RUSLE, the revised universal soil loss equation, is widely used for estimating potential soil erosion by water. Field measured model factors are however scarce for tropical regions. We derived RUSLE factors for several soil conservation measures based on three seasons of field plot measurements (2008-2010), in two contrasting landscape units of South Eastern Tanzania, the country's most important cashew growing area. Whereas the derived factors are useful for applying RUSLE in similar environments, this study points to the importance of understanding differences between soil types and landscape units when assessing potential soil erosion. On the Makonde plateau, rainfall erosivity was higher than on the inland plains (7,130 vs 5,783 MJ mm ha-(1)h(-1) year(-1)). The soil erodility K factor was also higher (0.014 t h MJ(-1) mm(-1)) on the sandy Cutanic Acrisols of the Makonde plateau than on the clayey Acric Ferralsols (0.006 t h MJ(-1) mm(-1)) of the inland plains. Likewise, soil loss on the Makonde plateau was much higher than on the inland plain (e.g. for maize 33-127 t ha(-1) season(-1) vs 3-10 t ha(-1) season(-1)). The differences between the C factor for "maize", and for "maize with crop residues", as well as the differences between the P factors for "lemon grass strips" and "ridges and furrows" indicate that although soils of the Makonde plateau are more susceptible to soil erosion, these soils are also more responsive to soil conservation measures compared to soils of the inland plains. Farmers' local technique of making "ridges and furrows" is particularly effective. Furthermore, the C factors for cashew groves are one order of magnitude lower (0.08-0.09) than for "maize", or for "maize with crop residues" (0.2-0.7), but are still much higher than for "bush fallow" (0.001). Deforestation for agriculture hence bears the risk of increasing soil erosion rates; however, this risk can be minimised by growing cashew trees.

This study assesses the farmer's understanding and perception of the causes and impacts of landslides in Bududa district in Eastern Uganda. Open-ended questions were designed to guide farmers in providing their experiences, understanding and observations in relation to the scientific findings. Steep slopes, areas with concavities and those with flow of water from underground were identified as areas prone to landslides. The soil characteristics for areas prone to landslides are stoniness, sandy and high water infiltration. Low lands and areas with sticky and strong soils were identified as stable. Rainfall was listed as the main triggering factor and most landslide occurrences are in rainfall events of low intensity but prolonged for days. Terraces are not popular in some of the areas because they promote water infiltration and trigger landslides. Loss of income from farms was mentioned as the main impact from these landslides. However, the damage to infrastructure such as roads and bridges was not identified as a problem to the farmers. Farmers in areas without landslides are less knowledgeable about the cause-effect issues related to landslides.

A study was conducted in the northern slopes of the Uluguru Mountains, Tanzania to investigate the effects of slope gradient, tillage depth, soil surface conditions and soil moisture on the rate of soil flux due to manual tillage. Soil flux was measured by means of an on-farm experiment in the farmers' fields. Twenty four plots (1.2 m wide and 8 m long) at different slopes: 31, 47, 51, 54, 58, 61, 65 and 67 percent were demarcated prior seasonal land preparation. Two sets of treatment at each slope site were done: deep tillage and shallow tillage under conditions of bare soil surface and soil surface with residues to both treatments. Effect of soil moisture condition was studied in areas under intensive agriculture at slopes 54 and 67 percent. Soil flux rates were monitored by Gerlarch trough method. Descriptive statistics (means, standard deviations, minimum and maximum) were widely employed in the exploratory analysis of soil flux rates and related factors. The effect of slope gradient and treatments were statistically analysed according to General Linear Model (GLM) of the Statistical Analysis System (SAS, 1999). Least Squares Means (LSMean) was used to compare the treatment means at 5 percent level of probability. The results showed that rates of soil flux due to tillage erosion generally increased with increasing slope gradient. Mean soil flux increased significantly (P < 0.05) from 16 kg/m/tillage pass at slope gradient 31% to more than 60 kg/m/tillage pass at slope gradient > 60%. The rates of soil flux from bare soil surfaces for both shallow and deep tillage were significantly higher (P < 0.05) than soil flux from soil surface with residues. Bare soil surface promotes tillage erosion than soil surface with residues. Further analysis showed that a combination of shallow tillage and presence of residues on the soil surface can cut down the rates of soil flux by 60% compared to deep tillage with bare soil surfaces. Therefore, fanners should be discouraged to clear their fields by removing all the residues prior to cultivation. The study also revealed that soil flux increased with moisture content, a condition attributed to greater tillage depth.

A survey was carried out to determine the effects of channel irrigation on land degradation in the vegetable growing area on the northern slopes of the Uluguru Mountains, Tanzania. Sixteen irrigation-induced landslides were characterised in terms of their dimensions, associated geomorphic characteristics, landslide typology and morphological and physical characteristics of the soils. Qualitative assessment and descriptive statistics were widely employed in the exploratory analysis of the collected data and related factors. This included the estimation of means and standard deviations of some critical variables of the study. Where applicable, Least Squares Means (LSMean) was used to compare the treatment means at 5 percent level of probability. From the results, it was observed that most of the landslides occurred on debris slopes on the linear/concave slope complex as earth flows and or earth slides with few occurring on the amphitheatres. The dominant slide scar angles ranged from 22-35 degrees. Channel irrigation in this area provoked relatively small sized landslides with maximum width and depth ranging from 7 to 19 m and 0.3 to 0.9 m respectively while their length ranged from 6 to 70 m. The mean damaged cropland area ranged from 211 to 1327m(2) while volume of soil loss ranged from 36 to 72m(3). Both the damaged cropland area by landslides and volume of soil loss due to the latter are the major indicators of land degradation due to channel irrigation and these parameters are proposed to be one of the yardsticks in determining the sustainability of production of vegetables in the study area. Damaged cropland area was more severe on flat cultivation system compared to ridge and contour cultivation systems (P <= 0.05). This phenomenon is explained in terms of loss of crop yield and reduced farmers income. The volume of soil loss followed the trend flat cultivation > contour cultivation > ridge cultivation though the values were not statistically significantly different.

The aim of this study was to carry out a detailed soil survey to determine soil types and their influence on landslide occurrence in Bududa District in eastern Uganda. Four transects were chosen following zones with and without landsides. Soil profile description and classification was done using FAO methods. Infiltration rates were measured as described by Landon in 1991. Results show that the soil types are those conditioned by topography and tropical climate namely Nitisols, Cambisols, Lixisols, Ferralsols, Leptosols, Gleysols, and Acrisols. Soil type was not significant in landslide occurrences. However soil texture in the horizons was significant in some of the landslides especially in the western zone. One factor that was common to all soils sampled in the western side was the same soil texture of clay down the profile and the subsequent absence of landslides in the surroundings of the profiles. In the eastern zone soil profile horizon is significant in some of the landslides but in the shallow landslides the slope and the shallow depth which creates a discontinuity between the saprolite and the rock causing water stagnation is the main influence. The clay minerals present are high plasticity clays; Kaolinite and Illite. The infiltration rate of the top soils is generally rapid in the top soils, allowing fast flow of water into the deeper horizons.

Broad quantitative relationships between the environmental factors of climate, parent material and topography and a range of important soil properties and World Reference Base (WRB) soil types were developed using the ISRIC WISE Global soil database Three different analytical approaches were used in the analysis, involving (i) multiple linear regressions, (ii) fitted decision trees and (iii) categorical analysis with median values. Despite the relatively low to moderate strengths of the derived relationships, they can provide useful first approximations of soil character under different environmental conditions and could be applied in broad quantitative soil modelling and mapping programs. They have the potential for widespread application as they should be universally applicable, are based on readily available data and do not require sophisticated quantitative modelling techniques. Most relationships are in accord with accepted pedological thinking and support the state factor model of soil formation, but some anomalies are observed and deserve further examination. The results reveal the dominant influence of climate and parent material in controlling the distribution of many soil properties, with the influence of topography being less evident, at least at the global scale. The WRB soil classification scheme is shown to be least partly guided by genetic factors.

The magnitude of interrill and rill erosion was determined on the northern slopes of the Uluguru Mountains, Tanzania which is representative for larger areas of East African Arch Mountains, where population pressure is high and land degradation is severe. The aim of the study was to develop a database to support soil conservation in the area. The study was done on two distinct geomorphic units with respect to altitude and hence rainfall distribution pattern: mountain ridges with an altitude ranging from 1000 to 1500 masl and mean annual rainfall of 2300 mm and mountain foothills whose altitude and mean annual rainfall are 550 to 900 masl and 900 mm, respectively. Total soil loss was measured on 36 individual bounded plots measuring 1.2 mx20 m using Gerlarch troughs on each day with rain from July 2000 to June 2001. The plots were located on six different geopedologic units, nine on mountain ridges and the rest on the mountain foothills. The slope gradient on the terrain ranged from 30% to 70%. The plots were put under maize cultivation as the main crop. Soil loss through rill erosion was estimated by volumetric measurements of rills on each soil erosion plot. The soil loss due to interrill erosion was obtained by subtracting soil loss through rill erosion from the total soil loss measured in the Gerlarch troughs. The results indicate that soil loss due to both interrill and rill erosion was very high with mean soil loss of 69 and 163 t/ha/year, respectively. Rill erosion accounted for about 58% of the total soil loss while interrill erosion contributed to the remaining 42%. Both interrill and rill erosion were higher in the mountain ridges with mean soil loss of 88 t/ha/year and 210 t/ha/year compared to 49 and 116 t/ha/year in the mountain foothills, respectively. Rill erosion was significantly higher (P <= 0.001) in all geopedologic units with slope gradient above 40% (mean soil loss ranged between 91 and 258 t/ha/year) compared to interrill erosion with mean soil loss varying from 41 to 115 t/ha/year. In geopedologic units with slope gradient above 60% both interrill and rill erosion were highly active while in geopedologic units with slope gradient below 40% the two processes were less active. The results demonstrate that rill erosion is more important than interrill erosion in the study area particularly where the slope gradient exceeds 40%. The results further show that the major part of the studied area has moderate interrill erosion (10-50 t/ha/year) and severe to very severe (> 100 t/ha/year) rill erosion. This study clarifies the magnitude of interrill and rill erosion which is important for designing soil conservation on agricultural fields. (c) 2008 Elsevier B.V. All rights reserved.

In this study, the LAPSUS-LS landslide model, together with a digital terrain analysis of topographic attributes, is used as a spatially explicit tool to simulate recent shallow landslides in Manjiya County on the Ugandan slopes of Mount Elgon. Manjiya County is a densely populated mountainous area where landslides have been reported since the beginning of the twentieth century. To better understand the causal factors of landsliding, 81 recent landslides have been mapped and investigated. Through statistical analysis it was shown that steep concave slopes, high rainfall, soil properties and layering as well as human interference were the main factors responsible for landslides in the study area. LAPSUS-LS is used to construct a landslide hazard map, and to confirm or reject the main factors for landsliding in the area. The model is specifically designed for the analysis of shallow landslide hazard by combining a steady state hydrologic model with a deterministic infinite slope stability model. In addition, soil redistribution algorithms can be applied, whereby erosion and sedimentation by landsliding can be visualized and quantified by applying a threshold critical rainfall scenario. The model is tested in the Manjiya study area for its ability to delineate zones that are prone to shallow landsliding in general and to group the recent landslides into a specific landslide hazard category. The digital terrain analysis confirms most of the causal topographic factors for shallow landsliding in the study area. In general, shallow landslides occur at a relatively large distance from the water divide, on the transition between steep concave and more gentle convex slope positions, which points to concentration of (sub)surface flow as the main hydrological triggering mechanism. In addition, LAPSUS-LS is capable to group the recent shallow landslides in a specific landslide hazard class (critical rainfall values of 0.03-0.05 in day(-1)). By constructing a landslide hazard map and simulating future landslide scenarios with the model, slopes in Manjiya County can be identified as inherently unstable and volumes of soil redistribution can yield four times higher than currently observed. More than half of this quantity can end up in the stream network, possibly damming rivers and causing major damage to infrastructure or siltation and pollution of streams. The combination of a high population density, land shortage and a high vulnerability to landslides will likely continue to create a major sustainability problem. (c) 2007 Elsevier B.V. All rights reserved.

Organic carbon levels of 542 soil samples from temperate lowland forest were determined by the original and modified Walkley-Black (WB) dichromate methods and total organic carbon (TOC) analysis. The performance and the lower and upper quantification limits of the WB method were assessed. Variable recovery rates were related to laboratory and field conditions and to the sample composition. The percentage carbon recovered by the original WB method was found to be systematically lower than commonly accepted, and the correction factor was estimated at 1.58 instead of 1.30-1.35. However, a good linear relationship with TOC enabled acceptable prediction of soil organic carbon which was most precise when using the original WB method. Texture class and pedogenetic horizon showed significant differences in recovery. Depending on the modifications of the WB method, recoveries varied significantly between laboratories, explaining up to 29% of the total variation of the topsoil carbon assessment of a site. Low recovery from samples was partly attributed to charcoal and resistant elementary carbon particles. No interference was found to be caused by iron or manganese compounds. In order to use WB carbon data of forest soils, laboratory- and method-specific determination of the recovery rate using a total analyser is strongly recommended. The original WB method was unable to predict reliably forest soil carbon contents higher than 8% TOC.

The ISRIC WISE Global soil database is used to demonstrate the important role that large, properly established soil databases can play in the understanding and modeling of the global distribution of soils and their properties. This database, which contains 4382 georeferenced soil profiles, was systematically examined with respect to 128 environmental regimes, which exhibited combinations of different parent material, climate, and topography. There was generally good correlation of the WRB soil types and key soil properties with these environmental parameters. While most of the results are in accord with the standard theories of soil formation, there are several unexpected findings and subtle complexities that deserve further examination. The results allow for a reflection on soil genesis relationships and provide a useful base for the development of global soil predictive models.

When farmers and scientists engage in participatory research, differences in their knowledge systems ought to be taken into account. Mr Napite is a farmer and plant expert with whom we studied relationships between soil fertility and fallow vegetation on the Makonde plateau in South Eastern Tanzania. Though his broad and detailed botanical knowledge is recognised by other local experts, this does not provide him any particular social status. Although he received extensive formal training, his botanical knowledge draws largely on personal and traditional concepts. Clear morphological characteristics, other than the reproductive related organs, are the key features he uses for identifying and classifying plants. His knowledge of plant species and their ecology is of comparable complexity with that of scientific knowledge. Though this is intricately linked to cultural aspects, this study illustrates that it is possible to bridge farmers' and scientists' insights during participatory research. (Indilinga: African Journal of Indigenous Knowledge Systems: 2002 2(2): 45-58)

Soil translocation due to shallow tillage by manual hoeing appears to be one of the most important erosion processes in the Uluguru Mountains. In order to quantify erosion rates caused by manual hoeing in the area a tillage experiment was set up and an on-farm survey was conducted during the dry season of the years 2000 and 2001, respectively. Soil flux rates on eight slope gradients (31–67%) were monitored by measuring the tillage step characteristics using Trapezoid-step method and by collecting soil material lost in Gerlarch troughs. Soil flux rates due to medium-term (30 years) manual hoeing along contour bands with grass barrier were also monitored by measuring volumes of tillage step below and colluvium accumulation above the surface of the original slope on six slope gradients (51, 52, 55, 56, 58 and 60%). Average tillage depth for superficial tillage was 5.2cm. The results obtained by the Trapezoid-step method ranged from 43 to 70kgm−1 per tillage pass with a mean tillage transport coefficient (k) of 107.5kgm−1 on the tested slopes. Mean soil flux rates obtained by Gerlarch trough method were slightly lower than those obtained by Trapezoid-step method with values ranging from 14 to 77kgm−1 per tillage pass and a tillage transport coefficient (k) of 83.9kgm−1 per tillage pass. The rates measured by both methods showed an increasing soil flux with slope gradient. Results on soil flux rates due to the medium-term tillage operation (step measurements) showed a negative trend with increasing slope gradient. Soil flux ranged from 148 to 42kgm−1 per year for slopes between 51 and 60%. Soil flux due to colluviation behind grass barriers showed a similar trend with values higher than those obtained by step measurements. The soil flux rates behind grass barriers ranged from 153kgm−1 per year on slope of 51% to 67kgm−1 per year on a 60% slope in approximately 30 years of cultivation. A reasonable correspondence between calculated displaced soil (area under original slope) and the accumulated colluvium (area above the original slope) was obtained indicating significant contribution of tillage erosion. Contribution due to water erosion processes ranged from 7kgm−1 per year on slopes of 51% to 25kgm−1 per year on a slope of 60%. The study demonstrated that tillage translocation rates due to manual superficial tillage are very high and could partly be held responsible for the development of shallow soils observed on steep slopes and the accumulation of colluvium behind grass barriers along contour bands in the Uluguru Mountains.

Cashew nut, a major cash crop of Tanzania, is mainly produced in the South Eastern part of the country. Sulphur dust is widely used for controlling powdery mildew disease caused by Oidium anacardii Noack. This can cause acidification of soils and thus, may threaten the productivity of cashew and its intercrops. To assess the extent and magnitude of the current acidification, pH of topsoil (0–20cm) and subsoil (20–40cm) of 70 farmers’ cashew groves where sulphur had been applied for up to 12 years, was compared to 70 similar undusted groves. On average topsoil pH of sulphur dusted groves on the Makonde plateau was 0.2U lower than of undusted groves; subsoil pH was 0.1U lower. However, in 29% of the groves the difference in topsoil pH between dusted and undusted groves was between 0.5 and 0.9U. For groves of the inland plains, no effect could be established. Soil pH on the Makonde plateau decreased with increasing number of years of sulphur use while it remained stable in the inland plains. Soils of the Makonde plateau have a high risk for acidifying to pH levels between 4.5 and 4.0 which could affect the cashew nut production and would be detrimental to intercrops such as sorghum, finger millet, and maize. This is due to the soils’ inherently low pH and low buffering capacity which is linked to their high sand content. Lime could be used to mitigate the effect of sulphur and can be obtained locally from fossil coral limestone, not exploited yet. Alternatively, the incidence of powdery mildew could be reduced by crop husbandry techniques or by using organic fungicides; the first alternative has the disadvantage of requiring farmers to understand aspects of the epidemiology, the second of being more costly and more toxic than sulphur and of requiring water for its application which is scarce on the Makonde plateau.

Abstract. Cashew soils of South Eastern Tanzania become acidified due to sulphur used for controlling powdery mildew disease (Oidium anacardii Noack). The buffering capacity of surface and subsurface horizons of 35 soil profiles of major cashew growing areas –‐ the Makonde plateau, its piedmont and inland plains –‐ was studied. The buffering capacity of surface and subsurface horizons was strongly correlated with clay content and weakly with organic carbon content. In addition, it was only weakly correlated with total exchangeable bases and available P of the surface horizon, but strongly with soil pH, base saturation and cation exchange capacity of the clay fraction of the subsurface horizon. Highly weathered sandy soils, dominant on the Makonde plateau and common on the Piedmont, had the lowest buffering capacity. Soils from the inland plains had better buffering capacities as they are generally more clayey or are less weathered. The risk of severe acidification and of a decline in productivity of cashew and of food crops is highest on the Makonde plateau. Further development and dissemination of methods which can reduce the use of sulphur are required.

It has been a matter of great concern that after hundred years of modern soil science a generally accepted system of soil classification has not yet been universally adopted [Dudal, R., 1990. Progress in IRB preparation. In: Rozanov, B.G. (Ed.), Soil Classification. Reports of the International Conference on Soil Classification, 12–16 September 1988, Alma-Ata, USSR. Centre for International Projects, USSR State Committee for Environmental Protection, Moscow. pp. 69–70]. This situation arises partly from the fact that soils constitute a continuum, which unlike easily identifiable plants and animals, needs to be placed into classes by convention. In order to remedy this the International Union of Soil Science has been working for the last 20 years with a working group RB, to develop a common language for naming the soils of the world: the World Reference Base for Soil Resources (WRB), which was endorsed by the IUSS World Congress at Montpellier in 1998. This paper reflects on the WRB, its objectives, its principles, goals as well as its implementation. Last but not least, projections are made on implications of WRB for soil inventories and small-scale land surveys.

Biophysical and participatory research methods were combined to examine factors contributing to soil erosion at field plot, village and regional scale on the sandstone dominated Udi-Nsukka Cuesta in southeastern Nigeria. At field plot scale, the properties of seven pedons were related to soil erodibility. Very high infiltration rates measured with a double ring infiltrometer and permeameter, were not in accordance to reported runoff and soil loss. The effect of groundcover and canopy height was incorporated into rainfall erosivity for plots under cashew, oil palm dominated forest and secondary natural vegetation. Cropping systems and field management practices were compared for different positions along a toposequence traversing the plateau and escarpment of the Udi-Nsukka Cuesta. Soil loss, calculated by a modified version of the universal soil loss equation, was 10 to 100 times higher on escarpment than on plateau plots. Farmers are adapting to the problems of interrill and rill erosion through careful crop selection and rotation, and contour ridging. At the village and regional scale, terrain observations were compared to archival research, historical accounts by villagers and geographic analysis of 1962 aerial photographs (1:40 000). Ravine and gully formations seemed influenced by a combination of infrastructure, geohydrology, topography, vegetation and land use. Both community efforts and state measures to combat erosion tend to be crisis managed, and are concentrated on repairing damage to economically important infrastructures. A conceptual diagram has been developed to show the complex interaction between various geophysical, agroecological, socio-economic and political components influencing soil erosion at farm, village and regional scale. Copyright (C) 1999 John Wiley & Sons, Ltd.

Infiltration data were collected on two rectangular grids with 25 sampling points each. Both experimental grids were located in tropical rain forest (Guyana), the first in an Arenosol area and the second in a Ferralsol field. Four different infiltration models were evaluated based on their performance in describing the infiltration data. The model parameters were estimated using non-linear optimization techniques. The infiltration behaviour in the Ferralsol was equally well described by the equations of Philip, Green-Ampt, Kostiakov and Horton. For the Arenosol, the equations of Philip, Green-Ampt and Horton were significantly better than the Kostiakov model. Basic soil properties such as textural composition (percentage sand, silt and clay), organic carbon content, dry bulk density, porosity, initial soil water content and root content were also determined for each sampling point of the two grids. The fitted infiltration parameters were then estimated based on other soil properties using multiple regression. Prior to the regression analysis, all predictor variables were transformed to normality. The regression analysis was performed using two information levels. The first information level contained only three texture fractions for the Ferralsol (sand, silt and clay) and four fractions for the Arenosol (coarse, medium and fine sand, and silt and clay). At the first information level the regression models explained up to 60% of the variability of some of the infiltration parameters for the Ferralsol field plot. At the second information kvel the complete textural analysis was used (nine fractions for the Ferralsol and six for the Arenosol). At the second information level a principal components analysis (PCA) was performed prior to the regression analysis to overcome the problem of multicollinearity among the predictor variables. Regression analysis was then carried out using the orthogonally transformed soil properties as the independent variables. Results for the Ferralsol data show that the parameters of the Green-Ampt and Kostiakov model were estimated relatively accurately (maximum R 2 = 0.76). For the Arenosol, use of the second information level together with PCA produced regression models with an R 2 value ranging from 0.38 to 0.68. For the Ferralsol, most of the variance was explained by the root content and organic matter content. In the Arenosol plot, the fractions medium and fine sand explained most of the observed variance.