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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    Sulfaat in veenweiden: gebiedsvreemd of gebiedseigen?
    Hendriks, R.F.A. ; Twisk, J.W.R. ; Gerven, L. van; Harmsen, J. - \ 2013
    H2O : tijdschrift voor watervoorziening en afvalwaterbehandeling 2013 (2013)mei. - ISSN 0166-8439 - p. 1 - 8.
    waterbodems - geochemie - veenweiden - bodemchemie - zure gronden - waterbeheer - krimpenerwaard - water bottoms - geochemistry - peat grasslands - soil chemistry - acid soils - water management - krimpenerwaard
    Sulfaat is een belangrijke stof in sloten in veenweidegebieden. Het wordt in de zuurstofloze waterbodem door micro-organismen omgezet in sulfide, dat zich bindt aan ijzer. Daardoor komt fosfaat vrij, wat slecht is voor de ecologische kwaliteit van het slootwater. De gedachte was altijd dat de inlaat van gebiedsvreemd water in de polders de grootste bron van sulfaat is. De laatste jaren is duidelijk geworden dat het sulfaat vooral afkomstig is uit de veenweidebodem zelf. In de Krimpenerwaard gaat het om 75%. Het inlaatwater blijkt de sulfaatconcentraties in de gemiddelde veensloot zelfs omlaag te brengen!
    Iron and sulphate as possible key factors in the restoration ecology of rich fens in discharge areas
    Kemmers, R.H. ; Delft, S.P.J. van; Jansen, P.C. - \ 2003
    Wetlands Ecology and Management 11 (2003)6. - ISSN 0923-4861 - p. 367 - 381.
    bodemchemie - veengronden - bodemwaterbeweging - calcium - zure gronden - soil chemistry - calcium - acid soils - peat soils - soil water movement
    Seven reference areas in the Netherlandswere selected to trial restoration measuresin acidified rich fens in discharge areas.In about half of the projects the measuresthat aimed to restore the high base statusof the topsoil failed. The aim of thepresent study was to identify the keyfactors and processes in base regulation ofrich fen systems, in order to underpinfuture restoration. We sampled soil andinterstitial water from distinct soilhorizons and analysed it for variablesinvolved in geohydrochemical processes. Wemonitored interstitial water chemistry andredox potentials to calibrate and validatea chemical speciation model, that we usedfor the interpretation of our observations.It appeared that soil pH, Ca2+saturation and iron contents weresignificantly lower at sites whererestoration efforts had failed. At the sametime, soils of these sites were verystratified instead of homogenous. Onlysoils with high iron contents recovered ahigh Ca2+ saturation. All sites werecharacterised by considerable downwardwater fluxes through the soil. Chemicalspeciation modelling was a useful tool forthe interpretation of processes underlyingour observations and helped elucidate thefactors and processes that control therecharge of the CEC by base cations. The modelling results suggested that the mainprocess in proton neutralisation ofsuccessful sites is the production ofinternal alkalinity by reduction of ironoxides. Additional redox capacity can besupplied by the ample presence ofsulphates. From our results we hypothesisethat the CEC will only be rechargedsuccessfully with base cations in thepresence of sufficient redox capacity ofthe soil. It seems that redox processesfacilitate the ionic exchange of protonsfor Ca2+ ions. Sites where restorationefforts failed changed from discharge areasto recharge areas, which caused irondepletion by leaching. We conclude thatproper understanding of the pedological andgeohydrochemical processes that control thebase status of soils is a prerequisite forsuccessful nature restoration. The role ofsoil processes cannot be ignored as itseems that the production of internalalkalinity upon reduction exceeds theexternal supply of alkalinity bygroundwater flow.
    Release rates of Al from inorganic and organic compounds in a sandy podzol, during laboratory experiments
    Salm, C. van der; Westerveld, J.W. ; Verstraten, J.M. - \ 2000
    Geoderma 96 (2000)3. - ISSN 0016-7061 - p. 173 - 198.
    bodemoplossing - bodem - aluminium - zure gronden - adsorptie - soil solution - soil - aluminium - acid soils - adsorption
    Research with respect to release rates of Al and Al concentrations in the soil solution has led to two contrasting hypotheses, stressing either the importance of kinetically constrained dissolution reactions or the role of complexation of Al to soil organic matter. The existence of two contrasting hypotheses is partly due to the fact that the interpretation of existing results is hampered by the lack of specificity of the extractants used to quantify the organic and inorganic pools of Al and by the fact that simultaneous measurements on the release of Al and the change in Al pools are missing. This study was conducted to obtain more information on the release rates of Al from various amorphous pools and to evaluate the validity of the above hypotheses. To overcome the above-mentioned shortcomings both release rates of Al and changes in the various,Al pools were measured during the experiment. Experiments were conducted for Ap, Bs and C horizons from a sandy podzol. Results indicated that Al was released from both the inorganic Al pool (oxalate minus pyrophosphate extractable Al) and the strongly bound organic Al pool (pyrophosphate minus CuCl2 extractable Al) according to a first-order reaction. The decline in the weakly bound organic Al pool (CuCl2 extractable minus adsorbed Al) could be described by a rapid dissolution of part of the pool, combined with an equilibrium reaction describing the complexation of Al to organic sites. Rate constants were highest for the non-complexed part of the weakly bound organic Al pool, intermediate for the inorganic Al pool and lowest for the strongly bound organic Al pool. Large differences exist in rate constants of the organic pools between the three horizons. Differences between the rate constants of the inorganic Al pool for the three horizons were not significant.
    Biological nitrogen fixation of soybean in acid soils of Sumatra, Indonesia
    Waluyo, S.H. - \ 2000
    Agricultural University. Promotor(en): W.M. de Vos; L. 't Mannetje; L.T. An. - S.l. : S.n. - ISBN 9789058082954 - 151
    glycine max - sojabonen - bodembiologie - stikstoffixatie - stikstofbindende bacteriën - rhizobium - bradyrhizobium - inoculatie - entstof - biochemische technieken - dna-fingerprinting - stamverschillen - stammen (biologisch) - zaadbehandeling - omhullen - zure gronden - bodemaciditeit - bekalking - sumatra - indonesië - glycine max - soyabeans - soil biology - nitrogen fixation - nitrogen fixing bacteria - rhizobium - bradyrhizobium - inoculation - inoculum - biochemical techniques - dna fingerprinting - strain differences - strains - seed treatment - pelleting - acid soils - soil acidity - liming - sumatra - indonesia

    The aim of this study is to improve soybean cultivation in transmigration areas, especially in Sitiung, West Sumatra. However, these soils are very acid, and have a high P-fixing capacity. To reduce the amounts of fertilisers, normally 5 - 7 ton lime ha -1 and 100 kg P as TSP, seed, pelleted with lime (60 kg ha -1 ) and TSP (10 kg ha -1 ), was introduced. In this way only 2 ton lime ha -1 are required.

    Soybean can fix nitrogen (BNF) in symbiosis with ( Brady ) Rhizobium bacteria. However, these acid soils in general, have low numbers of ( Brady ) Rhizobium . By inoculating the soils with ( Brady ) Rhizobium , BNF of soybean, and yield, were considerably improved.

    A study was made of the indigenous ( Brady ) Rhizobium population in view of the following:

      Although at the beginning the numbers may be low, by repeated soybean cultivation, the numbers will increase, and they may interfere with inoculation of effective ( Brady ) Rhizobium strains.These indigenous ( Brady ) Rhizobium are adapted to local stress conditions, and they may be useful for the improvement of strains, to be used as inoculants.

    Using molecular techniques, indigenous strains derived from soil samples from old soybean areas (Java) and from new soybean areas (Sumatra) were classified in more detail. Most likely B. japonicum is the dominant strain in Java while in Sumatra B. elkanii is more present. A Sinorhizobium fredii -like strain was isolated from one soil sample from Java.

    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
    Quantification and simulation of errors in categorical data for uncertainty analysis of soil acidification modelling
    Finke, P.A. ; Wladis, D. ; Kros, J. ; Pebesma, E.J. ; Reinds, G.J. - \ 1999
    Geoderma 93 (1999). - ISSN 0016-7061 - p. 177 - 194.
    zure gronden - zure regen - cartografie - ruimtelijke variatie - schaalverandering - landen van de europese unie - acid soils - acid rain - mapping - spatial variation - scaling - european union countries
    Uncertainty assessment in modelling soil acidification at the European scale: a case study
    Kros, J. ; Pebesma, E.J. ; Reinds, G.J. ; Finke, P.A. - \ 1999
    Journal of Environmental Quality 28 (1999)2. - ISSN 0047-2425 - p. 366 - 377.
    zure gronden - zure regen - modellen - nederland - acid soils - acid rain - models - netherlands
    Modelling impacts of atmospheric deposition, nutrient cycling and soil weathering on the sustainability of nine forest ecosystems
    Salm, C. van der; Vries, W. de; Olsson, M. ; Raulund-Rasmussen, K. - \ 1999
    Water Air and Soil Pollution 109 (1999). - ISSN 0049-6979 - p. 101 - 135.
    bosbouw - zure depositie - bodemchemie - zure gronden - voedingsstoffen - modellen - zweden - denemarken - nederland - forestry - acid deposition - soil chemistry - acid soils - nutrients - models - sweden - denmark - netherlands
    Biological management for productive and sustainable cropping systems on acid upland soil in the humid tropics : final report of a project funded under the European Communities STD3 programme 1994 - 1997; contract TS3* - CT94-0261
    Whitmore, A.P. ; Cadish, G. ; Hairiah, K. - \ 1998
    Wageningen : AB-DLO (Nota / Research Institute for Agrobiology and Soil Fertility (AB-DLO) 89) - 78
    teeltsystemen - middelgebergte - hooggelegen gronden - zure gronden - humide tropen - cropping systems - upland areas - upland soils - acid soils - humid tropics
    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.

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