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Interrill erodibility can be affected by soil aggregates, especially by those aggregate size classes that are dominant in the soil. In the Water erosion Prediction Project (WEPP) model, interrill soil erodibility (K i ) is estimated using very fine sand content. Despite that some studies have indicated an effect of aggregate stability on the K i , information on the relationship between the aggregate size class and K i and factors controlling it, particularly in semi-arid region is limited. This study was conducted to determine the variation of K i for different aggregate size classes under various rainfall intensities and evaluation of the WEPP model in estimating the K i for different aggregate fractions. Five aggregate size classes (0.25–2, 2–4.75, 4.75–5.6, 5.6–9.75 mm, and 9.75–12.7 mm) were separated from a sandy clay loam soil sampled in an agricultural land and put in laboratory flumes of 100 cm × 50 cm. The flumes were placed on a 9% slope and exposed to ten sequential rainfall simulations varying from 10 to 60 mm h −1 for 30 min. The K i of each aggregate size classes was determined using the interrill sediment delivery rate and compared this with the values estimated using WEPP. All physicochemical properties were also determined in the aggregate size classes. Organic matter content in the aggregate size classes was very low (0.65–0.73%) and didn't show strong relationships with the aggregate stability and hydraulic conductivity, whereas clay was major factor controlling determining these properties for the different aggregate fractions. Significant differences were found among the aggregate size classes in clay content ( P  < 0.05), aggregate stability measured using both wet-sieving method ( P  < 0.05) and water drop test method P  < 0.05, saturated hydraulic conductivity (K s ), and measured K i ( P  < 0.05). The measured K i was about 34 and 90 times bigger than the estimated K i for the fine aggregates and coarse aggregates, respectively. The fine aggregates showed higher susceptibility to interrill detachment with increasing rainfall intensity as compared with the coarse aggregates. Significant decrease was observed in the measured K i with increasing the aggregate size which was associated with increases in clay content, aggregate stability and K s . The stability of aggregates against raindrop impact (CND) was an important indicator describing the effect of aggregate size on the interrill erodibility in semi-arid soils. Therefore, this indicator can be taken into account as a soil structure measure to develop a proper equation for estimating interrill erodibility (K i ) for agricultural lands. The minimum use of tillage practices is essential to prevent aggregate breakdown and control interrill erosion in semi-arid regions. [ABSTRACT FROM AUTHOR]

Check dams can be used as a source of information for studies on sediment characteristics and soil particle erodibility. In this study, sediment yield and grain size distribution (GSD) were measured in twenty small catchments draining into a rock check dam in NW Iran for different runoffs during 2010–2011. Significant correlations were found between sediment yield and slope steepness, vegetation cover and soil erodibility factor (K) of the catchments. The erodibility of soil particles was determined using the comparison of GSD between sediment and original soil. Clay was the most erodible soil particle which showed 2.05 times more percentage in sediment than the original soil. The erodibility of soil particles were strongly affected by the rainfall erosivity (EI 30 ). Check dams showed more effectiveness in trapping coarse particles (sand and gravel). The effectiveness of check dams in trapping coarse particles enhanced with increase in the remaining capacity of check dams. [ABSTRACT FROM AUTHOR]

The effects of land use, tillage methods and slope gradient on soil erosion have been widely investigated. However, there is limited information about their effects on very weakly aggregated soils that can be found in semi-arid, nutrient limited regions of low productivity. This study was carried out to investigate the interaction of land use, tillage method and slope gradient on runoff and soil loss in a weakly aggregated soil in the north-west of Iran. Plots (3 m × 10 m) with three treatments and two replicates were installed in each of four slopes gradient categories (12.6, 15.3, 17.0, 19.4%). The three treatments were pasture with poor vegetation cover (27%) and rainfed wheat either cultivated up to down slope or along the contour. Wheat was sown in early autumn and runoff and soil loss was measured under natural rainfall during the eight months long growing period. Out of 53 precipitation events, 8 storms were classified erosive. The susceptibility of all plots to produce runoff and soil loss increased pronouncedly and highly significantly with subsequent rainfalls. The potential of a rainfall to produce runoff and soil loss was thus highly dependent on preceding rainfalls. Wheat cultivation increased runoff 13 times and soil loss 60 times compared to pasture. Runoff and soil loss increased about 5.5 and 35 times in plots cultivated up to down slope as compared with contour cultivated plots. The effects of land use increased pronouncedly with increasing slope gradient. These results showed that erosivities of rainfalls separated by several months were not independent from each other and that the effects of land use and slope gradient interacted. Also the effect of slope gradient on soil loss was much larger than estimated by current equations. All effects could be explained by the extremely weak aggregates. Soil erosion was thus not detachment limited but transport limited. Transport limitation decreased in the sequence of rainfalls due to loss of surface roughness and with increasing slope gradient due to increasing failure of roughness elements. Under conditions leading to extremely weak soil aggregates, land use and slope gradient thus exert a much larger impact on runoff and soil loss than what is commonly assumed. This should be better considered in soil conservation efforts but also in runoff and erosion modelling. [ABSTRACT FROM AUTHOR]

Soil erosion by water is a three-phase process that consists of detachment of soil particles from the soil mass, transportation of detached particles either by raindrop impact or surface water flow, and sedimentation. Detachment by raindrops is a key component of the soil erosion process. However, little information is available on the role of raindrop impact on soil losses in the semi-arid regions where vegetation cover is often poor and does not protect the soil from rainfall. The objective of this study is to determine the contribution of raindrop impact to changes in soil physical properties and soil losses in a semiarid weakly-aggregated agricultural soil. Soil losses were measured under simulated rainfalls of 10, 20, 30, 40, 50, 60 and 70 mm h − 1 , and under two conditions: i) with raindrop impact; and, ii) without raindrop impact. Three replications at each rainfall intensity and condition resulted in a total of 42 microplots of 1 m × 1.4 m installed on a 10% slope according to a randomized complete block design. The contribution of raindrop impact to soil loss was computed using the difference between soil loss with raindrop impact and without raindrop impact at each rainfall intensity. Soil physical properties (aggregate size, bulk density and infiltration rate) were strongly damaged by raindrop impact as rainfall intensity increased. Soil loss was significantly affected by rainfall intensity under both soil surface conditions. The contribution of raindrop impact to soil loss decreased steadily with increasing rainfall intensity. At the lower rainfall intensities (20–30 mm h − 1 ), raindrop impact was the dominant factor controlling soil loss from the plots (68%) while at the higher rainfall intensities (40–70 mm h − 1 ) soil loss was mostly affected by increasing runoff discharge. At higher rainfall intensities the sheet flow protected the soil from raindrop impact. [ABSTRACT FROM AUTHOR]

There is a strong need to develop a simple method for rapid estimation of erodibility using readily available data. In this study, soil erodibility was measured using eleven soil textures at the plot scale (60 cm × 80 cm) on a slope of 9% in a semi-arid region. A total of 110 soil erosion experiments were conducted using ten simulated rainfalls (50 mm h − 1 for 30 min). A regression model was developed based on silt and clay content (R 2 = 0.82, p < 0.001) and was applied to estimate erodibility for 231 soils in the textural triangle. Kriging was used to spatial interpolate erodibility using these data to unknown soils on the textural triangle. A soil erodibility triangle was developed using kriging technique and its accuracy was evaluated using seven other soils. The technique showed a 5.4% error and allowed the prediction of soil erodibility in semi-arid areas by using the soil erodibility triangle. [ABSTRACT FROM AUTHOR]

Land abandonment is widespread in the Mediterranean mountains. The impact of agricultural abandonment results in a shift in ecosystem evolution due to changes in soil erosion, but little is known about long-term soil and water losses. This paper uses 11 years of measurements in two paired plots (abandoned vs control) with four subplots to determine how soil and water losses evolved after abandonment within an agricultural parcel. For two years (2004–2005) both plots were under tillage, and after 2006 one plot was abandoned. The monitored plots measured runoff and sediment concentration after each rainfall event. The results show that during the two years after abandonment there was an increase in sediment yield followed by a decrease. Once the field was abandoned, a sudden increase in runoff (× 2.1 times) and sediment concentration (× 1.2 times) was found due to the lack of vegetation and tillage. After one year, the sediment concentration and, after two years, the runoff rates were lower in the abandoned than in the tilled plots. This short transition period ended in contrasting responses between the control and abandoned plot as the impact of abandonment resulted in 21 times less sediment yield after nine years of abandonment. This occurred despite the fact that the year after the abandonment the abandoned plot had 2.9 times more erosion due to low vegetation recovery and the development of a soil crust. Agriculture land abandonment resulted in lower erosion rates over the long term, but showed an increase in soil and water losses over the short term (two years). Therefore, in the first two years after abandonment there is a particular need to apply nature-based soil and water conservation strategies to prevent soil erosion. [ABSTRACT FROM AUTHOR]