Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Rescue and renewal of legacy soil resource inventories: A case study of the Limpopo National Park, Mozambique.
    Cambule, A. ; Rossiter, D.G. ; Stoorvogel, J.J. ; Smaling, E.M.A. - \ 2015
    Catena 125 (2015). - ISSN 0341-8162 - p. 169 - 182.
    acid sulfate soils - carbon sequestration - resurrection - uncertainty - gambia - maps
    Many areas of developing countries are covered by legacy soil surveys, which, however are hardly used, as they are not available in digital form, used outdated standards, and have unknown quality. There have been very few attempts to rescue and renew these surveys, nor are there established criteria for the evaluation of their quality. We therefore decided to test the applicability of the Cornell Adequacy Criteria (CAC) to assess the quality of several renewed soil surveys in or near the Limpopo National Park, Mozambique (centroid: 23° 18' 55.57¿ S, 31° 55' 16.24¿ E), using the concepts of digital soilmapping. The qualitywas assessed formapping andmonitoring soil organic carbon (SOC), in terms of geodetic control, positional accuracy, map scale, and texture and adequacy of map legend. Metadata was attached to the renewed maps. SOC stocks were estimated qualitatively based on the description of themap units and quantitatively by themeasure-and-multiply approach fromlegacy laboratory measurements. The positional accuracy of georegistrationwas 13 to 45% of the square root of aMinimumLegible Area (MLA). Point and area-class layers could be created with high positional accuracy. However the index of maximumreductionwas high, indicating that the original publication scale could be reduced.Map unit definitions and overall information content of the surveyswere adequate. Integration of remotely sensed optical imagery and digital elevation models could be used to derive accurate contours, against which the positional accuracy of contour-basedmap borderswas assessed. Less than 30% of their lengths were within a distance equal to the square root of MLA. These sources could not be used to evaluate internal map borders, due to the subdued topography and major land-use changes since the original survey. Qualitative estimates of SOC are between lowand medium, consistent with other studies in this area. The CAC proved to be a useful framework for determining the fitness for use of legacy surveys.
    Determination of drainage parameters in the low-lying acid sulphate coastal wetlands of Kerala, India
    Mathew, E.K. ; Vos, J. - \ 2003
    drainage - kattekleigronden - zoutwaterindringing - india - overstromingen - kustgebieden - drainage - acid sulfate soils - floods - salt water intrusion - coastal areas - india
    Kuttanad, the low-lying tract in Kerala State (South-west India), is a region where excess water has caused the agricultural production to remain low. This is even more severe in the potential acid sulphate soils of Kuttanad. Besides the problems inherent to these soils, the region also experiences floods, lack of fresh water and intrusion of saline water from the Arabian Sea. A subsurface drainage system consisting of 10 cm diameter clay tiles, each of 60 cm length, was installed in a pilot area to study the effect of drainage in alleviating the problems faced by these soils. The drains were installed at a depth of about 1 m with spacings of 15 m (replicated 5 times with a drain length of 75 m) and 30 m (replicated twice with a drain length of 100 m) in order determine the drainage parameters from the field data. The paper discusses on the evaluation of drainage parameters from field data obtained from a pilot area where subsurface drainage system was installed and the use these parameters for designing larger drainage systems. This particular study pertains to the polders of Kuttanad where the fields are always surrounded by water bodies. With the collected drain outflow and water table subsidence data, the drainage parameters namely the hydraulic conductivity and the drainable porosity were determined. A study conducted in subsurface drained field has shown that the hydraulic conductivity values were comparatively higher for the topsoil in the experimental area. It varied directly with the mid-spacing water table height for drains close to the outside water body and exponentially for drains away from the outside water body. The transition in the mode of variation took place at a distance of 60 m from the water body. The values also showed a decreasing trend with the distance of the field from the water body for the same mid-spacing water table heights. The average equivalent hydraulic conductivity computed was 0.167 m/d for regions up to 60 m from the water body and 0.055 m/d for regions beyond that. For areas near to outside water bodies, the drainable porosity increased as the mid-spacing water table height decreased. For areas that are away from the water bodies, the drainable porosity decreased with the mid-spacing water table height and became almost constant at lower mid-spacing water table heights. The average equivalent drainable porosity for the flow domain that are away from the water bodies is 0.04.
    Aluminum-contaminant transport by surface runoff and bypass flow from an acid sulphate soil
    Minh, L.Q. ; Tuong, T.P. ; Mensvoort, M.E.F. van; Bouma, J. - \ 2002
    Agricultural Water Management 56 (2002). - ISSN 0378-3774 - p. 179 - 191.
    kattekleigronden - bodemchemie - uitspoelen - aluminium - vietnam - acid sulfate soils - soil chemistry - leaching - aluminium - vietnam
    Quantifying the process and the amount of acid-contaminant released to the surroundings is important in assessing the environmental hazards associated with reclaiming acid sulphate soils (ASS). The roles of surface runoff and bypass flow (i.e. the rapid downward flow of free water along macropores through an unsaturated soil matrix) in transporting aluminum from three types of raised beds (soil ridges formed by piling up soil materials excavated from adjacent ditches) were studied in a Typic Sulfaquept in Can Tho, Vietnam. During the month of April, 1 h cumulative infiltration of the low raised beds (made only of the topsoil materials) and high raised beds (made of topsoil and jarositic layers) was significantly higher than that of the traditional raised beds (made of topsoil, jarositic and pyritic materials). As the rainfall season progressed, infiltration in July decreased four to seven-fold from the initial values in April, resulting in an increase in runoff. Due to surface crusting, the traditional raised beds yielded the highest runoff (110 versus 50–60 mm in the other types in July). Aluminum concentrations in the bypass flow (6–22 mmol l-1) associated with each of the three bed types were higher than in the runoff (3–14 mmol l-1). In low and high raised beds, the amounts of aluminum transported by bypass flow (15–16 kmol ha-1) was higher than in the runoff (4–6.5 kmol ha-1), while in the traditional type, the two components were similar (11–12 kmol ha-1). The total amount of aluminum released from the low raised beds was lowest. Low raised beds thus pose less environmental hazards to the surroundings compared to the other two types. Interventions that affect the amount of aluminum transport in runoff and in bypass flow are important in balancing agricultural production and environmental protection in ASS areas
    Acid sulfate soils
    Ritsema, C.J. ; Mensvoort, M.E.F. van; Dent, D.L. ; Tan, Y. ; Bosch, H. van den; Wijk, A.L.M. van - \ 2000
    In: Handbook of soil science / Sumner, M.E., - p. G121 - G154.
    kattekleigronden - pyriet - bodemchemie - bodembeheer - modellen - acid sulfate soils - pyrites - soil chemistry - soil management - models
    Spatial variability of acid sulphate soils in the Plain of Reeds, Mekong delta, Vietnam
    Husson, O. ; Verburg, P.H. ; Mai Thanh Phung, ; Mensvoort, M.E.F. van - \ 2000
    Geoderma 97 (2000). - ISSN 0016-7061 - p. 1 - 19.
    kattekleigronden - bodemtypen - rijst - vietnam - ruimtelijke variatie - geostatistiek - acid sulfate soils - soil types - rice - spatial variation - vietnam - geostatistics
    Soil and water indicators for optimal practices when reclaiming acid sulphate soils in the Plain of Reeds, Viet Nam
    Husson, O. ; Mai Thanh Phung, ; Mensvoort, M.E.F. van - \ 2000
    Agricultural Water Management 45 (2000). - ISSN 0378-3774 - p. 127 - 143.
    kattekleigronden - rijst - landverbetering - vietnam - waterstand - acid sulfate soils - rice - land improvement - vietnam - water level
    Water management for rice cultivation on acid sulphate soils in the Plain of Reeds, Vietnam
    Husson, O. ; Hanhart, K. ; Mai Thanh Phung, ; Bouma, J. - \ 2000
    Agricultural Water Management 46 (2000). - ISSN 0378-3774 - p. 91 - 109.
    rijst - zure gronden - waterbeheer - vietnam - kattekleigronden - rice - acid sulfate soils - acid soils - water management - vietnam
    Evaluation of water management strategies for sustainable land use of acid sulphate soils in coastal low lands in the tropics
    Bosch, H. van den; Phi, H.L. ; Michaelsen, J. - \ 1998
    Wageningen : DLO-Staring Centrum (Report / DLO-Staring Centrum 157) - 177
    zure gronden - kattekleigronden - bodemwater - drainage - tropen - indonesië - vietnam - acid soils - acid sulfate soils - soil water - drainage - tropics - indonesia - vietnam
    The use of upscaling procedures in the application of soil acidification models at different spatial scales
    Vries, W. de; Kros, J. ; Salm, C. van der; Groenenberg, J.E. ; Reinds, G.J. - \ 1998
    Nutrient Cycling in Agroecosystems 50 (1998)1-3. - ISSN 1385-1314 - p. 223 - 236.
    zure gronden - kattekleigronden - neerslag - chemische eigenschappen - zuurgraad - zure regen - modellen - onderzoek - geostatistiek - acid soils - acid sulfate soils - precipitation - chemical properties - acidity - acid rain - models - research - geostatistics
    Different soil acidification models have been developed for use on different scales, i.e., NUCSAM for the local scale, RESAM for the regional (national) scale and SMART for the continental scale. This paper focuses on the uncertainties associated with scale transfer by a simpler model description by (i) temporal aggregation of process descriptions, (ii) neglection of processes associated with vertical aggregation of soil layers and (iii) the use of less detailed formulations of processes (process aggregation) and by spatial aggregation of input data. Results obtained for simulations in acid (sandy) soils indicate that (i) temporal aggregation and process aggregation have a limited impact on the long-term (decades) annual response of soil solution chemistry to atmospheric deposition, (ii) vertical aggregation mainly affects predictions of solutes which show a strong concentration gradient with depth and (iii) spatial aggregation hardly affects the average output for a given forest/soil combination. However, ignoring the variability in input parameters, largely affects the frequency distribution of model outputs in a region. Results imply that model simplification is an adequate step in the upscaling of modelling results from a local to a regional scale.
    SMASS - a simulation model of physical and chemical processes in acid sulphate soils; Version 2.1
    Bosch, H. van den; Bronswijk, J.J.B. ; Groenenberg, J.E. ; Ritsema, C.J. - \ 1998
    Wageningen : DLO Winand Staring Centre (Technical document / DLO Winand Staring Centre 21) - 161
    zure gronden - kattekleigronden - fysicochemische eigenschappen - bodemeigenschappen - bodemchemie - infiltratie - hydraulisch geleidingsvermogen - kwel - modellen - onderzoek - chemische processen - acid soils - acid sulfate soils - physicochemical properties - soil properties - soil chemistry - infiltration - hydraulic conductivity - seepage - models - research - chemical processes
    The Simulation Model for Acid Sulphate Soils (SMASS) has been developed to predict the effects of water management strategies on acidification and de-acidification in areas with acid sulphate soils. It has submodels for solute transport, chemistry, oxygen transport and pyrite oxidation. The model must be used together with the water transport model SWACROP. It combines physical and chemical processes. The output includes the acidity and chemical quality of soil and groundwater, and the occurrence of toxic compounds. This user's manual presents an outline of input and output files, guidelines for installation on a VAX-VMS computer, and the description of an application.
    Tillage and water management for riceland productivity in acid sulfate soils of the Mekong delta, Vietnam.
    Minh, L.Q. ; Tuong, T.P. ; Mensvoort, M.E.F. van; Bouma, J. - \ 1997
    Soil & Tillage Research 42 (1997). - ISSN 0167-1987 - p. 1 - 14.
    zure gronden - kattekleigronden - bodem - uitspoelen - acid soils - acid sulfate soils - soil - leaching
    Acid sulfate soils are characterized by low pH and high concentrations of aluminum, sulfate, iron and hydrogen sulfide. Removal of at least part of these substances is a prerequisite for land use, at least in severely acid soils. In this study, the effectiveness of harrowing and flushing with surface water for the removal of toxic substances from the topsoil of acid sulfate soils (ASS) with different toxicity levels was investigated. During the flood recession period, at three experimental sites ranging from slightly, to moderately to strongly acid, two flushing treatments (once or three times, denoted as F1 and F3, respectively) combined with two harrowing treatments (also once or three times, denoted as H1 and H3, respectively) were applied. Soils were classified as very fine Typic Sulfaquepts. At all three sites, when F1 was practiced, H3 did not have a significantly lower soluble aluminum concentration compared with H1. In slightly ASS, the differences between H1 and H3 and between F1 and F3 were not significant. Under moderately acid conditions, the soluble aluminum concentration after H3 was not significantly different from after H1, but it was significantly lower after F3 compared with F1. In severe ASS, H3 combined with F3 gave a significantly lower soluble aluminum concentration compared with F3H1. In addition to soluble Al, Al at the exchange complex was also investigated. The combinations of flushing and harrowing did not significantly change Al at the exchange complex. The F3H3 treatment resulted in a significantly greater rice yield compared with other treatments (F3H1, F1H3 and F1H1). In order to minimize the contamination of surface water, the flood recession period is the optimal time for flushing aluminum out of ASS.
    Contamination of surface water as affected by land use in acid sulfate soils in the Mekong River Delta, Vietnam.
    Minh, L.Q. ; Tuong, T.P. ; Mensvoort, M.E.F. van; Bouma, J. - \ 1997
    Agriculture, Ecosystems and Environment 61 (1997). - ISSN 0167-8809 - p. 19 - 27.
    zure gronden - kattekleigronden - bodem - uitspoelen - aluminium - rivieren - waterlopen - kanalen - water - oppervlaktewater - waterverontreiniging - waterkwaliteit - Vietnam - acid soils - acid sulfate soils - soil - leaching - aluminium - rivers - streams - canals - water - surface water - water pollution - water quality - Vietnam
    Bypass flow and its role in leaching of raised beds under different land use types on an acid sulphate soil.
    Minh, L.Q. ; Tuong, T.P. ; Booltink, H.W.G. ; Mensvoort, M.E.F. van; Bouma, J. - \ 1997
    Agricultural Water Management 32 (1997). - ISSN 0378-3774 - p. 131 - 145.
    infiltratie - hydraulisch geleidingsvermogen - kwel - zure gronden - kattekleigronden - infiltration - hydraulic conductivity - seepage - acid soils - acid sulfate soils
    A better understanding of leaching processes in raised beds is useful in assessing management options for acid sulphate soils. Field and laboratory studies were carried out to quantify the effects of soil physical properties and bypass flow on leaching processes of new, 1-year-old and 2-year-old raised beds for yam and pineapple cultivation in a Typic Sulfaquept in Tien Giang, Vietnam. The methylene blue staining technique was used to characterize the water-conducting pores in terms of number, stained area, and total pore perimeter at 10 cm depth intervals of six 1 x 1 m subplots. Undisturbed 20 cm x 25 cm soil cores taken from the raised beds were subjected to three 30 mm h-1 rains. Volume, aluminum and sulphate concentration of the outflows were monitored. Consolidation with time decreased the area and perimeter of water-conducting pores in 2-year-old pineapple beds to about a third, and bypass flow rate to about 80% of those in newly constructed beds. Consolidation did not affect macropore network geometry in yam beds because they were subjected to annual tillage and yam tubers were uprooted regularly. Al3 and SO4/2- concentrations in the outflows of the newly constructed and 1-year-old raised beds were higher in pineapple, while those in 2-year raised beds were higher in yam
    Surface water management under varying drainage conditions for rice on an acid sulphate soil in the Mekong Delta, Vietnam.
    Hanhart, K. ; Ni, D. van; Bakker, N. ; Bil, F. ; Postma, I. ; Mensvoort, M.E.F. van - \ 1997
    Agricultural Water Management 33 (1997). - ISSN 0378-3774 - p. 99 - 116.
    verbetering - zure gronden - kattekleigronden - drainage - sloten - vietnam - improvement - acid soils - acid sulfate soils - drainage - ditches - vietnam
    Validation and application of soil acidification models at local, national and European scale; a compilation of articles on the models NuCSAM, ReSAM and SMART
    Kros, J. ; Groenenberg, J.E. ; Salm, C. van der; Vries, W. de; Reinds, G.J. - \ 1996
    Wageningen : DLO Winand Staring Centre - 158
    zure gronden - kattekleigronden - bosbouw - neerslag - zure regen - zure depositie - chemische eigenschappen - zuurgraad - modellen - onderzoek - acid soils - acid sulfate soils - forestry - precipitation - acid rain - acid deposition - chemical properties - acidity - models - research
    An overview is given of three dynamic soil acidification models for application on different spatial scales. NUCSAM, the model for the local scale, was validated on data from two intensively monitored research sites. Results of annual average soil solution concentrations and fluxes calculated with the validated NUCSAM model agreed well with those of the national-scale model RESAM and to a lesser extent with those of the European-scale model SMART. Various deposition scenarios for SOx, NOx and NHx on soils were evaluated with the three acidification models.
    Spatial variability of soil actual and potential acidity in the mangrove agroecosystem of West Africa.
    Sylla, M. ; Stein, A. ; Mensvoort, M.E.F. van; Breemen, N. van - \ 1996
    Soil Science Society of America Journal 60 (1996). - ISSN 0361-5995 - p. 219 - 229.
    zure gronden - kattekleigronden - dalen - west-afrika - geostatistiek - agro-ecosystemen - acid soils - acid sulfate soils - valleys - west africa - geostatistics - agroecosystems
    Soil knowledge for farmers, farmer knowledge for soil scientists : the case of acid sulphate soils in the Mekong delta, Viet Nam
    Mensvoort, M.E.F. van - \ 1996
    Agricultural University. Promotor(en): J. Bouma, co-promotor(en): V.T. Xuan. - S.l. : Van Mensvoort - ISBN 9789054855552 - 135
    zure gronden - kattekleigronden - landevaluatie - grondvermogen - bodemgeschiktheid - vietnam - acid soils - acid sulfate soils - land evaluation - land capability - soil suitability - vietnam

    Half the Mekong delta in Vietnam, i.e. around 2 million hectares, suffers soil related problems due to acid sulphate soils. These soils generate sulphuric acid due to the oxidation of pyrite after aeration. Pyrite is most easily formed in tidal swamps. Human interference through land drainage is the most important way in which the acidification takes place. The processes of pyrite formation, of acidification and of the solution chemistry of these soils have been well explained (e.g. van Breemen 1976, Dent 1986). The translation of this knowledge into practical recommendations for farmers is still problematic.

    The Can Tho University (CU), the only institution for higher education in the delta, saw it as its duty to assist the farming community on these soils and come up with practical recommendations for improved agricultural use. From 1980 - 1992 a project of co-operation between CU and the Wageningen Agricultural University, particularly the Soil Science Department, where specialised knowledge on the processes of formation and the chemistry of these soils was present, was carried out. Objectives of the project were (1) to train CU staff in acid sulphate soils formation and survey; (2) to carry out research for improved management of these soils and (3) to equip CU with the necessary facilities for such a research and training programme.

    The aims of this thesis are:

    1 . to review the recent literature on acid sulphate soils in order to screen themethodological developments for survey and identification, for chemical and physical support in field and laboratory, for simulation and mathematical modelling of the soil processes, for management and land use and for acid sulphate land evaluation;
    2. to screen the recent literature, particularly the information supplied by the world's leading specialists in acid sulphate soils in the form of the proceedings of the three most recent conferences on this subject, for its practical applicability by other groups involved with acid sulphate soils: farmers and local experts;
    3. to describe the way the project VH 10, a project of co-operation between the Universities of Can Tho (CU), Mekong delta, Vietnam, and Wageningen Agricultural University (WAU) carded out research for improved management of acid sulphate
    soils between 1980 and 1992 with particular emphasis on the balanced exchange of knowledge between the three groups of people involved: farmers, local experts and specialists;
    4. to describe the way the VH 10 project operated in view of the emphasis it placed onfarmer-expert-specialists knowledge exchange, its strong outreach component towards the farming community and its special ways of operation;
    5. to give some examples of studies which combine farmers, local expert and specialists knowledge to evaluate the acid sulphate land in the Mekong delta.

    The review of the recent literature (chapter II of this thesis) shows how difficult the diagnosis of acid sulphate land is. Some indications can be expected from the vegetation or the drainage patterns. Coastal wetlands, inland marshes and swamps and mine spoils are the land forms where potential acid sulphate soils occur. Surface water usually gives a first warning of acidification having taken place by an oily skin at the surface (iron) or suspicious water clarity (acidity and aluminium). Identification of acidified soils is usually easy through the appearance of pale-yellow jarosite mottles, but is much more difficult in potential acid sulphate soils (pyrite is invisible) or in acidified soils without jarosite. Field tests such as oxidation by hydrogen peroxide for potential acidity, or the azide-soap and the red lead paint for sulphide may help in identification. Moist incubation for prolonged periods is recommended to make sure. Soil survey is difficult because of land inaccessibility, high spatial variability of the diagnostic characteristics and the need for specialised laboratory assistance to identify acid sulphate components. The dynamic modelling of acid sulphate soils received much attention in recent years and resulted in sophisticated models encompassing the processes but inevitably requiring many detailed data for model application. Regardless of all research efforts many management decisions have still to be taken after the problems have already become manifest. Local farmers have, particularly in Southeast Asia, succeeded in adapting to the situation and they have developed interesting management systems for cultivation of rice, shrimp and fish, yams, pineapples, sugar cane and fruit trees.

    The proceedings of the three last conferences dedicated to acid sulphate soils show that most knowledge is communicated specialists to specialists; that some attention is paid to generating knowledge suited for the needs of the local experts such as soil survey methodologies and for the needs of the farmers and the extension workers such as fertiliser recommendations, on-farm water management strategies and crop choice. Only in a few cases, however, the indigenous knowledge of the farmers has been used to its full potential. It is particularly in the Mekong delta that the local farmers' knowledge has played a dominating role in acid sulphate soils research for practical application.

    The VH 10 project of CU and WAU profited from the strong embedding of CU, in particular its Faculties of Agriculture and of Water Management and Rural Engineering, in the rural society of the Mekong delta. The network of contacts with provincial and district agricultural services, with state farms and with private farmers could be used for gathering local farmer knowledge, for experimentation in line with farmers experience, for extrapolation of the findings to other locations in the delta and for knowledge dissemination through workshops and TV programmes.

    The research set-up of the project changed from a top-down technology driven approach in the early and mid-eighties to a system of a balanced knowledge exchange between farmers, local experts and soil/water specialists in the late eighties and early nineties. This approach generated much more successful recommendations for farmers than the top-down approach.

    The project had a number of deviating organisational aspects which might be interesting for application elsewhere: (1) no permanent foreign staff present in Vietnam; (2) large share of the responsibility for the execution of the project left with the Vietnamese counterparts; (3) long term continuity of the project with the same staff (twelve-and-a-half years); (4) mutual interest in project objectives by both partners; (5) applying the principle of learning from each other.

    The project profited from the political change of economic liberalisation in Vietnam in the second half of the eighties since recommendations for improved use of acid sulphate soils, emphasising small-scale development, could much better applied by small farmers than by large scale state farms.

    Two evaluation studies of the acid sulphate land in the Mekong delta (chapter V) showed that fresh water availability is the most important constraint to farming. Moderately and slightly acid land, characterised by a sulphuric horizon deeper than 50 cm, of which large tracts are present in the Mekong delta, can become suited for rice and tolerant upland crops such as yam, cassava or sweet potato when fresh water is available. However, severely acid land will only become marginally suited and should therefore not be given priority for development. Well constructed raised beds can improve the land and makes moderately acid land highly suited for pineapple and sugar cane, provided the coastal salt intrusion in the dry season is short (less than 3 months) and the annual Mekong river flood does not exceed a depth of about 60 cm. Both evaluation studies describe in detail farmers' practices of an unexpected wide variety of land use types and thereby emphasise the main focal point of this thesis which is the major input of farmer's expertise in developing innovative management schemes for these problem soils.

    Integrated soil and water management in acid sulphate soils : balancing agricultural production and environmental requirements in the Mekong Delta, Viet Nam
    Le, Q.M. - \ 1996
    Agricultural University. Promotor(en): J. Bouma, co-promotor(en): T.P. Tuong. - S.l. : Le Quang Minh - ISBN 9789054855569 - 134
    zure gronden - kattekleigronden - grondwaterspiegel - bodem - uitspoelen - aluminium - acid soils - acid sulfate soils - water table - soil - leaching - aluminium

    The objectives of this study in the Mekong delta, Vietnam, were: (1) to obtain a better understanding of the effects of soil physical properties and flow types on solute transport in ASS emphasing aluminum; (2) to quantify environmental hazards resulting from amelioration activities in acid sulphate soils (ASS); and (3) to identify measures which can increase agricultural production and reduce negative environmental side effects.

    This study was conducted on ASS in the Mekong delta, Vietnam and consisted of 5 experiments starting in the dry season and ending at the end of the flood season. All experiments were carried out under field conditions. Transport of soluble aluminum was investigated for different types of water flow, which are typical for each season such as capillary rise, bypass flow and runoff.

    During the dry season, soluble aluminum was accumulated in topsoil layers by capillary rise. Effects of land management methods on accumulation of aluminum was the main focus in this period: Plowing (P1) and mulching (Ml), compared with non-plowing (P0) and non-mulching (M0). Experiments were conducted in lysimeters, and under field conditions. In both experiments, topsoils were treated with P1M1, P1M0, P0M1, and P0M0. Three levels of ground water (GWL: 30, 60, and 90 cm below the ground surface) were maintained in the undisturbed soil columns in the lysimeters. Aluminum accumulation increased with increased evaporation. Under field conditions, where ground water levels were monitored but not controlled, mulching treatments gave a significantly lower aluminum accumulation as compared with the non-mulching treatments, whereas plowing did not result in a significant decrease of this accumulation. Rainfall during the first 3 weeks of the rainy season caused the ground water to rise rapidly while its aluminum concentration increased. This increased the soluble aluminum concentrations in the topsoils and eliminated the leaching effects of earlier land management practices.

    During the rainy season, the study was focused on aluminum transport with bypass flow and runoff in and on raised beds, which are constructed by soil materials excavated from adjacent lateral ditches with the objective to avoid flooding and to enhance leaching of soil. This is a very common technique to grow upland crops in ASS. Therefore, a better understanding of leaching processes in raised beds is needed to properly assess management options for ASS. Three types of raised beds, which are commonly constructed in the Mekong delta, were studied. In the low raised beds only topsoil material was used to construct the bed. In the high type both top soil and the jarosite layer were used. In the "traditional" raised beds, pyritic material was also found on top of the beds. The amount of runoff increased with cumulative rainfall due to a decrease of infiltration rates and saturated hydraulic conductivities. Due to surface crusting, traditional beds gave the highest runoff amounts among the three types. Concentrations of aluminum in bypass flow were consistently higher than in runoff In low and high beds, amounts of aluminum in bypass flow were also higher than in runoff, whereas in traditional bed-types it was slightly lower. However, the negative impacts on the surrounding surface water was not significantly different for the three types of beds. Therefore, the low bed type is the most desirable from an agricultural production point of view, because less effort is needed in construction.

    Pore system distribution can play a very important role in determining water flows in and on the raised beds and as a consequence, on the effectiveness of leaching toxic substances. Thus, field and laboratory studies were carried out to quantify the effects of soil physical properties and bypass flow on leaching processes of new, 1-year old and 2-year old raised beds for yam and pineapple cultivation. Water-conducting pores were characterized using Methylene Blue. Number, area, and perimeter of water- conducting pores at 10-cm depth intervals of six 1 x 1m subplots were investigated. Undisturbed 20 cm x 25 cm soil cores were subjected to three 30 mm h -1rains in 30 minutes. Volume, aluminum and sulphate concentration of outflows were monitored. Due to consolidation, the area and perimeter of water-conducting pores in 2-year old pineapple beds had decreased to about one third, and bypass flow rates to about 80% of those in newly constructed beds. Consolidation, however, did not affect macropore network geometry in yam beds because they were subjected to annual tillage and yam tubers were uprooted regularly. Al and SO42-concentrations in the outflows of newly constructed and 1-year old raised beds were higher in pineapple, while those in 2-year raised beds were higher in yam.

    A side effect of leaching of ASS may be the pollution of surrounding waters. In order to obtain a proper assessment of this problem, the concentration and the amount of aluminum in water leaching from ASS during cultivation of rice, pineapple and yam were investigated. The fields have been reclaimed for 2 months, 1 and 2 years, respectively. Pineapple and yam were cultivated on raised beds. Values of pH in drainage water ranged from 2.9 to 3.9 and aluminum concentration from 3 to 13 mmol(+) l -1. Mean monthly aluminum concentrations in the water discharged from pineapple and yam raised beds was about 3 times higher than from rice fields. Monthly total amount of aluminum released by the raised beds could be as high as 16,690 mol ha -1, and was 3 to 5 times higher than that from rice fields. Consolidation and crust formation in pineapple beds reduced the concentration and amount of aluminum released as the beds grew older. In June, leaching from ASS was most hazardous to the environment due to a combination of highest total aluminum released to the canal network and a relatively low river discharge.

    At the flood recession period, the effectiveness of flood water (in combination with harrowing) in flushing out toxic substances from the top soil of ASS was investigated. Three experimental sites with slight, moderate and strong acidity were selected. Treatments were the number of harrowings (one: H1 and three times: H3) and the number of flushings (one: F1 and three times: F3).Three times harrowing in combination with three times flushing was the most effective in leaching acid in the most acid soils. When flushing once, the number of harrowings had no effect. The quantity of aluminum adsorbed on the soil exchange complex was not affected by different harrowing and flushing treatments. F3H3 also gave a significantly higher rice yield as compared with other treatments. The flood recession period is the most appropriate moment for flushing topsoils for rice cultivation, which has a high water requirement.

    Developing management packages for acid sulphate soils based on farmer and expert knowledge : field study in the Mekong Delta, Viet Nam
    Quang Tri, Le - \ 1996
    Agricultural University. Promotor(en): J. Bouma; V.T. Xuan. - S.l. : Le Quang Tri - ISBN 9789054855583 - 200
    zure gronden - kattekleigronden - landevaluatie - grondvermogen - bodemgeschiktheid - ruimtelijke ordening - landgebruik - zonering - expertsystemen - vietnam - kunstmatige intelligentie - acid soils - acid sulfate soils - land evaluation - land capability - soil suitability - physical planning - land use - zoning - expert systems - vietnam - artificial intelligence

    Effective interaction of farmers' expertise and expert knowledge has been a special point of attention for this study. The objectives of the study were to describe the process of interaction between farmers and experts in improving the use of acid sulphate soils and to point out difficulties encountered. Actual conditions for four major areas were described including variabilities. Four representative areas: Tan Thanh, Tri Ton, Phung Hiep, and Hong Dan in the Mekong Delta, Viet Nam were selected for this study. Physical conditions were defined in terms of soil properties, as reflected by soil classification, and hydrological conditions were defined by climate data including flooding. Methods for land improvement in different areas were first defined by describing and analyzing measures taken by farmers, and by next developing schemes for improvement, using expert knowledge. These schemes were expressed by decision trees as a part of expert systems. But many questions were left and a series of experiments was designed and executed to answer those questions that could not be answered by experts.

    Four study areas were selected. Tan Thanh and Tri Ton (in the Plain of Reeds and Long Xuyen Quadrangle, respectively) have acid sulphate soils with sulphuric horizons within 50 cm from the soil surface, and deep flooding (>100cm) during the rainy season. The Phung Hiep area with moderately acid sulphate soils is not deeply flooded and is located in the fresh water area of Ca Mau peninsula. The Hong Dan area contains mainly moderately and strongly acid sulphate soils with salt water intrusion during the dry season. The main agricultural problems in these study areas, where most farmers are poor, arise from the fact that most modem practices or new cropping patterns are applied incompletely and at unequal levels. Also unfavourable soil acidity coincides with high flooding depth or salt water intrusion, poor infrastructure for irrigation and drainage and shortage of capital for farm production. Furthermore, price fluctuations of farm products are very high, which makes economic production very difficult.

    A study at farmers' level shows that the history of fanners' land use, including their soil-water-crop management practices clearly indicates changes of land use over time and the important role of expert knowledge in initiating these changes. Developments also illustrate the positive effects of the creative interaction between fanners and experts in developing innovative management systems. Ten, four, sixteen and eleven actual land use types, including land and water practices, were described for the Tan Thanh, Tri Ton, Phung Hiep, and Hong Dan areas, respectively. Water-soil-crop management practices such as construction of canals and infrastructure for irrigation, construction of high raised beds for cultivation of upland crops, and construction of a ditch system for the prawn/shrimp-rice system were essential parts of these land use systems.

    Studies by experts paid more attention to the cultivation of crops, mainly rice, and the associated water management practices. Sixteen promising land use types were defined for a land suitability classification study based on present land use systems of four study areas. Double cropping of modem rice varieties is present in all study areas. Eight land qualities were identified for a farm-level land evaluation. Land quality "(potential) soil acidity" is important for all land use types selected. Land qualities: "flood hazard", "drought hazard", "salt water intrusion", and "fresh water availability" are important for double cropping of modem rice varieties. Land qualities: "potential for daily tidal flooding and drainage" are critical for raising of prawn/shrimp. For land evaluation at farm level, decision trees were developed and used as an decision support system. Decision trees were made for each promising land use type. Using decision trees as a decision support system for land evaluation study at the farm level was shown to be helpful to identify optimal management decisions. Conditions for improvement of suitability were identified and visualized in those decision trees, in terms of improved soil and water practices based on farmers' expertise and expert knowledge.

    While developing these schemes, it became clear that many unanswered questions on land use requirements and water management practices were encountered. These were formulated and field experiments were carried out to answer the questions. Some conclusions were drawn from these experiments: (1) For yam cultivation in acid sulphate soil areas with a deep flood in the wet season, application of a mulch layer on top of the raised bed resulted in a 46% higher yield as compared with urimulched plots; (2) the use of fresh water in an irrigation frequency of 20 days, when available during the dry period of the cropping season, increased yields of yam by 31%. (3) Rolled-carpet raised beds gave higher yields as compared with mixed-raised beds. (4) A relatively high yield of yarn can be obtained by application of N 120 -P 60 -K 60 as is already being practised by farmers in the area or N 80 -P 160 -K 100 . Higher fertilizer applications give no better yields. Staking yam vines is of limited importance and does not increase yarn production. A planting density of 40 cm. x 50 cm is proposed for yam cultivation. (5) For pineapple cultivation in areas with dry season salinity, supplementary irrigation in the early dry season had no effect on pineapple yield. (6) Production was higher on high raised beds as compared with traditional lowraised beds because excess water in the rainy season. Old raised beds gave significantly higher yields as compared with younger raised beds because of lower acidity due to longer leaching by rain. (7) A yield increase of pineapple of about 20% can be obtained by a combination of high P and K fertilization ( 10N-7g P 2 O 5 -10K 2 O/plant). And (8) application of the zero-tillage technique was profitable as it shortened the duration of double cropping of Winter-Spring modem rice followed by Summer-Autumn rice in areas with long duration flooding. These accumulated results provided quantitative data to characterize land qualities and land use requirements relating to fresh water availability, soil acidity, and flooding hazard . Also data for agronomic practices were obtained by experiments to be used for formulating optimal management packages.

    Under different physical conditions, optimal management packages on acid sulphate soils were finally formulated for the four study areas in. These optimal management packages were based on the farmers' practice, expert knowledge, results of land evaluation study at farm level and accumulated results obtained by field experiments. There are many options including various cultural, soil and water management practices for the different physical conditions encountered. Double modem rice cropping, and growing yam, pineapple, and sugarcane, are suitable in areas where fresh water is available during the dry season. In areas with salt water intrusion during the dry season, land use types incorporating shrimp are more profitable. Melaleuca spp. is most suitable for remote and unfavourable areas for crop growth as a means for reforestation in order to protect natural environments. These results provides a good start to obtain description of realistic and acceptable systems. In the future, these description can also be used to identify areas of additional research by measurement or by simulation modelling.

    Scenario studies on soil acidification at different spatial scales
    Vries, W. de; Kros, J. ; Groenenberg, J.E. ; Reinds, G.J. ; Salm, C. van der; Posch, M. - \ 1995
    In: Scenario studies for the rural environment : selected and edited proceedings of the symposium scenario studies for the rural environment, Wageningen, The Netherlands, 12 - 15 September 1994 / Schoute, J.T.H., Finke, P.A., Veeneklaas, F.R., - p. 169 - 188.
    zure gronden - kattekleigronden - neerslag - chemische eigenschappen - zuurgraad - zure regen - modellen - onderzoek - acid soils - acid sulfate soils - precipitation - chemical properties - acidity - acid rain - models - research
    Three dynamic soil acidification models have been developed for application on local, national and continental (European) scales, namely NUCSAM, RESAM and SMART. This paper gives an overview of results of various model validation and scenario studies for the effects of SOx, NOx and NHx deposition on soils. Furthermore, the various strong and weak points of the models are evaluated in terms of uncertainties in model predictions, the use of the models in acidification abatement policies, and the limitations and possibilities of using the models in other scenario studies, such as changes in land use, hydrology and heavy-metal deposition.
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