E. Van Ranst

Baseline concentration levels of trace elements as a function of clay and organic carbon contents in soils in Flanders (Belgium)

Abstract Baseline concentration levels of trace elements in the soils of Flanders (Belgium) were assessed as a function of clay and organic carbon contents. Outliers in the data were identified and rejected according to statistical criteria. Median trace element concentrations in mg/kg dry wt. were As 7, Cd 0.18, Co 0.05, Cr 24.6, Cu 9.6, Hg 0.17, Ni 3.5, Pb 21.5, Zn 34.5. Clay and organic carbon contents were found to be significant in predicting soil trace element contents in unpolluted soils. The coefficients of determination ranged from 0.07 (Hg) to 0.69 (Ni). Based on confidence intervals of the observations, trace element concentrations that have a known probability of being exceeded can be assessed as a function of clay and organic carbon content and used as soil quality reference values.

Application of fuzzy logic to land suitability for rubber production in peninsular Thailand

Abstract This paper aims to determine the quantitative impact of land qualities on rubber production, using the theory of fuzzy logic. This theory is applied in a land suitability assessment for rubber production in the northern part of the rubber growing area of peninsular Thailand. The proposed method differs from the usual technical land evaluation procedures by (1) the use of an explicit weight for the effect of each land quality on crop performance, and (2) the way of combining the evaluation of land qualities into a final land suitability class or land suitability index. The methodology was tested by comparing the estimated yields and land indices calculated by fuzzy set theory with those obtained by conventional procedures: (1) maximum limitation method; (2) parametric-Storie method, and (3) multiple linear regression. In the last approach the land index is replaced by the predicted relative yield from multiple regression on the various land qualities. The considered rubber clone, RRIM 600 is grown on a wide range of soils under different climatic conditions. The best relationship is given by the fuzzy set approach, which illustrates the potential usefulness of this theory in land evaluation.

Mineralogy and Fertility Status of Selected Soils of the Eastern Cape Province, South Africa

Abstract Thorough knowledge of cultivated soils is necessary for their informed and sustainable management. This study was carried out to gain a better understanding of cropped soils in the Eastern Cape Province of South Africa. The mineralogical and chemical composition and nutrient status of topsoils collected from homestead gardens and fields of smallholdings in 5 of the 36 magisterial districts where smallholder farming prevails in the Province were determined. These data were supplemented with results of soil analyses conducted by an Analytical Services Laboratory that obtains its samples from the 31 magisterial districts where large‐scale farms are dominant. The soils studied were similar mineralogically, and all had a clay fraction that was dominated by quartz, mica, and/or kaolinite, which is fairly typical for many tropical and subtropical soils. Elemental analysis showed that the soils were generally low to very low in their total content of nutrients, except for sulfur (S), manganese (Mn), zinc (Zn), copper (Cu), and boron (B), reflecting the marine and sedimentary nature of their parent materials. The available nutrient status of the cultivated soils was generally low to very low, especially those found in smallholder fields. This was attributed to low soil organic matter levels and low geological reserves of some nutrients notably phosphorus (P), potassium (K), and calcium (Ca), coupled with continuous cultivation of the lands without adequate nutrient replenishment. Depending on location, 75–100% of the fields tested low in pH, 62–100% were low in organic carbon, 83–100% were low in extractable K, 62–93% were low in extractable Ca, and 79–100% were deficient in available phosphorus. The nutrient status of soils receiving moderate to high amounts of nutrients was generally satisfactory, as revealed by the nutrient content of garden soils found on smallholdings and the fields on large‐scale farms. In all cases, soil pH was low to critically low. The findings are used to propose a soil fertility management strategy for the communal areas of the Province.

A laboratory study of pyrite oxidation in acid sulfate soils

Abstract Acid sulfate soils cover an estimated 13 million hectares (ha) worldwide, the largest concentration (6.7 million ha) being in the coastal lowlands of Southeast Asia. In Malaysia, they occur mainly along the coastal plains of Peninsular Malaysia and Sarawak. Soils that have been drained are characterized by very low pH and high amounts of exchangeable aluminum (Al), both resulting from the oxidation of pyrite. This article explains the transformation of pyrite when pyrite-bearing sediments present in acid sulfate soils undergo weathering. Soil samples containing pyrite from Cg-horizons of selected acid sulfate soils in Peninsular Malaysia were incubated in the laboratory. Some samples were treated with peat, superphosphate, calcium silicate, or dolomite so as to reduce the oxidation of pyrite. Some were left unamended as a control. Changes in pyrite morphology were studied by scanning electron microscopy-energy dispersive x-ray (SEM-EDX). At the end of incubation period, water-soluble metals were determined. Pyrite in the unoxidized state has iron (Fe) to sulfur (S) ratio of 1:2, indicating the absence of heavy metal contamination in the pyrite structure. This suggests that when pyrite dissolves, there is little risk of pollution with respect to heavy metals. Pyrite dissolved quickly to form jarosite as its disintegration proceeded. The amounts of aluminum and iron in the water-soluble form were large, possibly reaching plant and aquatic life toxic levels. The application of superphosphate slowed down pyrite oxidation.

Fuzzy relational calculus in land evaluation.

In recent years, methods of fuzzy reasoning were developed for situations akin to those found in land evaluation, in which a decision about land suitability must often be based upon imprecise information. The accuracy of such land evaluations depends on the quality of weighing land qualities with respect to their effect on crop production. The advantage of the fuzzy set approach is that class boundaries are not sharply defined, thus allowing the possibility of partial membership to a class. However, the application of fuzzy set theory in land evaluation is often limited to the use of membership functions and has weaknesses with regard to the way weights are attributed to the land qualities considered. Fuzzy relational calculus is introduced to overcome these problems. This new approach is based on fuzzy relations between land qualities and land units. Such a relation mathematically describes the suitability for a particular crop. Relational calculus offers the possibility to construct new relations from those defined previously. It allows to introduce weight coefficients that account for the importance of each land quality considered.

An approach to predict land production potential for irrigated and rainfed winter wheat in Pinan county, China

Abstract The methodology described in this paper provides land evaluators and land use planners with a tool to predict the land production potential for irrigated and rainfed winter wheat in Pinan County (China), taking into account environmental conditions and management practices of the local farmers. The correlation between predicted yields and actual reported yields by local farmers suggests a close resemblance between the simulated production environment and the situation in which the farmers operate. Incorporation in the model of quantified effects of limiting factors on crop performance allows estimation of inputs necessary to improve the actual yield level.

Examining traditional irrigation methods, irrigation scheduling and alternate furrows irrigation on vertisols in northern Ethiopia

In northern Ethiopia, where traditional (farmers) irrigation management on Vertisols is widely practiced, sustainable food security has always been a challenge. The reasons for this are multi-dimensional, but of utmost importance is, low-tech irrigation water management. The main objective of the present study is, therefore, to examine technologies of irrigation water management that might enable farmers to increase water productivity (WP) on vertisols. A comparative study has been undertaken between the traditional irrigation management (every furrow-traditional scheduling) and alternative water management options on maize plots in northern Ethiopia. The options include alternate furrows-scientific scheduling and every furrow-scientific scheduling. A field experiment was undertaken over two irrigation seasons (1998/1999 and 1999/2000). Results were compared on the basis of yield, WP and economic productivity concepts. Yield-based comparison has shown that every furrow-scientific scheduling generates the highest yield levels followed by alternate furrows-scientific scheduling. The yield increase (by every furrow-scientific scheduling) over the traditional management was found to be 54%. WP-based comparison has shown that alternate furrows-scientific scheduling generates the highest WP values followed by every furrow-scientific scheduling. The increase (by alternate furrow irrigation, scientific scheduling) over the traditional irrigation management was 58%. Economic productivity-based comparison has shown that the highest economic return was obtained from every furrow-scientific scheduling followed by alternate furrows-scientific scheduling. The increase in income (by every furrow-scientific scheduling) over the traditional irrigation management was 54%. The overall observation is that depending on the availability of water and labour resources, one can decide to use either of the alternate management options to obtain economically reasonable yield. In northern Ethiopia, where water is limiting (and not labour), every furrow-scientific scheduling can be an option.

A new approach to assess long-term lava flow hazard and risk using GIS and low-cost remote sensing: the case of Mount Cameroon, West Africa

Mount Cameroon (MC), West Africas most active volcano, is a typical example of a hazardous volcano in a densely populated area, often inflicting damage by lava flows. The spatial variation of the lava flow hazard has not been mapped systematically at MC and at many other volcanoes in developing countries because they are insufficiently documented and not continuously, systematically monitored with integrated state‐of‐the‐art methods. Sophisticated lava flow models requiring the specification of numerous physical properties cannot yet be applied in such cases. Hence, a low‐cost approach is proposed to assess the medium‐ to long‐term spatial variation of lava flow hazard. The ‘lava flow zonation system using low‐cost methods’ (LAZSLO) approach takes advantage of freely available topographic data and moderate‐resolution (10–100 m) satellite imagery. For any eruption, the formulation used here expresses the probability of lava flow invasion at any location as a product of the spatial variation of eruption probability and exposure of low‐lying terrain to lava flow reach. The last term is derived by determining the upslope area from where lava flows can invade a given site. A standard UNESCO formula is then used to estimate the lava flow risk. Hazard assessment results at MC indicate that the southwest and northeast flanks are the most hazardous from lava flows, whereas the risk of damage is greatest in the area between Limbe, Mapanja and Batoke, where industrial, urban and tourism infrastructures are developing rapidly. The presented approach can be applied to assist local authorities with disaster preparedness and emergency planning at many poorly studied volcanoes, particularly in developing countries with limited financial resources.

Dissolution characteristics of hectorite in inorganic acids

The effect of acid type (HCl, HNO3 and H2SO4) and concentration on the dissolution rate of hectorite were monitored through chemical analyses and XRD. The rate of dissolution increased with increasing acid concentration during the first 2–4 h of contact. After that time, the correlation between acid concentration and the amounts of dissolved elements strongly decreased and often higher concentrations were found in 0.25 M solutions than in 1 M solutions. The monitoring of the amount of Si is somewhat more complex since it is the result of two processes: release from the mineral and reprecipitation as an amorphous end product. In the case of HCl, the behavior of Li, Mg and Fe differed from their behavior in the other acids, but further research is necessary to characterize the reactions that may occur. From the half times of dissolution, the dissolution curves and the XRD data, it could be concluded that the dissolution rate of hectorite decreased in the order H2SO4>HNO3≥HCl at the same molar concentration, which is the reverse of what was found by other investigators. After 8 h, for example, the 1 M H2SO4 treatment dissolved more than 70% of all Li present in the hectorite, whereas equal molar HNO3 and HCl dissolved 58% and 53%, respectively. Oriented XRD patterns only showed a background scatter after 6 h of contact with 0.25 M H2SO4 and after 4 h using a concentration of 1 M H2SO4. Treatments with 0.25 M HNO3 and 0.25 M HCl still gave reflections after 6 h and even after 8 h, the d(001) XRD peak could still be observed. In 1 M HNO3 and 1 M HCl, no more reflections could be seen after 4–6 h. At that time, XRD powder patterns showed that the crystal structure was still partly preserved in the a- and b-direction of the mineral. It must be stressed that absence or a decrease in intensity of the d(001) peaks may not be fully assigned to the breakdown of the mineral structure since the Si, extracted from the lattice reprecipitates as amorphous silica, which may disrupt the layer stacking and decrease the coherence of the reflections. For the comparison of the three acids on a normal basis, the quarter times of dissolution were found to be a more appropriate tool than the half times of dissolution. The results showed that the differences among the three acids were rather small and that the concentration of the acids was the main parameter affecting the dissolution rate of the hectorite, in particular, in the beginning of the treatment.

Properties, some criteria of classification and genesis of upland forest Podzols in Rwanda

Abstract In southwest Rwanda, upland forest soils developed on quartzites and micaceous sandstones along steep slopes have sometimes the macromorphological look of ‘true’ Podzols. An investigation of the micromorphological, mineralogical and chemical properties, however, reveals only weak indications of illuviation of amorphous organic complexes. This process of cheluviation seems to be secondary relative to biological activity, Fe precipitation and weathering. The concept that cheluviation is the dominant process in the formation of spodic horizons and spodic materials would exclude these soils for the class of Podzols. Definitions of spodic horizon and spodic materials proposed in international soil classification systems, should give preference to macro and micromorphological properties over chemical properties, because the former are directly related to different genetic processes (biological activity, oxido-reduction) which also could be responsible for their formation.