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Soil erosion by water and tillage are major drivers for soil degradation in the mountainous regions of NW Vietnam. Data on cumulative and recent erosion of bulk soil and soil organic carbon (SOC) are needed for carbon budgeting and to evaluate e.g. the impact of erosion on climate change, environmental services and subsequent socioeconomic consequences. Thus, the aims of the present study were (1) to quantify cumulative erosion and recent erosion rates of bulk soil (2) to quantify cumulative eroded SOC and (3) to estimate the proportions of water and tillage induced soil erosion after land use change from primary forest to continuous maize cultivation for up to 21 years. Soil erosion rates were determined by 137Cs and ranged from 12 to 89 t ha- 1 a- 1. A large part of the variation of cumulative bulk soil (R² = 0.79) and SOC loss (R² = 0.67) between the sites was simply but effectively explained by the ratio of site specific cumulative RUSLE LS factors to clay contents. The newly developed CIDE approach, which attributes SOC changes on steep slopes to either carbon input, decomposition or erosion, delivered 20% higher (up to 0.7 kg m- 2) and more reliable estimates on cumulative SOC erosion than a traditional approach, because CIDE considered the effects of soil profile truncation, decomposition and humification, which all affected SOC simultaneously to soil erosion. Tillage induced soil flux accounted for 38 ± 3 kg m- 1 per tillage pass, which was lower than found in similar studies. Soil erosion by water was higher than tillage induced erosion in middle and foot slope positions, accounting for 86 to 89% of total soil erosion. To prevent further soil degradation, erosion protection measures should be implemented. [ABSTRACT FROM AUTHOR]

The stability of some highly weathered soils of the tropics is controlled by their organo-mineral substances. Highly weathered soils from 10 different locations were sampled from their A and B horizons to determine their aggregate stability. The objective of the study was to determine the aggregate stability of the soils and their relationships with geochemical constituents. The major geochemical elements of the soils are quartz and kaolinite, SiO, AlO and FeO, while the dithionite extractable Fe and Al was greater than their corresponding oxalate and pyrophosphate forms. The mean-weight diameter from dried aggregates (MWD) and their corresponding wet mean-weight diameter (MWD) were related significantly (r = 0.64*). The dithionite extracted Al and Fe or the crystalline forms of these elements were outstanding in the stability of the aggregates. However, this did not diminish the influence of SOC reduced to third order level in the stability of the soils. The influence of SOC in these soils, however, indirectly manifested on the role of Fe and Al in the aggregation of these soils. The crystalline Fe and Al sesquioxides were very prominent in the aggregation and stability of these soils. [ABSTRACT FROM AUTHOR]

Abstract: The stability of microaggregates in soils as opposed to its dispersion is a very important soil phenomenon that checks degradation arising from unguided tillage and soil erosion. Ten soils from southeastern Nigeria were sampled from their typical A and B horizons for the study. The aim was to identify the extent of colloidal stability of the soils and the forms of Fe and Al oxides in the soils contributing to their stability. The soils are mostly Ultisols and Inceptisols formed on sandstones and shale parent materials. The soils are low in soil basic cations including the soil organic carbon (SOC). The major clay mineral is kaolinite while the soil is acid in reaction. The various forms of soil Fe and Al oxides are high with the total forms of Fe and Al being most dominant and >dithionite extracted Fe and Al>oxalate extracted Fe and Al>pyrophosphate extracted Fe and Al. The water-dispersible clay and silt (WDC) and (WDSi) which are index of dispersion in most soils are low to medium thus reflecting in the low to medium dispersion ratio (DR). The clay flocculation index (CFI) and aggregated silt+clay (ASC) were moderate to high implying the high potential stability of the soils. Soil organic carbon did not seem to be contributing much to the stability of the microaggregates while oxalate and pyrophosphate extractable Fe (Feox, Fep) and to some extent total Al (Alt) were among the different forms of oxides that act as aggregating agents. We propose here that rather than SOC acting as a disaggregating agent in the soils, it might have acted in association with these oxides in a linkage or bridge such as C–P–OM–C to ensure stability of the soils. [Copyright &y& Elsevier]

Abstract: Net N mineralization rate having very high annual dynamics is one of the basic parameters characterizing the N balance of the soil. The dynamics of the net N mineralization rates, and the effects of soil temperature and moisture on them, were analyzed for four soils: Eroded Haplic Luvisol, Calcaric Regosol, Gleyic–Calcaric Regosol and Eutric Cambisol located at different catena positions in the western part of the Kraichgau (Germany). The net N mineralization rates were measured in situ on unfertilized and N fertilized plots twice a month over a period of 6 years. Statistical analyses were conducted by a combination of the classical Time Series Analysis, particularly Census-I-Decomposition, with repeated-measures ANOVA using PROC MIXED of SAS. These statistical approaches allow to evaluate the seasonal, trend–cyclic and random components of the time series. In addition to the dynamics of soil temperature, soil moisture and net N mineralization rate, the following main characteristics were investigated: least square means of the investigated data series, their standard errors, and seasonal (annual) components of the series. The amplitudes of annual components of the time series were calculated by two methods: 1) as a half of the difference between maximal and minimal values of the seasonal components determined by Time Series Analysis and 2) based on regression coefficients of a cosine-function with an annual period estimated by the Fourier spectral analysis within the Linear Mixed Models approach. Repeated-measures ANOVA showed significant effects of soil type and location of the soils within the catena on temperature and moisture in 30 cm soil depth. The maximal amplitudes of annual variation of soil temperature and moisture were observed for Calcaric Regosol. This soil was characterized by a maximally pronounced annual cycle of net N mineralization rate, as well as by an increase of mineralization rate after fertilizer application. The annual cycle of net N mineralization rate in Calcaric Regosol was mainly determined by changes of soil temperature, not by the absolute temperature values. However, the long-term trend of net N mineralization rate in Calcaric Regosol followed the trend of soil moisture. The net N mineralization rate and subsequently the total amount of mineralized N increased in the following sequence: Eutric Cambisol

l-lardsetting soil properties are undesirable in agricultural soils because they hamper moisture movement and soil aeration. The soils of the floodplain of Niger River in eastern Nigeria hardsets upon drying, following dispersion, puddling, and slaking during the waterlogged period. Ten soil samples collected from a depth of 0-20 cm were analyzed for their properties. The soils are classified as Fluvaquentic Eutropepts or Dystric Gleysol (FAO). The objective was to investigate the influence of some soil properties on water-dispersible clay (WDC) of the soils, which is the precursor of the hardsetting process. The total clay content (TC) correlated significantly with WDC (r = 0.94**), whereas the water-dispersible silt (WDSi) was higher than its corresponding total silt content. The WDC showed a positive correlation with dithionite extractable Fe (Fed), Al (AId), and oxalate extractable Fe (Feo) (r = 0.75*, 0.89**, and 0.76* respectively). Exchangeable Mg2+ correlated significantly with WDSi (r = 0.70). Principal component analysis of the soil variables indicates that 15 soil components, which influence WDC as hardsetting properties, were reduced to 5 orthogonal components. The parameters that influence hardsetting properties are exchangeable Na+, K+, Ca2+, Mg2+, Fed, Alo, and Feo. Other soil properties are kaolinite, smectite, illite, and WDC, including soil organic carbon (OC), electrical conductivity (EC), and ESP. Therefore, those soil properties, which explain hardsetting characteristics most, are exchangeable Na+, Fed, OC, Mg2+ and Alo. There are negative consequences on the erodibility, runoff, infiltration and tillage of the soils at both submerged and dry conditions due to clay dispersion, low OC, and hardsetting behavior of the soil. [ABSTRACT FROM AUTHOR]

The objective of the investigation was to evaluate the effect of immobilizing substances and NaCl salinity on the availability of heavy metals: Zn, Cd, Cu, Ni, and Pb to wheat ( Triticum aestivum L.). In greenhouse pot experiment, a sewage sludge amended soil was treated with the following immobilizing substances: three clay minerals (Na-bentonite, Ca-bentonite and zeolite), iron oxides (goethite and hematite), and phosphate fertilizers (superphosphate and Novaphos). The pots were planted with wheat and were irrigated either with deionized or saline water containing 1600 mg L -1 NaCl. Wheat was harvested two times for shoot metal concentrations and biomass measurements. Metal species in soil solution were estimated using the software MINEQL+. The addition of metal immobilizing substances to the soil significantly decreased metal availability to wheat. The largest reduction in metal bioavailability was found for bentonites. The irrigation with saline water (1600 mg L -1 NaCl) resulted in a significant increase in metal chloride species (MCl + and MCl 2 0 ). The highest metal complexation with Cl occurred for Cd, which was about 53% of its total soil solution concentration. The total concentration of Cd (Cd T ) in soil solution increased by 1.6–2.8-fold due to saline water. The NaCl salinity caused a significant increase in uptake and shoot concentration of Cd for two harvests and small but significant increase in shoot Pb concentration for the second harvest. It was concluded that the use of bentonites is the most promising for the reduction of heavy metal availability to plants. Saline water containing 1600 mg L - 1 NaCl increased the availability of Cd and Pb to wheat and decreased the efficiency of bentonites to immobilize soluble Cd. [ABSTRACT FROM AUTHOR]

An incubation experiment lasting 111 d was carried out to study the effect of the addition of three clay minerals (Na-bentonite, Ca-bentonite, and zeolite) to soil derived from sewage sludge on water-extractable and exchangeable forms of four heavy metals (Zn, Cd, Cu, and Ni), as well as on soil organic matter mineralization, microbial biomass C and the release of inorganic N. The addition of clay minerals led to a significant decrease in water! extractable and exchangeable forms of heavy metals. The extent of decrease ranged from 14 to 75% for the water!extractable heavy metals and from 12 to 42% for the exchangeable form over the incubation time, as compared with untreated soil. The reduction in extractability of heavy metals was greater due to the addition of Na!bentonite and Ca-bentonite than that due to the addition of zeolite. Addition of clay minerals did not affect any of the following microbiological parameters in the soil: microbial biomass C, organic C (Corg) mineralization, and metabolic quotient (qCO2), and release of inorganic N during the first 3 weeks of incubation. However, as the incubation period increased, these parameters were significantly increased by the addition of clay minerals, especially by the addition of Na!bentonite and Ca-bentonite. This result is explained by a strong reduction in extractability of heavy metals after the addition of Na!bentonite and Ca-bentonite. [ABSTRACT FROM AUTHOR]

Carbonate coatings formed on the lower surfaces of pebble inclusions in the Holocene-Late Pleistocene sediments on the Irkutsk-Cheremkhovo Plain have been studied. The coupled analysis of the carbon isotope composition of the soil organic matter and carbonate coatings has indicated the formation of coatings under conditions of phytocenoses with the predominance of C3 plants. A significant effect of the atmospheric CO on the carbon isotope composition in the coatings has been noted, which could be related to their formation under low soil respiration rates. The latter was apparently due to the periodic freezing of the soil, which affected the structure of the coatings and was most manifested in the formation of spherulites in their outer layers. The carbonate coatings consist of two laminae significantly differing in their structure and stable isotope composition, which allows separating two main stages of their formation. The lightening of the carbon isotope composition in the outer (younger) layers of the coatings compared to their inner (older) ones coincides with the increase of the δO values, which points to changes of the environmental conditions in the studied area during the formation of the coatings. [ABSTRACT FROM AUTHOR]

The assessment of soil organic carbon ( SOC) loss and input after land-use change is based largely on comparisons between disturbed sites and an undisturbed reference site. At sites affected by soil erosion this comparison neglects the interactions between soil erosion, decomposition and SOC input. Our aim was to develop a stable carbon isotope-based method ( CIDE; carbon input, decomposition and erosion) to characterize SOC dynamics on sites affected by soil erosion. Using the CIDE approach, rates of (i) SOC loss by erosion, (ii) decomposition of forest-derived SOC and (iii) maize-derived net SOC input were determined. The approach was tested on a steep slope maize cultivation chronosequence of up to 20 years following deforestation of primary forest. An uncertainty analysis showed that even small erosion rates (0.3 kg soil m−2 year−1) underestimated SOC loss (sum of erosion and decomposition) and overestimated real SOC input using unadjusted measurement data. The misrepresentation was particularly large under conditions of severe erosion, small changes in SOC concentration with depth, large changes in δ13C with depth, and small changes in SOC stocks or δ13C with time. Twenty years after land-use change CIDE-derived SOC loss was 89% and 52% larger than the unadjusted SOC loss estimates based on the RUSLE (revised universal soil loss equation) erosion model and the RothC carbon turnover model, respectively. The unadjusted maize-derived SOC input was 36% and 14% larger when derived with the RUSLE and RothC model, respectively, 20 years after land-use change. This study demonstrates the care that must be taken when assessing SOC dynamics on erosion prone sites and provides a framework to address these challenges. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic carbon decline after land use change from forest to maize usually leads to soil degradation and elevated CO2 emissions. However, limited knowledge is available on the interactions between rates of SOC change and soil erosion and how SOC dynamics vary with soil depth and clay contents. The 13C isotope based CIDE approach (Carbon Input, Decomposition and Erosion) was developed to determine SOC dynamics on erosion prone slopes. The aims of the present study were: (1) to test the applicability of the CIDE approach to determine rates of decomposition and SOC input under particular considerations of concurrent erosion events on three soil types (Alisol, Luvisol, Vertisol), (2) to adapt the CIDE approach to deeper soil layers (10–20 and 20–30 cm) and (3) to determine the variation of decomposition and SOC input with soil depth and soil texture. SOC dynamics were determined for bulk soil and physically separated SOC fractions along three chronosequences after land use change from forest to maize (up to 21 years). Consideration of the effects of soil erosion on SOC dynamics by the CIDE approach yielded a higher total SOC loss (6–32%), a lower decomposition (13–40%) and a lower SOC input (14–31%) relative to the values derived from a commonly applied 13C isotope based mass balance approach. Comparison of decomposition between depth layers revealed that tillage accelerated decomposition in the plough layer (0–10 cm), accounting for 3–34% of total decomposition. With increasing clay contents SOC input and mass of sand sized stable aggregates increased. In addition, decomposition increased with increasing clay contents, too, being attributed to decomposition of labile SOC which was attached to clay particles in the sand sized stable aggregate fraction. In conclusion, this study suggests that in situ SOC dynamics on erosion prone slopes are commonly misrepresented by erosion unadjusted approaches leading to an overestimation of SOC input and underestimation of SOC loss. [Copyright &y& Elsevier]

Historical and recent aerial photograph and satellite images were analysed to study the change of land use/land cover and soil degradation in different agroecological zones of Nigeria and Benin. The sites were characterized by an expansion of farmland at the expense of forest and shrub, fallow and uncultivated land, at an increasing rate due to population growth, food demand and land scarcity. Sheet and gully erosion were the consequences of the land use intensification and have destroyed extensive areas of farmland and grazing land. Reduced agricultural and livestock production, declining revenue, as well as increased conflict from resource competition between farmers and pastoralists are expected for the future. To combat these problems, improved land use management through continuing land inventory, generating an environmental database, developing land use plans and controlling erosion through adequate soil conservation measures are recommended. [ABSTRACT FROM AUTHOR]

Abstract: Soil erosion is a serious problem in the forest-savanna transition zone or derived savanna of West Africa and Nigeria and needs to be reduced to maintain soil quality and to ensure food security. In 2007, the use of the fallout radionuclide 137Cs as a tracer for estimating the magnitude of medium-term (40–50 years) rates of soil redistribution was tested at a research station in Ibadan, Nigeria, to investigate, for the first time, its applicability in the derived savanna of West Africa. Because of the traditional tillage practice for cassava cultivation of creating downslope oriented ridges and furrows during the annual ploughing, there was a need to adapt the 137Cs approach to these specific condition. The mean inventory was determined for cores collected from both ridges and furrows at different positions down the slope and this value was used to estimate the downslope variation in the longer term soil redistribution rate. The mean 137Cs reference inventory obtained for an undisturbed site was 568±138Bqm−2. The average inventory for the upper slope of the cassava field (423±323Bqm−2) was generally lower than the average inventory for the middle slope (509±166Bqm−2) and for the lower slope (606±245Bqm−2) and these results provided clear evidence of the downslope movement of soil. The mean 137Cs inventory for the study area within the cassava field (496±273Bqm−2) was 13% lower than the reference inventory, indicating that some of the soil mobilised and redistributed by erosion had been exported beyond the field. Using 137Cs data set and the conversion model mass balance model 2 (MBM2), the gross erosion rate from the cultivated site was estimated to be 18.3tha−1 year−1 and the net erosion rate 14.4tha−1 year−1, providing a sediment delivery ratio of 78%. These estimates are comparable to the rates generated by conventional soil loss measurements made close to the study site. The study demonstrates that the 137Cs technique can be successfully used to obtain data on medium-term soil redistribution in the derived savanna of Nigeria, and that it could be a useful tool for supporting the improvement of soil conservation on farmland in West Africa. [Copyright &y& Elsevier]

Abstract: Integrated modeling is a novel approach to couple knowledge and models from different disciplines and research fields and to use their potential in the strategic planning of water management at the river basin scale. The MOSDEW integrated regional model has been developed in the Neckar basin, a 14,000km2 river catchment in South–West Germany as a model cascade of nine submodels covering large scale hydrology, groundwater flow, water demand, agricultural production, point and non-point pollution and chemical as well as biological water quality. The models are being tested and validated in the Neckar basin as well as in additional river basins in West Africa (Ouémé basin) and Central Asia (Chirchik–Ahangaran–Keles basin, CHAB) with contrasting ecological, hydrological and socio-economic boundary conditions. The transfer to the CHAB basin required changes in the submodel selection and integration structure due to the strong anthropogenic modifications of the flow regime in the downstream area. There, water is conveyed from the Chirchik river to other catchments and distributed in a complex channel system to satisfy the demand of competing water users (irrigation, urban water supply, energy production). In the Ouémé basin, the ecohydraulic model was not integrated due to lack of input data for ecological requirements of fish species whereas the groundwater flow model was not applicable to the predominant presence of aquifers in fractured rock. The model results obtained so far are promising with respect to their accuracy to be used in scenario simulations for the strategic basin wide planning of water management. [Copyright &y& Elsevier]

Abstract: Mobile wind tunnels are essential tools for the field examination and quantification of wind erosion processes on natural non-imitated surfaces under standardized, quasi-natural wind conditions. A mobile wind tunnel was constructed at the IBS of the University of Hohenheim to measure wind erosion susceptibilities under different conditions and sediment emission on dominant surfaces formed under semi-arid conditions on a transect in the Republic of Niger/West Africa. This paper gives an overview which considerations are necessary for the construction of a mobile field wind tunnel, presents calibration data and reports on first field measurements. Designing a wind tunnel for wind erosion research, several aerodynamic prerequisites need to be considered, mainly the tunnel''s dimension and the related specifications of the fan (power, size, the ability to overcome pressure drag). Main requirement is the establishment of a quasi-natural boundary layer featuring realistic energy transmission and an equilibrated layer of saltating particles with reduced flux-limitations. Specific project requirements need also to be included in the design. In the present case, this affects mainly the choice of the instruments (what should be measured) and their spatial arrangement (to minimize air resistance and to avoid crosswise influence on measurements). Instruments at the end of the 9.40m test section include sediment catchers and pitot tube anemometers for wind profile measurement, both arranged in a logarithmic profile, an isokinetic filter sampler and a saltiphone for saltation flux measurement. During calibration and field work, the tunnel proved to simulate quasi-realistic wind conditions. Technical problems occurred only with the use of the saltiphone. A first analysis of the obtained data shows similarities with field measurements during natural monsoon storm events in the same investigation area. Nevertheless, a direct comparison of the results is complicated, mainly due to the physical restrictions of wind tunnel employment. [Copyright &y& Elsevier]

Lychee ( Litchi chinensis Sonn.) is widely grown under irrigation in the tropical northern Thailand highlands. Water efficient irrigation requires sound irrigation scheduling for which the requisite soil moisture information can be obtained from water balance modeling. A prerequisite for water balance predictions are plant parameters which describe interception, root distribution evaporation and transpiration. These parameters depend on climate, soil, as well as plant physiology, variety and age. This study investigated the plant parameters for 7-year-old lychee trees in tropical granite landscapes, as they are as yet unavailable. Interception could be satisfactorily predicted with the modified Gash model. The Gash parameters (canopy capacity per canopy cover area ( S c), canopy cover factor ( c)) were determined to be 21.8 mm and 0.22, respectively. The spatial distribution of lychee tree roots depended on slope inclination. On the level plateau position, root length density (RLD) distribution was trunk-symmetrical and could be predicted with an empirical function. On the slope, the asymmetrical and irregular root development was not predictable. The suitability of the dual crop coefficient approach predicting daily potential evaporation ( E pot) and daily potential transpiration ( T pot) rates for water balance modeling was limited due to the weak correlations of E pot and T pot with the potential reference evapotranspiration (ETo). As a result, no universal values for the potential evaporation coefficient ( K e,max) and the potential transpiration coefficient ( K cb) could be determined. Hence, E pot and T pot measurements are mandatory if accurate E pot and T pot data are necessary. In the case of missing measurements, K e,max values of 0.6 and 1.6 are recommended for rough E pot estimates underneath and in-between the lychee tree canopies. For T pot predictions in irrigation scheduling, a relatively high K cb of 0.8 is recommended in order to ensure a water stress free fruit development within the irrigation season. [ABSTRACT FROM AUTHOR]

A comparative study of Raseneisenstein (bog iron ore, only oxidized type) and Ortstein was performed to develop archetypes of both hardened horizons. Therefore, we conducted chemical analyses on 15 samples of Raseneisenstein and 14 Ortstein samples and compared our results with data reported from literature. Micromorphological analyses were accomplished on six representative, undisturbed samples of each. Raseneisenstein showed a spongy microstructure composed almost exclusively of iron hydroxides, whereas Ortstein is characterised by a bridge microstructure between quartz grains. Distinct differences between the two materials were noted in the chemical composition and morphology of the coatings, as well as the type of organic matter. The only common feature is the microskeleton, which in both cases is composed of quartz. Chemical analyses indicated distinct differences between the hardened horizons as well. Raseneisenstein was characterised by a considerably higher content of redox-sensitive elements (Fe, Mn), phosphorus, as well as a higher pH and lower mobile Al content compared to Ortstein. In addition, Ortstein often showed a higher content of organically bound iron and aluminium. From additional observations regarding relief and groundwater level, we concluded that Ortstein formation is related to podzolization and Raseneisenstein to gleying processes. Archetypes were developed on basis of chemical and micromorphological evidences. [Copyright &y& Elsevier]