试验,测定土壤溅蚀速率,同时采样制作土壤切片,分析不同直径团粒对黄绵土溅蚀速率和结皮形成的影响。结果表明：0.15 mm≤D＜2.0 mm和D＜0.038 mm的团粒土壤较易形成结皮,在降雨历时5 min时,土壤表面有结皮形成,随着降雨的继续,土壤表面结皮形成趋于完善;而中度直径0.038 mm≤D＜0.15 mm的团粒土壤不易形成结皮,在降雨历时5 min时,土壤表面都没有结皮形成。在团粒直径范围是0.105 mm≤D＜0.22 mm,随着土壤团粒直径的减小,土壤的溅蚀速率逐渐增加,直径位于0.096~0.15 mm之间的团粒结构土壤的溅蚀速率达到最大,随后,随着土壤团粒直径的减小,土壤溅蚀速率逐渐降低。     

红壤结皮发育特征及其与土壤溅蚀的关系

研究红壤表土结皮发育特征及其与土壤溅蚀的关系,可为理解红壤的侵蚀机理提供理论依据。通过人工模拟降雨溅蚀试验,采样制作土壤切片,同时测定红壤溅蚀速率,观察分析红壤土表结构的变化特征以及与土壤溅蚀的关系。结果表明：土壤母质和质地是影响土壤结皮形成的主要因素。母质是花岗岩的红壤不易形成结皮,而母质是红砂岩和第四纪红色粘土的红壤较易形成结皮。石砾和粗砂含量较多的红壤不易形成结皮,而粉粒和粘粒含量越多,红壤表面越易形成结皮。     

Interactions between water quality and polymer treatment on infiltration rate and clay migration

The electrical conductivity (EC) and sodium adsorption ratio (SAR) of irrigation water significantly affect water transmission properties of soil. Commercially produced polymers which are soluble in water may potentially mitigate the negative consequences of water quality on infiltration rate. Waters were synthesized to have combinations of EC equal to 0.5, 2.0 and 5.0 dS m⁻¹ and SAR of 5, 15 and 25. These waters were applied through a laboratory scale rainfall simulator to 12 × 20 cm trays containing soil. Untreated and treated waters with 10 mg L⁻¹ concentration of a cationic polysaccharide were used in the study. Untreated waters were applied to uncovered soil or to soil covered with fiberglass sheets 0.5 cm above the soil to disrupt the impact energy. The polymer treated waters were only applied to uncovered soil. The steady state infiltration rates were significantly affected by SAR and EC with the trend toward increasing infiltration rate with increasing EC and/or decreasing SAR under all conditions. Impact energy greatly reduced the infiltration rate as compared to no impact energy. The polymer treatment significantly increases the infiltration rate for each water. The relative beneficial effects of polymer tended to be greater with increasing EC and/or decreasing SAR. The clay in runoff and leachate had several significant interactions between waters and treatments. Treatments that tended to produce more fine particulates leading to crust formation and reduced infiltration rate tended to have less clay in the runoff and leachate. Apparently crust formation partially inhibits clay migration.     

Environmental impact of soil erosion under different cover and management systems

Runoff, soil loss and physical chemical composition of surface soil, runoff water and eroded sediment were measured for three erosive rainstorms of the 1988 Autumn-Winter season, on clay soil slopes (Typic Chromoxeret) under different cover and management systems in a locality of Sicily.Four years reconsolidated natural grass-sod (Avena fatua and Lolium tumulentum), natural grass-sod with implanted forage shrubs (Atriplex halimus) and natural grass-rod afforested with Pine trees (Pinus halepensis), reduced significantly runoff and soil loss in comparison with tilled fallow following four years durum wheat cultivation.While differences in runoff and soil loss between reconsolidated systems were not significant, the higher biomass yield (Stringi et al. 1991) and the better soil cover (Chisci et al. 1991) of the Atriplex system, increased O.M. content of the soil and prevented soil erosion under very intense rainstroms of the semiarid Mediterranean area.The comparison of textural and aggregate grain-size composition of surface soil and sediment confirmed that physico-mechanical composition of sediment detached and transported by over-land flow on clayey soils is better estimated by pseudo-textural grain-size composition of surface soil (Chisci et al. 1989) than from textural composition.Soil loss amounts, and O.M., N and P enrichment ratios, combined in a specifically devised Environmental Impact Index (EI), demonstrated the excellent environmental protection value of reconsolidation of arable soils. However, Pinus system was somewhat less efficient than Atriplex and good natural grass-sod systems.     

Effect of surface treatments on soil crusting and infiltration

The effects of phosphogypsum and plant residue mulches on soil crusting and infiltration were studied on a Rhodic Paleustalf in Northern Natal, South Africa. Under field conditions infiltration rates were considerably higher than those obtained with a laboratory type rainfall simulator. Both ameliorants were effective in countering crust formation. Their effect continued over a growing season (4–5 months). Scanning electronmicrographs showed that under moist conditions microbial hyphae and residues were prominent in the surface crust. Extractable soil P built up to high levels in the phosphogypsum treated plots.     

云南磷石膏堆存对区域水环境的影响研究

伴随着磷肥产量增加,磷石膏产排量对环境污染等问题愈加突出。为解决磷石膏堆放对环境造成的威胁和磷石膏的资源化利用,本研究通过对云南省磷矿资源主要集中地磷石膏堆场的实地调查、采样并结合模拟试验、建立预测模型等方法,明确磷石膏对区域水体环境介质存在的影响。结论如下：（1）不同堆存点磷石膏均呈酸性。滇池流域的磷石膏含磷量较高、抚仙湖流域的磷石膏含氟量较高。（2）通过地表径流试验,地表水总磷和氟化物的含量基本呈现随迁移距离增加而不断下降的趋势。并建立地表水污染物沿程迁移变化回归模型。地表径流中总磷和氟化物分别迁移至距堆场186.45 m和167.30 m外,可达到地表Ⅲ类水标准。（3）通过土柱淋溶试验,淋出液中总磷含量随淋溶次数的增加整体呈下降的趋势。不同土柱淋出液中氟含量呈现正相关的变化趋势,除个别土柱淋出液外,其他深度的淋出液氟含量在0.15～0.45 mg/L范围之内,可达到地下水的Ⅰ类至Ⅲ类标准。本研究为解决磷矿区乃至流域内磷石膏对水环境等造成的污染负荷问题,提供定量化的理论基础。     

Comparison of soil and sediment properties of a loamy sand soil

Ten 25 m² runoff plots at the Hilton experimental site, east Shropshire, UK, have been used to compare the physicochemical properties of loamy sand plot soils and sediment eroded from the plots over one year. Sediment contained more sand (2 mm–60 μm) and less clay (< 2 μm), silt (2–60 μm) and coarse fraction (> 2 mm) than soil. Erosion rates increased with slope and proportionally more silt and particularly clay were eroded on steeper slopes. Selective clay depletion has serious implications for soil structure and fertility. Correlations existed between the organic matter contents and particle size distributions of soil and sediment, but the sediment had less organic matter and lower pH values than soil. Sediment also contained lower concentrations of calcium, iron, potassium, magnesium, manganese and phosphorus than soil. Relationships between erosion and soil textural change appear to be partly technique-dependent, which suggests more uniformity in approach would be beneficial in studies on the effects of erosion on soil fertility.     

Effects of reduced tillage on soil surface properties affecting wind erosion in semiarid fallow lands of Central Aragón

In Central Aragón (NE Spain), where strong and dry winds are frequent all year round, fallow lands are susceptible to wind erosion due to insufficient crop residues on the surface and loose, finely divided soils by multiple tillage operations. Effects of conventional tillage (CT — mouldboard ploughing followed by a compacting roller) and reduced tillage (RT — chisel ploughing) on soil surface properties affecting wind erosion were studied during three experimental campaigns in a dryland field of Central Aragón. RT provided higher soil protection than CT through a lower wind erodible fraction of soil surface (on average, 10% less) and a significantly higher percentage of soil cover with crop residues and clods (30% higher). Random roughness was also higher after RT than after CT (15 vs. 4%). These results indicate that RT can be an effective soil management practice for wind erosion prevention during the fallow period in semiarid Aragón. The study shows, likewise, that significant changes in soil aggregate size distribution associated with wind erosion processes may occur in short periods of time. Thus, temporal variability of soil surface properties, including crust and clods stability, needs to be considered in wind erosion research in agricultural soils.     

Soil organic matter and erosion processes on arable loamy sand soils in the west midlands of England

Plot studies at the Hilton experimental site, Shropshire (U.K.) show that small reductions in soil organic content markedly increase erodibility and erosion rates. Soil organic material varies vertically within crusting topsoils, with more organic-rich material ingressing to a ‘filtration pavement’ beneath the surface crust. Consequently, the organic content of soils eroded from plots is less than in situ plot soil. Soil organic content decreased through time on bare soils.     

Influence of a polyacrylamide soil conditioner on runoff generation and soil erosion: Field tests in Baringo District,Kenya

Following promising laboratory results the effect of low concentration applications of a polyacrylamide soil conditioner SEPARAN AP30 on soil properties was tested under field conditions in a severely degraded semi-arid region in northern Kenya. Tests of conditioner performance on tilled and undisturbed soils were carried out under simulated rainfall on crusting Eutric or Calcaric Fluvisols at two sites on alluviolacustrine flats adjacent to Lake Baringo. Tests were carried out in two series separated by up to six weeks of sunshine and natural rainfall, to determine the longevity and residual effects of conditioner application.Runoff generation and soil loss were significantly reduced on all runoff plots during the first rainfall simulation, but the most dramatic results occurred when conditioner application was combined with raking. This inhibited crust development and virtually eliminated runoff and soil loss. Under natural weathering, surface crust had developed on all plots before the second rainfall simulations. Some residual effects of the conditioner on infiltration rates were still noted, but the residual effect on soil loss was greatly diminished.The tests indicate that low concentration applications of SEPARAN are not useful on undisturbed soils, but can provide useful temporary reductions in sheet and rillwash hazard when combined with tillage and could be effectively combined with grass re-seeding for more permanent reclamation.     

不同下垫面条件下土壤养分流失研究概况

中国的土壤侵蚀十分严重,而随着土壤侵蚀的发生发展将导致土壤养分流失、土壤贫瘠、土地生产力降低等多种问题。影响土壤侵蚀和土壤养分流失的主要因素包括降雨、下垫面条件和人为因素。通过总结多年来对不同下垫面条件下土壤养分流失情况的研究结果,分析下垫面条件中地表植被、坡度、坡长、土壤含水量、土壤颗粒等因素对土壤养分流失的影响,总结目前正在试验或用于实践的各种用于控制或者减少土壤养分流失状况的措施,以期对下一步的研究工作提供参考。     

Stabilizing steep slopes with geomembranes

The effects of five types of geomembranes, placed at the soil surface, on runoff and erosion on steep earth slopes were studied under laboratory and field conditions. In the laboratory, the soil samples were packed in boxes held at a 50% slope and subjected to three consecutive simulated rainstorms of 120 mm each. The membranes dissipated the drops' impact and reduced runoff significantly compared with the control. There was no significant difference among the membranes regarding their effect on the runoff. In the field, the membranes lined earth dikes of 33–60% slope and 12–20 m length, during 2 years. There was no runoff and erosion from the lined plots compared with 80–125 tonne ha⁻¹ of erosion in the control plots. No considerable wear and tear of the membranes was observed.     

Reduction in soil loss from erosion-susceptible soils amended with humic substances from oxidized coal

Soils that pose high risk of erosion require amendment with either natural or synthetic soil conditioners to reduce soil loss hazards. The objective of this study was to evaluate the potential of using coal-derived humic substances (as soil conditioners) to reduce runoff erosion on erosion-susceptible soils. Surface (0–20 cm) samples of severely degraded soils from Principina in Tuscany (Orthic Xerofluvent) and Bovolone in Venice (Udic Ustochrept) in Italy were used to assess the effects of five rates (0, 0.05, 0.10, 0.50 and 1.00 g/kg) of humic acids (HA) on soil loss and other hydrological parameters. A rainfall simulator was used to apply approximately 40 mm/h intensity rain for 1 h on soil beds of dimensions 2 m × 0.5 m × 0.01 m, packed at a bulk density of 1.20 Mg/m³ and inclined at a slope of 15%. The amount of soil eroded (E) and the time to initiate runoff (Rt) and drainage (Dt) were related to changes in the water-holding capacity and aggregate stability of the soils following the HA treatments. In the control treatments, the values of E, Rt and Dt were higher in the Principina than Bovolone soil. Increasing HA rates generally delayed Rt, accelerated Dt and reduced E substantially on both soils. On the Principina soil a reduction of about 36% in soil loss was obtained by adding only 0.05 g/kg of HA (equivalent to 100 kg/ha). On the sandier Bovolone soil, the same magnitude of reduction was achieved with 0.10 g/kg (200 kg/ha) of HA. Improvements in Rt and Dt from the HA amendments explained between 58 and 81% of the variation in E from both soils. Furthermore, improvements in the water retention capacity more than in the aggregate stability of these soils accounted for the reduced runoff erosion. These results show that amending erosion-susceptible soils with low rates of coal-derived humic substances is a potentially effective soil management practice for reducing erosion rates.     

Effect of antecedent soil water content and rainfall regime on microrelief changes

Surface microrelief substantially affects surface sealing, runoff, and soil erosion processes on bare soils. Yet, the stability of microrelief for different antecedent soil water contents and rainstorms is not well understood. This study investigates the effect of surface microrelief and antecedent water content on the decay of microrelief under different rainstorm regimes. Two different rainstorm regimes were studied in laboratory experiments: continuous rainfall for a total amount of 60 mm applied at 30 mm/h intensity, and intermittent rainfall consisting of five successive rainstorms of 12 mm each, again with an intensity of 30 mm/h and separated by one week drying cycles. Rough, medium, and fine microrelief surface conditions representing different degrees of seedbed preparation were studied for three soils at antecedent soil water contents of 2–4% and 14–20%. Before and after rainfall, digital elevation models determining the surface microrelief were developed using a laser scanner with 2 mm grid spacing. The specific surface area calculated from microrelief data was used as an index to characterize microrelief. Microrelief stability increased with increasing initial roughness and was much higher for the antecedent wet soils than for the dry soils. Microrelief stability for the continuous rainstorm regime was higher than for intermittent rainfall. Differences in microrelief stability were mostly attributed to different aggregate stabilities. Additionally, the higher stability for the rougher microrelief surfaces was attributed to the lower drop impact density and splash density on the surfaces with larger specific surface area. Aggregate slaking due to air escape and rapid wetting was found to be responsible for the low microrelief stability at initially dry conditions.     

Changes in microrelief and their effects on infiltration and erosion during simulated rainfall

The erosivity of soils under a given rainfall energy appears to vary greatly among soil orders, probably reflecting differences in clay composition and organic matter content. This study was conducted to quantify microrelief, infiltration, and sediment yield changes during three consecutive simulated rain events on a Udic Haploboroll and a Typic Hapludalf from Minnesota, and a Mollic Kandiudalf, and Typic Palehumult from Uganda. Air dry aggregates (< 5 mm) were packed in 19 1 containers tilted to a 5% slope and were subjected to three consecutive high energy rain storms (63 mm h⁻¹) for a duration of 1 h. Runoff and sediment were continuously monitored during a storm. Infiltration was measured by continued weighing of the soil and containers. An automated non-contact laser relief meter was used to measure changes in soil roughness initially and after each storm. Soil surface roughness decreased during the rain events indicating that aggregate breakdown was the dominant process in seal formation. For example, random roughness decreased form 5.9 to 4.0 mm on Barnes loam and from 9.7 to 6.9 mm on Renova silt loam with cumulative rainfall of 0 and 126 mm. These infiltration rates indicated that the Barnes Loam (Haploboroll) and Kabanyolo clay (Kandiudalf) were unstable soils while Kachwekano clay (Palehumult) and Renova silt loam (Hapludalf) were quite stable. Final infiltration rates after 3 consecutive rainfalls on Kachwekano clay (15 mm h⁻¹) and Renova silt loam (13 mm h⁻¹) [the stable aggregate soils] were significantly higher than those of Barnes loam (4 mm h⁻¹) and Kabanyolo clay (3 mm h⁻¹). For the two stable soils a high infiltration rate on a rough surface was maintained until aggregate breakdown occurred and runoff began. Sediment yield from Barnes loam (29 kg m⁻²) and Kabanyolo clay (28 kg m⁻²) was significantly greater than soil loss from Kachwekano clay (0 kg m⁻²) and Renova silt loam (6 kg m⁻²). The microrelief method to quantify aggregate stability is an improvement over wet sieving and other related measurements because of its rapidity and because the statistical quantification can be linked to physical processes.     

Soil surface densification under simulated high intensity rainfall

The formation of surface crusts in agricultural soils has adverse effects on seedling emergence and infiltration and causes excessive water loss by runoff. Changes in soil surface characteristics of Zamora soil were examined under high intensity (76.2 mm/hr) simulated rainstorms A hard, dense, several-cm-thick, consolidated layer developed on the soil surface upon drying. The thickness and bulk density of this layer were strongly related to rainfall duration. A strong exponential function was found between the thickness of the consolidated layer and the soil wetted depth. Soil surface strength was strongly correlated with rainfall duration and with the initial bulk density of the soil despite the marked change in the density of the consolidated layer. The largest changes in both strength and bulk density occurred within the first 10 min of the rainstorm. Mechanisms known to be responsible for crusting appear to partly hold for the densification process, but they do not adequately explain the deeper consolidation. Particle reorganization and close-packing associated with settling under saturated or near-saturated conditions appear to provide more logical mechanisms. The relative change in bulk density was inversely correlated with the initial soil bulk density. Measurements of soil strength with a small penetrometer probe indicated an agreement between surface strength and the cohesion of the consolidated layer as determined by a triaxial shear test. Temperature of drying had slight, but mostly inconsistent effects on the strength and density of the consolidated layer. Soil densification was also found to markedly decrease the infiltration rate. The physical properties of both the consolidated layer and the subsoil, however, appeared to control the infiltration process.