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1.
The loss of P in overland flow from most cultivated soils is controlled by erosion, and in‐turn soil moisture. We evaluated the effect of soil moisture on erosion and P transport in overland flow by applying rainfall (7 cm h?1) to packed soil boxes (1 m long and 0·15 m wide) and field plots (1 and 10 m long by 1 m wide) of silt loams in a central Pennsylvania (USA) catchment. Flow from packed soil boxes took longer to initiate as antecedent soil moisture decreased from field capacity (2 min) to air dried (8 to 9 min). Even in the more complex field plots (i.e. soil heterogeneity and topography), the wetter site (1 by 10 m plot; 70% field capacity) produced flow more quickly (3 min) and in greater volume (439 L) than the drier site (1 by 10 m plot; 40% field capacity, 15 min, and 214 L, respectively). However, less suspended sediment was transported from wetter soil boxes (1·6 to 2·5 g L?1) and field plots (0·9 g L?1) than drier boxes (2·9 to 4·2 g L?1) and plots (1·2 g L?1). Differences are attributed to their potential for soil aggregate breakdown, slaking and dispersion, which contribute to surface soil sealing and crusting, as dry soils are subject to rapid wetting (by rainfall). During flow, selective erosion and antecedent moisture conditions affected P transport. At field capacity, DRP and PP transport varied little during overland flow. Whereas P transport from previously dry soil decreased rapidly after the initiation of flow (6 to 1·5 mg TP L?1), owing to the greater slaking and dispersion of P‐rich particles into flow at the beginning than end of the flow event. These results indicate that soil moisture fluctuations greatly effect erosion and P transport potential and that management to decrease the potential for loss should consider practices such as conservation tillage and cover crops, particularly on areas where high soil P and erosion coincide. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

2.
Ten representative research sites were selected in eastern Spain to assess soil erosion rates and processes in new citrus orchards on sloping soils. The experimental plots were located at representatives sites on limestone, in areas with 498 to 715 mm year?1 mean annual rainfall, north‐facing slopes, herbicide treated, and new (less than 3 years old) plantations. Ten rainfall simulation experiments (1 h at 55 mm h?1 on 0·25 m2 plots) were carried out at each of the 10 selected study sites to determine the interill soil erosion and runoff rates. The 100 rainfall simulation tests (10 × 10 m) showed that ponding and runoff occurred in all the plots, and quickly: 121 and 195 s, respectively, following rainfall initiation. Runoff discharge was one third of the rainfall, and sediment concentration reached 10·4 g L?1. The soil erosion rates were 2·4 Mg ha?1 h?1 under 5‐year return period rainfall thunderstorms. These are among the highest soil erosion rates measured in the western Mediterranean basin, similar to badland, mine spoil and road embankment land surfaces. The positive relationship between runoff discharge and sediment concentration (r2 = 0·83) shows that the sediment availability is very high. Soil erosion rates on new citrus orchards growing on sloped soils are neither tolerable nor sustainable. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

3.
Improved knowledge of the effects of grass and shrub cover in overland flow can provide valuable information for soil and water conservation programs.Laboratory simulated rainfall studies were conducted to determine effects of grass and shrub on runoff and soil loss and to ascertain the relationship between the rate of soil loss and the unit stream power of runoff for a 20°slope subjected to rainfall intensities of 45,87,and 127 mm/h.The results indicated that the average runoff rates ranged from 4.2 to 73.1 mm/h for grass plots and from 9.3 to 58.2 mm/h for shrub plots.Runoff rates from shrub plots were less than those from grass plots for all but the 45 mm/h rainfall intensity regime. Average soil loss rates varied from 5.7 to 120.3 g/min.m~2 for grass plots and from 5.6 to 84.4 g/min.m~2 for shrub plots.Soil loss rates from shrub plots were generally lower than those from grass plots.Runoff and soil loss were strongly influenced by soil surface conditions due to the formation of erosion pits and rills.The rate of soil loss increased linearly with the unit stream power of runoff on both grass and shrub plots.Critical unit stream power values were 0.0127 m/s for grass plots and 0.0169 m/s for shrub plots.Shrub plots showed a greater stability to resist soil detachment and transport by surface flow than grass plots.  相似文献   

4.
Wei Wei  Liding Chen  Bojie Fu  Yihe Lü  Jie Gong 《水文研究》2009,23(12):1780-1791
Rainfall extremes (RE) become more variable and stochastic in the context of climate change, increasing uncertainties and risks of water erosion in the real world. Vegetation also plays a key role in soil erosion dynamics. Responses of water erosion to RE and vegetation, however, remain unclear. In this article, on the basis of the data measured on 15 plots (area: 10 m × 10 m and 10 m × 5 m) and the definition of World Meteorological Organization (WMO) on rainfall extremes, 158 natural rainfall events from 1986 to 2005 were analysed, and rain depth and maximal 30‐min intensity (MI30) were used to define RE. Then, water erosion process under RE and five vegetation types (spring wheat, alfalfa, sea buckthorn, Chinese pine, and wheatgrass) were studied in a key loess semiarid hilly area, NW China. The following findings were made: (1) The minimal thresholds of depth and MI30 for defining RE were determined as 40·11 mm and 0·55 mm/min, respectively. Among the studied rainfall events, there were four events with both the variables exceeding the thresholds (REI), five events with depths exceeding 40·11 mm (REII), and four events with MI30 exceeding 0·55 mm/min (REIII). Therefore, not only extreme rainstorm, but also events with lower intensities and long durations were considered as RE. Moreover, RE occurred mostly in July and August, with a probability of 46 and 31%, respectively. (2) Extreme events, especially REI, in general caused severer soil‐water loss. Mean extreme runoff and erosion rates were 2·68 and 53·15 times of mean ordinary rates, respectively. The effect of each event on water erosion, however, becomes uncertain as a result of the variations of RE and vegetation. (3) The buffering capacities of vegetation on RE were generally in the order of sea buckthorn > wheatgrass > Chinese pine > alfalfa > spring wheat. In particular, sea buckthorn reduced runoff and erosion effectively after 3–4 years of plantation. Therefore, to fight against water erosion shrubs like sea buckthorn are strongly recommended as pioneer species in such areas. On the contrary, steep cultivation (spring wheat on slopes), however, should be avoided, because of its high sensitivities to RE. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

5.
After the Valley Complex Fire burned 86 000 ha in western Montana in 2000, two studies were conducted to determine the effectiveness of contour‐felled log, straw wattle, and hand‐dug contour trench erosion barriers in mitigating postfire runoff and erosion. Sixteen plots were located across a steep, severely burned slope, with a single barrier installed in 12 plots (four per treatment) and four plots left untreated as controls. In a rainfall‐plus‐inflow simulation, 26 mm h?1 rainfall was applied to each plot for 1 h and 48 L min?1 of overland flow was added for the last 15 min. Total runoff from the contour‐felled log (0·58 mm) and straw wattle (0·40 mm) plots was significantly less than from the control plots (2·0 mm), but the contour trench plots (1·3 mm) showed no difference. The total sediment yield from the straw wattle plots (0·21 Mg ha?1) was significantly less than the control plots (2·2 Mg ha?1); the sediment yields in the contour‐felled log plots (0·58 Mg ha?1) and the contour trench plots (2·5 Mg ha?1) were not significantly different. After the simulations, sediment fences were installed to trap sediment eroded by natural rainfall. During the subsequent 3 years, sediment yields from individual events increased significantly with increasing 10 min maximum intensity and rainfall amounts. High‐intensity rainfall occurred early in the study and the erosion barriers were filled with sediment. There were no significant differences in event or annual sediment yields among treated and control plots. In 2001, the overall mean annual sediment yield was 21 Mg ha?1; this value declined significantly to 0·6 Mg ha?1 in 2002 and 0·2 Mg ha?1 in 2003. The erosion barrier sediment storage used was less than the total available storage capacity; runoff and sediment were observed going over the top and around the ends of the barriers even when the barriers were less than half filled. Published in 2007 by John Wiley & Sons, Ltd.  相似文献   

6.
An understanding of the sources of variation in the use of erosion plots and of their feasibility to meet the objectives of each specific research project is key to improving future field designs, selecting data for modelling purposes and furthering knowledge of soil erosion processes. Our own field experiences from ongoing research on soil erosion processes since 1989, have allowed us to detect several methodological problems that cause measurement variability. Here several examples are presented concerning: (i) differences in long‐term soil erosion data between open and closed plots; (ii) differences in soil loss derived from replica soil erosion plots; and (iii) differences in soil loss data derived from plots at a range of spatial scales. Closed plots are not the most suitable method for long‐term monitoring of soil erosion rates due to the risk of exhaustion of available material within the plot. The difference in time after which exhaustion occurs depends on the surface soil characteristics, the climatological conditions and the size of the plots. We detected four and seven years as ‘time to exhaustion’. Different results are frequently obtained between pairs of replica plots. Differences up to a factor of nine have been detected in total soil loss between replica plots due to different spatial patterns of surface components. Different constraints appear depending on the spatial scale of measurement of soil loss. We obtained lower runoff percentages at coarser scales; however, larger sediment concentrations are observed at coarser scales (1·32 g l?1, catchment; 0·30 g l?1, 30 m2; 0·17 g l?1, 1 m2 scales). The smaller the plot, the larger the hydrological disconnection within the system, the lower the energy flows due to short distances and the quicker the response to runoff due to an artificial decrease of concentration times for continuous flow. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

7.
Obtaining good quality soil loss data from plots requires knowledge of the factors that affect natural and measurement data variability and of the erosion processes that occur on plots of different sizes. Data variability was investigated in southern Italy by collecting runoff and soil loss from four universal soil‐loss equation (USLE) plots of 176 m2, 20 ‘large’ microplots (0·16 m2) and 40 ‘small’ microplots (0·04 m2). For the four most erosive events (event erosivity index, Re ≥ 139 MJ mm ha?1 h?1), mean soil loss from the USLE plots was significantly correlated with Re. Variability of soil loss measurements from microplots was five to ten times greater than that of runoff measurements. Doubling the linear size of the microplots reduced mean runoff and soil loss measurements by a factor of 2·6–2·8 and increased data variability. Using sieved soil instead of natural soil increased runoff and soil loss by a factor of 1·3–1·5. Interrill erosion was a minor part (0·1–7·1%) of rill plus interrill erosion. The developed analysis showed that the USLE scheme was usable to predict mean soil loss at plot scale in Mediterranean areas. A microplot of 0·04 m2 could be used in practice to obtain field measurements of interrill soil erodibility in areas having steep slopes. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

8.
Cryptogams are communities of non-vascular plants that live on the soil surface. Numerous functions have been attributed to these crusts, including changes in soil fertility and nutrient status, soil hydrology and soil erosion. Most significant for this paper is the reported benefit of cryptogams in reducing soil erosion by water in semi-arid areas. However, to date there have been few attempts to understand the soil conservation value of cryptogams in subsistence agricultural systems or in humid mountain environments. This paper investigates the potential of cryptogams in soil erosion by water on agricultural hillslope terraces (bariland) in the Nepal Middle Hills of the southern monsoonal Himalaya. The research is significant because the loss of fertile topsoil is considered by some to be the biggest threat to the livelihoods of subsistence farmers in the area in the medium and long term. The current study was conducted in the field between two of the weeding events that take place under maize cover, grown in the traditional manner. Three groundcover types which represented (i) maize only (types A), (ii) maize and weed cover (types B), and (iii) maize and cryptogam cover (types C) were monitored utilizing multiple microerosion plots. Measurements of runoff and soil loss data were collected sequentially on a storm-by-storm basis throughout the monitored period from 24 July 1997 to 29 August 1997. Measurements of infiltration rates were also taken on each of the groundcover types at selected times. Results collected from the erosion plots demonstrate that runoff and soil losses over distances of <2 m can be significantly reduced by up to 50 per cent with cryptogam cover, compared to maize-only canopies. Mean runoff for all storm events sampled from plot types A, B and C were 3·4 l m−2, 1·6 l m−2 and 1·5 l m−2 respectively. For soil loss, the results were 21·7 g m−2, 11·3 g m−2 and 10·2 g m−2 respectively. Therefore, cryptogams would appear to offer a similar degree of protection to the soil surface from runoff and raindrop erosion, to that afforded by weed cover. Weed and cryptogam covers protect the soil surface from rainfall kinetic energies and work to preserve surface microtopographies, depressional storage and surface water detention. Terminal infiltration rates taken at the end of the monitored period showed that well developed maize- and cryptogam-covered soil surfaces (types C) have a mean terminal infiltration rate of 35·0 mm h−1 compared to 44·5 mm h−1 for comparable maize- and weed-covered soil surfaces (types B), and 15·5 mm h−1 for maize-only soil surfaces (types A). These results show that cryptogams and weeds also have relatively higher infiltration rates than comparable maize-only covered plots, devoid of groundcover. The findings in this study may have implications for traditional weed management practices used by local hill farmers, which often destroy cryptogam soil coatings two to three times during the maize growing period. However, further work needs to be done to ascertain farmers' understandings of cryptogams. It is hoped that conservationists will benefit from incorporating cryptogams into the design of future soil erosion studies relating to development programmes. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

9.
Despite the high risk of erosion in olive orchards located in mountainous areas in Spain, little research has been carried out to account for the complexity and interaction of the natural processes of runoff and soil erosion on the catchment scale or small catchment scale. In this study, a microcatchment of 6·7 ha in a mountainous area under no‐tillage farming with bare soil was set up to record runoff and sediment. Soil erosion and runoff patterns were monitored over a two‐year period. Totally, 22 events were observed. The data were analysed, and then used to calibrate the AnnAGNPS model, which allowed us to complete the data period and describe the hydrological and erosive behaviour on a monthly and annual basis. A high variability in catchment responses was observed, due to differences in the storms and to the effect of the surface soil moisture content. Maximum intensities of 10 and 30 min determined the final runoff values while the total sediment loads were dependent on the rainfall depth. The impact of management on the reduction of porosity can explain the relationship between runoff and intensity in the microcatchment. However, the impact of the spatial scale meant that the transport of sediment required substantial rainfall depths to ensure a continuous flow from the hillslopes. The results of the calibration (E >0·60 and r >0·75) on the event and monthly scale confirmed the applicability of AnnAGNPS to predict runoff and erosion in the microcatchment. The predicted average runoff coefficient was 3·3% for the study period and the total average sediment loads, 1·3 Mg/ha/yr. Despite these low values, the model simulation showed that much larger runoff coefficients and soil losses can be expected for periods with several consecutive years in which the annual rainfall depth was over 500 mm. The use of cover is recommended to prevent the high levels of erosion associated with these conditions. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

10.
A database composed of 673 natural rainfall events with sediment concentration measurements at the field or plot scale was analysed. Measurements were conducted on similar soil type (loess soils prone to sealing phenomenon) to apprehend the variability and complexity involved in interrill erosion processes attributable to soil surface conditions. The effects of the dominant controlling factors are not described by means of equations; rather, we established a classification of potential sediment concentration domain according to combination of the dominant parameters. Thereby, significant differences and evolution trends of mean sediment concentration between the different parameter categories are identified. Further, when parameter influences interact, it allows us to discern the relative effects of factors according to their respective degree of expression. It was shown that crop cover had a major influence on mean sediment concentration, particularly when soil surface roughness is low and when maximum 6‐min intensity of rainfall events exceeds 10 mm h?1: mean sediment concentration decreases from 8·93 g l?1 for 0–20 per cent of coverage to 0·97 g l?1 for 21–60 per cent of coverage. The established classification also indicates that the increase of the maximum 6‐min intensity of the rainfall factor leads to a linear increase of mean sediment concentration for crop cover over 21 per cent (e.g. from 2·96 g l?1 to 14·44 g l?1 for the 1–5 cm roughness class) and to an exponential increase for low crop cover (e.g. from 3·92 g l?1 to 58·76 g l?1 for the 1–5 cm roughness class). The implication of this work may bring perspective for erosion prediction modelling and give references for the development of interrill erosion equation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

11.
Field‐ and laboratory‐scale rainfall simulation experiments were carried out in an investigation of the temporal variability of erosion processes on interrill areas, and the effects of such variation upon sediment size characteristics. Poorly aggregated sandy soils from the semi‐arid environment of Senegal, West Africa, were used on both a 40 m2 field plot and a 0·25 m2 laboratory plot; rainfall intensity for all experiments was 70 mm h?1 with a duration of 1 to 2 hours. Time‐series measurements were made of the quantity and the size distribution of eroded material: these permitted an estimate of the changing temporal balance between the main erosion processes (splash and wash). Results from both spatial scales showed a similar temporal pattern of runoff generation and sediment concentration. For both spatial scales, the dominant erosional process was detachment by raindrops; this resulted in a dynamic evolution of the soil surface under raindrop impact, with the rapid formation of a sieving crust followed by an erosion crust. However, a clear difference was observed between the two scales regarding the size of particles detached by both splash and wash. While all measured values were lower than the mean weight diameter (MWD) value of the original soil (mean 0·32 mm), demonstrating the size‐selective nature of wash and splash processes, the MWD values of washed and splashed particles at the field scale ranged from 0·08 to 0·16 mm and from 0·12 to 0·30 mm respectively, whereas the MWD values of washed and splashed particles at the laboratory scale ranged from 0·13 to 0·29 mm and from 0·21 to 0·32 mm respectively. Thus only at the field scale were the soil particles detached by splash notably coarser than those transported by wash. This suggests a transport‐limited erosion process at the field scale. Differences were also observed between the dynamics of the soil loss by wash at the two scales, since results showed wider scatter in the field compared to the laboratory experiments. This scatter is probably related to the change in soil surface characteristics due to the size‐selectivity of the erosion processes at this spatial scale. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

12.
Studies of soil erosion on small plots present upscaling problems. The results in the literature on the effect of slope length (i.e. scale) on runoff and soil erosion are contradictory. Furthermore, most studies that examine scale effects measured through erosion plots have been conducted in Mediterranean environments. The objective of this study was to assess the effects of plot size on runoff and soil loss in a subtropical environment. Other measurements were taken to appraise the topsoil property changes inside the plots. The soil was ploughed twice, the surface was leveled with a hoe and it was kept bare during the experiment. Data were collected from 10 paired plots, five plots measuring 10 m × 1 m and five plots measuring 1 m × 1 m, installed in the same pedo‐geomorphologic unit. Measurements were carried out from November 2008 to November 2009. During this period, 97 natural storms were registered. The results indicate that the small plots tended to have higher runoff (30% higher) compared to larger plots, especially during periods of greater rainfall volume, duration and intensity. The soil loss was similar in both the 1 m2 plots (6·33 kg/m2) and the 10 m2 plots (6·26 kg/m2). Moreover, the dynamics of the soil loss during the experiment was relatively similar across both plot sizes. The large plots tended to have a greater internal complexity. In these plots, the steps retreat were higher, the overland flow scars were more frequent, and points of rill initiation and protochannels emerged in several parts of the plots. The results of the small plots were comparable to the results obtained on the large plots, especially in relation to soil loss. These plots were useful for short‐term assessments of soil erosion. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

13.
Although the impact of sheet erosion on the selective transportation of mineral soil particles has been widely investigated, little is yet known about the specific mechanisms of organic carbon (OC) erosion, which constitutes an important link in the global carbon cycle. The present study was conducted to quantify the impact of sheet erosion on OC losses from soils. Erosion plots with the lengths of 1‐ and 5‐m were installed at different topographic positions along a hillslope in a mountainous South African region. A total of 32 rainfall events from a three years period (November 2010 up to February 2013), were studied and evaluated for runoff (R), particulate and dissolved organic carbon (POCL and DOCL). In comparison to the 0–0·05 m bulk soil, the sediments from the 1‐m plots were enriched in OC by a factor 2·6 and those from the 5‐m long plots by a factor of 2·2, respectively. These findings suggest a preferential erosion of OC. In addition, total organic carbon losses (TOCL) were incurred mainly in particulate form (~94%) and the increase in TOCL from 14·09 ± 0·68 g C m?1 yr?1 on 1‐m plots to 50·03 ± 2·89 g C m?1 yr?1 on 5‐m plots illustrated an increase in sheet erosion efficiency with increasing slope length. Both TOCL and sediment enrichment in OC correspondingly increased with a decrease in soil basal grass cover. The characteristics of rainstorms had no significant impact on the selectivity of OC erosion. The results accrued in this study investigating the links between sheet erosion and OC losses, are expected to be of future value in the generation of carbon specific erosion models, which can further help to inform and improve climate change mitigation measures. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

14.
Flume experiments simulating concentrated runoff were carried out on remolded silt loam soil samples (0·36 × 0·09 × 0·09 m3) to measure the effect of rainfall‐induced soil consolidation and soil surface sealing on soil erosion by concentrated flow for loess‐derived soils and to establish a relationship between soil erodibility and soil bulk density. Soil consolidation and sealing were simulated by successive simulated rainfall events (0–600 mm of cumulative rainfall) alternated by periods of drying. Soil detachment measurements were repeated for four different soil moisture contents (0·04, 0·14, 0·20 and 0·31 g g?1). Whereas no effect of soil consolidation and sealing is observed for critical flow shear stress (τcr), soil erodibility (Kc) decreases exponentially with increasing cumulative rainfall depth. The erosion‐reducing effect of soil consolidation and sealing decreases with a decreasing soil moisture content prior to erosion due to slaking effects occurring during rapid wetting of the dry topsoil. After about 100 mm of rainfall, Kc attains its minimum value for all moisture conditions, corresponding to a reduction of about 70% compared with the initial Kc value for the moist soil samples and only a 10% reduction for the driest soil samples. The relationship estimating relative Kc values from soil moisture content and cumulative rainfall depth predicts Kc values measured on a gradually consolidating cropland field in the Belgian Loess Belt reasonably well (MEF = 0·54). Kc is also shown to decrease linearly with increasing soil bulk density for all moisture treatments, suggesting that the compaction of thalwegs where concentrated flow erosion often occurs might be an alternative soil erosion control measure in addition to grassed waterways and double drilling. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

15.
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.  相似文献   

16.
On the basis of detailed rill surveys carried out on bare plots of different lengths at slopes of 12 per cent, basic rill parameters were derived. Rill width and maximum depth increased with plot length, whereas rill amount and cross‐sectional area, expressed per unit length, remained similar. On smaller plots, all rills were connected in a continuous transport system reaching the plot outlet, whilst on larger plots (10 and 20 m long) part of the rills ended with a deposition areas inside the plots. Amounts of erosion, calculated from rill volume and soil bulk density, were compared with soil loss measured at the plot outlets. On plots 10 and 20 m long, erosion estimated from volume of all rills was larger than measured soil loss. The latter was larger than erosion estimated from volume of contributing rills. To identify contributing soil loss area on these plots, two methods were applied: (i) ratio of total soil loss to maximum soil loss per unit area, and (ii) partition of plot area according to the ratio of contributing to total rill volume. Both methods resulted in similar areas of 21·8–23·5 m2 for the plot 10 m long and 31·2 m2 for the plot 20 m long. Identification of contributing areas enabled rill (5·9 kg m?2) and interrill (2·6 kg m?2) erosion rate to be calculated, the latter being very close to the value predicted from the Universal Soil Loss Equation. Although rill and interrill rates seemed to be similar on all plots, their ratio increased slightly with plot length. Application of this ratio to compute slope length factor of the Revised Universal Soil Loss Equation resulted in similar values to those predicted with the model. The achieved balance of soil loss suggested that all the sediment measured at the plot outlet originated from contributing rills and associated contributing rill areas. The results confirmed the utility of different plot lengths as a research tool for analysing the dynamic response of soil to rainfall–runoff. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

17.
R. M. Bajracharya  R. Lal 《水文研究》1998,12(12):1927-1938
Sealing and crusting of soil surfaces have dramatic effects on water infiltration into and runoff from soils, thereby greatly influencing erosion processes. This study focused on the effect of the initial stage of crusting on inter-rill erosion processes for a crust-prone Alfisol sampled from south-central India. Soil aggregates ranging from 2·4 to 8 mm collected from ploughed (PL) and naturally vegetated (NV) treatments were subjected to rainfall simulation under laboratory conditions. Runoff from PL soil aggregates was 2–2·5 times higher, while percolation was 20–100% lower, than for NV aggregates. Soil wash and splash losses were 0·5–3 times greater for PL than for NV soil. Runoff and inter-rill erosion were significantly higher during the wet simulation run compared with the dry run. The results indicated that NV soil aggregates were more resistant to breakdown from raindrop impact and slaking, and subject to less rapid sealing, than PL soil. Total soil loss was influenced most by initial aggregate stability and the extent of seal development. Splash and wash losses of soil both increased as a result of surface sealing regardless of soil condition for short (30–60 min) rainfall durations. High drying rates resulted in the highest crust bulk densities. Increased crust strength for PL soil compared with NV soil reflected the greater susceptibility of cultivated soil to surface sealing and crusting. © 1998 John Wiley & Sons, Ltd.  相似文献   

18.
The decay of roughness is an important factor governing surface processes such as infiltration and soil erosion. Thus the decay of surface roughness under different surface conditions was investigated and related to quantitative amounts of soil loss, runoff and sediment concentration in a laboratory experiment. Rainfall with an intensity of 128 mm/h was applied to a bare or mulched surfaces of a sandy loam soil with known surface roughness at specified time intervals. The decay of roughness as expressed by roughness ratio, in this experiment, was better predicted when related to an exponential function of the square root of cumulative kinetic energy of rainfall rather than with the cumulative rainfall. The roughness decay equations in literature did not predict breakdown under mulched surfaces accurately. Thus the exponent parameters of the roughness decay equations were adjusted to reflect the reduced decay occurring under mulched surfaces. In a bare soil, regression equations expressing the dependent variables as a function of initial roughness index were significant, but with low coefficients of determination, being 0·39 for soil loss, 0·12 for runoff and 0·36 for sediment concentration. In addition to initial roughness index, cumulative kinetic energy of rainfall was further included in the regressions. This led to an increase in coefficients of determination, which was 0·81 for soil loss, 0·74 for runoff and 0·49 for sediment concentration. The coefficients of determination (0·87 for soil loss, 0·85 for runoff and 0·51 for sediment concentration) were further increased when the final roughness index was included in addition to initial roughness index and cumulative kinetic energy in the regressions. This work shows that soil loss and runoff could be predicted from bare soil surface provided the initial roughness and the energy of rainfall is known. However, field verifications of these relationships are needed under different tillage tools and under natural rainfall. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

19.
To date, most studies of the effectiveness of geotextiles on soil erosion rates and processes have been conducted in laboratory experiments for less than 1 h. Hence, at Hilton (52°33′ N, 2°19′ W), UK, the effectiveness of employing palm‐mat geotextiles for soil erosion control under field conditions on arable loamy sands was investigated. Geotextile‐mats constructed from Borassus aethiopum (Borassus palm of West Africa) and Mauritia flexuosa (Buriti palm of South America) leaves are termed Borassus mats and Buriti mats, respectively. Duplicate runoff plots (10 m × 1 m on a 15° slope) had five treatments (bare, permanent grass, Borassus total plot cover, Borassus buffer strip and Buriti buffer strip). Borassus covered plots had about 72% ground cover and to differentiate between this treatment and Borassus buffer strips, the former treatment is termed Borassus completely‐covered. Runoff and eroded soil were collected from each bounded plot in a concrete gutter, leading to a receptacle. Results from 08/01/2007–23/01/2009 (total precipitation = 1776·5 mm; n = 53 time intervals) show that using Borassus buffer strips (area coverage ～10%) on bare soil decreased runoff volume by about 71% (P > 0·05) and soil erosion by 92% (P < 0·001). Bare plots had nearly 29·1 L m?2 runoff and 2·36 kg m?2 soil erosion during that period. Borassus buffer strip, Buriti buffer strip and Borassus completely‐covered plots had similar effects in decreasing runoff volume and soil erosion. Runoff volumes largely explain the variability in soil erosion rates. Although buffer strips of Borassus mats were as effective as whole plot cover of the same mats, the longevity of Borassus mats was nearly twice that of Buriti mats. Thus, use of Borassus mats as buffer strips on bare plots is highly effective for soil erosion control. The mechanisms explaining the effectiveness of buffer strips require further studies under varied pedo‐climatic conditions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

20.
It is important to evaluate the impacts of grasses on soil erosion process so as to use them effectively to control soil and water losses on the Loess Plateau. Laboratory-simulated rainfall experiments were conducted to investigate the runoff and sediment processes on sloped loess surfaces with and without the aboveground parts of grasses and moss (GAM: grass and moss; NGAM: no grass and moss) under slope gradients of 5°, 10°, 15°, 20°, 25° and 30°. The results show that runoff from GAM and NGAM plots increased up to a slope gradient of 10° and decreased thereafter, whereas the runoff coefficients increased with gradient. The average runoff rates and runoff coefficients of NGAM plots were less than those of GAM plots except for the 5° slope. This behaviour may be due to the reduction in water infiltration under moss. The difference between GAM and NGAM plots in average runoff rates varied from 1·4 to 8%. At the same gradients, NGAM plots yielded significantly (α = 0·05) more sediment than GAM plots. Average sediment deliveries for different slopes varied from 0·119 to 3·794 g m−2 min−1 from GAM plots, and from 0·765 to 16·128 g m−2 min−1 from NGAM plots. Sediment yields from GAM plots were reduced by 45 to 85%, compared with those from the NGAM plots. Plots at 30° yielded significantly higher sediments than at the other gradients. Total sediments S increased with slope gradients G in a linear form, i.e. S = 9·25G − 39·6 with R2 = 0·77*, for the GAM plots, and in an exponential model, i.e. S = 40·4 exp(0·1042G) with R2 = 0·93**, for the NGAM plots. In all cases, sediment deliveries decreased with time, and reached a relative steady state at a rainfall duration of 14 min. Compared with NGAM plots, the final percentage reductions in sediment delivery from GAM plots were higher than those at the initial time of rainfall at all slopes. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

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