Accelerated soil erosion is drawing a growing attention with the recognition that the rate of soil loss is too great to be met by soil formation rate. Weenen Game Reserve (WGR) is an area with an unfortunate history of prolonged soil erosion due to excessive overgrazing that led to severe land degradation with prominent visible scars. This problem triggered the general objective of estimating and mapping potential soil erosion in WGR. Assessing soil loss in the area objectively has important implications for the overall management plans as it is reserved for ecological recovery. The most important variables that affect soil erosion are considered as inputs in soil loss estimation models. In this study the RUSLE model, which uses rainfall, soil, topography, and cover management data, was employed. From the rainfall data, an erosivity factor was generated by using a regression equation developed by relating EI30 index and total monthly rainfall. The soil erodibility factor was calculated using the soil erodibility nomograph equation after generating the relevant data from laboratory analysis of soil samples gathered from the study area. Using exponential ordinary kriging, the point values of this factor were interpolated to fill in the non-sampled areas. The topographic effect, which is expressed as the combined impact of slope length and slope steepness, was extracted from the DEM of the study area using the flow accumulation method. For mapping of the land cover factor, in situ measurements of cover from selected sites were undertaken and assigned values from the USLE table before being related with MSAVI of Landsat 7 ETM+ image. These values were then multiplied to get the final annual soil loss map. The resulting potential soil loss values vary between 0 and 346 ton ha-1 year-l with an average of 5 ton ha-1 year-l. About 58% of the study area experiences less than 1 ton ha-1 year-1 indicating the influence of the highest values on the average value. High soil erosion rates are concentrated in the central part extending as far as the south and the north tips along the eastern escarpments and these areas are the ones with the steepest slopes. The results indicate a high variation of soil loss within the study area. Nevertheless, the majority of the area falling below the average might foresee that the soil erosion problem of the area can be minimized significantly depending largely on soil management. The most important areas for intervention are the medium and low erosion susceptible parts of WGR, which are mainly found in the flatter or gently sloping landscapes. The steepest areas are mostly covered with rocks and/or vegetation and hence less effort must be spent in managing them. Overall, the reported increasing density of the vegetation community in the area that reduces the exposure of soil from the impact of direct raindrops and surface-flowing water must be pursued further. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

Soil water erosion is recognized as the principal mechanisms behind soil organic carbon (SOC) losses from soils, a soil constituent essential for ecosystem functions. SOC erosion can thus be far-reaching, affecting the future human welfare and the sustainability of ecosystems. Little research has yet been done to investigate the main mechanisms involved in the lateral translocation of SOC on the landscape. Understanding the effects of the different water erosion mechanisms, which control SOC losses (SOCL) at the hillslope level, creates scope for further scientific studies. Empirical data from 357 plots, with a range in slope length from 1 (n=117) to 22.1m (n=240) were analysed to estimate the global variations of particulate organic carbon content (POCC), POC losses (POCL) and sediment POC enrichment ratio (ER). The global average POCL rate was calculated to be 12.1 g C m-2 y-1. Tropical clayey soil environments revealed the highest POCL (POCL=18.0 g C m-2 y-1), followed by semi-arid sandy (POCL=16.2 g C m-2 y-1) and temperate clayey soil environments (POCL=2.9 g C m-2 y-1). The global net amount of SOC displaced from its original bulk soil on an annual basis was calculated to be 0.59±0.09 Gt C, making up an approximated 6.5% of the net annual fossil fuel induced C emissions (9 Gt C). POCL data for different spatial scales revealed that up to 83% of the eroded POC re-deposits near its origin in hillslopes, and is not exported out of the catchment. The low organic carbon sediment ER obtained from the data of clayey soils (ER of 1.1) suggests that most of the eroded POC remains protected within soil aggregates. Consequently, erosion-induced carbon dioxide (CO2) emissions in tropical areas with clayey soils are likely to be limited (less than 10%), as the process of POC re-burial in hillslopes is likely to decrease the rate of organic matter (OM) decomposition and thus serve as a potential carbon sink. Water erosion in sandy and silty soils revealed organic carbon sediment ER as high as 3.0 and 5.0, suggesting that in these soils the eroded POC is not re-buried, but is made vulnerable to micro-decomposers, thus adding to the atmospheric CO2 influx. The results obtained in the review study only reaffirm that large variations of POCL are evident across the different pedo-climatic regions of the world, making it a scientific imperative to conduct further studies investigating the link between SOC erosion by water and the global carbon cycle. A field study was designed to quantify the POC exported in the eroded sediments from 1x1m2 and 2x5m2 erosion plots, installed at different hillslope aspects, and to further identify the main erosion mechanisms involved in SOC erosion and the pertaining factors of control. The erosion plots were installed on five topographic positions under different soil types, varying vegetation cover, and geology in the foothills of the Drakensberg mountain range of South Africa. Soil loss (SL), sediment concentration (SC), runoff water (R) and POCL data were obtained for every rainfall event from November 2010 up to February 2013. Scale ratios were calculated to determine which erosion mechanism, rain-impacted flow versus raindrop erosion, dominates R, SL and POCL. Averaged out across the 32 rainfall events, there were no significant differences in R and POCL between the two plot sizes but SL were markedly higher on the 5m compared to the 1m erosion plots (174.5 vs 27g m-1). This demonstrates that the sheet erosion mechanism has a greater efficiency on longer as opposed to shorter slopes. Rain-impacted flow was least effective where soils displayed high vegetation coverage (P < 0.05) and most efficient on steep slopes with a high prevalence of soil surface crusting. By investigating the role of scale in erosion, it was possible to single out the controlling in situ (soil surface related conditions) and ex situ (rainfall characteristics) involved in the export of SOC from soils. This information will in future contribute toward generating SOC specific models and thus further inform erosion mitigation. / M. Sc. University of KwaZulu-Natal, Durban 2013.

In mehrjährigen Stoppelbearbeitungsversuchen mit Grubbern, Scheiben- und Kreiseleggen sollten Einsatzhinweise zur Verringerung der Bodenerosion bei pflugloser Bodenbearbeitung für verschiedene Maschinentypen entwickelt werden. Dazu wurde vor allem die Bodenbedeckung mit Mulchmaterial als wichtiger Indikator für den Schutzgrad beobachtet. Zusätzlich wurden Daten zur Stroheinarbeitung in den Boden sowie zur Ausprägung der Bodenoberflächen und Bearbeitungssohlen ermittelt und der Zugleistungsbedarf für die Geräte gemessen. Im Ergebnis konnte der Bodenbedeckungsgrad nur wenig durch Veränderung der Einsatzbedingungen der Stoppelbearbeitungsmaschinen beeinflusst werden. In erosionsgefährdeten Gebieten kommt daher dem Zwischenfruchtanbau und Bodenbearbeitungsverfahren, die einen hohen Bodenbedeckungsgrad gewährleisten (Streifenbodenbearbeitung, Direktsaat), eine entscheidende Rolle zu. Der Bericht enthält die vollständigen Ergebnisse der Untersuchung.

No description available.

Soil erosion from American cropland poses a problem to society in many ways. Ground and surface water is polluted by chemicals carried on the eroded soil, silt builds up in rivers and other water bodies, soil particles carried by wind pollute the air, and finally there is a decline in the productivity of the remaining cropland soil. The rate that soil is eroded from cropland is directly affected by the type of crops planted, tillage systems used and government agricultural programs. This thesis presents the economic costs of soil erosion from cropland and the private and social benefits that can be obtained by reducing erosion rates. Many conservation programs have been less than effective in controlling erosion levels and some commodity and income programs have actually increased erosion rates. A survey of government policies and their various effects on soil erosion rates is included in this thesis. Alternative government policy options are presented.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1996. / Includes bibliographical references (leaves 152-159). / Microfiche. / xi, 159 leaves, bound ill. 29 cm

Soil erosion is recognized as a global threat against the sustainability of the natural ecosystem and the environment because of its severe effects in agricultural productivity, damage to infrastructure and pollution of water bodies. Adverse impacts due to human activities resulting in accelerated soil erosion process have been well documented. Much more attention has been given to study the mechanisms associated with the process of soil erosion in the second half of the 20th century. Different mathematical models have been developed to simulate soil erosion processes and incorporate the result in different options of erosion controls. Modelling soil erosion is a complex process that involves numerous parameters. It is for this reason that even highly sophisticated and advanced erosion prediction models like Water Erosion Prediction Project (WEPP) do not incorporate all mechanisms of the soil erosion process. An obvious gap is the satisfactory explanation and incorporation of soil erosion mechanism associated with the initial portion of microchannels where both inter-rill and rill erosion exist. This study attempts to fill this gap through extension of knowledge in the area of soil erosion mechanism, specifically within the initial portions of rill where both splash erosion and erosion due to shear stress exist. Detachment of soil particles from the soil surface depends on the kinetic energy imparted by raindrops. Therefore, it is essential to estimate kinetic energy as accurately as possible to enable study of soil erosion and infiltration mechanisms. Rainfall simulation is widely used to generate rainfall of desired intensities and durations to study soil erosion, infiltration and other dynamic behaviours of soil. Kinetic energy of a rainfall event is often estimated from its intensity. The actual kinetic energy imparted on a soil surface is generally less than the total value of kinetic energy of a rainfall event. This is because of the cushioning effect of the overland flow. Therefore, there is a potential risk of over prediction of splash erosion by an erosion prediction model that does not account for this cushioning effect. In this study, experiments were carried out to estimate the kinetic energy of three different simulated rainfall events produced by three different combinations of pressures and nozzle sizes. The equipment consisted of a multipurpose hydraulic flume, 2m long and 1.4m wide. Five highly sensitive force transducers were mounted on the surface of the flume to measure the impact of raindrops. Different slopes were represented in the experiment by tilting the flume in four different angles from 0 to 15 degrees. Two tipping bucket rain gauges were used to measure rainfall intensity. The nozzles were placed at a height sufficient to produce terminal velocity by the falling rain drops before they hit the flume surface. Overland flow was generated by continuously supplying water to the inlet tank constructed at the upstream of the hydraulic flume. Responses received from the transducers (in the form of voltage) and from the tipping bucket (in the form of pulses) were recorded at regular intervals. Based on this experimental study, a logarithmic energy loss model that accounts for the depth of shallow overland flow, rainfall intensity and bed slope to estimate potential loss of kinetic energy is proposed. Analysis of the results from the study indicated a significant reduction in kinetic energy when the surface flow starts to build up. The analysis also indicated that a significant portion of the energy is lost even though the flow depth is small. This implies that while splash erosion initially contributes to the total amount of soil erosion, most of the erosion after the initial phase is due to the flow induced shear stress. Another important conclusion of this study is that steeper the slope, the lesser the expected overland flow depth and hence more potential for splash erosion and sheet erosion. The Nash Sutcliffe model efficiency statistic of 90% obtained from this study signifies that the model could be used as a useful predictive tool to estimate rainfall kinetic energy loss. The energy loss model developed as a result of this study can be incorporated in process-based soil erosion models to accurately estimate splash erosion and improve the predictive power of these models. In Addition, the model can be used to estimate the critical depth of overland flow when the kinetic energy approaching the soil surface is practically nil. This critical depth can be used to define the transition zone and explicitly define the term “Rill”. The multipurpose hydraulic flume designed and developed for this study can be used for further studies in area of hydraulic and soil erosion research. The methodology developed in this research will be helpful in carrying out further experiments and improve the proposed energy loss model. The potential Future improvements to the model include the followings: i) incorporating the effect of sediment concentration, ii) using wider ranges of intensities, and iii) using an actual soil bed. / Doctor of Philosopy (PhD)

The ginger industry is one of the key industries identified by the Fiji government in its diversification strategy to accommodate the remnants of the withdrawal of the European Union’s sugar preferences. There is considerable pressure on small industries such as ginger in search of ways in which they can be made to operate efficiently and sustain the economy. Expansion of commercial agriculture into marginal land which is unsustainable adds enormous pressure on land causing soil erosion. Coupled with this is the quality issue which is a serious problem of ginger production and has reduced its competitiveness over the years. This study focuses on two types of losses in ginger production to provide an integrated approach to policy making and computing production losses. One is the observable output loss at the farm site that is not sold due to sub-standard quality related to disease and the other is the unobserved output loss due to inefficient production. The research attempts to answer the question of whether the Fiji ginger farmers are producing efficiently, and at what levels. The relative importance of each input in ginger production is examined. The study undertakes to determine the effects of key variables on farm efficiency. Also examined is the overall farm profiles based on the efficiency rankings of the ginger producers. Furthermore, this research attempts to determine factors that influence soil erosion, and those that influence the observed ginger loss. Using cross-sectional data from a ginger farm survey conducted in June 2007, this research estimates a stochastic production frontier which incorporates soil erosion as an input in the framework. Very few studies have looked at the impact of soil erosion in this context; hence, this study fills the gap by incorporating land quality in the analysis. Farms were found to produce at 69% of their maximum potential output and soil erosion resulted in 6.8% loss in ginger output. This also implies that using the same resources, technology and farming techniques efficiently can lead to a 31% increase in output. While unobserved loss to farm income is a 27% (F$4.6m) increase over the observable loss at farm site, the revenue loss to the whole industry is at least 30% (F$5.07m). Profit was a key determinant of both losses, but staying on farm, slope of land, manure use and hot water treatment affected the observed but not unobserved loss. Although farmer education had no effect on both losses, it was important for undertaking soil conservation. Fiji is in a good position to increase production as education, age and experience of farmers were not significant determinants of efficiency. Thus, displaced farmers from sugar cane farming (given serious concerns of the viability of that industry) can be encouraged to move with ease into ginger as an alternative livelihood. Lastly, the study highlights some practical implication which calls for an integrated package of policies related to use of best farming techniques, land tenure and, agricultural extension and support services for sustainable agricultural growth.

Control of water erosion of soil at mine sites requires an ability to predict the effects of different management practices on soil loss. Using soil loss models such as the Revised Universal Soil Loss Equation (RUSLE) requires calibration of the model for materials and situations that are not defined in the model’s handbook or software. The outer slopes of bauxite residue disposal areas are potentially highly erodible surfaces, and a recent evaluation of previous rehabilitation practices at Worsley Alumina, Collie, Western Australia, identified areas on the bauxite residue disposal areas where vegetation establishment and management of long term soil loss could be improved. Field experiments commencing in April 2000 at Worsley Alumina’s bauxite refinery, Collie, and laboratory tilting flume experiments run at the University of Queensland, were designed to quantify the effectiveness of different surface treatments on reducing short-term soil loss, and to model long-term erosion risks. Crushed ferricrete caprock – rock-pitch – and different types of mulches, seed mixes and fertiliser rates were applied to the compacted clay batter slopes used to contain bauxite residue, with runoff, soil loss and vegetation establishment monitored periodically over 27 months. Laboratory tilting flume results were related to the field data using the soil erosion models MINErosion, the Modified Universal Soil Loss Equation (MUSLE) and RUSLE to predict event-based and annual soil loss for different treatments. Turbo-mulch, a blocky, coarse pine bark, was the most effective surface treatment for promoting vegetation establishment, reducing rill formation and reducing soil loss, a result supported in both the field and laboratory results. Turbo-mulch and vegetation did not reduce runoff, but resulted in decreased soil loss. This shows the importance of protecting soil from raindrop impact and of the soil holding capacity of vegetation. Increased seed and fertiliser rates did not significantly affect native plant numbers or foliage cover on topsoil without turbo-mulch. Rock-pitch was found to be resistant to erosion and mass movement along a rock-pitch/compacted clay interface. Field erosion measurements ranged from 0.87 t/ha/yr for turbo-mulched treatments to 7.41 t/ha/yr for a treatment with a different seed mix, lacking turbo-mulch and lacking underlying rock-pitch. RUSLE soil loss predictions based on soil properties and soil loss estimates from the MINErosion model ranged from 0.27 to 60.0 t/ha/yr. RUSLE predictions based on tilting flume data ranged from 0.14 to 81.1 t/ha/yr. RUSLE overpredicted soil loss for treatments without turbo-mulch, and underestimated soil loss for turbo-mulched treatments, necessitating calibration based on the unique materials trialed in this study. The relative soil loss measured in the field was best represented by RUSLE predictions based on tilting flume data rather than the MINErosion model. MINErosion did not adequately describe the effect of bulk density and infiltration on soil loss of compacted/consolidated materials. MUSLE and RUSLE are adequate models for the Western Australian conditions of this study, but further research is required to calibrate the C factor for turbo-mulched surfaces and calibrate the P factor for rock-pitch.

Thesis (M.Sc.). / Written for the Dept. of Bioresource Engineering. Title from title page of PDF (viewed 2008/12/09). Includes bibliographical references.