Riparian grass buffers reduce the velocity of water flowing over the soil surface during storms, capturing surface runoff (SR) and trapping soil particles eroded from cultivated slopes. Rarely quantified under steep slope conditions (>45 %), this phenomenon probably occurs in many mountain agroecosystems in the humid tropics. In Southeast Asia, teak plantations are often established on steep slopes where they can lead to significant soil loss (SL), particularly when the understory is removed. Therefore, we aimed to: quantify the effect of riparian grass buffers on SR and SL downstream of a teak plantation; and estimate the trapping efficiency of riparian grass buffers for water (WTE) and sediment (STE). Field measurements were carried out in Northern Lao PDR during the2014 rainy season, considering riparian zones with contrasted ground covers: (1) uncovered (URZ - 7-year-old teak trees with mean grass and litter densities of 7 % (SD 2 %) and 4 % (SD 3 %), respectively; (2) transitional (TRZ - 7-year-old teak trees with mean grass and litter densities of 19 % (SD 10 %) and 56 % (SD 9 %), respectively; and (3) covered (CRZ - grassed areas without teak trees with mean grass and litter densities of 46 % (SD 13 %) and 47 % (SD 21 %), respectively). WTE and STE were estimated based on measurements carried out from 6 July to 6 September2014 under natural rainfall conditions, using pairs of triplicate Gerlach troughs installed at the upper and lower margins of 5- and 10-m riparian sections (encompassing areas of similar to 25 and 50 m(2), respectively). Runoff coefficient (Rc), SL, and soil surface features were measured on the occasion of 20 rainfall events in 1-m(2) microplots. Rc and SL were higher in URZ (56 %, 5791 gm(-2)) than in TRZ (13 %, 250 gm(-2)) and CRZ (19 %, 159 gm(-2)). Median WTE and STE were the highest along the 10-m TRZ + CRZ riparian grass buffer at 85 % and 97 % respectively. Partial Least Square Regression (PLSR) modelling yielded a good agreement between observation and prediction for WTE and STE at seasonal scale. Overall, the results of this work indicate that 5 to 10 m riparian grass buffers limit the export of surface water and sediment downstream during small (24-h rainfall <= 20.9 mmd(-1), return period <= 1 year) to large storms (40.0 mmd(-1) < 24-h rainfall <= 84.5 mmd(-1), 1.01 year

The use of pesticides in agriculture has raised concerns due to their potential impact on human, animal and ecosystem health. Within a collaborative research framework, a study was co-constructed between researchers and local stakeholders in rural communities of Nan province (Thailand) to assess pesticide exposure levels. A total of 1,023 human serum samples were collected from volunteer participants. The level of exposure to organophosphate compounds showed that 12 (1.1%) and 134 (13%) individuals had hazardous or risky conditions, respectively. Generalized linear modeling revealed that age (older participants), chemical usage (spraying pesticide), habitat landscape characteristics (i.e., villages surrounded by orchard, forest, teak, rubber and rain-fed rice) and soil erosion appeared significant factors to explain the level of exposure. In addition, domestic animals (dogs and cattle) and wildlife (rodents and fishes) living in the vicinity were also assessed for their level of exposure. Applying the One Health principle helps understand pesticide exposure in people, domestic animals and wildlife by linking environmental characteristics at the local scale and thereby developing appropriate policies and regulations to be implemented.

Microplastics (MPs) are increasingly being studied because they have become ubiquitous in aquatic and terrestrial environments. However, little is known about the negative effects of co-contamination by polypropylene microplastic (PP MPs) and heavy metal mixtures on terrestrial environment and biota. This study assessed the adverse effects of co-exposure to PP MPs and heavy metal mixture (Cu 2+ , Cr 6+ , and Zn 2+ ) on soil quality and the earthworm Eisenia fetida . Soil samples were collected in the Dong Cao catchment, near Hanoi, Vietnam, and analyzed for changes in extracellular enzyme activity and carbon, nitrogen, and phosphorus availability in the soil. We determined the survival rate of earthworms Eisenia fetida that had ingested MPs and two doses of heavy metals (the environmental level — 1 × — and its double — 2 ×). Earthworm ingestion rates were not significantly impacted by the exposure conditions, but the mortality rate for the 2 × exposure conditions was 100%. Metal-associated PP MPs stimulated the activities of β-glucosidase, β- N -acetyl glucosaminidase, and phosphatase enzymes in soil. Principle component analysis showed that these enzymes were positively correlated with Cu 2+ and Cr 6+ concentrations, but negatively correlated with microbial activity. Zn 2+ showed no correlation with soil extracellular enzyme activity or soil microbial activity. Our results showed that co-exposure of earthworms to MPs and heavy metals had no impact on soil nitrogen and phosphorus but caused a decrease in total soil carbon content, with a possible associated risk of increased CO 2 emissions.

In tropical montane South-East Asia, recent changes in land use have induced increased runoff, soil erosion and in-stream suspended sediment loads. Land use change is also contributing to increased microbial pathogen dissemination and contamination of stream waters. Escherichia coli (E. coli) is frequently used as an indicator of faecal contamination. Field rain simulations were conducted to examine how E. coli is exported from the surface of upland, agricultural soils during runoff events. The objectives were to characterize the loss dynamics of this indicator from agricultural soils contaminated with livestock waste, and to identify the effect of splash on washoff. Experiments were performed on nine 1 m2 plots, amended or not with pig or poultry manure. Each plot was divided into two 0.5 m2 sub-plots. One of the two sub-plots was protected with a mosquito net for limiting the raindrop impact effects. Runoff, soil detachment by raindrop impact and its entrainment by runoff, and E. coli loads and discharge were measured for each sub-plot. The results show that raindrop impact strongly enhances runoff generation, soil detachment and entrainment and E. coli export. When the impact of raindrops was reduced with a mosquito net, total runoff was reduced by more than 50%, soil erosion was on average reduced by 90% and E. coli export from the amended soil surface was on average 3 to 8 times lower. A coupled physics-based approach was performed using the Cast3M platform for modelling the time evolutions of runoff, solid particles detachment and transfer and bacteria transport that were measured for one of the nine plots. After estimation of the saturated hydraulic conductivity, soil erodibility and attachment rate of bacteria, model outputs were consistent with measured runoff coefficients, suspended sediment and E. coli loads. This work therefore underlines the need to maintain adequate vegetation at the soil surface to avoid the erosion and export of soil borne potential pathogens towards downstream aquatic systems.

Notre planète disposera-t-elle encore de suffisamment de sols pour nourrir 9,7 milliards d’habitants en 2050 ? Les surfaces destinées à la production alimentaire devraient d’ici là se réduire de 400 millions d’hectares, sous l’effet de la poursuite de la dégradation des sols (érosion, salinisation, subsidence acidification, contamination), des changements climatiques, de l’urbanisation, et d’une demande accrue en agrocarburants, textiles et autres produits biosourcés. Sans renouveler les erreurs d’un modèle agricole unique, des compromis restent à définir entre les exigences environnementales (climat, sols, eaux, biodiversité) et les besoins alimentaires. Les prémices de cette transition agricole s’appuient sur des innovations agroécologiques, technologiques et numériques.

The export of dissolved organic carbon (DOC) from agricultural soils can represent an important path-way of soil organic carbon loss. Here we present the data of a series of rain simulation experiments aimed at examining DOC export from sloping lands in North Vietnam. Three regularly used agricultural practices were tested and compared with Bare soils. We also compared the impact of leaf litter in two planted forest sites.

Mountain regions of the humid tropics are characterized by steep slopes and heavy rains. These regions are thus prone to both high surface runoff and soil erosion. In Southeast Asia, uplands are also subject to rapid land‐use change, predominantly as a result of increased population pressure and market forces. Since 1998, the Houay Pano site, located in northern Lao PDR (19.85°N 102.17°E) within the Mekong basin, aims at assessing the long‐term impact of the conversion of traditional slash‐and‐burn cultivation systems to commercial perennial monocultures such as teak tree plantations, on the catchment hydrological response and sediment yield. The instrumented site monitors hydro‐meteorological and soil loss parameters at both microplot (1 m 2 ) and small catchment (0.6 km 2 ) scales. The monitored catchment is part of the network of critical zone observatories named Multiscale TROPIcal CatchmentS (M‐TROPICS). The data shared by M‐TROPICS in Houay Pano are (1) rainfall, (2) air temperature, air relative humidity, wind speed, and global radiation, (3) catchment land use, (4) stream water level, suspended particulate matter, bed particulate matter and stones, (5) soil surface features, and (6) soil surface runoff and soil detachment. The dataset has already been used to interpret suspended particulate matter and bed particulate matter sources and dynamics, to assess the impact of land‐use change on catchment hydrology, soil erosion, and sediment yields, to understand bacteria fate and weed seed transport across the catchment, and to build catchment‐scale models focused on hydrology and water quality issues. The dataset may be further used to, for example, assess the role of headwater catchments in large tropical river basin hydrology, support the interpretation of new variables measured in the catchment (e.g., contaminants other than faecal bacteria), and assess the relative impacts of both climate and land‐use change on the catchment.

Tropical clay Oxisols have a strong granular structure, as opposed to other clay-textured soils, such as Vertisols. Their highly aggregated structure favors infiltration and drainage, while Vertisols favor runoff, due to their high content of swelling clays. Most global scale pedotransfer functions (PTFs) are derived from soils of temperate regions where Oxisols are absent, which does not allow to represent this type of tropical soils.In ORCHIDEE, which is a state-of-the-art land surface model (LSM), soil hydraulic properties are derived from a soil texture map, using PTFs of temperate regions (Carsel and Parrish, 1988), which does not allow to represent tropical clay Oxisols. This has been shown to induce large negative evapotranspiration biases in areas effectively covered by clay Oxisols, and mapped as clay (Tafasca et al., 2020). In order to distinguish the two types of clays of different behavior, we introduce a new soil class to represent clay Oxisols. This is equivalent to splitting the clay soil texture in two sub-classes: clay Oxisols and swelling clay. First, we modify the Reynolds soil texture map (Reynolds et al., 2000) such as to represent clay Oxisols based on the FAO Soil Order Map of the World. Then we obtain the corresponding Van Genuchten parameters based on previous studies from the litterature. We evaluate the new PTFs and the modified soil texture map using the ORCHIDEE LSM.Using the new soil texture mapping increases evapotranspiration by 11%, allowing to correct important negative bias in tropical areas. In these zones, the mean annual river discharge decreases, consistently with the observations.

The term soil crusting refers to the forming processes and the consequences of a thin layer at the soil surface with reduced porosity and high penetration resistance. Surface crusts are largely blamed for initiating runoff, favoring interrill soil erosion and inhibiting seedling emergence. Some authors (after Arndt, 1965a and Remley and Bradford, 1989) distinguished surface sealing, defined as the initial or wetting phase in crust formation, and crusting as the hardening of the surface seal in the subsequent drying phase. Although soil crusting is now recognized as one of the major forms of soil degradation, it has been long confused with its causes (dispersion, …) or with its effects (compaction, …). Even recently, in the legend of the world map of the status of human-induced soil degradation, Oldeman et al. (1991) included sealing and crusting in the same section as compaction caused by the use of heavy machinery. However, soil crusting has been increasingly regarded as a specific form of soil degradation which deserves detailed scientific investigations and publications (Cary and Evans, 1974). The first symposium devoted to soil crusting was organized in Ghent (Belgium) in 1985 (Callebaut et al., 1986) and was followed by those of Athens (U.S.) in 1991 (Sumner and Stewart, 1992) and of Brisbane (Australia) in 1994 (So et al., 1995).

Due to high rainfall erosivity and rapid land-use changes, South-East Asia is one of the hot spots of soil degradation worldwide. In recent decades, several studies showed that the expansion of rubber tree (RT) plantations into previously forested areas has caused a major increase in soil erosion. However, the effects of cropland conversion to RT plantations on surface runoff and soil detachment are still unclear. Here we show that mature RT plantations considerably increase runoff and soil detachment compared to annual crops or young RT plantations with intercrop, mostly due to the absence of understorey. Monitoring 1 m(2) microplots over four years in mountainous Northern Thailand, we found that runoff and detachment increased with time since the onset of the rainy season and with rainfall height, but more so in mature RT plantations than in young RT plantations and maize. This led to much higher annual soil detachment in mature RT plantations (5.7 kg/m(2) on average) than in maize and young RT plantations with intercrop (0.36 kg/m(2)). We identified two main factors explaining this difference: first, rubber tree leaf litter, although abundant, seemed ineffective in reducing runoff at the end of the rainy season. Secondly, the cover by low-growing plants in mature rubber tree plantation was usually sparse and provided little protection. In particular we showed that increasing the cover by low-growing plants from quasi-null cover to >31% cover decreased runoff coefficient by 32%. Our results demonstrate that afforestation by RT, at least under current management practices and on steep slopes, is overall detrimental to soil conservation but that its effects could be mitigated by the adoption of less intense weeding practices.

Many mountainous regions of the humid tropics experience serious soil erosion following rapid changes in land use. In northern Lao People’s Democratic Republic (PDR), the replacement of traditional crops by tree plantations, such as teak trees, has led to a dramatic increase in floods and soil loss and to the degradation of basic soil ecosystem services such as water filtration by soil, fertility maintenance, etc. In this study, we hypothesized that conserving understory under teak trees would protect soil, limit surface runoff, and help reduce soil erosion. Using 1 m2 microplots installed in four teak tree plantations in northern Lao PDR over the rainy season of 2017, this study aimed to: (1) assess the effects on surface runoff and soil loss of four understory management practices, namely teak with no understory (TNU; control treatment), teak with low density of understory (TLU), teak with high density of understory (THU), and teak with broom grass, Thysanolaena latifolia (TBG); (2) suggest soil erosion mitigation management practices; and (3) identify a field visual indicator allowing a rapid appraisal of soil erosion intensity. We monitored surface runoff and soil loss, and measured teak tree and understory characteristics (height and percentage of cover) and soil surface features. We estimated the relationships among these variables through statistics and regression analyses. THU and TBG had the smallest runoff coefficient (23% for both) and soil loss (465 and 381 g·m−2, respectively). The runoff coefficient and soil loss in TLU were 35% and 1115 g·m−2, respectively. TNU had the highest runoff coefficient and soil loss (60%, 5455 g·m−2) associated to the highest crusting rate (82%). Hence, the soil loss in TBG was 14-times less than in TNU and teak tree plantation owners could divide soil loss by 14 by keeping understory, such as broom grass, within teak tree plantations. Indeed, a high runoff coefficient and soil loss in TNU was explained by the kinetic energy of rain drops falling from the broad leaves of the tall teak trees down to bare soil, devoid of plant residues, thus leading to severe soil surface crusting and soil detachment. The areal percentage of pedestal features was a reliable indicator of soil erosion intensity. Overall, promoting understory, such as broom grass, in teak tree plantations would: (1) limit surface runoff and improve soil infiltrability, thus increase soil water stock available for both root absorption and groundwater recharge; and (2) mitigate soil loss while favoring soil fertility conservation.

Soil physical properties play an important role in estimating soil water and energy fluxes. Many hydrological and land surface models (LSMs) use soil texture maps to infer these properties. Here, we investigate the impact of soil texture on soil water fluxes and storage at different scales using the ORCHIDEE (ORganizing Carbon and Hydrology in Dynamic EcosystEms) LSM, forced by several complex or globally uniform soil texture maps. At the point scale, the model shows a realistic sensitivity of runoff processes and soil moisture to soil texture and reveals that loamy textures give the highest evapotranspiration and lowest total runoff rates. The three tested complex soil texture maps result in similar water budgets at all scales, compared to the uncertainties of observation-based products and meteorological forcing datasets, although important differences can be found at the regional scale, particularly in areas where the different maps disagree on the prevalence of clay soils. The three tested soil texture maps are also found to be similar by construction, with a shared prevalence of loamy textures, and have a spatial overlap over 40% between each pair of maps, which explains the overall weak impact of soil texture map change. A useful outcome is that the choice of the input soil texture map is not crucial for large-scale modelling, but the added value of more detailed soil information (horizontal and vertical resolution, soil composition) deserves further studies.

In the past decades, the expansion and modernisation of agriculture in the mountainous areas of Southeast Asia has had severe impacts on biodiversity, as the once species-rich forests were turned into homogeneous fields receiving ample external inputs. A common feature of permanent cropping with annual crops is the frequent change of crop choice, depending on market opportunities or other motives. However, the precise effect of crop shifts on weeds in tropical areas is largely unknown. In this study, we investigated the short-term effect of crop sequences on the diversity of weed communities in smallholder fields of Northern Thailand. Crop choices were upland rice, maize, fallow and young tree plantations with or without intercrop. We counted the number of crop shifts and the number of crops involved during a 3-years period preceding weed sampling. We showed that the number of crop shifts did not affect weed density and biomass. However, herbaceous species number and diversity (measured as Shannon index) increased by 36% and 46% respectively, while herbaceous species dominance decreased by 38%, in fields with yearly crop shifts compared to fields with no shifts in the previous three years. The effect of a particular crop on diversity, or the effect of intercropping with young trees, was weaker. It was likely due to the more variable resources (especially light) in fields with two crop shifts, allowing species with different niches to co-exist. Crop type and frequent crop shifts did not affect shrub and tree species number, diversity or dominance. Some species were strongly associated with fields with no crop shift in the sequence (e.g. the tree Antidesma velutinosum) or to fields with two crop shifts in the sequence (e.g. the herb Centella asiatica, the C-4 grass Digitaria radicosa). Overall, this study showed that in this agronomical system, maintaining yearly crop shifts does not significantly affect weed abundance, but supports in-field plant species diversity, which is likely to impact the services provisioned by tropical mountainous agro-ecosystems.

The environmental risks associated with the concentration of metals in soils and sediments due to their toxicological properties on living organisms are not yet sufficiently studied in North Vietnam. Soil samples and sediments collected from three weirs (W1, W2 and W4) of the Dong Cao catchment (49.7 ha) and from the downstream Cua Khau reservoir (CK) were analyzed for heavy metal concentrations and geochemical parameters. Bioassays were then applied to assess the toxicity of these soils and sediments based on a test of phytotoxicity with garden cress (Lepidium savitum) and the BioTox test for toxicity to bacteria, using Allivibrio fischeri. Metal concentrations in sediments (Cr and Cu) were significantly higher in the Dong Cao catchment (W1 and W4) in comparison with the reservoir area. The toxicity of soils and sediments of W1 and W4 was detected at a low level by the two bioassay tests. Inhibition of light emission by Allivibrio fischeri was slightly reduced for soils and sediments of W1 and W4 after 15-min of the contact. Similarly, this slight impact has been reflected in the growth and seed germination of Lepidium savitum in the sediment samples collected from the weirs of Dong Cao catchment. The major pollutant metals were Cr, Cu and Zn. Cr contamination is undoubtedly derived from rocks whereas Cu and Zn are most likely associated with human activities (local agricultural inputs and atmospheric fallout).

Humid tropical mountainous area experiences serious soil erosion due to rapid changes in landuse, sometimes implying erosion prone management practices. In this study, we hypothesized that keeping understorey in teak tree plantation would protect soil and avoid soil erosion. We assessed the effects of 4 management practices in teak tree plantation area on water and soil losses using 6 replicated 1-m2 microplots in four plantations situated in Northern Laos during the wet season of 2017. The landuses in the four plantations were teak without understorey (TNU), teak with low density of understorey (TLU), teak with high density of understorey (THU), and teak with broom grass, Thysanolaena latifolia (TBG). During the wet season of 2017, we monitored surface runoff and soil loss for 22 rainfall events. We also measured some of the teak tree and understorey characteristics (i.e. height and percentage of cover) and the percentage areas of soil surface features (i.e. litter, free aggregates, crusting, etc.). Relationships among these variables was estimated through multiple statistics and regression analyses. We found that runoff coefficient and soil loss were the smallest for THU and TBG: runoff coefficient was 23% for both treatments, and soil losses were 465 and 381 g m-2, respectively. Runoff coefficient and soil loss for TLU were 35% and 1115 g m-2, respectively. We observed the highest runoff coefficient and soil loss under TNU (60%, 5455 g m-2) associated to the highest crusting rate (82%). High runoff coefficient and soil loss under TNU was explained by the kinetic energy of rain drops falling from the broad leaves of the tall teak trees down to bare soil, devoid of plant residues, thus leading to severe soil surface crusting and detachment. Overall, promoting understorey such as broom grass in teak tree plantations would (1) limit surface runoff and improve soil infiltrability, thus increase the soil water stock available for both root absorption and groundwater recharge, and (2) mitigate soil loss and favour soil fertility conservation.

Tropical montane areas of Southeast Asia are exposed to high-intensity rainfall during the monsoon period. This is particularly problematic in areas where soils on steep slopes are cultivated as it can lead to heavy runoff, high soil erosion, and water pollution. The objective of this paper is to analyse the effect of the impact of raindrops on the dynamics of runoff on such steep fields. Experiments under simulated rainfall were performed at the plot scale (1 m2) to quantify water export from the surface of upland agricultural soils during overland flow events. Four 1 m2 plots were divided in duplicated treatment groups: (a) control with no amendments, and (b) amended with pig manure. Each plot was divided into two 0.5 m2 rectangular subplots. One subplot was designated as a rain splash treatment; the other sub-plot was covered with a 2 mm grid size wire screen that was located 12 cm above the soil surface. The purpose of the screen was to break the raindrops into fine droplets and to reduce fall height in order to drastically reduce their kinetic energy. Runoff was measured for each sub-plot. The results show that raindrop impact drastically enhances runoff generation on both bare soils and on manure amended soils. When the impact of raindrops was limited by screening, runoff was higher on amended soils than on bare soils. The temporal evolution of runoff was correctly modelled using a soil hydraulic conductivity that exponentially decreases over time of exposure to rainfall. Both experimental and modelling results showed that droplet energy induces a rapid evolution of the hydraulic properties of the soil surface due to crusting, resulting in a reduction of hydraulic conductivity and a concomitant increase in runoff rate.

Chapter 3 Erosion and Principles of Soil Conservation Christian Valentin, Christian ValentinSearch for more papers by this authorJean Louis Rajot, Jean Louis RajotSearch for more papers by this author Christian Valentin, Christian ValentinSearch for more papers by this authorJean Louis Rajot, Jean Louis RajotSearch for more papers by this author Book Editor(s):Christian Valentin, Christian ValentinSearch for more papers by this author First published: 30 November 2018 https://doi.org/10.1002/9781119438298.ch3 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary It is common to distinguish two main types of erosion: natural erosion and accelerated erosion by human action. Erosion can also be classified into mechanical erosion and chemical erosion based on the processes. This chapter focuses on the accelerated and mechanical erosion of continental soils and the main principles of soil conservation. It briefly discusses three consequences of erosion, distinguishing between on-site and off-site effects, and historical consequences. On-site effects mainly concern soil quality. Off-site impacts concern impacts downstream of detachment areas, and therefore transport and deposition. Any erosion process involves three mechanisms: soil particle detachment, transport and deposition. Streambank erosion is also an important source of sediment. Wind erosion affects the climate, geochemical cycles, as well as air quality and human health. The main difficulty of modeling arises from the multiplicity of scales and processes that must be clearly defined each time. There are a variety of approaches: statistical, physically based, and hybrid. Soils as a Key Component of the Critical Zone 5: Degradation and Rehabilitation, Volume 5 RelatedInformation

The introduction of cash crops and the evolution of farming practices in the uplands of Southeast Asia have drastically changed the agricultural landscape of the region during these last decades. This evolution has significantly increased soil erosion leading to important on and off-site effects. A long-term multi-scale monitoring of soil erosion was initiated in the early 2000's in the Houay Pano catchment located near the city of Luang Prabang in Northern Laos to assess these effects and propose sustainable land management solutions. We report here the analysis and the modelling of the soil erosion measurements made during the whole period on 1m(2) plots for different land uses. As expected, land use has an important impact on runoff production and soil erosion. The mean annual runoff coefficient increased from 0.05 for established fallow (4 years) to 0.45 for old teak trees plantation (14 years) with intermediate values for crops. The mean soil loss followed the same trend with respect to land use, from 25 g m(-2) y(-1) to 3765 g m(-2) y(-1). These measurements confirm that established fallow promotes infiltration and reduces erosion and, at the opposite, teak tree increases soil crusting, lowers the infiltration rate and enhances soil detachment. The splash and wash erosion component of a process-oriented model developed for terrace erosion was used. This model describes the soil loss after a rainfall event as the product of an effective soil detachability, the rainfall kinetic energy, the runoff coefficient and different attenuation factors linked to soil surface features. The agreement is good, both at the event and the yearly scales. When aggregated by land use, surface features percentages have low standard deviations and soil detachability variability may be described by a log-normal distribution. This suggests that each land use has a unique signature in the erosion process given by the percentages and the distribution. We conclude that: (i) leaving the litter layer and an understorey in crops and trees plantations is the best way to minimize soil erosion, and (ii) the splash and wash model may be helpful to set up optimal agronomic strategies for a sustainable land use of Southeast Asia uplands.