Accelerated Soil Erosion Research Articles

Effects of environmental factors on classification of loessderived soils and clay minerals variations, northern Iran

Land-use type under different topographic conditions and human activities affects soil development. We investigated the effects of land-use, topography and human activity on soil classification changes in the Toshan watershed in northern Iran. Seven representative pedons derived from loess parent materials were studied on different land-uses and topographic positions. The studied pedons in forest (FO) on backslopes and footslope were classified as Calcic Haploxeralfs and Typic Haploxeralfs, respectively. The soils in abandoned lands (AB) and orchards (OR), where formerly under natural forests, located on the shoulder and backslopes positions were classified as Calcic Haploxeralfs and Vertic Haploxeralfs, respectively. Well-developed argillic horizons as indicators for higher degrees of soil evolution were observed in more-stable areas under the natural forest or less disturbed areas. Clay lessivage through these soil profiles have led to formation of Typic or Calcic Haploxeralfs, while under croplands (CP) were classified as Typic Calcixerepts. Conversion of sloping deforested areas to CP along with inappropriate management have accelerated soil erosion, resulting in unstable conditions in which decalcification and formation of developed soils cannot occur. Paddy cultivation in flat areas has caused to reduced conditions and formation of Typic Haplaquepts. Because of unfavorable conditions for chemical weathering (e.g. lower water retention compared to more-stable areas) no vermiculite was detected in the CP. The results showed that evolution and classification of the studied soils were strongly affected by land-use type, topography and management.

Long‐term impact of land use changes on soil erosion in an agricultural catchment (in the Western Polish Carpathians)

AbstractThe change in land use and land cover (LULC) from natural vegetation to agricultural in mountain areas usually dramatically accelerates soil erosion rates if the land is used for crop production. The aim of research was to calculate soil erosion magnitude basing on the Revised Universal Soil Loss Equation (RUSLE) in response to long‐term changes in LULC in an agricultural Homerka catchment (19.3 km2) of the Polish Carpathians. The changes in LULC were derived from cadastral maps for 1846 and orthophotomaps for 2009. Three variants with different factors, rainfall–run‐off erosivity (R), practice support (P), and LULC, were analysed to investigate which has had the greatest impact on soil erosion changes over the last 160 years. An increase in forest area (by 67.81%) and decrease in cultivated land (by 91.94%) were observed, primarily due to the collapse of the communist system. The estimated soil erosion using the RUSLE model in the analysed catchment decreased by 77% (from 18.13 t ha−1 yr−1 in 1846 to 4.11 t ha−1 yr−1 in 2009). The long‐term changes in soil erosion rates and their spatial distribution are mainly associated with transformation from cultivated land to forest or grassland. The P factor was responsible for reduction of soil erosion rates by 8%, a minor impact. Over the last 160 years, the average and maximum annual precipitation changes were also statistically insignificant. Results reveal a dominant role of human impact, particularly with respect to LULC on soil erosion changes in mid‐mountain areas.

Rainfall erosivity and sediment load over the Poyang Lake Basin under variable climate and human activities since the 1960s

Accelerated soil erosion exerts adverse effects on water and soil resources. Rainfall erosivity reflects soil erosion potential driven by rainfall, which is essential for soil erosive risk assessment. This study investigated the spatiotemporal variation of rainfall erosivity and its impacts on sediment load over the largest freshwater lake basin of China (the Poyang Lake Basin, abbreviate to PYLB). The spatiotemporal variations of rainfall erosivity from 1961 to 2014 based on 57 meteorological stations were detected using the Mann–Kendall test, linear regression, and kriging interpolation method. The sequential t test analysis of regime shift (STARS) was employed to identify the abrupt changes of sediment load, and the modified double mass curve was used to assess the impacts of rainfall erosivity variability on sediment load. It was found that there was significant increase (P < 0.05) in rainfall erosivity in winter due to the significant increase in January over the last 54 years, whereas no trend in year and other seasons. Annual sediment load into the Poyang Lake (PYL) decreased significantly (P < 0.01) between 1961 and 2014, and the change-points were identified in both 1985 and 2003. It was found that take annual rainfall erosivity as the explanatory variables of the double mass curves is more reasonable than annual rainfall and erosive rainfall. The estimation via the modified double mass curve demonstrated that compared with the period before change-point (1961–1984), the changes of rainfall erosivity increased 8.0 and 2.1% of sediment load during 1985–2002 and 2003–2014, respectively. Human activities decreased 50.2 and 69.7% of sediment load during the last two periods, which indicated effects of human activities on sediment load change was much larger than that of rainfall erosivity variability in the PYLB.

Accelerated Soil erosion as a source of atmospheric CO2

Soil erosion, physical transport of soil over the landscape by alluvial and aeolian processes as source of energy, has a strong impact on the global carbon cycle (GCC). Being a light fraction (bulk density of 0.6–0.8 Mg/m3) and concentrated in vicinity of soil surface, soil organic carbon (SOC) is preferentially removed by water and wind erosion. The process of erosion and the attendant transport of SOC are accelerated by conversion of natural to agroecosystems. Whereas the human-induced acceleration of soil erosion has depleted the SOC stock of agroecosystems, the fate of SOC transported over the landscape and that deposited in depressional sites is not understood. While a fraction of SOC transported to and buried under aquatic ecosystems (e.g., flood plains, lakes, ocean) may be protected because of limited microbial activity, labile fractions of SOC being transported over the landscape enroute to the depositional site are vulnerable to decomposition. Depending on the site-specific conditions with regards to the hydrothermal regimes and the degree of aeration, the decomposition may lead to emission of CO2 under aerobic environments, CH4 under anaerobic conditions, and N2O under both situations. The process of soil erosion, especially that by water, is a 4-stage process: (i) detachment, (ii) splash, (iii) transport and redistribution, and (iv) deposition. Breakdown of aggregates, during the first three stages, exposes the hitherto encapsulated SOC to microbial processes and exacerbates its vulnerability to decomposition. Thus, the fate of SOC subject to erosion must be assessed for all landscape positions and integrated over the watershed. Lack of credible data regarding the fate of SOC at different erosional stages is a major cause of uncertainties. Thus, well-planned research at a watershed-level is needed to assess the impacts of erosional processes on decomposition of SOC, gaseous emission, and the soil/ecosystem C budget for diverse soils and management systems in global biomes/ecoregions. The data on global C budget is incomplete without consideration of the impact of erosion on SOC and the attendant gaseous emissions.

Assessment of soil erosion in a monsoon-dominated mountain river basin in India using RUSLE-SDR and AHP

ABSTRACTThe long-term average annual soil loss (A) and sediment yield (SY) in a tropical monsoon-dominated river basin in the southern Western Ghats, India (Muthirapuzha River Basin, MRB; area: 271.75 km2), were predicted by coupling the Revised Universal Soil Loss Equation (RUSLE) and sediment delivery ratio (SDR) models. Moreover, the study also delineated soil erosion risk zones based on the soil erosion potential index (SEPI) using the analytic hierarchy process (AHP) technique. Mean A of the basin is 14.36 t ha−1 year−1, while mean SY is only 3.65 t ha−1 year−1. Although the land use/land cover types with human interference show relatively lower A compared to natural vegetation, their higher SDR values reflect the significance of anthropogenic activities in accelerated soil erosion. The soil erosion risk in the MRB is strongly controlled by slope, land use/land cover and relative relief, compared to geomorphology, drainage density, stream frequency and lineament frequency.

Sedimentary record and luminescence chronology of palaeoflood events along the Gold Gorge of the upper Hanjiang River, middle Yangtze River basin, China

Palaeoflood slackwater deposits (SWDs) along the river banks have important implications for the reconstruction of the past hydro-climatic events. Two palaeoflood SWD beds were identified in the Holocene loess-soil sequences on the cliff river banks along the Gold Gorge of the upper Hanjiang River by field investigation and laboratory analysis. They have recorded two palaeoflood events which were dated by optically stimulated luminescence to 3.2–2.8 ka and 2.1–1.8 ka, respectively. The reliability of the ages obtained for the two events are further confirmed by the presence of archaeological remains and good regional pedostratigraphic correlation. The peak discharges of two palaeoflood events at the studied sites were estimated to be 16,560–17,930 m3/s. A correlation with the palaeoflood events identified in the other reaches shows that great floods occurred frequently during the episodes of 3200–2800 and 2000–1700 a BP along the upper Hanjiang River valley during the last 4000 years. These phases of palaeoflood events in central China are well correlated with the climatic variability identified by δ18O record in the stalagmites from the middle Yangtze River Basin and show apparent global linkages. Palaeoflood studies in a watershed scale also imply that strengthened human activities during the Shang dynasty (BCE 1600–1100) and Han dynasty (BCE206–CE265) may have caused accelerated soil erosion along the upper Hanjiang River valley.

Identifying Possible Locations to Construct Soil Water Conservation Structures by Using Hydrogeological and Geospatial Analysis

Abstract Identification of soil water conservation structures (SWCs) necessitates as the proximity of study area (Shivganga watershed) to the Western Ghats imparts high rainfall and runoff, resulting to accelerate soil erosion. To decrease soil erosion and improve water storage as well as recharge, the investigation of new possible structures is necessary. With this intent, suitable sites for SWC structures (check dam and percolation ponds) were identified by using hydro-spatial data such as soil, land use/cover, slope, runoff, infiltration data from IRS P6 LISS-IV imagery and other collateral data. Further, acquired data were processed to derive runoff by employing Soil Conservation Service Curve Number (SCS-CN) method and infiltration by Allen (2008) method. The Integrated Mission for Sustainable Development (IMSD) specifications were used for the identification of locations for constructing SWC structures. The results revealed that about 28% area is suitable for implementation of SWC structures. Total 45 locations SWC structures were derived with the present method, out of that 20 were already built. The superimposition of derived and existing locations shows (80-100%) accuracy, authenticates the reliability of the method. The present modified method will definitely help in speedy identification of a location for SWC structures.

An assessment of the global impact of 21st century land use change on soil erosion

Human activity and related land use change are the primary cause of accelerated soil erosion, which has substantial implications for nutrient and carbon cycling, land productivity and in turn, worldwide socio-economic conditions. Here we present an unprecedentedly high resolution (250 × 250 m) global potential soil erosion model, using a combination of remote sensing, GIS modelling and census data. We challenge the previous annual soil erosion reference values as our estimate, of 35.9 Pg yr−1 of soil eroded in 2012, is at least two times lower. Moreover, we estimate the spatial and temporal effects of land use change between 2001 and 2012 and the potential offset of the global application of conservation practices. Our findings indicate a potential overall increase in global soil erosion driven by cropland expansion. The greatest increases are predicted to occur in Sub-Saharan Africa, South America and Southeast Asia. The least developed economies have been found to experience the highest estimates of soil erosion rates.

Hydraulic characteristics of varying slope gradients, rainfall intensities and litter cover on vegetated slopes

Abstract Litter produced by forests performs crucial functions in rainfall interception and soil conservation, particularly in the condition that larger raindrops formed by canopy accelerate soil erosion. To explore how forest litter exerts runoff hydrological characteristics and sediment yield processes, experiments on forest covered (Vitexnegundo var. heterophylla) slopes were conducted under various combinations of rainfall intensities and slope gradients. The results showed that litter reduced runoff yield rate by 9–31% and reduced sediment yield rate by 65–90%, with mean runoff and sediment reductions of 18% and 76% for all treatments. On forest covered slopes, Reynolds number and runoff power generally increased with the increase in both rainfall intensity and slope gradient. Litter layer reduced Reynolds number and runoff power with 8–29% and 56–80%, respectively. Darcy–Weisbach resistance coefficient decreased by increasing rainfall intensity and slope gradient. Litter layer increased Darcy–Weisbach resistance coefficient by three to nine times. Relationships between sediment yield rate and Reynolds number, runoff power, Darcy–Weisbach resistance coefficient were described by exponential, linear, power functions, respectively. The critical runoff power values for slopes with and without litter were 0.0027 and 0.0010 m/s, respectively. Reynolds number was the best hydrodynamic parameter for dynamic erosion characterizing.

Rivers of God, Rivers of Empire: Climate Extremes, Environmental Transformation and Agroecology in Colonial Mexico

Abstract This paper explores the social-ecological effects of the Little Ice Age (1300-1850) in colonial Central Mexico. Archival research reconstructs the history of climate, soil, water and agriculture in two Central Mexican watersheds: the Zahuapan River in Tlaxcala and the San Juan River in the Teotihuacan Valley. I clarify social-ecological and landscape responses to climate stress, along with changing human resilience/vulnerability to anomalous weather. The methodology is interdisciplinary, comparing natural climate archives (plant and mineral) to historical climate archives (texts and images), examining hydrological and edaphic evidence and contextualising social-ecological change within a framework of indigenous agrarian innovation. Together, this research reveals a critical transition from nature-induced to anthropogenic cataclysms after the Late Maunder Minimum (1684-1713). Before this disjuncture, floods were rare events driven by extraordinary precipitation and without significant hydromorphological change. Afterward, cataclysms were frequent, poorly correlated to precipitation trends and determined by anthropogenic accelerated soil erosion that transformed watersheds. Evidence from both basins demonstrates the rapid onset of deep hillside erosion and valley sedimentation after 1715. I argue that the combined ecological shock of colonialism and climate was mediated by early-colonial indigenous agrosystems, resulting in transformation without lasting degradation. The transformative potential of the Little Ice Age lay dormant until the Late Maunder Minimum intersected with the metepantli system, a new agrarian regime based on the cultivation of agave plants in monocropped sloping terraces for the extraction of pulque (a beer-like beverage), whose economic wealth belied its impoverished ecology. Not only does this paper challenge - even negate - arguments that link degradation to early-colonial biology, pre-Columbian agriculture or eighteenth-century population growth; it identifies the Late Maunder Minimum as a transformative moment in colonial ecosystems - and, by extension, society - that gave rise to a degraded and devious landscape.

Hydro-sedimentary flow modelling in some catchments Constantine highlands, case of Wadis Soultez and Reboa (Algeria)

Abstract Erosion is a major phenomenon that causes damage not only to soil and agriculture, but also to the quality of the water amounting to tonnes of matter annually transported on the earth's surface. This fact has attracted the interest of researchers to understand its mechanism and explain its causes and consequences. This work is a comparative study of water erosion in the two semi-arid catchments of Wadi Soultez and Wadi Reboa; located in the North-East of Algeria. The approach adopted for the quantification of sediment transport consists on researching the best regressive model to represent the statistical relation between the sediment yield and the measured water discharge at different scales: annual, seasonal and monthly. The available data cover 27 years from 1985-2012. The results show that the power model has given the best correlation coefficient. Results have indicated that Wadi Reboa transported an average of 14.66 hm3 of water and 0.25 million tonnes of sediments annually. While Wadi Soultez has transported 4.2 hm3 of water and 0.11 million tonnes of sediments annually. At a seasonal scale, sediment amounts have showed significant water erosion in autumn with around 44% and secondarily in the spring with 29% in Wadi Soultez. Unlike Wadi Reboa, sediment transport represents 32% and 46% in autumn and spring respectively. Based on the obtained sediment amounts; it is found that the physical factors: such as steep reliefs, vulnerable lithological nature of rocks and poor vegetal cover, have significantly contributed in accelerating soil erosion.

Predicting land at risk from wind erosion using an index-based framework under a climate change scenario in Durango, Mexico

Land degradation takes place primarily in drylands which make up for almost 50% of the cultivated lands, globally. The 90% of Mexican territory is currently experiencing land deterioration mainly due to anthropogenic land use changes and still expecting further deterioration. While efforts have been directed toward the impact of land use changes on wind erosion in dryland ecosystems, there is still high uncertainty on the nature of wind erosion sources. This challenge was addressed by developing and evaluating a method for completing spatial assessments of vulnerable zones currently experiencing accelerated soil erosion and to predict those areas where soil erosion is likely to occur in the near future. This approach is tested over a study area in the Comarca Lagunera, Durango, Mexico. Spatiotemporal patterns and variability in soil erosion and aridity were evaluated, as well as the identification of key characteristics driving soil degradation in the area. Results demonstrate that the suggested methodology can be effectively used to spatially delineate potential locations susceptible to soil degradation (e.g., moderate-risk zones and/or high-risk zones), not only in the present time but also to predict those locations in the near future. This provides the opportunity of spatially defined areas of interest based on specific relationships between edaphological properties and its vulnerability to climate variability. This type of approach could be valuable to identify critical locations that should be treated as a priority for monitoring and managing accelerated soil degradation.

Stability and instability on Maya Lowlands tropical hillslope soils

Substantial lake core and other evidence shows accelerated soil erosion occurred in the Maya Lowlands of Central America over ancient Maya history from 3000 to 1000years ago. But we have little evidence of the wider network of the sources and sinks of that eroded sediment cascade. This study begins to solve the mystery of missing soil with new research and a synthesis of existing studies of tropical forest soils along slopes in NW Belize. The research aim is to understand soil formation, long-term human impacts on slopes, and slope stability over time, and explore ecological implications. We studied soils on seven slopes in tropical forest areas that have experienced intensive ancient human impacts and those with little ancient impacts. All of our soil catenas, except for one deforested from old growth two years before, contain evidence for about 1000years of stable, tropical forest cover since Maya abandonment. We characterized the physical, chemical, and taxonomic characteristics of soils at crest-shoulder, backslopes, footslopes, and depression locations, analyzing typical soil parameters, chemical elements, and carbon isotopes (δ13C) in dated and undated sequences. Four footslopes or depressions in areas of high ancient occupation preserved evidence of buried, clay-textured soils covered by coarser sediment dating from the Maya Classic period. Three footslopes from areas with scant evidence of ancient occupation had little discernable deposition. These findings add to a growing corpus of soil toposequences with similar facies changes in footslopes and depressions that date to the Maya period. Using major elemental concentrations across a range of catenas, we derived a measure (Ca+Mg)/(Al+Fe+Mn) of the relative contributions of autochthonous and allochthonous materials and the relative age of soil catenas. We found very low ratios in clearly older, buried soils in footslopes and depressions and on slopes that had not undergone ancient Maya erosion. We found high (Ca+Mg)/(Al+Fe+Mn) values on slopes with several lines of evidence that suggest relative youth, soils possibly formed since Maya abandonment. Carbon isotopes (δ13C) also provide some evidence of past vegetation change on slopes. We found strong evidence for maize or other alien C4 species in an ancient terrace soil and additional evidence in buried footslopes but only evidence for C3 species (like tropical trees) on the backslopes and other crest-shoulders. The fact that steep slopes preserved no evidence of C4 species inputs may mean that the ancient Maya maintained forests here. Alternatively, ancient Maya land uses eroded slopes, with the δ13C signatures detected today being the result of more recent soil development under forest over the last millennium. Additional evidence that these soils are recent in age includes elevated (Ca+Mg)/(Al+Fe+Mn) values, skeletal soil profiles, and low soil magnetic susceptibility. Besides the evidence for truncating backslopes and aggrading footslopes, the ancient Maya built agricultural terraces that accumulated soils and altered drainage. All these ancient Maya slope alterations would have influenced modern tree distributions, because many tree species in the modern forest show strong preferences for different soil types and topographic situations that the ancient Maya changed.

Assessment of soil erosion in a tropical mountain river basin of the southern Western Ghats, India using RUSLE and GIS

Revised Universal Soil Loss Equation (RUSLE) model coupled with transport limited sediment delivery (TLSD) function was used to predict the longtime average annual soil loss, and to identify the critical erosion-/deposition-prone areas in a tropical mountain river basin, viz., Muthirapuzha River Basin (MRB; area = 271.75 km2), in the southern Western Ghats, India. Mean gross soil erosion in MRB is 14.36 t ha−1 yr−1, whereas mean net soil erosion (i.e., gross erosion–deposition) is only 3.60 t ha−1 yr−1 (i.e., roughly 25% of the gross erosion). Majority of the basin area (∼86%) experiences only slight erosion (<5 t ha−1 yr−1), and nearly 3% of the area functions as depositional environment for the eroded sediments (e.g., the terraces of stream reaches, the gentle plains as well as the foot slopes of the plateau scarps and the terrain with concordant summits). Although mean gross soil erosion rates in the natural vegetation belts are relatively higher, compared to agriculture, settlement/built-up areas and tea plantation, the sediment transport efficiency in agricultural areas and tea plantation is significantly high, reflecting the role of human activities on accelerated soil erosion. In MRB, on a mean basis, 0.42 t of soil organic carbon (SOC) content is being eroded per hectare annually, and SOC loss from the 4th order sub-basins shows considerable differences, mainly due to the spatial variability in the gross soil erosion rates among the sub-basins. The quantitative results, on soil erosion and deposition, modelled using RUSLE and TLSD, are expected to be beneficial while formulating comprehensive land management strategies for reducing the extent of soil degradation in tropical mountain river basins.

Late Holocene erosion events in the Valley of Teotihuacan, central Mexico: Insights from a soil-geomorphic analysis of catenas

This paper addresses the timing of accelerated soil erosion and landscape degradation in central Mexico. It shows data on erosion sequences in the Valley of Teotihuacan, an area where agricultural dates back to at least since 1100BCE, and an ideal setting to test ideas on the effect of preconquest versus post-conquest anthropogenic impacts on the environment. The methods include stratigraphy, detailed description of soil profiles and soil micromorphology, along with analysis of pottery sherds and radiocarbon dating. A chronology of events for two catenas, focusing on periods of landscape stability and change, establish the sequence of erosion events from pre-Hispanic to modern times. Six erosion phases are recognized over the last 2000years in Teotihuacan. Although results suggest that the most intense erosion occurred after Spanish conquest, in the 16th century, several erosion phases took place during pre-Hispanic times and also in the postcolonial period, including the 20th century. Probable causes for these impacts are related to settlement dynamics, population variability, and land use changes. Thus, it provides new information for the discussion on the timing and causes of erosion, sedimentation and landscape modification in the central Mexican Highlands during the late Holocene.

Identification and prioritization of critical erosion areas based on onsite and offsite effects

Accelerated soil erosion is considered as one of serious agro-environmental threats to sustainable development all over the word. Tolerable erosion concept is a tool for awareness and assessment of soil erosion status and its economic, social, and environmental hazards. This study was conducted to design a framework for evaluating and identifying spatial patterns of erosion hazard in Haji-Ghushan watershed, based on tolerable erosion concept, by using the SWAT model. The framework was consisted of two parts: the erosion tolerance index (ETI), and the sediment-phosphorous index (SPI) for evaluating onsite and offsite effects of soil erosion, respectively. Four hazard levels were defined for each index. The results of sediment simulation indicated that the maximum rate of erosion belonged to agricultural lands located on steep slopes in the central part of the watershed, and the minimum rate was from forest lands, despite their steep slopes. The map of spatial distribution of erosion hazard showed that, in terms of both onsite and offsite effects, a major part of the watershed (around 65%) had experienced an erosion rate lower than the erosion tolerance threshold; hence, these areas were not faced with erosion hazard. The spatial distribution of the areas exposed to the onsite erosion hazard, however, was differed from those confronted by the offsite erosion hazard. Identified high hazard areas based on the erosion offsite impacts were mainly located in sub-basins close to the watershed outlet where the sediment and phosphorous yield was high due to the high sediment-phosphorous delivery ratio. High hazard areas with high risk of soil degradation and productivity reduction are distributed throughout the watershed, depending on the magnitude of the erosion rate. These findings revealed that, in addition to erosion rate, sediment delivery ratio is also an important parameter in evaluating soil erosion hazard. For achieving the sustainable agro-environment, it is necessary to consider both the onsite and offsite effects of soil erosion to identify the high hazard areas. Also the results showed that the designed framework was capable of identifying the high hazard and hot spot areas well. The findings of this study are useful for officials and policy makers of soil conservation and environmental protection agencies in the region.

English

Accelerated soil erosion remains the major challenge that is adversely affecting the agricultural performance in Ethiopia. Efforts towards soil and water conservation (SWC) goal were started since the mid-1970s and 80s to alleviate soil erosion and low crop productivity. However, the effectiveness of SWC practices on improving soil properties remains less studied. Soil physical analysis (%sand, silt and clay) and chemical analysis (pH, exchangeable potassium (K+), available phosphorous (P), total nitrogen (TN), soil organic carbon (SOC) and cation exchange capacity (CEC)) were analyzed. A total of 36 soil samples from two sub watersheds (SWs) with SWC and without SWC practices (Elmo without, Elmo with, Hobene without and Hobene with) from three landscapes with three landscape positions (upper slope, middle slope, and bottom) were studied. The results showed that soil pH, K+, P, TN, SOC, %clay and CEC were significant (p≤0.05) for SWC practices. The sand and silt fractions were not significant (p< 0.05) for SWC practices. P, SOC, %silt and CEC were significantly different for landscape position. The study indicated the effectiveness of SWC practices in improving the soil properties. There should be a continuous awareness creation for technically efficient implementation and proper maintenance of SWC practices for optimum improvement of soil properties. Key words: Soil erosion, soil and water conservation (SWC) practices, landscape position, sub watershed.

Native desert grassland plant species declines and accelerated erosion in the Paint Gap Hills of southwest Texas

Due to the hotter droughts occurring with climate change, grasslands of southwestern deserts and southern plains in the United States are predicted to increasingly lose cover of native plant species, be invaded by nonnative species, and have accelerated soil erosion. We evaluated these predictions for desert grasslands in the Paint Gap Hills of Big Bend National Park, Texas. We used data from 10 monitoring transects established in 1981 and surveyed vegetation composition, canopy cover, and soil surface elevations in 1981, 1983, 1995, and 2014. Four longer and hotter droughts occurred between 1985 and 2014. We found that by 2014 canopy covers of two dominant native warm-season perennial grasses, Bouteloua curtipendula and Bouteloua ramosa, were reduced to near zero, and the cover of many native shrubs and subshrubs had notably declined. By 2014 two nonnative perennial grasses, Eragrostis lehmanniana and Pennisetum ciliare, had invaded, and their expansion could have long-term ecological consequences. Soil surfaces changed from accumulating sediments at a rate of 0.7 mm/year for 1983–1995 to eroding at −1.6 mm/year for 1995–2014. These soil and vegetation changes support predictions of major declines in native desert grasslands and emphasize their vulnerability to climate change.

Determinants of farmers’ perception to invest in soil and water conservation technologies in the North-Western Highlands of Ethiopia

Soil erosion by water is a severe and continuous ecological problem in the north-western Highlands of Ethiopia. Limited perception of farmers to practice soil and water conservation (SWC) technologies is one of the major causes that have resulted accelerated soil erosion. Therefore, this paper examines the major determinants of farmers’ perception to use and invest in SWC technologies in Ankasha District, north-western highlands of Ethiopia. A detailed field survey was carried out among 338 households, randomly selected from two rural sample kebeles (called villages here after). Descriptive statistics and logistic regression model were used to analyse the effects of multiple variables on farmers’ perception. The results indicate that educational level of the respondents and their access to trainings were found to have a positive and very significant association (P<0.01) with farmers’ perception. Likewise, land ownership, plot size, slope type, and extension contact positively and significantly influenced farmers’ perception at 5% level of significance. On the other hand, the influence of respondents’ age and plot distance from the homestead was found to be negative and significant (P<0.05). The overall results of this study indicate that the perception of farmers to invest in SWC technologies was highly determined by socioeconomic, institutional, attitudinal and biophysical factors. Thus, a better understanding of constrains that influence farmers' perception is very important while designing and implementing SWC technologies. Frequent contacts between farmers and extension agents and continues agricultural trainings are also needed to increase awareness of the impacts of SWC benefits.

Using Credible Soil Loss Tolerance Value for Conservation Planning and Managing Diverse Physiographic Regions in Rajasthan

Accelerated soil erosion degrades soil quality and undermines ecosystem functions and services. It is important to assess the severity of erosion, demarcate tolerable limits for sustainable crop production, conservation planning for soil resources, and identify the alternative land uses. Irrespective of soil type, climate and vegetation cover, the tolerable level of soil erosion in India has traditionally been taken as 11.2 Mg ha−1 year−1. However, this is an excessive rate for most agro-ecosystems and land uses; hence, this study aims to establish credible soil loss tolerance (‘T’ values) for some soils of western India on the basis of critical soil parameters (i.e., bulk density, infiltration rate, total organic carbon and soil reaction). The condition of a soil or ‘soil state’ (S) is defined through a quantitative model involving different soil functions. The ‘T’ values for some soils of western India ranged between 2.5 and 12.5 Mg ha−1 year−1 compared to default ‘T’ value of 11.2 Mg ha−1 year−1. About 50% of the land area has ‘T’ value >10 Mg ha−1 year−1, and the remaining 50% has <7.5 Mg ha−1 year−1, of which 13.02 M ha is having only ‘T’ value of 2.5 Mg ha−1 year−1. Using the revised ‘T’ values for soil mapping units will help in planning of appropriate conservation measures for effective erosion control, sustainable crop production and improved watershed management in the Rajasthan State of western India.