Erosion Control Measures Research Articles

DETERMINATION OF SLOPE LENGTH AND STEEPNESS FACTOR (LS) FOR DURUJI RIVER BASIN

Based on the application of the Revised Universal Soil Loss Equation (RUSLE) and modern GIS technology (ArcGis 10.2.2.), the article presents a method for calculating the erosion potential of the relief (LS) of the Duruji river basin (north-eastern part of Georgia). The most erosion-hazardous areas have been identified, which is approximately 75.1% of the total area of ​​the Duruji river basin. It has been established that special attention should be paid to a detailed study of the identified erosional areas of the Duruji river basin, taking into account all the influencing factors on soil erosion for the successful design of erosion control measures.

Assessment and management of soil erosion in the hilltop mining dominated catchment using GIS integrated RUSLE model

The Saranda forest region, which is well known for its biodiversity in India, is now confronted by rapid socio-economic development, particularly the hilltop mining activities. Hilltop mining areas of this region have always been responsible for producing excessive soil erosion in the associated river basin. This erosion phenomenon becomes hazardous during the rainy season, thereby contributing to various environmental problems, and consequently, necessitating soil erosion control planning in the Saranda forest. Hence, this study aimed to estimate average annual soil erosion in the Saranda region in terms of the spatial distribution using the Geographic Information System (GIS) integrated Revised Universal Soil Loss Equation (RUSLE) model. The erosion was quantified at a spatial resolution of 10 m (pixel by pixel) using the GIS-based RUSLE inputs. This study also applies GIS integrated Analytic Hierarchy Process (AHP) model to identify the favorable zones for sediment deposition in the study area. On the basis of erosion severity, the entire study area is classified into six categories (very low to extreme). The study reveals that the Saranda forest's average annual soil erosion is 76 tons per hectare per year (t/ha/yr). Approximately 63% of the total area is categorized under very low to low erosion category, and the relevant area is mainly covered by forest land, whereas the mining region comprises less than 1% of the total study area with extremely high soil erosion (156 t/ha/yr) potential. As envisaged from the present study, the erosion-prone mining areas are located within a 1–5 km range of the adjacent Karo and Koina rivers, thereby, necessitating the erosion control strategy to avoid the possible threats. From this perspective, the study also investigates the favorable zones for sediment deposition using the GIS integrated AHP model to suggest the appropriate erosion control measures. Finally, the RUSLE and AHP models are combined on the GIS platform to identify the distressed catchment area. Moreover, 42% (41,060 ha) of the total area is disturbed due to the present mining activities, which involves 11 sub-watersheds, and their associated 50 micro-watersheds. From the context of watershed conservation, erosion control measures are also recommended. The methodology adopted in this study can be easily extended to any global mining-dominated catchment for sustainable conservation planning.

Kondisi dan Pengelolaan Kawasan Hulu DAS Belawan Hubungannya dengan Tingkat Bahaya Erosi pada Lahan Budidaya di Kabupaten Deli Serdang

The Belawan watershed is located at Deli Serdang Regency and Medan City, with mountainous terrain (70.58%), hills (35.15%), and slopes (20.28%). This study aims to identify the risk of erosion of cropland, especially coffee, corn, and chocolate, to identify more appropriate erosion control measures to achieve regional protection objectives . The research was conducted in the upstream Belawan watershed in the Sibolangit, Bandar Baru, and Kutalimbaru regions from September 2020 to December 2020. The magnitude of the erosion hazard value is analysed using the USLE approach . The USLE method on the amount of erosion is determined by 5 (five) factors, these factors are the rainfall erosion factor (R); soil erodibility factor (K); vegetation factor (C); conservation factor (P) and topography factor (LS). The erosion rate valuefor land use types varies from 95.27 tons/Ha.yr to 232.43 tons/Ha.yr. The amount of erosion that can be tolerated in land use for coffee, corn, and cacao ranges from 19.94 tons/Ha.yr to 39.79 tons/Ha.yr. The risk level for erosion in coffee areas 4.83 and 10.86 with high criteria and very high criteria; in areas of corn event 6.29 and 8.38 with high criteria and in brown areas 5.24 and 3.88 with high criteria and medium criteria.

Evaluation of the economic costs of beach erosion due to the loss of the recreational services of sandy beaches - The case of Tetouan coast (Morocco)

Coastal managers and investors are increasingly aware that seaside tourism can only be sustainable if the coastal natural assets, in particular sandy beaches, are protected from erosion. Tetouan coast, which relies heavily on tourism is experiencing strong retreat. This study aims to value the lost profits to the tourism sector, if Tetouan beaches were to disappear. We also analyzed the costs of beach nourishment as erosion control measure. Through the integration of physical and economic simulations, the findings showed that beach erosion would have significant negative economic impacts on the tourism sector, and it will cost much more than the continuous control by artificial recharging, provided the availability of sand stocks. The study highlights the benefits of using economic valuation to promote investment in conservation and restoration measures, that maintain beach width and sustainably secure tourism business and the livelihoods of coastal communities.

Numerical Model for Quantifying the Function of Soil Erosion and Sediment Transport Controls at Slope Agricultural Lands

The objective of this study was to build a numerical model that has the capability to account for the effect of various water and soil conservation practice scenarios in reducing erosion rate and sediment loads along slope cultivated lands. As further, inter-rill and rill erosion were implicitly represented by the raindrop and overland flow soil detachments. The observed surface runoff and sediment concentration data in response to incoming water from the rainfall within selected agricultural river catchments were used to evaluate the performance of spatially distributed, processed-based Hillslope Erosion and Sediment Transport Model (HESTM). As erosion and sediment yield from slope lands are primarily determined by rainfall, surface runoff, topography, vegetative canopy cover, ground surface cover, soil erodibility, and sediment properties. Thus, several scenario-based control strategies according to three clusters of water erosion and sediment control measures had been examined. They are agronomic measures and soil management; field management; and mechanical approach. Accordingly, scenario-based water and soil conservation practices were designed for setup numerical experiments of the model at selected water catchments located in the Upper Citarum and Cimanuk River basins, West Java which dominated by planted seasonal crops (carrot and potato). The study area was discretized into a spatial resolution of 30 x 30 m for considering heterogeneity and control measures function in rainfall-runoff-erosion-sediment process mechanisms.

Climate resilience in rural Zambia: evaluating farmers’ response to El Niño-induced drought

AbstractThis paper aims at identifying whether and how sustainable land management practices and livelihood diversification strategies have contributed to moderating the impacts of the El Niño-related drought in Zambia. This is done using a specifically designed survey called the El Niño Impact Assessment Survey, which is combined with the Rural Agricultural Livelihoods Surveys, as well as high resolution rainfall data at the ward level over 34 years. This unique panel data set allows us to control for the time-invariant unobserved heterogeneity to understand the impacts of shocks like El Niño, which are expected to become more frequent and severe as a result of climate change. We find that maize yields were substantially reduced and that household incomes were only partially protected from the shock thanks to diversification strategies. Mechanical erosion control measures and livestock diversification emerge as the only strategies that provided yield and income benefits under weather shock.

Economic analysis of choices among differing measures to manage coastal erosion in Hoi An (a UNESCO World Heritage Site)

The paper presents one of the first economic analyses of residents’ choice of different coastal erosion control measures in a developing country — Vietnam. Hoi An, a UNESCO World Heritage Site, was selected given the frequency of coastal erosion events which have caused increasing damages to property, tourism activities and the livelihood of local people in an iconic tourist destination. We designed a discrete choice experiment based on responses from 399 households in order to estimate the willingness to pay (WTP) for differing coastal erosion control measures. Using the generalized multinomial logit model, empirical results yield five important findings. First, residents prefer wider, more public beaches having both trees and restaurants and are willing to accept visible structures such as groynes and stair revetment to prevent further erosion. Second, residents place a higher value on a beach that is protected by robust permanent structures. In particular, residents have the highest WTP for groynes. Third, there exists preference and scale heterogeneity across respondents which are driven by level of education, knowledge of the problem, and the stated level of choice certainty. Fourth, knowledge and experience of coastal erosion are shown to have a strong influence on the valuation residents place on the choice of protective structures. Finally, on average, a resident is willing to pay USD 1.7 per year for a coastal erosion management program that increases beach width by additional 50 meters, beach access by additional 25%, restaurants and trees on the beach and groynes as the erosion protection structure.

Organic manure input and straw cover improved the community structure of nitrogen cycle function microorganism driven by water erosion

Water erosion process induces differences to the nitrogen (N) functional microbial community structure, which is the driving force to key N processes at soil-water interface. However, how the soil N transformations associated with water erosion is affected by microorganisms, and how the microbial respond, are still unclear. The objective of this study is to investigate the changes of microbial diversity and community structure of the N-cycle function microorganisms as affected by water erosion under application of organic manure and straw cover. On the basis of iso-nitrogen substitution, four treatments were set up: 1) only chemical fertilizer with N 150 kg ha−1, P2O5 60 kg ha−1 and K2O 90 kg ha−1 (CK); the N was substituted 20% by 2) organic manure (OM); 3) straw (SW); and 4) organic manure + straw (1:1) (OMSW). The results showed that applying organic manure and straw to sloping farmland can increase soil N contents, but reduce runoff depth, Kw, sediment yield and N loss, especially in the OMSW. Straw cover and straw + organic manure increased the diversity (Chao1) of nitrifier (AOB), and both diversity and uniformity (Shannon) of denitrifier (nirK/S) were increased in the OMSW. All erosion control measures reduced N-fixing bacteria diversity and increased their uniformity, and the combined application of organic manure and straw cover was a better erosion control measure than the single application of them. Improved soil chemistry and erodibility were the main drives for the changes of N-functional microbial community structure and the appearance of dominant bacteria with different organic materials.

The proportion of jet flow and on-wall flow and its effects on soil loss and plunge pool morphology during gully headcut erosion

Gully headcut erosion is recognized as the primary process of gully erosion and is the main contributor to sediment yield of gully erosion. However, the proportion of jet flow and on-wall flow induced by headcut and its effects on soil loss and plunge pool morphology are still unclear. A simulated flow-scouring experiment was conducted to explore the proportion of jet flow and on-wall flow and their contributions to soil loss and the effect of on-wall flow erosion on plunge pool morphology under different flow discharge (q0 = 3.0–7.2 m3 h−1) and headwall height (H0 = 0.3–1.2 m) conditions. Our results showed that jet flow and on-wall flow accounted 15.7% − 22.6% and 77.4% − 84.3% of total flow volume upstream headcut, respectively. Jet flow, on-wall flow and their interaction contributed 53.5%, 34.9% and 11.6% of total soil loss amount, respectively. Furthermore, H0 exhibited greater effect on soil loss caused by jet flow and its interaction with on-wall flow, but the soil loss caused by on-wall was mainly controlled by q0. The width and depth of plunge pool logarithmically increased with scouring time, and the q0 and H0 significantly affected the development of plunge pool morphology. On-wall flow reduced plunge pool depth by 27.8%–71.4%, and it weakened plunge pool width by 24.3%−57.3% only under H0 of 0.3–0.9 m, but for H0 of 1.2 m and q0 of >4.8 m3 h−1, it improved the plunge pool width by 7.5%. The energy consumption of jet flow showed the closest relationship with plunge pool morphology. The concentrated flow upstream gully head exhibited the stronger effect on plunge pool morphology than H0. This study is helpful to deepen the understanding of gully erosion mechanism and provide scientific reference for the design of gully erosion prevention and control measures.

Local soil knowledge, sustainable agriculture and soil conservation in Central Vietnam

Efforts to support farmers living near forests to achieve sustainable agriculture and natural resource conservation have predominantly focused on services or schemes such as agricultural extension and community-based forest management, with little attention being focused on farmers' local soil knowledge (LSK). This paper provides insights into farmers' LSK, their agricultural and soil conservation practices and economic reliance on natural forests. Household survey (n = 146) and key informant interviews (n = 24) with farmers was conducted in two communes of the buffer zone of Bach Ma National Park, Central Vietnam. The results indicated that 70% of farmers had reasonable LSK, and farmers with comprehensive LSK (21%) were more familiar with their soils and the relationships between essential soil properties that reflect soil problems. Most farmers used soil colour to allocate crop types because of its association with soil fertility or plant yields. Erosion was identified as a major production constraint, yet less than a fifth of farmers had placed soil erosion control measures into practice. However, low-cost techniques, such as growing native plant cover (e.g.“lồ ô” (Bambusa balcooa)), were suggested by a few farmers to address soil loss. The Katu farmers had greater potential to secure LSK as the next generation are continuing to farm, while the Kinh farmers' LSK is threatened by a lack of engagement in farming by the younger generation. However, Katu farmers have less opportunity to use their LSK due to limitations in farm size and cropping options. These findings have raised different challenges to the succession of farmers' LSK for sustainable agriculture and natural resources conservation in the two communes. Finally, this study highlighted the importance of involving farmers' LSK in the early stages of designing and conducting research through forums or workshops to improve relevance and adoption of practices developed so they align with local people's understanding and practice.

ОЦЕНКА ЭРОЗИОННОГО СОСТОЯНИЯ ЗЕМЕЛЬ ПОДТАЕЖНОЙ ЗОНЫ ТОМСКОЙ ОБЛАСТИ С ПОМОЩЬЮ ГИС

An analysis of a number of morphometric values (slope and length of slopes, exposition, vertical depth and density of horizontal relief dissection) was performed, the erosion potential (USLE) of the territory was calculated using the example of catchment basins of small rivers of the Tomsk region - Basandayki and Tugoyakovka on an area of 72000 hectares. The analysis was carried out using the free GIS Quantum GIS Desktop 3.12.2 with GRASS 7.8.2 and SAGA 2.3.2 based on the SRTM Earth Explorer digital relief model with a resolution of 30x30 m per pixel. The analysis showed that the studied territory is predisposed to the development of water erosion; the combination of the studied factors causes an increase in the degree of erosion development in the east-west direction from the center of the inter-river space of the Tomi and Yai rivers to the channel of the Tomi River. Based on the obtained data on the density of horizontal dissection of the terrain and the slope of the territory within the territory under study, agroecological groups of land were identified. The following ratio (native/agricultural) was determined: placors - 7.5 %/8.6%, low erosion lands - 24.3 %/28.7%, medium erosion lands - 54.9 %/53.6%, strong erosion 12.8 %/8.5%, very strongly erosion - 0.5 %/0.6%. The potential for water erosion varies from insignificant to very strong: most of the territory is characterized by average (86.3%) and strong (10.77%) potential erosion, which is expressed in soil flushing from 1 to 5 tons/ha/year and from 5 to 10 tons/ha/year, respectively. Very severe erosion (10 to 29.1 tons/ha/year) is potentially affected by 1.9% of the area. For the analyzed indicators, vector thematic maps have been created containing information about the areas and values of indicators with reference to the OSM Standard topographic base and the Google satellite online map, which provides the ability to quickly amend the digital terrain model and allows you to plan activities in accordance with the current infrastructure. The data obtained by means of GIS and materials of the remote sensing of Earth (RSE), objectively describe an erosive situation in the explored territory and are combined with the literary data based on land observations and also supplement them. The created materials can be useful in medium-scale soil erosion mapping of land and for planning erosion control measures in the territory of the underground zone of the Tomsk region.

Exploring rainfall kinetic energy induced erosion behavior and sediment sorting for a coarse-textured granite derived soil of south China

Screen covering is a widely used soil conservation practice to control water erosion in coarse-textured soil areas. A better understanding of the effects of screen covers at reducing rainfall kinetic energy (KE) on the erosion behavior will improve erosion prediction and control measures development. The objective of this study was to investigate and quantify the effects of rainfall KE on the soil loss and sediment sorting for developing a prediction model in a coarse-textured soil. A series of rainfall simulation experiments were conducted in three horizons of a coarse-textured soil under five rainfall KEs (628, 443, 324, 231, and 110 J m−2 h-1) which were obtained by covering the soil surface with wire screens of different apertures at a coincident intensity of 90 mm h-1. The results showed that the increase in rainfall KE increased runoff rate and soil erosion rate. The soil erosion rate also increased with depth of the soil layer exposed to the soil surface. Based on the soil clay content, a power relationship could describe the relationships between soil erosion rate and geometric mean diameter of sediment and stream power. With increasing rainfall KE and runoff duration, although the percentage of clay- and silt-sized particles in the sediment decreased, both were still higher than the content in the original soil. The enrichment of fine particles in runoff produced a coarsening layer on the slope surface, which might restrain the subsequent erosion in situ. The observed large preferential loss of clay- and silt-sized particles by erosion emphasizes the importance of sediment sorting for subsequent erosion in these coarse-textured soils. These results suggest that the relationship of rainfall KE to erosion should be considered for practical and effective estimation and prediction of the potential erosiveness of rainstorms.

Vicia sativa Roth. Can Reduce Soil and Water Losses in Recently Planted Vineyards (Vitis vinifera L.)

Elevated soil loss and runoff rates can reduce soil fertility; therefore, soil erosion control strategies must be implemented at the hillslope and watershed scale when plantations are established and the soil is bare. In this research, we propose the use of the Vicia sativa Roth. to reduce the soil losses during the first year to control the peak of soil erosion after the plantation in tilled vineyards. To test its efficiency, rainfall simulation experiments were carried out with field surveys in The Casa Pago Gran, in the Eastern Iberian Peninsula. Our results demonstrate that soil properties (organic matter and soil bulk density) and soil erosion (soil loss, runoff and sediment concentration) were significantly different between the control plot (tilled) and with cover crops along with August 2016, 2017 and 2018 measurement periods, but not during January 2016, coinciding with the initial survey before the vetch sown. Runoff initiation was delayed in 3.7 times after 3 years (from 190 till 709 s). The runoff discharge was reduced by the Vicia sativa from 32.87 till 13.68%, the sediment concentration went down from 18.54 till 3.81 gr l−1 and the soil erosion from 3.36 to 0.29 Mg ha−1 year−1. An increase in soil bulk density was registered but did not affect the runoff generation either the soil losses, that was reduced by the plant cover. We conclude that it is necessary to include soil erosion control measures such as the use of Vicia sativa to reduce soil erosion processes during the first stages of the vineyard plantations due to the soil quality improvements and the reduction in soil and water losses.

Accessibility and Reliability of Information Sources in Dissemination of Soil Fertility Management in Eastern Kenya

Increased recognition of soil fertility depletion as the main factor limiting crop production in many small holder farms in sub-Saharan African has renewed interest in the dissemination of soil fertility management technologies. Despite soil technology development and research outputs, few of the recommendations from various soil fertility management research activities have been adopted by the small-scale farmers on a large-scale level. Only a small proportion of allocated research resources is invested in dissemination among research institutions. The objective of the study was to investigate communication channels used in dissemination of soil fertility management practices in Mbeere and Meru South Districts. Two hundred and forty randomly selected farmers were interviewed. Data collected was analyzed using SPSS. The study revealed that 32.5% of the farmers who used combined organic and inorganic fertilizers received information from government extension officers while 41.3% of the farmers who use animal manure utilized their own farming experience. In disseminating soil erosion control measures, 51.2% of the farmers indicated that, farmer to farmer extension was the most commonly used. Also, 33.8% mentioned demonstration as the main method used in training soil fertility management practices. In general, the most common source of information was other farmers while there was least participation of researchers and agro input dealers in dissemination of soil fertility technologies. Thus, the study recommended more participation of stakeholders other than government extension officers as well as use of combined extension methods with farmer involvement in dissemination of soil fertility management practices. Keywords: manure, extension agents, farmer to farmer extension method, demonstration DOI: 10.7176/DCS/10-11-03 Publication date: November 30 th 2020

Assessment of Soil Erosion Using the RUSLE Model for the Epworth District of the Harare Metropolitan Province, Zimbabwe

Urban development without adequate soil erosion control measures is becoming a major environmental concern in developing urban areas across Africa. These environmental disturbances encompass rampart Land Use and Land Cover changes (LULC) due to a high population growth rate and increased economic activities. To understand the influence of accelerated LULC changes and urban expansion as major drivers in landscape degradation in the Epworth district of the Harare Metropolitan Province, the RUSLE model was employed. This considers land use, soil, climate and topography as input parameters in the assessment of the extent and impact of these drivers on soil erosion. The Revised Universal Soil Loss Equation (RUSLE) was used to predict the potential erosion between 1984 and 2018 and soil erosion risk for the years 2000 and 2018. The mean rate of the predicted potential soil erosion was 13.2 t ha−1 yr−1 (1984–2018); areas especially vulnerable to erosion were predicted for foot slope areas with direct tributaries to the major streams and steep sloping zones. The average soil erosion risk was estimated at 1.31 t ha−1 yr−1 for the year 2000 and 1.12 t ha−1 yr−1 for 2018. While the overall potential soil loss decreased between 2000 and 2018, the potential soil loss was observed to increase tremendously in residential areas, which doubled in extent between 2000 and 2018. The findings reveal that about 40% of the Epworth district was threatened by unsustainable soil loss resulting from increased soil erosion risk within the built-up areas.

GIS-based geomorphometric analysis for potential applications in reversing land and biosystem degradation.

Watershed morphometric assessment is about measurements and calculations of land surface forms for the purpose of understanding hydro-geomorphological character and patterns. Important natural environment geo-information and summary of the spatial characteristics of Tana River Basin (TRB) in Kenya have been obtained through hydro-geomorphometric analysis. Advanced Spaceborne Thermal Emission and Reflection Radiometer Digital Elevation Model (ASTERDEM) data and ArcGIS (ESRI Inc., version 10.4.1) together with published mathematical equations were applied to extract morphometric parameters of the drainage basin, which covers a total area of 94,930 km2 and a span of 527.75 km. The quantitative morphometric analysis considered a total of 28 relief, areal, and linear hydro-morphometric characteristics of the TRB. Relief parameters of the basin suggest moderate-to-low overall watershed steepness, upland with rolling land surface patterns, rugged landforms susceptible to erosion and sediment transportation, and a landscape in evolution process tending towards maturity. This means stability of the land surface can be attained with intensive land degradation reversing strategies like erosion control measures. Areal characteristics further support the basin's susceptibility to erosion as shown by stream length, stream drainage density, and circulatory ratio values. Also, the areal aspects portray peak runoffs with short duration flashes. Linear parameter value results such as bifurcation ratio imply that infiltration capacity varies with stream orders across the watershed. This hydro-geomorphometric analysis would be useful to land and water managers, researchers and practitioners of TRB, and other similar systems in designing and planning soil and water conservation and management practices such as soil erosion control, groundwater recharge activities, catchment modelling, runoff and flood studies, prospecting groundwater mapping, and biological applications.

ОРГАНИЗАЦИЯ УСТОЙЧИВОГО СЕЛЬСКОХОЗЯЙСТВЕННОГО ЗЕМЛЕПОЛЬЗОВАНИЯ НА ОСНОВЕ ЛАНДШАФТНОГО АНАЛИЗА

The aim of the work was the landscape analysis of agricultural geographical landscapes in the Altai Territory and elaboration of measures aimed at the rational use of agricultural lands. Environmental and landscape (landscape) approach became the main method of scientific research used in the analysis of modern agricultural landscapes. The cartographic method, using GIS-technologies, made it possible to digitize the obtained materials. Synthesized maps of agro-ecological, natural and other zoning of territories are based on topographic, soil, geobotanical and other thematic maps made during land surveying during the field survey. Retrospective analysis, induction and deduction methods,analysis and synthesis, as well as the abstract-logic method were also used in the work. Our main result was the analysis of land use territory for agricultural enterprise in municipal district of Altai Krai. Exploration of lands indicates a pronounced plant-growing specialization of JSC “Pobeda” with a developed animal breeding direction. Limiting factors affecting the rational use of land are natural and climatic conditions, terrain,unsystematic anthropogenic activity and, as a result, the development of erosion processes. The degree of eroded and deflated arable land is more than 50%, hay and pasture lands are also very unstable. Landscapes have been typified, based on which eleven types of land have been identified and their geomorphological description has been carried out. The first five types of land can be used for agricultural production with limitations compensated by crop technology and erosion control measures, the sixth and seventh types require grassing and, in some cases,conservation, the eighth and ninth types can be partially used for pasture and area valorization; the remaining two are not suitable for agricultural use but should be potentially used for planting and forest management. As a result of the presented transformation of agricultural lands, the structure of cultivated areas has changed. The area of arable land decreased by 877 ha, and of pastures by 365 ha,while the area under hayfields, fallow lands, and forest lands increased by 295, 191, and 875 ha respectively. Low-productive lands were withdrawn from agriculture. We suggested that the sustainability of agricultural land use was mainly caused by the reduction of anthropogenic load and increase in ecological equilibrium of the territory.

Erosion and soil and water conservation in South‐Kivu (eastern DR Congo): The farmers' view

AbstractDespite being one of the hotspots for soil erosion in the world, little is known regarding farmer's knowledge of soil erosion in the highlands of South‐Kivu in the Democratic Republic of Congo. A proper understanding of farmers' knowledge regarding soil erosion and conservation measures is a prerequisite for implementing resilient erosion control measures. The objective of this study was therefore to assess farmers' knowledge of soil erosion, to document existing soil and water conservation (SWC) measures and to identify their adoption constraints in the highlands of South‐Kivu. Data were collected using interviews with a semi‐structured questionnaire involving 720 respondents from eight watersheds in four territories. Farmers reported eight main erosion indicators. As opposed to gullies (80% of farmers), rills were perceived as important erosion indicators by only 50% of farmers, despite their common occurrence. Farmers were largely unaware of the potential impact of their crops and cropping practices on erosion. Farmers knew about only a limited range of SWC measures, which were perceived to be little to moderately efficient. Furthermore, the average level of adoption was very low (21%). Adoption constraints varied widely depending on the SWC measure. Thus, future interventions need to place much greater emphasis on awareness regarding soil erosion and SWC measures, to strengthen farmers' capacity for experimentation and adaptation to new technologies and finally to create a policy and institutional environment that stimulates widespread adoption of SWC techniques.

Effectiveness of terracing techniques for controlling soil erosion by water in Rwanda

Despite long-standing efforts in terracing, limited field-based evidence of its effectiveness as implemented within rural farming systems of humid tropical regions, such as Rwanda, is available. This study aimed to reveal regional differences in effectiveness of two widely used terracing techniques. Traditional slope farming (NP) was compared to bench (BT) and farmers’ based progressive terraces (PT) in terms of runoff, soil losses, and topsoil fertility in two contrasting agro-ecological zones, the Eastern Plateau (Murehe) and Buberuka Highlands (Tangata). During four consecutive rainy seasons, event-based data were collected using erosion plots (5 m width x 22.2 m length). Effectiveness indices of both terracing systems, as well as (R)USLE P-factor values, were calculated. The annual average soil losses under NP ranged from 4.71 ± 5.02 ton ha−1 to 46.01 ± 7.28 ton ha−1 in Murehe (14% slope gradient) and Tangata (43% slope gradient), respectively. Bench terracing clearly outperformed the farmer-based progressive terrace at both locations, leading to negligible soil losses. In terms of runoff reduction, an effectiveness of 70 and 85% respectively, was observed at Murehe and Tangata. The effectiveness of PT reached 52% for runoff control and 93% for soil loss control at Tangata, thereby confirming its huge potential as erosion control measure, even in mountainous areas. In the hilly landscape of Murehe, the runoff generated by PT – in some years - can exceed that under traditional farming, while the measure reduced soil losses by half on average. Associated USLE P-factors varied between seasons with an annual average values of 0.001–0.02 for BT, and 0.07 to 0.55 for PT at Tangata and Murehe, respectively. These variations in performance by site and terracing system also resulted in differences in topsoil chemical fertility, with BT generally outperforming both PT and NP at Tangata. At Murehe, PT showed a significantly lower chemical fertility compared to BT and NP. Poor quality risers explained the overall lower performance of PT at Murehe. The study thus confirmed the huge potential of (bench) terraces to sustainably reduce soil erosion rates when established within an integrated approach, paying attention to correct installation and fertility-supporting agronomic practices. More attention should be given to riser installation (e.g. distance) and maintenance of PT. Adoption of these erosion control measures can be recommended to similar agro-ecological zones for sustainably protecting the lands while mitigating or adapting the effects of climate change.

The Use of Straw Mulches to Mitigate Soil Erosion under Different Antecedent Soil Moistures

Straw mulch cover is one of the most important soil erosion control measures applied to reduce runoff and soil loss in cultivated areas. However, in developing countries such as Iran, without a clear tradition or knowledge about soil erosion control measures, the use of straw mulch is rare, and its impact in the most extended crops is not well understood. We investigated the separate and combined effects of colza (Brassica napus L.) and corn (Zea mays L.), to mitigate the activation of soil loss and runoff in sandy-loam soils, under different antecedent soil moisture conditions, in a rainfed plot in Northern Iran. Under laboratory conditions, we used a rainfall simulator device. The experiments were performed by using a rainfall intensity of 50 mm h−1, with a duration of 10 min and an inclination of 30%, with three replications. These conditions were used to evaluate the soils under extreme meteorological and topographical conditions. Two types of straw mulch, colza and corn, separated and combined with three different cover levels (25, 50 and 75%) and four distinct antecedent soil moisture conditions (0, 15, 20 and 30%), were used. The results showed that the applied straw mulches had significant effects on the reduction of soil loss and sediment concentration, by almost 99%. The maximum reduction of soil loss and sediment concentration was observed for the treatments with 0% moisture and 75% of corn, colza + corn and colza, with a reduction of 93.8, 92.2 and 84.9% for soil loss, respectively, and 91.1, 85.7 and, 60.7% for sediment concentration, respectively. The maximum reduction of runoff was also obtained with 0% soil moisture and a cover of 75%, reducing 62.5, 48.5 and 34.8% for colza, colza + corn and corn, respectively. The corn straw mulch showed the highest effectivity on reducing soil loss and sediment concentration toward colza treatment. But the colza straw mulch showed the best results on reducing runoff toward corn treatment. We conclude that the application of straw mulch is affordable and useful in reducing soil loss and runoff, instead of bare soils.