Water Erosion Rates Research Articles

Soil translocation by weeding on steep-slope swidden fields in northern Vietnam

This study investigated soil translocation associated with weeding on steeply sloped swidden fields attended by ethnic Da Bac Tay farmers in Hoa Binh Province in northern Vietnam. Annual soil loss rates of 4–6 Mg ha −1 year −1 were found on 20 m plots located on two separate hillslopes. Median soil flux rates were equivalent to 2.6–3.9 kg m −1 pass −1 for experiments conducted on slopes ranging from 0.54 to 0.84 m m −1. The primary soil translocation process, the mechanical movement of soil via contact with a small hoe ( ngheo), contributed approximately 60% of the weeding-related soil flux. Ravel, which is the rolling, bouncing, and sliding of soil clods downslope, was a secondary translocation process that accounted for almost 40% of the soil flux. Soil flux was most appropriately described with an exponential function that could predict the occurrence of ravel on steeper slopes. The observed soil fluxes were much smaller than those determined during weeding and hoeing at other tropical and subtropical sites, primarily because the tillage depth was very shallow (<1 cm) and weed density was low at the time of experimentation. The erosion rates associated with weeding were an order of magnitude lower than reported water erosion rates; therefore, the contribution to landscape change was believed to be small. Combined water and tillage erosion estimates indicated a possible unsustainable increase in soil loss on some steep-slope fields within the last few decades that has resulted from shorter fallow periods, longer periods of cultivation before fallowing, and greater weed pressure. Additional work is needed to verify these latter interpretations.

Soil erosion from sugar beet in Central Europe in response to climate change induced seasonal precipitation variations

This study estimates the implications of projected seasonal variations in rainfall quantities caused by climate change for water erosion rates by means of a modeling case study on sugar beet cultivation in the Central European region of Upper-Austria. A modified version of the revised Morgan–Morgan–Finney erosion model was used to assess soil losses in one conventional and three conservation tillage systems. The model was employed to a climatic reference scenario (1960–89) and a climate change scenario (2070–99). Data on precipitation changes for the 2070–99 scenario were based on the IPCC SRES A2 emission scenario as simulated by the regional climate model HadRM3H. Weather data in daily time-steps, for both scenarios, were generated by the stochastic weather generator LARS WG 3.0. The HadRM3H climate change simulation did not show any significant differences in annual precipitation totals, but strong seasonal shifts of rainfall amounts between 10 and 14% were apparent. This intra-annual precipitation change resulted in a net-decrease of rainfall amounts in erosion sensitive months and an overall increase of rainfall in a period, in which the considered agricultural area proved to be less prone to erosion. The predicted annual average soil losses under climate change declined in all tillage systems by 11 to 24%, which is inside the margins of uncertainty typically attached to climate change impact studies. Annual soil erosion rates in the conventional tillage system exceeded 10 t ha − 1 a − 1 in both climate scenarios. Compared to these unsustainably high soil losses the conservation tillage systems show reduced soil erosion rates by between 49 and 87%. The study highlights the importance of seasonal changes in climatic parameters for the discussion about the impacts of global climate change on future soil erosion rates in Central Europe. The results also indicate the high potential of adaptive land-use management for climate change response strategies in the agricultural sector.

Root characteristics of representative Mediterranean plant species and their erosion-reducing potential during concentrated runoff

Gully erosion is an important soil degradation process in Mediterranean environments. Revegetation strategies for erosion control rely in most cases on the effects of the above-ground biomass on reducing water erosion rates, whereas the role of the below-ground biomass is often neglected. In a Mediterranean context, the above-ground biomass can temporally disappear because of fire or overgrazing and when concentrated flow erosion occurs, roots can play an important role in controlling soil erosion rates. Unfortunately, information on root characteristics of Mediterranean plants, growing on semi-natural lands, and their effects on the topsoil resistance to concentrated flow erosion is lacking. Therefore, typical Mediterranean grass, herb, reed, shrub and tree root systems of plants growing in habitats that are prone to concentrated flow erosion (i.e. in ephemeral channels, abandoned fields and steep badland slopes) are examined and their erosion-reducing potential was evaluated. Root density (RD), root length density (RLD) and root diameters are measured for 26 typical Mediterranean plant species. RD values and root diameter distribution within the upper 0.10–0.90 m of the soil profile are then transformed into relative soil detachment rates using an empirical relationship in order to predict the erosion-reducing effect of root systems during concentrated runoff. Comparing the erosion-reducing potential of different plant species allows ranking them according to their effectiveness in preventing or reducing soil erosion rates by concentrated flow. RD in the 0.10 m thick topsoil ranges between 0.13 kg m−3 for Bromus rubens (L.) and 19.77 kg m−3 for Lygeum spartum (L.), whereas RLD ranges between 0.01 km m−3 for Nerium oleander (L.) and 120.43 km m−3 for Avenula bromoides ((Gouan) H. Scholz.) Relative soil detachment rates, compared to bare soils, range between 0.3 × 10-12 and 0.7 for the 0.10 m thick topsoil. The results show that grasses such as Helictotrichon filifolium ((Lag.) Henrard), Piptatherum miliaceum ((L.) Coss.), Juncus acutus (L.), Avenula bromoides ((Gouan) H. Scholz), Lygeum spartum (L.) and Brachypodium retusum ((Pers.) Beauv.) have the highest potential to reduce soil erosion rates by concentrated flow in the 0–0.1 m topsoil. But also shrubs such as Anthyllis cytisoides (L.) and Tamarix canariensis (Willd.), having high root densities in the topsoil, can reduce erosion rates drastically. Among the species growing in channels, Juncus acutus (L.) has the highest erosion reducing potential, whereas Phragmites australis (Cav.) is the least effective. On abandoned fields, Avenula bromoides ((Gouan) H. Scholz) and Plantago albicans (L.) are the most effective species in reducing concentrated flow erosion rates, while Thymelaea hirsuta (L. (Endl.)) and Bromus rubens (L.) perform the worst. On steep badland slopes, Helictotrichon filifolium ((Lag.) Henrard) and Anthyllis cytisoides (L.) perform the best in the analysis of erosion reducing potential, while Ononis tridentata (L.) is the least effective species. These findings have implications for ecological restoration and management of erosion-prone slopes.

Impact of root architecture on the erosion‐reducing potential of roots during concentrated flow

AbstractMany studies focus on the effects of vegetation cover on water erosion rates, whereas little attention has been paid to the effects of the below ground biomass. Recent research indicates that roots can reduce concentrated flow erosion rates significantly. In order to predict this root effect more accurately, this experimental study aims at gaining more insight into the importance of root architecture, soil and flow characteristics to the erosion‐reducing potential of roots during concentrated flow. Treatments were (1) bare, (2) grass (representing a fine‐branched root system), (3) carrots (representing a tap root system) and (4) carrots and fine‐branched weeds (representing both tap and fine‐branched roots). The soil types tested were a sandy loam and a silt loam. For each treatment, root density, root length density and mean root diameter (D) were assessed. Relative soil detachment rates and mean bottom flow shear stress were calculated. The results indicate that tap roots reduce the erosion rates to a lesser extent compared with fine‐branched roots. Different relationships linking relative soil detachment rate with root density could be established for different root diameter classes. Carrots with very fine roots (D &lt; 5 mm) show a similar negative exponential relationship between root density and relative soil detachment rate to grass roots. With increasing root diameter (5 &lt; D &lt; 15 mm) the erosion‐reducing effect of carrot type roots becomes less pronounced. Additionally, an equation estimating the erosion‐reducing potential of root systems containing both tap roots and fine‐branched roots could be established. Moreover, the erosion‐reducing potential of grass roots is less pronounced for a sandy loam soil compared with a silt loam soil and a larger erosion‐reducing potential for both grass and carrot roots was found for initially wet soils. For carrots grown on a sandy loam soil, the erosion‐reducing effect of roots decreases with increasing flow shear stress. For grasses, grown on both soil types, no significant differences could be found according to flow shear stress. The erosion‐reducing effect of roots during concentrated flow is much more pronounced than suggested in previous studies dealing with interrill and rill erosion. Root density and root diameter explain the observed erosion rates during concentrated flow well for the different soil types tested. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Tillage erosion: a review of controlling factors and implications for soil quality

Tillage erosion has been identifed as an important global soil degradation process that has to be accounted for when assessing the erosional impacts on soil productivity, environmental quality or landscape evolution. In this paper, we present a summary of available data describing tillage erosion. This provides insights in the controlling factors determining soil redistribution rates and patterns by tillage for various implements used in both mechanized and non-mechanized agriculture. Variations in tillage depth and tillage direction cause the largest variations in soil redistribution rates, although other factors, such as tillage speed and implement characteristics, also play an important role. In general, decreasing tillage depth and ploughing along the contour lines substantially reduce tillage erosion rates and can be considered as effective soil conservation strategies. Implement erosivities reported in literature, characterized by the tillage transport coeffcient, are very consistent and range in the order of 400–800 kg m-1yr-1and 70–260 kg m-1yr-1for mechanized and nonmechanized agriculture, respectively. Comparison of tillage erosion rates with water erosion rates using a global data set indicates that tillage erosion rates are at least in the same order of magnitude or higher than water erosion rates, in almost all cases. Finally, we discuss how tillage erosion increases the spatial variability of soil properties and affects soil nutrient cycling. Considering the widespread use of tillage practices, the high redistribution rates associated with the process and its direct effect on soil properties, it is clear that tillage erosion should be considered in soil landscape studies.

Responses of a semi-arid landscape to human disturbance: A simulation study of the interaction between rock fragment cover, soil erosion and land use change

Landscape responses to human-induced changes cannot always be studied using field monitoring and/or the analysis of sedimentological archives. Simulation models can provide additional information on the time scale and the way that landscapes respond to human interference. We present an adapted version of the SPEROS model that is subsequently used to study the interaction of water erosion, tillage erosion and rock fragment cover under various land use scenarios on semi-arid hillslopes in southeast Spain. The simulation results show that such a model, based on a relatively simple representation of erosion processes is capable of capturing the essential characteristics of rock fragments patterns in this area, i.e. a semi-logaritmic increase of rock fragment cover with slope gradient on abandoned land and a linear relationship between rock fragment cover and curvature on intensively cultivated land. The model simulations indicate that such patterns develop in a decadal time scale and that the pattern on arable land is the result of the combined action of tillage and water erosion. The model simulations also allow to assess the effects of land use changes on overall sediment production rates due to water erosion. Land abandonment leads to an exponential decline of water erosion rates and hence of sediment export over a time scale of 50–70 years. Conversion of abandoned land to intensively cultivated arable land (e.g. almond groves) will lead to a peak in water erosion, lasting again for several decades after which the water erosion rates decrease again due to the increase of rock fragment cover on the hillslope due to intensive chisel tillage. Only under the traditional system of light mouldboard tillage relatively high water erosion rates can be sustained for a long time period. The temporal and spatial patterns observed are clearly related to the interaction of water and tillage erosion: this interaction must therefore be accounted for in any long-term impact study.

Soil losses due to potato and sugar beet harvesting in NE China

AbstractThe study of soil loss due to crop harvesting (SLCH) started only recently in soil erosion research. It describes the mass of adhering soil, soil clods and rock fragments that is lost from arable land during the harvesting of crops such as potato, sugar beet, sweet potato and cassava. Some research on mechanized agriculture in Europe revealed that soil loss rates due to crop harvesting can be comparable to water and tillage erosion rates. However, little is known about soil losses caused by manually harvested crops in other parts of the world. This study investigated SLCH for potato and sugar beet plots on farmer's fields spread over four regions in northeast China where harvesting is carried out by hand. Soil losses for sugar beet were on average 1·0 Mg/ha/harvest, ranging from 0·2 to 1·9 Mg/ha/harvest, and SLCH for potato ranged from 0·2 to 3·0 Mg/ha/harvest with an average of 1·2 Mg/ha/harvest. Soil moisture content, average root mass and plant density could explain 45 to 67 per cent of the variability of SLCH for sugar beet. The effect of soil texture was the opposite to findings of other studies, which could be attributed to the strong correlations among the variables and to the effect of the harvesting operator. SLCH variability for potatoes could best be explained by soil texture. SLCH for sugar beet was much lower than European SLCH values for this crop, which can be explained by differences in harvesting technique and agronomic practices. SLCH for potato was comparable to soil losses measured in Belgium, especially if clods are removed on the harvesting machine. However, clay contents of the soils were larger in this study and soil losses were lower than in Belgium for comparable clay contents. Although SLCH is not the dominant soil erosion process in NE China, it contributes to overall soil loss rates, which have already exceeded their critical tolerance limits in this region. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Impact of plant roots on the resistance of soils to erosion by water: a review

Vegetation controls soil erosion rates significantly. The decrease of water erosion rates with increasing vegetation cover is exponential. This review reveals that the decrease in water erosion rates with increasing root mass is also exponential, according to the equation SEP e b RP where SEP is a soil erosion parameter (e.g., interrill or rill erosion rates relative to erosion rates of bare topsoils without roots), RP is a root parameter (e.g., root density or root length density) and b is a constant that indicates the effectiveness of the plant roots in reducing soil erosion rates. Whatever rooting parameter is used, for splash erosion b equals zero. For interrill erosion the average b-value is 0.1195 when root density (kg m 3) is used as root parameter, and 0.0022 when root length density (km m 3) is used. For rill erosion these average b-values are 0.5930 and 0.0460, respectively. The similarity of this equation for root effects with the equation for vegetation cover effects is striking, but it is yet impossible to determine which plant element has the highest impact in reducing soil losses, due to incomparable units. Moreover, all the studies on vegetation cover effects attribute soil loss reduction to the above-ground biomass only, whereas in reality this reduction results from the combined effects of roots and canopy cover. Based on an analysis of available data it can be concluded that for splash and interrill erosion vegetation cover is the most important vegetation parameter, whereas for rill and ephemeral gully erosion plant roots are at least as important as vegetation cover.

A comparison of methods for evaluating soil redistribution in the severely eroded Stavropol region, southern European Russia

In this paper, we combined several erosion assessment methods to construct a sediment budget describing soil redistribution and sediment delivery within a study area containing grassed upper slopes, a large arable field of 1.3 km 2 with a semipermanent rill and ephemeral gully network and a downslope buffer zone of a grassed dry valley (balka) bank with depositional fans. The study site is in the Stavropol Upland—one of the most severely eroded, intensively cultivated areas of European Russia. The methods include two variations of the soil survey approach; a proportional 137Cs conversion model; a mass balance 137Cs conversion model; a 137Cs-based tracer budget; direct measurement of gully volume by theodolite; examination of 137Cs depth profiles; and a version of the USLE model modified and calibrated for Russian conditions. Our results highlight the importance of (i) comparing such techniques, (ii) validating the results from them, and (iii) the value of combining the outputs of different measurement methods. In particular, the soil survey approach was able to separate the influence of sheet and linear erosion; the proportional 137Cs and mass balance 137Cs models estimated similar soil redistribution rates (5.5±0.8 and 5.3±0.8 kg m −2 year −1, respectively) and were improved when combined with direct measurements of gully volumes. Rates and locations of sediment redeposition within sinks, such as grassed valley banks, were best evaluated by combining 137Cs depth profile analysis and conversion models with soil profile descriptions. There was good agreement between the soil survey and the 137Cs tracing (combined with gully volume measurement) approaches. Average erosion rates estimated using the Russian version of the USLE model were lower by a factor of six compared to the physically based approaches. It may have been successful in assessing water erosion rates within inter-rill areas, and the discrepancy may provide insight into the contribution of tillage erosion. We conclude that the USLE model should be used only in combination with other techniques on arable fields where intensive rill erosion, ephemeral gullying, and mechanical translocation of soil take place.

Erosion-preventive crop rotations and water erosion rates on undulating slopes in Lithuania

A combination of perennial grass species and selected crop rotations can help prevent soil erosion in upland regions and minimize the risk of soil erosion and associated water pollution (to both terrestrial and aquatic ecosystems). Research data were obtained on sandy loam Eutric Albeluvisols at the Kaltinenai Research Station of the Lithuanian Institute of Agriculture on the undulating hilly topography of the Zemaiciai Uplands of Western Lithuania. The aim was to identify crops and crop rotations that would minimize soil erosion. Measured water erosion rates over 18 yr of field experiments were: 3.2–8.6 m3 ha-1 yr-1 under winter rye, 9.0–27.1 m3 ha-1 yr-1 under spring barley and 24.2–87.1 m3 ha-1 yr-1 under potatoes. Perennial grasses completely prevented water erosion, while the erosion-preventive grass-grain crop rotations (&gt;50% grass) decreased soil losses on arable slopes of 2–5°, 5–10° and 10–14° by 75–80%. The grain-grass crop rotation (&lt;50% grass) decreased rates by 23–24% compared to the field crop rotation. The main attributes of the proposed soil conservation systems were the careful selection of optimum erosion-preventive ecosystems (sod-forming perennial grasses or erosion-preventive crop rotations) with high erosion-resisting capabilities. These selected systems varied in response to slope gradient and thus assist erosion control and ecological stability of the undulating topography of Lithuania. These results may have wider applicability on the undulating landscapes of the temperate agricultural zone. Key words: Undulating upland topography, water erosion rates, erosion-preventive crop rotations, temperate climate

A process‐based conversion model for caesium‐137 derived erosion rates on agricultural land: an integrated spatial approach

AbstractThere is increasing recognition that 137Cs data remain one of the few sources of spatially distributed information concerning soil erosion. However, many of the conversion models that have been used to convert 137Cs data into soil redistribution rates failed to account for some of the key factors affecting the redistribution of 137Cs in agricultural landscapes. The conversion model presented in this paper aims to overcome some of the limitations associated with existing models and therefore to provide more realistic estimates of soil erosion rates on agricultural land. The conversion model aims at coupling soil redistribution processes directly with 137Cs redistribution. Emphasis is placed on the spatial representation of soil redistribution processes and the adequate simulation of tillage processes. The benefits of the presented model arise from the two‐dimensional spatial integration of mass balance models with soil erosion models. No a priori assumptions about the intensity of any soil redistribution process are necessary and the level of agreement between observed and simulated 137Cs inventories enables us to evaluate the performance of the model. The spatial implementation and the use of fuzzy parameter sets also allow us to assess the uncertainties associated with soil erosion estimates. It was shown that an adequate simulation of tillage processes is necessary and that simplified tillage models may lead to erroneous estimates of soil redistribution. The model was successfully applied to a study site in the Belgian Loam Belt and the results indicated that tillage is the dominant process. Furthermore, the uncertainties associated with the estimation of water erosion rates were much higher than those associated with tillage, especially for depositional areas. Copyright © 2003 John Wiley &amp; Sons, Ltd.

The importance of plant root characteristics in controlling concentrated flow erosion rates

AbstractWhile it has been demonstrated in numerous studies that the aboveground characteristics of the vegetation are of particular importance with respect to soil erosion control, this study argues the importance of separating the influence of vegetation on soil erosion rates into two parts: the impact of leaves and stems (aboveground biomass) and the influence of roots (belowground biomass). Although both plant parameters form inseparable constituents of the total plant organism, most studies attribute the impact of vegetation on soil erosion rates mainly to the characteristics of the aboveground biomass. This triggers the question whether the belowground biomass is of no or negligible importance with respect to soil erosion by concentrated flow. This study tried to answer this question by comparing cross‐sectional areas of concentrated flow channels (rills and ephemeral gullies) in the Belgian Loess Belt for different cereal and grass plant densities. The results of these measurements highlighted the fact that both an increase in shoot density as well as an increase in root density resulted in an exponential decrease of concentrated flow erosion rates. Since protection of the soil surface in the early plant growth stages is crucial with respect to the reduction of water erosion rates, increasing the plant root density in the topsoil could be a viable erosion control strategy. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Assessment of soil losses on cultivated land by using the [formula omitted] technique in the Upper Yangtze River Basin of China

This paper presents the results of using the 137 Cs technique to assess soil erosion rates of both sloping cultivated land and flat terraces in the Upper Yangtze River Basin, China. The study was carried out on eighteen sloping cultivated fields and four flat terrace fields in eight counties and cities over the eastern part of the basin. The 137 Cs -reference inventory ranged from 620.5 to 2573.2 Bq/m 2. For the 18 sloping cultivated fields, the average 137 Cs inventory over a field ranged from 204.9 to 1847.7 Bq/m 2, which accounts for 15–77% of the local 137 Cs reference inventory, and the average water erosion rate ranged from 758 to 9854 t/km 2 per year, with erosion rates of <1000 t/km 2 per year in two fields; 1000–5000 t/km 2 per year in eight fields; and >5000 t/km 2 per year in eight fields. It is apparent that most of the sloping cultivated fields suffer severe or very severe soil erosion. For the four terrace fields under this study, the average 137 Cs inventory over a field ranged between 915.8 and 2675.4 Bq/m 2, which accounts for 97–104% of the local 137 Cs reference inventory. However, water erosion is very slight on the terrace fields and little soil is lost from the terraces. The study also indicated that the severity of soil erosion is strongly related to soil texture and slope gradient.

Erosion-preventive crop rotations for landscape ecological stability in upland regions of Lithuania

A combination of perennial grass species and selected crop rotation can help prevent soil erosion in upland regions. Research data were obtained on sandy loam Dystric Albeluvisols at the Kaltinenai Research Station of the Lithuanian Institute of Agriculture on the undulating hilly topography of the Zemaiciai Uplands of Western Lithuania to identity crop and crop rotations that would minimise soil erosion. Measured water erosion rates during long-term field experiments were: 5.4–17.0 Mg ha −1 under winter rye, 18.0–62.8 Mg ha −1 under spring barley and 44.4–186.2 Mg ha −1 under potatoes. Perennial grasses completely prevented water erosion. The erosion-preventive grass–grain crop rotations (>50% grass) decreased soil losses on arable slopes of 2–5°, 5–10° and 10–14° by 77–81%, while the grain–grass crop rotation (<50% grass) decreased rates by 21–24%, compared with the field crop rotation. The mean annual metabolisable energy accumulated by the erosion-preventive grass–grain crop rotations under optimum ground and fertiliser treatments on slopes of varying gradient was 96.7 GJ ha −1. This was 24.8% higher than under the field crop rotation and 20.2% higher than under the grain–grass crop rotation. The mean digestible protein productivity of sod-forming perennial grasses was 13.1% higher than the mean productivity of grass–grain crop rotations and 53.7% higher than the grain–grass crop rotation on slopes of 10–14°. The erosion-preventive capability of crop rotations depends on their structure and composition. The grass–grain crop rotations and sod-forming perennial grasses significantly increased soil aggregate stability compared with grain–grass crop rotations on 10–14° slopes, thus both these systems decrease soil erodibility. The main attributes of the proposed land conservation and sustainable land-use system were the careful selection of optimum erosion-preventive ecosystems (sod-forming perennial grasses or erosion-preventive crop rotations) with high erosion-resisting capabilities. These systems must vary in response to slope conditions. Such ecosystems assist erosion control and thus the ecological stability of the undulating topography of Lithuania. These results may have wider applicability on the undulating landscapes of the Temperate Zone.

Use of caesium-137 data for validation of spatially distributed erosion models: the implications of tillage erosion

Validation of spatially distributed models using spatially distributed data represents a vital element in the development process; however, it is rarely undertaken. To a large extent, this reflects the problems associated with assembling erosion rate data, at appropriate temporal and spatial scales and with a suitable spatial resolution, for comparison with model results. The caesium-137 ( 137 Cs ) technique would appear to offer considerable potential for meeting this need for data, at least for longer timescales. Nevertheless, initial attempts to use 137 Cs for model validation did not prove successful. This lack of success may be explained by the important role of tillage erosion in redistributing soil within agricultural fields and, therefore, contributing to the 137 Cs -derived soil redistribution rates. This paper examines the implications of tillage erosion for the use of 137 Cs in erosion model validation and presents an outline methodology for the use of 137 Cs in model validation. This methodology acknowledges and addresses the constraints imposed by the need to: (1) separate water and tillage erosion contributions to total soil redistribution as represented in 137 Cs derived rates; (2) account for lateral mixing of 137 Cs within fields as a result of tillage translocation; (3) simulate long-term water erosion rates using the model under evaluation if 137 Cs -derived water erosion rates are to be used in model validation. The methodology is dependent on accurate simulation of tillage erosion and tillage translocation. Therefore, as greater understanding of tillage erosion is obtained, the potential for the use of 137 Cs in water erosion model validation will increase. Caesium-137 measurements remain one of the few sources of spatially distributed erosion information and, therefore, their potential value should be exploited to the full.

Rates and patterns of tillage and water erosion on terraces and contour strips: evidence from caesium-137 measurements

Despite the widespread use of contour-strips and terraces for soil conservation little is known concerning the impact of such measures on rates and patterns of tillage erosion and tillage translocation. Caesium-137 ( 137 Cs ) measurements would appear to offer a rapid means of assembling data relevant to the evaluation of tillage erosion and tillage translocation. However, use of 137 Cs data in this way requires an approach to the analysis of 137 Cs data which accounts for both tillage erosion and tillage translocation. The latter is particularly significant on short slopes. A method of analysing 137 Cs data has been developed, that employs a linear, multistore, mass-balance model of soil and 137 Cs redistribution to permit estimation of the contributions to erosion from both water and tillage erosion. This method is outlined and results from its application are discussed using case studies from Yanting, in Sichuan Province, China; Ha Sofonia, in Lesotho; and, Chinamora, in Zimbabwe. These case studies confirm the viability of the approach and provide valuable evidence for the importance of tillage erosion and translocation on terraces and contour-strips subject to cultivation by animal traction. Gross rates of tillage erosion were found to be of comparable or greater magnitude than gross rates of water erosion on the fields examined. It is, therefore, suggested that any evaluation of on-site impacts of erosion must take account of tillage erosion. Relationships between annual soil fluxes due to tillage and slope tangent were found to be very similar to the relationships established for a single pass of equivalent tillage equipment with mechanical traction. Furthermore, because tillage by animal traction necessitates downslope turning of the soil on every occasion, net downslope fluxes of soil associated with animal traction may exceed the levels associated with tillage by mechanised traction, in which the soil is typically turned in opposing directions on successive occasions.

Tillage erosion, water erosion and soil quality on cultivated terraces near Xifeng in the Loess Plateau, China

This study sought to contribute to the understanding of soil redistribution by tillage on terraces and the extent and causes of within-field variation in soil properties by examining the spatial distributions of soil redistribution rates, derived using caesium-137, and of total nitrogen and total phosphorus concentrations, within a ribbon and a shoulder terrace in a yuan area of the Loess Plateau of China. Additional water erosion rate data were obtained for nine other terraces. Water erosion rates on the ribbon terraces were low (<1 kg m−2 yr−1), unless slope tangents exceeded 0·1. However, despite the use of animal traction, high rates of tillage erosion were observed (mean 5·5 kg m−2 yr−1). Soil nitrogen concentrations were related to rates of soil redistribution by tillage on the ribbon terrace examined in detail. In general, higher rates of water erosion (0·5–2·9 kg m−2 yr−1) and lower rates of tillage erosion (mean 1·4 kg m−2 yr−1) were evident on the longer shoulder terraces. On the shoulder terrace examined in detail, soil phosphorus concentrations were related to net rates of soil redistribution. A statistically significant regression relationship between water erosion rates and the USLE length and slope factor was used in conjunction with the simulation of tillage erosion rates to evaluate a range of terrace designs. It is suggested that off-site impacts of erosion could be further reduced by ensuring that the slope tangents are kept below 0·06 and lengths below 30 m, especially on the shoulder terraces. Tillage erosion and the systematic redistribution of soil nutrients could be reduced by modification of the contour-cultivation technique to turn soil in opposing directions in alternate years. Copyright © 1999 John Wiley & Sons, Ltd.

Evaluation of the Gum from Hakea gibbosa as a Sustained-Release and Mucoadhesive Component in Buccal Tablets

The objective of this paper was to evaluate the mucoadhesive and sustained-release properties of the water-soluble gum obtained from Hakea gibbosa (hakea), for the formulation of buccal tablets. Flat-faced tablets containing hakea were formulated using chlorpheniramine maleate (CPM) as a model drug. Two types of tablets were prepared: uncoated tablets (type I) and tablets in which all but one face of the type I tablet was coated with hydrogenated castor oil (Cutina) using a compression coating technique (type II). In an attempt to explain the observed sustained-release effect, the potential for a chemical interaction between hakea and CPM was evaluated by FTIR, differential scanning calorimetry (DSC), UV spectroscopy, and acid–base titrations. Mathematical modeling of the CPM release data was developed to elucidate the mechanism of drug release. The mucoadhesive strength was evaluated by quantitating the force of detachment. Finally, the rates of water uptake and erosion were determined for the buccal tablets. The time required for 90% of the CPM to be released in vitro (t90%) was used as a basis for comparison. For formulations that did not contain hakea, the t90% was 14 min for both directly compressed and wet granulated tablets, whereas the t90% for wet granulated tablets containing 2 or 32 mg hakea/tablet was 36 and 165 min, respectively. Directly compressed tablets containing 2, 12, 22, and 32 mg hakea/tablet displayed t90% values of 48, 120, 330, and 405 min, respectively. DSC, FTIR, UV spectroscopy and acid–base titration experiments suggested the absence of chemical interactions. The force of detachment for directly compressed and wet granulated tablets increased from 0.70 ± 0.3 to 4.08 ± 0.52 N and from 0.65 ± 0.28 to 3.94 ± 0.31 N as the amount of hakea per tablet was increased from 0 to 32 mg, respectively, at a 5 N attachment compression force. The novel natural gum, hakea, may not only be utilized to sustain the release of CPM from a unidirectional-release buccal tablet, but it also exhibited excellent mucoadhesive properties. The mechanism by which CPM release was sustained was more likely due to slow relaxation of the hydrated hakea. The mucoadhesive strength can be modulated by altering the amount of hakea in the tablet.

Relative efficiency of three representative matorral species in reducing water erosion at the microscale in a semi-arid climate (Valencia, Spain)

In the Mediterranean region, where rainfall is scarce but often of high intensity, the matorral vegetation cover provides essential protection to the soil against the erosivity of rainfall and reduces considerably the water erosion rate. Three representative species of the Mediterranean matorral displaying different morphologies ( Rosmarinus officinalis, L., Stipa tenacissima, L., Anthyllis cytisoides, L.) were selected for study at the microscale (plant scale) for their relative efficiency in reducing water erosion on slopes. The mechanical protection of the soil against raindrop detachment, and the improvement of the soil properties by the biological influence of an isolated plant, were compared for the three species. The quantification of interrill erosion and splash erosion rates under natural rainfall conditions was obtained using erosion microplots of individual plants, and splash cups placed at different distances from the plant axis, respectively. Soil samples were also taken in the microenvironment of the plants in order to evaluate possible differential influences of the three species on soil properties relevant to water erosion. The results show that the three selected species reduced runoff and soil loss in different ways. The `screen effect' arising from the very dense canopy of Stipa tussocks, represents an effective way to counteract rainfall erosivity and reducing splash erosion. However, in the case of Rosmarinus, in addition to the mechanical protection offered by its canopy and litter covers, the latter (which lies permanently at the soil surface under the plant canopy) improves moreover the topsoil structure because of the important incorporation of organic matter below the canopy cover. The role of litter cover in controlling erosion seems therefore to be predominant under Rosmarinus. As for Anthyllis, these deciduous shrubs provide little physical protection against the energetic impact of rain at the soil surface as compared to a bare surface. Nevertheless, the three plant species have a positive influence on their microenvironment, through the improvement of soil properties under their canopy. Thus, in open matorral (patchy vegetation), fertile soil islands developed below the plant canopy. These differ considerably from the bare soil inter-plant areas that give rise to higher soil loss rates.

Erosion processes and landform evolution on agricultural land — new perspectives from caesium-137 measurements and topographic-based erosion modelling

Despite growing interest in soil erosion on agricultural land, relatively little attention has been paid to the influence of erosion processes on the pattern of contemporary landform evolution. This in part reflects the problems associated with upscaling the results of short-term process studies to temporal and spatial scales relevant to the study of landform evolution. This paper presents a new approach to examining the influence of erosion processes on landform evolution on agricultural land which employs: caesium-137 (Cs-137) measurements to provide medium-term (c.40 years) estimates of rates of landform change; experimental data and a topographic-based model to simulate soil redistribution by tillage; a mass-balance model of Cs-137 redistribution to separate the water erosion and tillage components of the Cs-137 'signatures'; and field observations of water erosion for validation. This approach is used to examine the relative importance of water erosion and tillage processes for contemporary landform evolution at contrasting sites near Leuven, in Belgium, and near Yanan, in Shaanxi Province, China. This application of the approach provides good agreement between the derived water erosion rates and field observations, and hitherto unobtainable insights into medium-term patterns and rates of contemporary landform evolution, At Huldenberg in Belgium, despite rill incision of slope concavities and ephemeral gully incision of the valley floor, contemporary landform evolution is dominated by infilling of slope and valley concavities (rates >0.5 mm a(-1)) and gradual lowering of slope angles as a result of tillage. In contrast, at Ansai (near Yanan) the slope is characterized by increase in slope angle over most of the length, recession of the steepest section at a rate >5 mm a(-1) and by increasing planform curvature, At this site, contemporary landform evolution is dominated by water erosion. The constraints on the approach are examined, with particular attention being given to limitations on extrapolation of the results and to the sensitivity of the models to parameter variation. (C) 1997 by John Wiley & Sons, Ltd.