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Christian Valentin - One of the best experts on this subject based on the ideXlab platform.
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linking crop structure throughfall Soil surface conditions runoff and Soil detachment 10 land uses analyzed in northern laos
Science of The Total Environment, 2018Co-Authors: Guillaume Lacombe, Christian Valentin, Phabvilay Sounyafong, Anneke De Rouw, Bounsamai Soulileuth, Norbert Silvera, Alain Pierret, Oloth Sengtaheuanghoung, Olivier RibolziAbstract:In Montane Southeast Asia, deforestation and unsuitable combinations of crops and agricultural practices degrade Soils at an unprecedented rate. Typically, smallholder farmers gain income from "available" land by replacing fallow or secondary forest by perennial crops. We aimed to understand how these practices increase or reduce Soil erosion. Ten land uses were monitored in Northern Laos during the 2015 monsoon, using local farmers' fields. Experiments included plots of the conventional system (food crops and fallow), and land uses corresponding to new market opportunities (e.g. commercial tree plantations). Land uses were characterized by measuring plant cover and plant mean height per vegetation layer. Recorded meteorological variables included rainfall intensity, throughfall amount, throughfall kinetic energy (TKE), and raindrop size. Runoff coefficient, Soil loss, and the percentage areas of Soil surface types (free aggregates and gravel; crusts; macro-faunal, vegetal and pedestal features; plant litter) were derived from observations and measurements in 1-m2 micro-plots. Relationships between these variables were explored with multiple regression analyses. Our results indicate that TKE induces Soil Crusting and Soil loss. By reducing rainfall infiltration, crusted area enhances runoff, which removes and transports Soil particles detached by splash over non-crusted areas. TKE is lower under land uses reducing the velocity of raindrops and/or preventing an increase in their size. Optimal vegetation structures combine minimum height of the lowest layer (to reduce drop velocity at ground level) and maximum coverage (to intercept the largest amount of rainfall), as exemplified by broom grass (Thysanolaena latifolia). In contrast, high canopies with large leaves will increase TKE by enlarging raindrops, as exemplified by teak trees (Tectona grandis), unless a protective understorey exists under the trees. Policies that ban the burning of multi-layered vegetation structure under tree plantations should be enforced. Shade-tolerant shrubs and grasses with potential economic return could be promoted as understorey.
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gully erosion impacts factors and control
Catena, 2005Co-Authors: Christian Valentin, Jean Poesen, Yong LiAbstract:Gully erosion attracts increasing attention from scientists as reflected by two recent international meetings [Poesen and Valentin (Eds.), Catena 50 (2–4), 87–564; Li et al., 2004. Gully Erosion Under Global Change. Sichuan Science Technology Press, Chengu, China, 354 pp.]. This growing interest is associated with the increasing concern over off-site impacts caused by Soil erosion at larger spatial scales than the cultivated plots. The objective of this paper is to review recent studies on impacts, factors and control of gully erosion and update the review on dgully erosion and environmental change: importance and research needsT [Poesen et al., 2003. Catena 50 (2–4), 91–134.]. For the farmers, the development of gullies leads to a loss of crop yields and available land as well as an increase of workload (i.e. labour necessary to cultivate the land). Gullies can also change the mosaic patterns between fallow and cultivated fields, enhancing hillslope erosion in a feedback loop. In addition, gullies tend to enhance drainage and accelerate aridification processes in the semi-arid zones. Fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat Soil erosion. In this respect, tracers such as carbon, nitrogen, the nuclear bomb-derived radionuclide 137 Cs, magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment. Recent studies conducted in Australia, China, Ethiopia and USA showed that the major part of the sediment in reservoirs might have come from gully erosion. Gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in Soils subjected to Soil Crusting such as loess (European belt, Chinese Loess Plateau, North America) and sandy Soils (Sahelian zone, north-east Thailand) or in Soils prone to piping and tunnelling such as dispersive Soils. Most of the time, the gullying processes are triggered by
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responses of Soil Crusting runoff and erosion to fallowing in the sub humid and semi arid regions of west africa
Agriculture Ecosystems & Environment, 2004Co-Authors: Christian Valentin, Jeanloup Rajot, Danielle MitjaAbstract:Abstract Systems including a long fallow period have proven to be sustainable in the tropics for they enable the transfer of the rich store of nutrients from the vegetation to the ensuing crops. These systems have been mainly studied in the forest zone with a peculiar focus on the maintenance of organic and chemical fertility. By contrast, the effects of the fallow on Soil physical properties have not been widely documented especially in the drier areas. The objectives of this paper are: (i) to summarise the fragmented and not readily accessible information on the responses of Soil Crusting, runoff, water and wind erosion to fallowing in the sub-humid and semi-arid regions of West Africa; (ii) to infer possible scenarios of land use change from the recent past. Two main examples have been taken in northern Ivory Coast and southern Niger. In the Ivorian example, physical properties are restored after a fallow duration of 10 years on sandy clay loam whilst crusts persist over a longer period on sandy Soils, partly due to the foraging activities of termites. In the sandy Sahelian Soils, cultivation destroys the erosion crusts that develop as the fallow proceeds as a result of dust deposition and colonisation by blue green algae. This crust development is inherent to the Sahelian ecosystem and favours the natural concentration of water resources. The net balance of dust is negative in millet fields (−0.25 t ha −1 per year) and positive in young fallows (+0.68 t ha −1 per year) so that a slight increase in the field/fallow ratio can transform the region from an accumulation zone to a source zone with consequences on regional fertility transfer. Finally, in both regions the sandy Soils have specific dynamics that should be accounted in land management planning. Despite a higher water erosion risk, the sub-humid zone offers a better potential for intensification than the semi-arid zone.
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Soil Crusting and infiltration on steep slopes in northern thailand
European Journal of Soil Science, 2003Co-Authors: J L Janeau, Jean P Bricquet, Olivier Planchon, Christian ValentinAbstract:Summary Predicting the rate at which rain infiltrates on steep slopes is very uncertain. There is no consistent information in the literature. We have therefore related infiltrability to slope gradient under field conditions by experimenting on a gravelly loamy Soil occupying the upper half of a cultivated convex hill in northern Thailand. Fifteen 1 m × 1 m plots with slope gradients ranging from 16 to 63% were established, and simulated rain was allowed to fall on them at controlled rates and for fixed times. We obtained the following results. The surface fell 0.4–7.2 mm due to compaction and Soil loss. The proportions of crust (0–40%) and embedded gravel (10–60%), the runoff coefficient (0.05–0.78 mm mm−1), the mean sediment concentrations (0–5.6 g l−1), and Soil detachment (10–313 g m−2) were more pronounced on the gentle slopes than on the steep ones. The steady final infiltration rate (1–107 mm hour−1) increased sharply with increasing slope gradient. Microaggregates tended to behave like sand and become tightly packed on gentle slopes (packing crust). These results suggest that the vertical component of kinetic energy, which is greater on gentle slopes, has a dominant role. Nevertheless, the differences in compaction and in sediment concentration could not be ascribed to the vertical component of kinetic energy alone. On steep slopes the horizontal component of the kinetic energy is transformed into shear stress, hampering the development of crusts so that water can still infiltrate. On steeper slopes, the water film was thinner, thereby limiting the role of splash. We conclude that the relationship between slope gradient and infiltrability depends on the nature of the Soil and must be examined in the light of surface Crusting processes.
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morphology genesis and classification of surface crusts in loamy and sandy Soils
Geoderma, 1992Co-Authors: Christian Valentin, L M BressonAbstract:Abstract In an attempt to organize the knowledge of Soil Crusting processes and to group Soil crusts on the basis of common morphological features and physical properties, we synthesized and reinterpreted information from previous publications. As a result, we propose a classification system for surface crusts formed by rainfall in loamy and sandy Soils. Although this system does not aim to be comprehensive, it was designed from the study of a great number of crust samples collected in the temperate and tropical zones, thus corresponding to a wide range of environmental and land use conditions. Three main classes of crusts: structural, erosion and depositional, were distinguished, each with subclasses. Where possible, correspondence has been made with former systems. This system helps predict infiltrability in accounting not only for total porosity of surface crusts but also for pore shape and continuity. Since crust classes are genetically related, this classification system also supplies some insight into predicting Soil degradation and selecting the most suitable control techniques.
Jeanlouis Rajot - One of the best experts on this subject based on the ideXlab platform.
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evolution des paysages sahelines au cours des six dernieres decennies dans la region de niamey de la disparition de la brousse tigree a l encroutement de surface des sols sahelian landscape evolution during the six last decades in the niiamey vicinit
Pangea infos, 2010Co-Authors: Amadou Abdourhamane Toure, Jeanlouis Rajot, Rodrigue Guillon, Z Garba, Christophe Petit, Vincent Bichet, Alain Durand, David SebagAbstract:Au Sahel, l'explosion demographique de ces dernieres decennies et les variations climatiques ont provoque d'importants changements environnementaux. L'objectif de ce travail est de mesurer les impacts de la pression anthropique sur les ecosystemes dans la region de Niamey au cours des six dernieres decennies. L'etude est fondee sur une cartographie diachronique d'une aire de 100 km² situee pres de Niamey au moyen de photographies aeriennes (1950 et 1975) et releves au GPS (2009). Il est apparu ainsi qu'entre 1950 et 2009, la vegetation de la brousse tigree a ete completement deboisee. Dans les vallees sableuses, les surfaces cultivees ont connu une extension passant de 20,7 % a 69,4 % entre 1950 et 1975. Ceci a favorise l'emprise des erosions hydrique et eolienne qui ont abouti a une degradation des terres par encroutement des sols. Celui-ci est a l'origine de la baisse des surfaces cultivees entre 1975 et 2009 (de 69,4 % a 54,4 %). Dans les bas- fonds, la tendance est au comblement du fait d'un taux de sedimentation de plus de 4 cm par an. In the Sahel, the rapid increase of the population during the last decades and the climate variation lead to an important environmental degradation. This work aims to measure the impacts of the human pressure on ecosystem during the six last decades. A diachronic cartography of a 100 km² area close to Niamey was done with aerial photographs (1950 and 1975) and GPS measurements (2009). Results showed that the tiger bush vegetation was completely cleared between 1950 and 2009 while the fallow decreases from 7 % to 1 %. In the sandy valley, the increase of cultivated fields from 20,7 % (1950) to 69,4 % (1975) favoured wind and water erosions which allowed surface Soil Crusting. Between 1975 and 2009, the bare crusted Soil dramatically developed at the expense of the cultivated area which represents only 54,4 % of the studied area. The valleys are going to be overloaded because of high sedimentation rate (> 4 cm per year).
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Soil Crusting on sandy Soils and its influence on wind erosion
Catena, 2003Co-Authors: Jeanlouis Rajot, S C Alfaro, L Gomes, A GaudichetAbstract:Abstract Under rainfall, a crust forms at the surface of most Soils. For Soils rich enough in clay (clay content >5%), it is well known that a physical crust is responsible for a supply limitation of particles available for wind erosion. Sandy Soils are very prone to Crusting as well as to wind erosion. Indeed, structural ‘sieving’ crusts develop on sandy Soils even after light rainfalls. This kind of crust shows a loose sand layer at the surface overlying a thin layer where fine particles are concentrated. The main objectives of this study were to determine whether such a crust formation limits the availability of (1) sand grains for entrainment into saltation and (2) fine particles for uptake into a vertical wind erosion flux (suspension in atmosphere of particles
S Maigayaleu - One of the best experts on this subject based on the ideXlab platform.
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Soil Crusting impact on Soil organic carbon losses by water erosion
Catena, 2013Co-Authors: S Maigayaleu, I Guiguemde, Hamma Yacouba, Harouna Karambiri, Olivier Ribolzi, A Bary, R Ouedraogo, Vincent ChaplotAbstract:Abstract The Sahelian region, characterized by erratic, heavy rainfalls and low Soil organic carbon (SOC) stocks, is highly vulnerable to land degradation. While water erosion is recognized as being a main mechanism of SOC losses, little research has yet been done to investigate the role which Soil surface Crusting might have on SOC losses. The main objective of this study was to evaluate the impact of Soil surface Crusting on SOC losses. This study was conducted in Tougou Catchment (37 km 2 ), northwest of Burkina Faso, which receives a cumulative mean annual rainfall of 500 mm y − 1 . The area is characterized by sandy Soils with varying types of surface crusts. The four different crust types studied were: structural crusts (STRU), which were found under cultivated Soils, which were plowed annually; perennial desiccation crusts (DES), gravel (GRAV) and erosion (ERO) crusts, generally found in the degraded semi-arid savannas. Three micro-scale runoff plot (1 × 1 m 2 ) replicates were installed on each of the different types of surface crusts observed in the catchment. Water and sediment samples were collected from the runoff plots after every rainfall event (n = 10) of the 2011 rainy season. The sediment samples were analyzed for organic carbon (OCsed), while the water samples were examined for dissolved organic carbon (DOC). The average of organic carbon losses with sediment (OC L sed), was 0.37 g C m − 2 y − 1 for ERO, 0.36 g C m − 2 y − 1 for DES, 0.24 g C m − 2 y − 1 for STRU and 0.15 g C m − 2 y − 1 for GRAV. DOC accounted for a minute contribution to SOC losses i.e. less than 0.05%. STRU with 10.42 mg C l − 1 showed the highest DOC content, followed by GRAV (6.13 mg C l − 1 ), DES (5.06 mg C l − 1 ) and ERO (4.92 mg C l − 1 ). The OC enrichment ratio (ER) of sediments to that of the 0–0.1 m bulk Soil was less than one for DES, GRAV and ERO (0.39, 0.69 and 0.75, respectively) and reached 1.14 for STRU. This pointed to a greater SOC protection from erosion by the perennial crusts of the degraded savannas (DES, GRAV and ERO), as compared to crusts of cultivated fields. Thick, sand-enriched crusts, DES and GRAV, seemed to provide the greatest OC protection. This study pointed out a significant relationship between Soils Crusting on SOC erosion. It showed that the formation of loose and sandy crusts provides greater SOC protection from water erosion, which in turn may improve SOC stabilization and associated Soil functions, such as Soil fertility, water-holding capacity and sequestration of atmospheric carbon.
A Gaudichet - One of the best experts on this subject based on the ideXlab platform.
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Soil Crusting on sandy Soils and its influence on wind erosion
Catena, 2003Co-Authors: Jeanlouis Rajot, S C Alfaro, L Gomes, A GaudichetAbstract:Abstract Under rainfall, a crust forms at the surface of most Soils. For Soils rich enough in clay (clay content >5%), it is well known that a physical crust is responsible for a supply limitation of particles available for wind erosion. Sandy Soils are very prone to Crusting as well as to wind erosion. Indeed, structural ‘sieving’ crusts develop on sandy Soils even after light rainfalls. This kind of crust shows a loose sand layer at the surface overlying a thin layer where fine particles are concentrated. The main objectives of this study were to determine whether such a crust formation limits the availability of (1) sand grains for entrainment into saltation and (2) fine particles for uptake into a vertical wind erosion flux (suspension in atmosphere of particles
Dirk Goossens - One of the best experts on this subject based on the ideXlab platform.
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effect of Soil Crusting on the emission and transport of wind eroded sediment field measurements on loamy sandy Soil
Geomorphology, 2004Co-Authors: Dirk GoossensAbstract:Abstract Field data are reported for the horizontal and vertical flux of wind-eroded sediment on an agricultural field in northern Germany. Measurements were made during a windstorm that hit the region on 18 May 1999. The magnitude of both fluxes was significantly affected by the presence of a surface crust covering the test field. Measuring the physical crust strength at 45 locations with a torvane, the relationships between crust strength (τ) and the horizontal (Fh) and vertical (Fv) sediment fluxes were investigated. Both fluxes decreased as the surface crust became stronger. The decay behaved as an exponential function for both types of flux. The horizontal sediment flux over a crusted surface can be accurately predicted by completing Marticorena and Bergametti's [Journal of Geophysical Research 100 (1995) 16415] erosion model with a crust function. The vertical particle flux over crusted Soil can be calculated by adding a similar function to Alfaro and Gomes's [Journal of Geophysical Research 106D (2001) 18075] dust production model. The study also suggests that the gradual bombardment of a surface crust by impacting particles does not immediately result in a decay of the crust's protective effect, provided that the crust has a minimum thickness. However, once the crust becomes perforated, its protective effect disappears very quickly, leading to much higher horizontal and vertical sediment fluxes than predicted for undamaged crusted Soil.