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Spatial distribution of bowal and differences in physicochemical characteristics between bowal and woodland soils in Benin, West Africa

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... The process has also an impact on the morphological structures of plants as shown by Padonou et al. (2012) for Combretum nigricans. Bow e are found exclusively on hardened ferruginous soils in the semi-arid and subhumid climate zones with unimodal rainfall in Benin (Padonou et al., 2015). Bow e have significantly lower values of electrical conductivity, organic matter, total N, silt and extractable phosphorus than woodland soils but higher amounts of exchangeable potassium (Padonou et al., 2015). ...
... Bow e are found exclusively on hardened ferruginous soils in the semi-arid and subhumid climate zones with unimodal rainfall in Benin (Padonou et al., 2015). Bow e have significantly lower values of electrical conductivity, organic matter, total N, silt and extractable phosphorus than woodland soils but higher amounts of exchangeable potassium (Padonou et al., 2015). The rural population in Benin developed different cropping and livestock breeding techniques to adapt to bowalization (Padonou et al., 2014). ...
... The study was undertaken in Benin in the semi-arid (7°30 0 N-9°45 0 N and 0°45 0 E-3°55 0 E) and subhumid (7°30 0 N and 9°45 0 N and 0°45 0 E-3°55 0 E) climate zones where bow e occur (Padonou et al., 2015). All the phytogeographical districts of the climate zones considered were explored. ...
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Bowalization is a particular form of land degradation and leads to lateral expansion of ferricrete horizons. The process occurs only in tropical regions. In this study, the most adapted and resistant species towards climate change were identified on bowé. The 15 most common bowé species of the subhumid and semi-arid climate zones of Benin were submitted together with significant environmental variables (elevation, current bioclimatic variables, soil types) to three ecological niche modelling programmes (Maxent, Domain and GARP). For future prediction (2050), IPCC4/CIAT and IPCC5/CMIP5 climate data were applied. Asparagus africanus, Andropogon pseudapricus and Combretum nigricans were identified as the most resistant species for ecological restoration of bowé in the semi-arid climate zone and Asparagus africanus, Detarium microcarpum and Lannea microcarpa in the subhumid climate zone. The ‘Pull’ strategies were identified as appropriate for ecological restoration of bowé in Benin.
... Bowé have low values of electrical conductivity, organic matter, nitrogen, silt and extractable phosphorus but high values of exchangeable potassium (Padonou et al., 2015). Similar observations are found in Burkina Faso where nutrient availability in soil is low on bowé (Zwarg et al., 2012). ...
... Bowé cover plateaus (high and low) and hillslopes in unimodal precipitations condition on different ferruginous soil types namely: depleted tropical ferruginous soils, slightly leached tropical ferruginous soils and leached tropical ferruginous soils ( Figure 2) corresponding to previous observations made by Maignien (1958), CPCS (1967), Grandin and Thiry (1983), Faure and Volkoff (1998) also linked to the occurrence of ferricrete soils in West Africa (Padonou et al., 2015). ...
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Bowal (plural bowé) is a particular form of degraded land on hardened ferruginous soils (ferricrete) found in tropical regions with unimodal precipitation. It is characterized by ferricrete exposure due to soil surface erosion. The drivers for bowé establishment are deforestation, intensive monocrop production and/or climatic dryness. Bowé are characterized by reduced water retention capacity and electrical conductivity, low organic matter, nitrogen, silt and extractable phosphorus but high amounts of exchangeable potassium and increased soil temperature. Bowalization leads to loss of biodiversity and changes in vegetation structure. The vegetation on bowé is characterized by annual herbaceous plants and trees with impeded roots growth and structural adaptions (e.g Combretum nigricans develops more stems, more branches and larger crown diameter on bowal compared to surrounding soils). Bowalization has negative consequences for crop production. Farmers in West Africa have adopted methods for growing cowpea and groundnut on bowé using a hoe for manual tillage and weed control. Livestock herders exploit the short season with annual grasses and practice transhumance or use food supplies during the dry season. Bowalization is predicted to persist and increase in extent in the future.
... In Benin, bowé are found in both semiarid and sub-humid climate zones [21]. Since bowé are a particular form of degraded land, one could expect the same vegetation characteristics in the two climate zones. ...
... The study was conducted in two climate zones in Benin where bowé are distributed [21]: the semiarid zone (between the latitudes 9°45' N -12°25' N and longitudes 0 o 45'E -3 o 55'E) and the sub-humid zone (between the latitudes 7°30' N -9°45' N and longitudes 0 o 45'E -3 o 55'E). Data were collected in the phytogeographical districts of Mekrou-Pendjari in the semiarid zone and Zou in the sub-humid zone (Fig. 2). ...
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Bowé are particular form of degraded land where ferricrete, a hard erosion-resistant layer, is exposed. This study investigated vegetation characteristics of bowé (species composition, life form, chorological type, and plant family) in the semiarid and sub-humid climate zones in Benin. In both climate zones, bowé sites were characterized by grassland and savanna. The species composition on bowé varied according to the climate zone. Woody species were frequent on bowé in sub-humid (51% of the total species recorded) than in semiarid (44%). Geophytes, hemicryptophytes and phanerophytes were frequent on bowé in the sub-humid than in the semiarid climate zone. The difference between the two climate zones on the occurrence of therophytes on bowé was not significant. The frequency of chamaephytes was higher on bowé sites in the semiarid zone. Afro-tropical, Afro-Malgache, Pluri regional African and Pantropical chorological types were frequent on bowé than in woodlands in each climate zone while the opposite was found for Guineo-Congolian and Sudano-Zambesian chorotypes. Plant families such as Amaranthaceae, Zingiberaceae, Chrysobalanaceae, Connaraceae, Loganiaceae, Moraceae and Ochnaceae were only found on bowé in the sub-humid climate zone, while Convolvulaceae, Loganiaceae, Rhamnaceae, Araceae, Colchicaceae, Cucurbitaceae, Olacaceae, Pedaliaceae, Amaranthaceae, and Cyperaceae were only found on bowé in the semiarid zone.
... Bowalization is a result of the exposure of ferricrete due to erosion of the soil surface or soil hardening caused by a combination of drought and deforestation . Bowé are characterised by a reduced capacity to retain water, a shallow topsoil and a low content of organic matter, silt and nutrients (nitrogen and extractable phosphorus), but high amounts of exchangeable potassium (Padonou, Bachmann, Kakaï, Lykke, & Sinsin, 2015). Bowalization leads to a loss of biodiversity and changes in vegetation structure (Padonou, Assogbadjo, Bachmann, & Sinsin, 2013;Zwarg, Schmidt, Janßen, Hahn, & Zizka, 2012). ...
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en Bowé (hardened ferricrete soils formed by erosion, drought or deforestation) are often associated with termite mounds, but little is known about these mounds and their role in the restoration of soils and plant biodiversity on bowé. This study examined termite mounds on bowé and their effects on soil depth and plant richness. Sixty‐four sampling plots were laid out randomly on bowé sites with mounds and on adjacent bowé sites without mounds. The height and circumference of each mound were measured. Species inventories were made and soil depth measured in each plot. Linear mixed effects and generalised mixed effects models with Poisson error distribution were used to assess the variation in soil depth and plant species richness in mound and nonmound microsites. Two types of mounds (small vs. large) associated with different termite species were observed on bowé, with the small mounds being most common. Plots with either large or small mounds had deeper soils and higher plant richness than the adjacent plots without mounds. Conservation of termite mounds is important for restoring soils and plant richness on bowé, and termite mounds should be taken into consideration in biodiversity and soil management strategies for bowé. Résumé fr Les bowé (sols ferricrètes durcis formés par l'érosion, la sécheresse ou la déforestation) sont souvent associés aux termitières, mais on sait peu de choses sur ces monticules et leur rôle dans la restauration des sols et de la biodiversité végétale sur les bowé. Cette étude a examiné les termitières sur les bowé et leurs effets sur la profondeur du sol et la richesse végétale. Soixante‐quatre parcelles d'échantillonnage ont été disposées au hasard sur les sites de bowé avec termitières et sur les sites de bowé adjacents sans termitières. La hauteur et la circonférence de chaque termitière ont été mesurées. Des inventaires des espèces ont été réalisés et la profondeur du sol mesurée sur chaque parcelle. Des modèles linéaires et généralisés à effets mixtes ainsi qu'une distribution des erreurs suivant une loi de poisson ont été utilisés pour évaluer la variation de la profondeur du sol et de la richesse en espèces végétales sur les microsites avec termitières et sans termitières. Deux types de termitières (petites par rapport à grandes) associées à différentes espèces de termites ont été observés sur les bowé, les petites termitières étant les plus courantes. Les sols des parcelles contenant à la fois de grandes et de petites termitières étaient plus profonds et la richesse végétale y était plus importante que sur les parcelles adjacentes sans termitières. La conservation des termitières est importante pour restaurer les sols et la richesse végétale des bowé et les termitières doivent être prises en compte dans les stratégies de gestion de la biodiversité et des sols pour les bowé.
... 1042.8, and 344.0 mg/kg of Na, K, Ca, Mg, and P, respectively, and 5.5412%, 5.4751%, and 0.3121% of C, organic carbon (C-org), and N, respectively. The climate of the region is semimoist, with an average annual temperature of 25-29 C and an annual average rainfall of 900-1110 mm (Padonou et al. 2015a(Padonou et al. , 2015b. The rainfall distribution is constant, with heavy rains from April to October and drought in the other months. ...
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We examined three arbuscular mycorrhizal fungi (AMF; phylum Glomeromycota) producing glomoid spores. The mode of formation and morphology of these spores suggested that they represent undescribed species in the genus Rhizoglomus of the family Glomeraceae. Subsequent morphological studies of the spores and molecular phylogenetic analyses of sequences of the nuc rDNA small subunit (18S), internal transcribed spacer (ITS1-5.8S-ITS2 = ITS), and large subunit (28S) region (= 18S-ITS-28S) confirmed the suggestion and indicated that the fungi strongly differ from all previously described Rhizoglomus species with known DNA barcodes. Consequently, the fungi were described here as new species: R. dalpeae, R. maiae, and R. silesianum. Two of these species lived hypogeously in the field in habitats subjected to strong environmental stresses. Rhizoglomus dalpeae originated from an inselberg located within Guineo-Sudanian transition savanna zone in Benin, West Africa, where the temperature of the inselberg rock during a 5-mo drought ranges from 40 to 60 C. Rhizoglomus silesianum originated from a coal mine spoil heap in Poland, whose substrate is extremely poor in nutrients, has unfavorable texture, and may heat up to 50 C. By contrast, R. maiae was found in more favorable habitat conditions. It produced an epigeous cluster of spores among shrubs growing in a tropical humid reserve in Brazil. Moreover, the compatibility of phylogenies of species of the family Glomeraceae reconstructed from analyses of sequences of 18S-ITS-28S and the largest subunit of RNA polymerase II (RPB1) gene was discussed.
... The natural vegetation of this region is characterized by a mosaic of woodland, dry forest, tree and shrub savanna and gallery forest (Adomou et al., 2006). This zone was selected for study because it is dominated by the ferruginous soils ( Fig. 1) on which bowé occur (Padonou et al., 2014(Padonou et al., , 2015a. Bowé could occur anywhere within the study area. ...
Article
Desertification and land degradation are worldwide problems affecting soil, vegetation and the livelihoods of rural populations. Bowal (plural bowé) is a particular form of degraded land that occurs in tropical regions and leads to the exposure of ferricretes, which are unsuitable for farming. Bowé are more common on farmland and degraded savanna. Changes in land use/land cover were used to map a region of 6.7 million ha in northern) were used to predict the occurrence of bowé in the period up to 2050 using Markovian chain analysis. The results showed a considerable change in land use/land cover during the three periods. The types of land on which bowé occur (farmland and degraded savanna) increased in northern Benin by 5.4% per year during the period 1975–1990 and 9.5% per year during the periods 1990–2010, while the natural vegetation (forest, woodland and tree savanna) decreased by the same amount. The future scenarios also predicted the same trend. In the period 1975–1990, 1.28 million ha (26%) of natural vegetation was converted to degraded savanna and farmland while 2.23 million ha (53%) of natural vegetation was converted to degraded savanna and farmland in the period 1990–2010. Based on the dynamics recorded during the period 1975–1990 and 1990–2010 respectively, a total of 1.28 million ha (26% of the natural vegetation that was present in 1975) and 1.29 million ha (31% of the natural vegetation that was present in 1990) will be converted to farmland and degraded savanna in the study area by 2050.Thus bowalization will persist and increase in the period up to 2050. The natural vegetation could disappear if protection and restoration measures are not taken. It is thus important to take measures to stop the degradation and to implement programs to restore soils on bowé based on the soil and water conservation techniques used on highly degraded West African soils, such as zaï pit and stone rows with grass strips. Some native plants species adapted to bowalization and resistant to climate change in northern Benin (e.g. Asparagus africanus, Andropogon pseudapricus and Combretum nigricans) should be used in association with soil and water conservation techniques on bowé.
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Political ecology and science studies have found fertile meeting ground in environmental studies. While the two distinct areas of inquiry approach the environment from different perspectives - one focusing on the politics of resource access and the other on the construction and perception of knowledge - their work is actually more closely aligned now than ever before. "Knowing Nature" brings together political ecologists and science studies scholars to showcase the key points of encounter between the two fields and how this intellectual mingling creates a lively and more robust framework for the study of environmental politics. The contributors all actively work at the interface between these two fields, and here they use empirical material to explore questions of theoretical and practical import for understanding the politics that surround nature-society relations, from wildlife management in the Yukon to soil fertility in Kenya. In addition, they examine how various environmental knowledge claims are generated, packaged, promoted, and accepted (or rejected) by the different actors involved in specific cases of environmental management, conservation, and development. Finally, they ask what is at stake in the struggles surrounding environmental knowledge, how such struggles shape conceptions of the environment, and whose interests are served in the process.
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Water–rock reactions are driven by the influx of water, which are out of equilibrium with the mineral assemblage in the rock. Here a mass balance approach is adopted to quantify these reactions. Based on field experiments carried out in a granito-gneissic small experimental watershed (SEW), Mule Hole SEW (~ 4.5 km2), quartz, oligoclase, sericite, epidote and chlorite are identified as the basic primary minerals while kaolinite, goethite and smectite are identified as the secondary minerals. Observed groundwater chemistry is used to determine the weathering rates, in terms of ‘Mass Transfer Coefficients’ (MTCs), of both primary and secondary minerals.
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Savannas and grasslands in South Africa are adapted to fire, yet long-term effects of fire on soil, water and nutrients remain largely unknown. To determine whether frequent burning increases the tendency of soils to crust and alters soil chemistry, topsoils from 19 sites were examined in Mpumalanga, KwaZulu-Natal and the Eastern Cape where annual burning and fire exclusion experiments had been conducted for at least 28 years. A comparison of soils from burnt and unburnt plots revealed that composite samples taken to a depth of 10 cm from burnt plots had lower laboratory infiltration, electrical conductivity (EC) of 1:5 extracts, water-soluble K, water-soluble NH4, total C, total N and labile C. Burnt plots had higher pH in KCl, water dispersible clay and modulus of rupture. Rate of soil respiration from composite samples (0–2 cm) from burnt plots was lower than from unburnt plots (means of 21 vs. 36 ng C g−1 s−1). Rainfall simulation on the same samples demonstrated that burnt plots crusted more rapidly than unburnt plots (19 vs. 35 mm h−1), while results from sampling at 1-cm intervals revealed that the greatest differences between burnt and unburnt plots were in the 0–1 cm layer. The top few centimetres of soil are likely to have a disproportionate effect on ecosystem functioning by influencing the rate of infiltration and mineralisation of soil organic matter. This thin surface layer has been named the pedoderm in this paper. Soil from 0–1 cm in burnt plots had lower total C (means of 0.8% vs. 2.7% for burnt and unburnt plots, respectively), total N (0.07% vs. 0.23%), (NH4)OAc-extractable Ca (7 vs. 17 mmolc kg−1), Mg (2 vs. 7 mmolc kg−1), K (0.8 vs. 1.5 mmolc kg−1) and a greater exchangeable Na percentage (17% vs. 8%). The results indicate that burning increases soil crusting. This was ascribed to a decrease in humus content (and associated disaggregating effect) and an increase in the dispersion of clay. Nutrients are lost from burnt plots over time, probably by the removal of ash in surface runoff. Calcium, Mg, and K were lost more readily than Na probably because plants take up these nutrients in greater concentration than Na. The net effect was an increase in the exchangeable sodium percentage (ESP). Crusting on burnt plots may be self-perpetuating, because increased runoff is likely to increase the loss of soluble salts.
Article
This transfer is modeled here as an accelerated diffusion process. Raindrop impacts are assumed to increase the diffusion coefficient in the top 2-cm layer of soil to constant or exponentially diminishing values with depth. Transient development of a thin, well-stirred water layer on the soil surface is allowed. Process equations are solved by a finite-difference numerical scheme. The model was evaluated on experimental data for Br in runoff with time from three soils with three infiltration rates. For a moderately soil-adsorbed chemical, transfer to runoff is also increased significantly with accelerated diffusion, and the effect of infiltration is also very high. More of an adsorbed (vs. a mobile) chemical is lost to runoff; however, chemical transfer to runoff did not greatly change the shape and magnitude of a surface-applied chemical pulse moving downward in soil. -from Author
Article
Laowanchang gold deposit, located in Qinglong County, Guizhou Province, Southwest China, is the first-discovered laterite type gold deposit in Guizhou Province. Although most scholars are inclined to agree that ore-forming substance was closely correlated with “Dachangceng layer”, it still remained controversial. Former researchers did not find existences of visible Au grains in limonite, clay minerals or pyrite under SEM observation; therefore, they considered Au occurrence mainly as micro-disseminated form.In this study, mineral composition, chemical components and chemical index of alteration of laterites indicated that three chemical weathering processes, including argillaceous, bauxitic and ferric process can be observed in Laowanchang laterization. Geochemically, such laterization can be attributed to early laterization stage. Components of K2O, Na2O, and CaO were highly leached during weathering indicating a strong chemical alteration.Concentrations of ore-forming elements (Au, As and Sb) varied greatly along laterite profiles. Concentrations of Au were usually in the range of 40×10−9–4551×10−9; As in 0.1–0.9% with the highest value of 1.8%; Sb
Article
This study was conducted to determine the effects of absorbed Mg in erosion of soils exposed to rain. The effects of adsorbed Mg and Ca in soil erosion and infiltration rate (IR) of two soils (a Calcic Haploxeralf and a Typic Rhodoxeralf) exposed to rainfall, in the absence and presence of adsorbed Na, was studied. The erosion rate of the soils was higher for the Mg-soils than for the Ca-soils. It was suggested that the steady-state infiltration and soil erosion rates are the result of two processes that occur in opposite directions: seal formation and soil detachment. -from Author
Article
Bowal or ferricrete, the final of land degradation, occurred only in tropical region. This study aimed at assessing the effects of bowalization on phytodiversity, life forms and morphological response of plant species using Combretum nigricans Leprieur ex Guill. & Perr. as a case study. Morphological parameters (height, number of stems, number of branches, diameter at breast height and crown diameter) of C. nigricans were determined in the sub-humid zone of Benin. Plant communities were determined according to Multi-Response Permutation Procedures analysis. Plant communities were more diversified on sand-clay and concretion soils (control) compared with those described on bowal. C. nigricans developed more stems (3.6 ± 1.4 stems vs. 1.3 ± 0.4 stems), more branches (5.9 ± 2.4 branches vs. 3.2 ± 0.6 branches) and large crown diameter (5 ± 1.48 m vs. 3.4 ± 1.2 m) on bowal than on sand-clay soil. The best adapted life forms on bowal were therophytes. Bowalization induced loss of phytodiversity, changes in species life forms and provoked local adaptation of tree species.
Article
The thick weathering profiles of humid tropical areas are an important, yet generally neglected, source of information on landscape evolution. Six complete profiles of the weathering mantle were sampled by drilling on the three stepped levels of the Campos do Jordão Plateau, on the NW flank of the Continental Rift of Southeastern Brazil. Mineralogical and micromorphological analyses of drill core samples, complemented by geochemical interpretations and by previous data on the upper saprolite, indicate continuity of a general lateritic trend during the entire process of mantle formation. Lateritization phases of different intensity were defined and considered to reflect adjustment to changes in environmental conditions created by the gradual uplift of the plateau to its present position. Older and more superficial materials related to intense lateritic weathering are characterized by allitization with direct formation of gibbsite from silicates, probably related to tropical climates existing immediately before the formation of the continental rift, during the Paleogene, and also before any significant increase in altitude. Monosialitization phase with general kaolinitization and restricted indirect formation of gibbsite from silicates could be associated to less aggressive climates that followed the Neogene (Miocene?) accentuation of uplift rates along the continental rift. The changes produced by uplift in the tropical climate eventually favored the development of a podzolization trend in soils above 1800 m.
Article
This study is based on 598 phytosociological relevés and 1021 plant species taken during an extensive vegetation survey in the Republic of Benin. Site selection was primarily directed towards forest reserves to understand the potential vegetation patterns countrywide. Distributional patterns assessed by means of numerical analyses suggested a meaningful subdivision of Benin into ten phytogeographical districts (PDs). Chorological analysis proved to be valuable as a complementary approach to the characterisation of the phytosociologically-defined districts and allowed their merging into three major phytochorological zones, namely the Guineo-Congolian and Sudanian regions, linked by the Guineo/Sudanian transition zone. The phytogeographical patterns described were consistent with the hypothesis of water availability-driven variation in species and chorotype compositions. While the climate in terms of several climate elements was the primary factor, rainfall considered alone failed to explain the observed patterns. The biogeographical particularities of the PD Pobè in southern Benin were elucidated by the exclusive presence of many Guineo-Congolian endemic genera. The PDs Bassila and Atacora Chain turned out to be of great ecological and biogeographical relevance within the Sudanian regional centre of endemism. Evidence is provided for a former floristic connection of these PDs to the West African Forest Blocks. The results show how the phytosociology approach through numerical analyses of a large dataset constitutes an effective methodological tool for clarifying phytogeographical patterns at meso-scale. Moreover, phytosociology and chorology appear as complementary approaches to phytogeography.
Article
Since the colonial era, environmental degradation in Fouta Djalon has been systematically described and denounced as a direct consequence of agropastoral practices. An extremely pessimistic scenario involving extensive farming practices, population increase, environmental degradation, and emigration has gradually emerged, without solid grounding in reality. Although regularly forecasted, the catastrophe is still to come. Elaboration of this crisis scenario is based on received ideas. These ideas have warped the initial diagnosis, led to an erroneous perception of local economic and social dynamics and of their potential for evolution, and ultimately account for the sometimes fantastic character of representations and predicted evolution of environmental dynamics. This misperception of reality is one cause of the low global efficacy of rural development programs.
Article
Highly weathered soils in the southeastern United States may suffer from dispersion-related degradation of physical properties with additions of Na, either from fertilizer or wastewater sources. A clayey Southern Coastal Plain soil used in this study showed severely reduced infiltration and much higher soil loss rates, when NaNO3 was surface-applied to the soil at fertilizer rates in a rainfall simulator experiment conducted in small runoff pans. Gypsum applications, often used to reclaim naturally sodic soils, resulted in significant increases in infiltration and decreases in soil loss, when applied both alone and with NaNO3. Gypsum added to a previously Na-impacted soil improved infiltration and soil loss levels to roughly the level of untreated soil. Clay dispersion was observed in the untreated soil in the form of primary clay in the sediment; the amount of this sediment clay was greatly increased by NaNO3 treatment and was virtually eliminated by gypsum treatment, applied either alone or in combination with NaNO3. We suggest this dispersion accounts for the observed differences in runoff and soil loss between NaNO3, gypsum, and untreated soils. The use of gypsum may be advised on similar soils if Na is added and may be a useful amendment in the absence of applied Na as well. (C) Williams & Wilkins 1988. All Rights Reserved.
Article
Regular application of slurry manure in large quantities is thought to degrade soil structure and increase erodibility. One hypothesis links this to the large input of potassium which increases the exchangeable potassium percentage (EPP) and, thereby, dispersion. The effect of EPP on erodibility was quantified in three experiments. In the laboratory, eleven rainfall experiments were conducted using a silty topsoil from a typic Hapludalf which was fertilized to EPPs of 4 to 18%. Field rainfall experiments on 22 Inceptisols and Alfisols were used to examine whether the long-term application of monovalent cations (Na+, K+ and NH4+) with slurry manure had changed soil properties, especially erodibility. In addition, erodibilities of 32 soils determined with natural and simulated rains were taken from literature. The experiments on these 65 soils together covered a wide range of soils, slopes and rainfalls. Dispersion by a large percentage of highly hydrated ions (K+, Na+) reduced the infiltration rate faster, caused runoff up to 5 min earlier, and increased sediment concentrations by 15g/l compared to low EPP soils. These changes increased soil erodibility of the Universal Soil Loss Equation (USLE) by 0.021 t × h/N × ha (where N = Newtons) for each 1% increase in EPP + ESP (exchangeable sodium percentage). The ESP contributed little to this increase as ESP was less than 1/10 of EPP in the experiments. Fields with long-term manure application had similar chemical, physical and microbiological soil properties as fields without slurry manure except for slightly greater pH (+ 0.6) and P (+ 17 mg/kg) values. We conclude that, as long as the potassium input and output are balanced, the long-term use of slurry manure does not increase erodibility.
Article
Land use influences physico-chemical and water transmission properties of soil, which ultimately determine the suitability of land for different purposes. In present study, impact of different land use (forest and agriculture) on selected physicochemical and hydrological properties of soil was evaluated and compared with a reference site (uncultivated ravinous wasteland). Land use influenced infiltration rate, bulk density, mean weight diameter of aggregates and plant available water of soils. After 25years of plantation of forest species, soil organic carbon content increased by more than twofold and mean weight diameter of aggregates by 2- to 6-fold in comparison to reference site. Significant reduction in soil bulk density (4–18%) and increase in steady state infiltration rate (1.5–2 times) was observed under the forest land use system. Conversion of ravine to forest system resulted in significant improvement in moisture retention capacity of soil. Conversion of ravine landform to agriculture adversely affected the soil bulk density and infiltration rate. The study provided practical information regarding rehabilitation potential of different tree species (Prosopis juliflora, Leucaena leucocephala, Acacia nilotica and Azadirachta indica) that could be used for restoration of ustifluvent soil susceptible to gully erosion in the semi-arid region. KeywordsLand use-Soil organic carbon-Bulk density-Water stable aggregates-Infiltration rate-Soil moisture characteristic curve
Article
The Bashang area, located in the semiarid agropastoral zone, represents a typical degraded ecosystem under intensified human activities. This region has undergone profound land use changes during the past century. Natural grasslands had been progressively cultivated, and subsequently, part of cultivated lands had been abandoned by farmers due to severe desertification. In this study, we collected soil samples (0–20 cm depth) from four farmlands on both flat and gentle slope lands where cultivation had occurred for 0, 8, 30, and 50 years to assess the effects of grassland cultivation on soil degradation. In addition, soil samples were taken and plant species were investigated from eight sites in age sequence of 0- to 50- year-old abandoned field to assess natural restoration process following field abandonment. The results showed that cultivation of grassland result in a significant soil degradation which is manifested by the coarsening in soil texture and the losses in organic C and nutrients. After 50 years of cultivation, soil organic C, total N, and total P concentrations had declined 73–79%, 60–70%, and 67–68% in the 0–20 cm plough layer, respectively. Over half of these losses occurred during the first 8 years of cultivation, and subsequent was slow. After fields were abandoned, vegetation got self-restoration, and plant species composition moved toward that of the natural grassland community with time. Soil organic C, total N, and total P levels gradually improved with increasing years of land abandonment, with a faster restoration rate in the early vegetation recovery stage and a slower rate in the late succession stage. The results suggested that soil degradation may occurred drastically by inappropriate land use and management with a short time, while soil restoration for a degraded ecosystem may take long period of time, especially in this fragile ecosystem. From the perspective of soil resource management and desertification control, conservational tillage and management for farmlands and proper grazing management for recovered grassland should be taken into account in this area.
Article
This study appraises the effects of land use on soil properties in a typical watershed in the northwestern highland of Ethiopia. Soil samples were collected from major land use types in the watershed: natural forests, cultivated lands, grazing lands and Eucalyptus plantations. The natural forests served as a control against which to assess changes in soil properties resulting from the establishment of the other land use types. Samples were taken at two depths (0–15 and 15–30 cm) in the upstream and downstream areas of the watershed and analyzed for a range of soil properties. The soils in the cultivated fields, grazing lands and Eucalyptus plantations showed significantly higher sand content, but lower Ca2+ and Mg2+ contents and cation exchange capacity (CEC) compared to soils under natural forests. Eucalyptus soils had a statistically significant higher bulk density (BD) than soils under the other three land use types. The forest and Eucalyptus soils also differed significantly from each other in their soil organic matter (SOM) and total N contents. A significant difference in available P among soils of the four land use types was caused by the difference between cultivated and Eucalyptus soils. In contrast, the distribution of soil silt fraction Na+, K+ and pH values did not differ among the four land use types. Significant differences in many of the soil properties were also observed between soils in the two sampled villages. The study underscores the need for policies and strategies for sustainable land use that will attune objectives of economic development to environmental management at the regional and local levels.
Article
the principles and mechanisms of geochemical dispersion and the formation of anomalies govern the effective use of exploration geochemistry. In any terrain, the dispersion characteristics can be summarized in the form of geochemical exploration models that illustrate the nature of the surface expression of mineralization and that in turn should aid the planning, execution and interpretation of future surveys. In much of the tropics and sub-tropics, and in some areas in higher latitudes, evidence of weathering under former seasonal tropical conditions is preserved. These regions have similarities in landforms, deeply weathered regoliths and hence geochemical dispersion patterns relating to such weathering conditions. Geochemical models can be based on these common features and their subsequent modification under different climatic regimes. Two model systems are described, one in which the deeply weathered profile is preserved and the other in which the profile has been partially truncated. These models can be used to compare and contrast the surface expression of mineralization under present-day arid, savanna and equatorial rainforest environments, thereby, in effect, extending the data base for exploration of such areas.
Article
We determined the total mass loss and rate of chemical weathering from three minimally eroded, Hawaiian lava flows that are ∼ 10, 170, and 350 ka old. Using a backhoe, we sampled the entire weathering zone at 28 sites and measured the depletion or enrichment of each major element in each soil horizon relative to parent material. We were able to assess the influence of both climate and substrate age on chemical weathering because each flow crosses a precipitation gradient from ∼ 600 to ∼ 2500 mm yr− 1. Mass loss rates were highest for the 0–10 ka interval under the wettest climatic conditions (54 t km− 2 yr− 1), and decreased to near zero in the wet sites during the 10–170 and 170–350 ka intervals. Not surprisingly, weathering rates were lower in drier sites; ∼ 24 t km− 2 yr− 1 from 0–10 ka to < 2 t km− 2 yr− 1 thereafter. However the effects of precipitation were non-linear. There was a precipitation threshold below which mass loss was relatively small, and above which mass loss was substantial but insensitive to increased rainfall. Chemical weathering rates depend on tectonic uplift, erosion, climate, rock type or some combination thereof. By working on stable, uneroded surfaces of a single rock type across a well-constrained precipitation gradient, we were able to identify another potential driver: the rate of dust deposition. Although Hawaiʻi is one of the least dusty places in the northern hemisphere, dust inputs reached 82% of the total mass loss from the weathering zone at some sites, and averaged 30% on the 170 ka flow. This highlights the potential importance of dust as a component of observed weathering fluxes from catchments worldwide.
Article
Spatial distribution of the parent materials, color, clay-eluviated horizon thickness, textural profile type, presence and position of the ferruginous nodules and ferricretes in the profile are analyzed at a small scale using the thematic information content of the published 1:200,000 soil map of Benin. Analyses indicate that there is a regional differentiation of the soil cover which is first drawn on that of the geological provinces, sedimentary basins, great morpho-structural units, and then determined by the factors that control the preservation or the transformation and erosion of an ancient lateritic mantle. These factors are directly influenced by differential changes of the local base levels.
Climatic Geomorphology A basis for geochemical exploration models for tropical terrains
  • J Büdel
Büdel, J., 1982. Climatic Geomorphology. Princeton University Press, Princeton, New Jersey. Butt, C.R.M., 1987. A basis for geochemical exploration models for tropical terrains. Chem. Geol. 60, 5–16.