The effects of slope shape and polyacrylamide application on runoff,erosion and nutrient loss from hillslopes under simulated rainfall

Natural hillslopes are mostly composed of complex slope shapes, which significantly affect soil erosion. However, existing studies have mainly focused on uniform slopes to simplify complex hillslopes, and the mechanisms responsible for the influence of slope shape on soil and nutrient losses are still not well understood, especially in the application of soil improvers to reduce soil loss. To investigate the effects of slope shape and polyacrylamide (PAM) application on runoff, soil erosion and nutrient loss, this study conducted artificial field rainfall experiments involving two PAM application rates and nine slope shapes. The results indicate that the average amount of soil loss from convex slopes was 1.5 and 1.3 times greater than that from concave and uniform slopes, respectively, and the average amount of ammonia nitrogen loss and phosphate loss increased by 24.0%–58.6%. Soil and nutrient losses increased as the convexity of the convex slopes increased. For runoff, there was little difference between concave and convex slopes, but the runoff amount for both slopes was greater than that for uniform slopes. After PAM application, the soil loss decreased by more than 90%, and the nutrient loss decreased by 28.2%–68.1%. The application of PAM was most effective in reducing soil erosion and nutrient loss from convex slopes, and it is recommended to appropriately increase the PAM application rate for convex slopes. A strong linear relationship between ammonia nitrogen and phosphate concentrations and sediment concentrations was found in the runoff on slopes with no PAM application. However, this linear relationship weakened for slopes with PAM application. The findings of this study may be valuable for optimizing nonpoint source pollution management in basins.     

Rate of soil erosion processes on vineyards in central Piedmont (NW Italy)

The ‘Tertiary Basin of Piedmont’ is a hilly region, mainly composed of marine sediments, such as marls, silts and sands. The slopes, largely devoted to grape production, are usually kept bare of vegetation and are thus prone to soil erosion processes. For two years we have measured soil loss in relation to rainfall on experimental plots located in vineyards. In all the plots considered erosion started with low rainfall intensities (0·07 mm/min), and above 0·4 mm/min the amount of soil loss dramatically increased (to over 1800 g/m in one event). Most of the erosion occurs during summer rainstorms, but the behaviour of the soil under erosive rainfalls is very different from one site to another, depending only in part upon the various rainfall rates, soil and geometrical characteristics of the plots. It can be seen that soil loss varies from nearly negligible values (20 g/m/yr) to unacceptably high levels (to over 4·7 kg/m/yr), according to the different types of land cultivation. Deep ploughing and heavy herbicide treatment give rise to accelerated erosion processes leading to soil losses much higher than in other vineyard plots in Europe.     

PROCESSES OF HEADCUT GROWTH AND MIGRATION IN RILLS AND GULLIES

lINTRoDUCTIONHeadcuterosionwithinrills,ephemeralguIlies,classicgullies,andstreamscausesseriousenvironmentalproblems.Headcuterosionacceleratesthelossoftopsoilanddecreasestheproductivityofagriculturallands.Erodedsedimentsoftenendupinreceivingstreams,causingwaterqualityproblemsandnegativelyimpactingbioIogicalprocesses.Inadditiontolandscapedegradation,gulliesarethedominantformofdamagetoearthspillways.lfagullycanmovethroughanearthspillwayandbreachthecrestofadam,thentheimpoundedfloodwaterswiI1…     

DEVELOPMENT OF SOIL EROSION INDEX MODEL IN TAIWAN WATERSHEDS

1 INTRODUCTIONSoil erosion of land surface caused by over development has become more and more serious.Environmental damage resulted from accelerated soil erosion has attracted much attention especi ally overthe past 20 years. Soil erosion stUdies have focused primarily on soil characteristics and climaticvariations. Great achievements have been made in understanding the mechanism of soil erosion, whichallows the develoPment of evaluation models for all types of soil erosion problems. Th…     

Topographic thresholds for plant colonization on semi‐arid eroded slopes

Soil erosion plays an important role in plant colonization of semi‐arid degraded areas. In this study, we aimed at deepening our knowledge of the mechanisms that control plant colonization on semi‐arid eroded slopes in east Spain by (i) determining topographic thresholds for plant colonization, (ii) identifying the soil properties limiting plant establishment and (iii) assessing whether colonizing species have specific plant traits to cope with these limitations. Slope angle and aspect were surrogates of erosion rate and water availability, respectively. Since soil erosion and water availability can limit plant establishment and both can interact in the landscape, we analysed variations in colonization success (vegetation cover and species number) with slope angle on 156 slopes, as a function of slope aspect. After determining slope angle thresholds for plant colonization, soil was sampled near the threshold values for soil analysis [nitrogen, phosphorous, calcium carbonate (CaCO₃), water holding capacity]. Plant traits expressing the plant colonizing capacity were analysed both in the pool of species colonizing the steep slopes just below the threshold and in the pool of species inhabiting gentler slopes and absent from the slopes just below the threshold. Results show that the slope angle threshold for plant colonization decreased from north to south. For the vegetation cover, threshold values were 63°, 50°, 46°, 41° for the north, east, west and south slope aspect classes, respectively, and 65°, 53°, 49° and 45° for the species richness and the same aspect classes. No differences existed in soil properties at slope angle threshold values among slope aspects and between slope positions (just below and above the threshold) within slope aspect classes. This suggests that variations between slope aspect classes in the slope angle threshold result from differences in the colonizing capacity of plants which is controlled by water availability. Long‐distance dispersal and mucilage production were preferably associated with the pool of colonizing species. These results are discussed in the perspective of a more efficient ecological restoration of degraded semi‐arid ecosystems where soil erosion acts as an ecological filter for plant establishment. Copyright © 2009 John Wiley & Sons, Ltd.     

Soil erosion and conservation on land cultivated and drained for afforestation

Erosion of soil from pre-afforestation plough furrows has been measured on four soil types in Scotland for 12 to 18 month periods between 1987 and 1990. Rainfall-run-off was also measured at one site. Run-off is directly proportional to furrow length and rainfall intensity, and for a wide range of intensities (typically > 6 mm hr^?1) small amount of soil is flushed out of the furrows. However, for furrow spacings of 3.8 m, a critical downslope run-off increment associated with significant soil loss is of the order of 25 cm³ s^?1 m^?1, which is in accord with a storm of five years return period and a maximum intensity of 25 mm hr^?1. The total run-off volume for any hydrograph is commensurate with the total rainfall in the rainstorm — typically 40–80% by the hydrograph peak and approaching 100% by the end of the hydrograph; i.e. long term storage is negligible. A positive relationship was recorded between furrow length, slope angle and sediment yield, with deposition predominating in furrows less than 30 m in length on slopes less than a few degrees. Soil loss is proportional to the excess streampower expended by the run-off with an exponent in the range 1–1.5. For the soils examined, significant differences in soil loss when comparing sites for low power expenditure become undifferentiated at high power expenditures. For the rainfall regimes monitored, maximum soil losses were in the region of 40 kg per meter run-length of furrow, when soil peds were ripped from the bed. Laboratory data concerning the critical erosion threshold power and shear stress to erode soil peds are in general accord with the threshold furrow run-lengths defined using the field data for a five year storm and the soil losses observed.     

EROSION RATES ON UPLAND AREAS IN THE MIDSOUTH USA

lINTR0DUCTIONSoilerosi0n0fslopingagriculturallandoccursduringandimmediatelyafterrainfalleventswherethesoilsurfaceisn0tadequatelyprotectedfromtheerosiveforces0frainfallandrunoffThebestaltemativefortheconservationplarinerist0minimizesoilerosionasmuchasp0ssible.Managementofsoilsurfaceconditionsinvolvesexperienceandjudgmeniinselectingmanagementpracticesthatutilizecr0presiduesandminimizedisturbancebytillage.Concentfatedrun0ffs0metimescausessevereerosi0n,particularlyonunprotectedsteepslopes.Ril…     

Assessment of the impacts of land-use change and slope position on soil loss by magnetic susceptibility-based models

Soil loss is a global environmental problem resulting from the erosion process caused by many factors,including land use and slope position. Estimation of total soil loss from agricultural fields is useful for understanding the consequences of historical and current erosion. The main purposes of the current study are to explore the application of magnetic measurements in the mapping and measuring soil redistribution in cultivated(MZ13) and forested(MZ17) transects in a Moroccan subcatchment, to ...     

ESTIMATION OF SOIL EROSION IN A RESERVOIR WATERSHED USING ^137CS FALLOUT RADIONUCLIDE

Sedimentation from soil erosion is a critical reservoir watershed management issue. Due to the difficulty of field investigations, empirical formulas are commonly used to estimate the soil erosion rate. However, these estimations are often far from accurate. An effective alternative to estimating soil erosion is to analyze the spatial variation of 137Cs inventory in the soil. 137Cs can be adsorbed by the soil and is widely assumed to change its distribution only when disturbed by rainfall and human activities. Thus, 137Cs distributed in soils can be a useful environmental tracer to estimate soil erosion. In this study, the net soil loss estimate is 108,346 t/yr and the gross erosion and net erosion rates are 10.1 and 9 t/ha yr respectively. The sediment delivery ratio is therefore estimated to be 0.9 based on the two erosion rates. Because of the steep hillsides in the watershed, only 10% of the sediment yield stayed in the deposition sites and 90% was transported to the river as the sediment output. Soil erosion estimates from spatial variations of the 137Cs activity in the Baishi river watershed showed satisfactory accuracy when compared to sediment yield data. Using soil 137Cs concentrations is therefore a feasible method for estimating soil loss or deposition in Taiwan. Data sampling, analysis and result of this approach are given in this paper.     

Effects of rainfall and slope on runoff,soil erosion and rill development: an experimental study using two loess soils

Runoff generation and soil loss from slopes have been studied for decades, but the relationships among runoff, soil loss and rill development are still not well understood. In this paper, rainfall simulation experiments were conducted in two neighbouring plots (scale: 1 m by 5 m) with four varying slopes (17.6%, 26.8%, 36.4% and 46.6%) and two rainfall intensities (90 and 120 mm h^?1) using two loess soils. Data on rill development were extracted from the digital elevation models by means of photogrammetry. The effects of rainfall intensity and slope gradient on runoff, soil loss and rill development were different for the two soils. The runoff and soil loss from the Anthrosol surface were generally higher than those from the Calcaric Cambisol surface. Higher rainfall intensity produced less runoff and more sediment for almost each treatment. With increasing slope gradient, the values of cumulative runoff and soil loss peaked, except for the treatments with 90 mm h^?1 rainfall on the slopes with Anthrosol. With rainfall duration, runoff discharge decreased for Anthrosol and increased for Calcaric Cambisol for almost all the treatments. For both soils, sediment concentration was very high at the onset of rainfall and decreased quickly. Almost all the sediment concentrations increased on the 17.6% and 26.8% slopes and peaked on the 36.4% and 46.6% slopes. Sediment concentrations were higher on the Anthrosol slopes than on the Calcaric Cambisol slopes. At 90 mm h^?1 rainfall intensity, increasingly denser rills appeared on the Anthrosol slope as the slope gradient increased, while only steep slopes (36.4% and 46.6%) developed rills for the Calcaric Cambisol soil. The contributions of rill erosion ranged from 36% to 62% of the cumulative soil losses for Anthrosol, while the maximum contribution of rill erosion to the cumulative soil loss was only 37.9% for Calcaric Cambisol. Copyright © 2014 John Wiley & Sons, Ltd.     

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

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

An evaluation of the universal soil loss equation and field techniques for assessing soil erosion on a tropical alfisol in western Nigeria

Four techniques for soil erosion assessment were compared over two consecutive seasons for bare-fallow plots and a maize-cowpea sequence in 1985 at IITA, Ibadan, Nigeria. The techniques used were: tracer (aluminium paint), nails (16 and 25), the rill method, and the Universal Soil Loss Equation (USLE). Soil loss estimated by these techniques was compared with that determined using the runoff plot technique. There was significantly more soil loss (P < 0·01) in bare-fallow than in plots under maize (Zea mays) or cowpea (Vigna unguiculata). In the first season, soil loss from plots sown to maize was 40·2 Mg ha^?1 compared with 153·3 Mg ha^?1 from bare-fallow plots. In the second season, bare-fallow plots lost 87·5 Mg ha^?1 against 39·4 Mg ha^?1 lost from plots growing cowpea. The techniques used for assessing erosion had no influence on the magnitude of soil erosion and did not interfere with the processes of erosion. There was no significant difference (P < 0·05) between soil erosion determined by the nails and the runoff plot technique. Soil loss determined on six plots (three under maize, three bare-fallow) by the rill technique, at the end of the season, was significantly lower (P < 0·05) than that determined by the runoff plot technique. The soil loss estimated by the rill method was 143·2, 108·8 and 121·9 Mg ha^?1 for 11, 11, and 8 per cent slopes respectively, in comparison with 201·5, 162·0, and 166·4 Mg ha^?1 measured by the runoff plot method. Soil loss measured on three bare-fallow plots on 10 different dates by the rill technique was also significantly lower (P < 0·01) than that measured by the runoff plot. In the first season the USLE significantly underestimated soil loss. On 11, 11, and 8 per cent slopes, respectively, soil loss determined by the USLE was 77, 92, and 63 per cent of that measured by the runoff plot. However, in the second season there was no significant difference between soil loss determined by the USLE and that determined by the conventional runoff plot technique.     

Effects of rainfall intensity and slope gradient on the application of vetiver grass mulch in soil and water conservation

The objective of this study is to investigate the effect of rainfall intensity and slope gradient on the performance ofvetiver grass mulch (VGM) in soil and water conservation.The study involved field ...     

Erosion of strip-mine dumps in la salle county,illinois: Preliminary results

Direct measurement of slope retreat on three unvegetated slope profiles on unmodified, pre-1939, strip-mine dumps revealed average ground losses ranging from 29 to 33 mm/year. Measured ground losses are twice those estimated from the Universal Soil Loss Equation. Slope length seems less significant than frost action in influencing erosion on these slopes.     

Long-term erosion on granitic roadcuts based on exposed tree roots

Exposed roots were used to estimate soil and bedrock erosion on the cut slopes of a 45-year-old road constructed in granitic soils of the Idaho Batholith. The original roadcut surface was defined by projecting a straight line from the toe of the cut past the end of the exposed root to the intersection of a straight line projected along the surface of the hillslope. A cross-sectioning technique was then used to determine erosion to the present roadcut surface. A total of 41 exposed root sites were used to estimate erosion on a 1350 m-long section of road. Average erosion was 1·0 and 1·1 cm/year for soil and bedrock respectively. Buttressing by tree roots caused lower erosion rates for soil as compared to bedrock. Both soil and bedrock erosion rates showed statistically significant correlations with the gradients of the original cut slope. The bedrock erosion data provide a reasonable estimate of the disintegration rate of exposed granitic bedrock exhibiting the weathering and fracturing properties common to this area. The road is located in a study watershed where long-term sediment yield data are available. Sediment data from adjacent study watersheds with no roads were compared to sediment data from the roaded watershed to estimate the long-term increase in sediment yield caused by the road. The increase amounts to about 2·4 m³/year. This figure, compared to the average annual on-site road erosion, provides an erosion to sediment delivery ratio of less than 10 per cent. Based on study results, road construction and maintenance practices are suggested for helping reduce roadcut erosion.     

EFFECTS OF SOIL CRUSTING ON SOIL MOISTURE, RUNOFF AND EROSION: FIELD OBSERVATIONS

1 INTRODUCTION Soil crusting, or soil sealing, is one of the common phenomena in agricultural lands or semi-arid and arid soils. Due to the breakdown of soil aggregates by raindrops, soil surface develops a very thin, often less than a few millimeters, dense layer. Many studies indicated that such a thin layer significantly reduces infiltration capacity and increases surface runoff (i.e. McIntyre, 1958; Edward and Larson, 1969; Agassi et al., 1985; Bradford et al., 1986; Romkens et al.,…     

Estimation of soil losses within plots as affected by different agricultural land management

Abstract

Proper agricultural land management strategies improve soil structural properties, thereby reducing soil loss by water erosion. This study was conducted to estimate soil losses from plots of different agricultural land management using the Water Erosion Prediction Project (WEPP) (95.7) model. The study took place in a semiarid region in Kenya. The mean annual rainfall was 694 mm. The WEPP (95.7) model was initially used to estimate total sediment loading from the catchment into a reservoir. The estimate was about 2871 t corresponding to an average sedimentation rate of 1063 t km^?2 year^?1, which was about 76% of the measured total sediment inflow into the reservoir. Soil losses were estimated within 10 plots on the catchment of different sizes and slopes with the following treatments: conventional tillage (hand hoeing) with maize and soybean intercropping (HOCOBE); conservation tillage (disc plough) with maize and soybean intercropping (COBEAN); conservation tillage with only maize cultivation (CNTCORN); and conservation tillage with only soybean cultivation (CNTBEAN). The soil loss reduction of COBEAN, CNTCORN and CNTBEAN relative to HOCOBE ranged between 27–47%, 16–29% and 12–25%, respectively, depending on the size and slope of the plot. In general, conservation tillage reduced soil loss relative to conventional tillage. However, with conservation tillage, the single cropping system resulted in greater soil loss than the intercropping system. In the case of single cropping with conservation tillage, the soil loss reduction for maize ranged between 4 and 9%, relative to soybean. Overall, the study showed that there would be a significant reduction of soil losses from plots if conservation tillage with an intercropping system (maize and soybean) were to be adopted on agricultural lands in semiarid regions.     

THE EQUIVALENT SLOPE - A NEW METHOD FOR CALCULATING SOIL LOSS FROM IRREGULAR SLOPES

he slopes in field conditions are always irregular, but the supposed uniform slopes are used in most erosion models. Some studies used several uniform slopes to approximate an irregular slope for estimating soil erosion. This approximation is both time-consuming and weak in physical insights. In this paper, the concept of equivalent slope is presented based on that runoff potential on uniform slope is equal to that of irregular slope, and the equivalent uniform slope is used to estimate soil erosion instead of the irregular slopes. The estimated results of slope-length factors for convex and concave slopes are consistent with those from the method of Foster and Wischmeier, The experiments in the southern part of the Loess Plateau in China confirmed the applicability of the present method. The method is simple and has, to some extent, clear physical meanings, and is applicable for estimating soil erosion from irregular slopes.     

Factors affecting rill erosion of unpaved loess roads in China

This study explores factors that affect road surface erosion in a small watershed on the Loess Plateau. Global positioning system (GPS)‐assisted field surveys and geographical information system methods were applied. The results show that road surface rills in the watershed are more easily formed on main roads, which are disturbed by intensive human activities. Secondary unpaved road networks occupied the largest road surface area and contributed 49% of the total road surface rill volumes. Spatial analysis reveals that roads near residential areas or leading to other human‐disturbed land‐use types are at high risk of soil loss. In each road segment, slope gradient, road segment length and drainage area have impacts on surface rill formation and development. Among these factors, slope gradients have been verified as a controlling factor of rill erosion intensification. Both road segment length (R = 0.83, N = 82) and drainage area (R = 0.72 for road segment and 0.76 for upslope drainage areas, N = 82) significantly influence total road surface rill volumes. The interaction variable of road segment length multiplied by slope is more closely correlated with road segment soil loss than that of the independent variables alone. Linear equations composed of slope gradient, road segment length and upslope drainage area are proposed. The new equation performs much better at predicting surface soil loss from secondary road segments compared with the previous models, which have not considered upslope drainage areas. The relationships and equations from this study will be helpful for road erosion evaluation in a small watershed of the study area. Copyright © 2014 John Wiley & Sons, Ltd.     

Runoff and sediment loss responses to rainfall and land use in two agricultural catchments on the Loess Plateau of China

Soil erosion is a severe problem hindering sustainable agriculture on the Loess Plateau of China. Plot experiments were conducted under the natural rainfall condition during 1995–1997 at Wangdongguo and Aobao catchments in this region to evaluate the effects of various land use, cropping systems, land slopes and rainfall on runoff and sediment losses, as well as the differences in catchment responses. The experiments included various surface conditions ranging from bare soil to vegetated surfaces (maize, wheat residue, Robinia pseudoacacia L., Amorpha fruticosa L., Stipa capillata L., buckwheat and Astragarus adsurgens L.). The measurements were carried out on hill slopes with different gradients (i.e. 0 ° to 36 °). These plots varied from 20 to 60 m in length. Results indicated that runoff and erosion in this region occurred mainly during summer storms. Summer runoff and sediment losses under cropping and other vegetation were significantly less than those from ploughed bare soil (i.e. without crop/plant or crop residue). There were fewer runoff and sediment losses with increasing canopy cover. Land slope had a major effect on runoff and sediment losses and this effect was markedly larger in the tillage plots than that in the natural grass and forest plots, although this effect was very small when the maximum rainfall intensity was larger than 58·8 mm/h or smaller than 2·4 mm/h. Sediment losses per unit area rose with increasing slope length for the same land slope and same land use. The effect of slope length on sediment losses was stronger on a bare soil plot than on a crop/plant plot. The runoff volume and sediment losses were both closely related to rainfall volume and maximum intensity, while runoff coefficient was mainly controlled by maximum rainfall intensity. Hortonian overland flow is the dominant runoff process in the region. The differences in runoff volume, runoff coefficient and sediment losses between the catchments are mainly controlled by the maximum rainfall intensity and infiltration characteristics. The Aobao catchment yielded much larger runoff volume, runoff coefficient and sediment than the Wangdongguo catchment. Copyright © 2001 John Wiley & Sons, Ltd.