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The observations of a long-term experiment on the use of saline water were used to check the hypothesis whether models developed for drought conditions are valid for yield prediction in case of salinity. The models for the relation between yield and evapotranspiration, proposed by Stewart and Hagan (1973) and Stewart et al. (1977), were used for maize, sunflower, potatoes and soybean. The yield estimation for maize and sunflower was quite accurate, for potatoes somewhat less, but unsatisfactory for soybean. The estimated yield of soybean under saline conditions was higher than the measured one. This may be attributed to the differences in salt tolerance between soybean varieties or to an additional effect of salinity on the nitrogen supply of this legume.

To assess the drainable surplus of an irrigated area, a methodology based on a groundwater-balance approach was developed and applied in Schedule I-B of the Fourth Drainage Project near Faisalabad in Pakistan. To determine the seasonal net recharge in this area, a numerical groundwater model was run in inverse mode. The data input for the model consisted of the geometry of the aquifer system, the aquifer parameters, and historical watertable elevations. The seasonal net recharge values, calculated from the individual recharge and discharge components, were "tuned" with the results of the inverse modelling. The advantage of such an integrated approach is that all these components are linked. The design net recharge was estimated from the historical net recharge of the wettest monsoon in the study period. Its rainfall recharge values were then substituted for those of a design monsoon. In this substitution procedure, the rainfall recharge methodology and parameters were adopted from the tuning procedure. From this design net recharge, estimates could be made of the required drainable surplus, with and without drainage simulation.

Increasing competition for water of good quality and the expectation that at least half of the required increase in food production in the near-future decades must come from the world's irrigated land requires to produce more food by converting more of the diverted water into food. Reuse of the non-consumed fraction ('drainage water') of the irrigation water already diverted is a proven but risky option for better fresh water management. This paper presents an overview of different options for reuse of drainage water and guidelines for its safe use. Criteria for maximum irrigation water salinity to prevent soil deterioration and crop yield reduction, for the maximum concentration of toxic substances and limits for bacteriological water quality are given. Examples of sustainable reuse of drainage water in Egypt, India and the USA are presented. The usefullness of simulation models for the analysis of regional water and salt balances is demonstrated.

In the Netherlands a law will enforce the use of closed growing systems in greenhouses. A project is initiated at IMAG-DLO to introduce ion-selective measurement and controlled injection of singular liquid nutrients in closed growing systems. As part of this project step and impulse response tests are carried out to study the dynamic behaviour of salinity changes in an NFT growing channel. The paper describes a time delay algorithm for the trickle irrigation system and an aggregated dead zone model for the growing channels in closed NFT growing systems. It suggests a Smith Predictor as a controller for a nutrient dispenser system. Ion-selective measurement on a practical scale will only be available for a few nutrient ions. Controlled injection of singular liquid fertilizers will need information on plant uptake of ions which cannot be measured in relation to ions which can be measured

Salinity and sodicity of soils are two common problems encountered in the Hola Irrigation Scheme in east Kenya. Both result in poor crop performance and reduced yields. Based upon a detailed survey in a 405 ha area consisting of 45 irrigation blocks, the spatial variability of pH, EC e and ESP was studied. Data obtained were analyzed using geostatistical procedures in a geographical information system. As it turned out, sodicity in the area has a clear spatial structure. Also differences in homogeneity per block were observed. Reclamation will be necessary, mainly because of the sodicity in the area, while salinity is still at an acceptable level for all crops grown and only small amounts of water are needed to maintain these EC levels. This results in varying gypsum requirements for reclamation for different blocks. A Geographical Information System (GIS) was used to handle large amounts of data and to compare the effects of different land use scenarios.

An integrated approach is developed to assess a priori the effects of irrigation management interventions on soil salinity, sodicity and transpiration. The approach is tested for a 75,000 ha irrigation system in Pakistan, where canal and groundwater are used conjunctively. The main hypothesis is that by reallocating good quality canal water, the use of poor quality groundwater can be restricted, thus combating salinity and sodicity and mitigating their effects on crops. The study has three components. Firstly, interventions in canal water deliveries to tertiary units are analyzed using an unsteady state hydraulic model, based on the St. Venant equations, and linked with a regulation module, which captures the operational decisions of the irrigation agency. By changing the operational rules at the main canal, and by redimensioning the outlets in secondary canals, the water can be distributed equitably to tertiary units or delivered to those units that require it for salinity control. Secondly, the impact of irrigation on salinity, sodicity and transpiration is assessed for farmers' fields, using a combined soil water flow and solute transport model, based on Richard's equation and the convection-dispersion equation, and a regression equation, based on the irrigation quality and soil texture. A curvilinear relationship with a decreasing tangent was found between the irrigation quantity and soil salinity. Increases in the EC of the irrigation water result in a parallel curve with higher salinity levels. Adapting the irrigation quantity and quality to the existing soil types and depth to groundwater table can, therefore, reduce salinity and sodicity, thus avoiding soil degradation, which already occurs at an ESP of 4%. Thirdly, both components are combined with a parallel, socio-economic study, where farmers' decisions related to the crop portfolio and acquisition/application of water, were captured in Linear Programming models. The individual models of both studies are interfaced to develop a tool, capable of quantifying the effect of irrigation management interventions. For a secondary canal serving 14,000 ha, it is shown that the area threatened by sodicity is reduced by 40% by reallocating canal water, without affecting the agricultural production. The results of the developed tool should not be taken as accurate predictions, as there are likely to be unforeseen events due to the complexity of irrigation systems. Instead, the approach should be evaluated for its effectiveness in supporting actors' decisions in irrigation system management, by enhancing their understanding of the effects of interventions on salinity, sodicity and agricultural production. The application of the approach, in two case studies, shows that it allows the investigation of a wide range of policy and management interventions, and captures adequately the complexity of an irrigation system, thus providing indications about its transferability. However, the tools should be applied as part of an integrated concept, which includes phases of diagnosis, identification of relevant processes and parameters, and discussions with actors.; Une approche intégrée est développée pour évaluer l'impact d'interventions dans la gestion de l'irrigation sur la salinité des sols, la sodicité et la transpiration. L'approche est appliqué à un système irrigué de 75,000 ha au Pakistan, caractérisé par une utilisation conjointe des eaux douces de canal et eaux souterraines de faible qualité, dans l'hypothèse que la reallocation de l'eau de canal contribue à minimiser l'utilisation des eaux souterraines, ainsi diminuant la salinité et la sodicité, et leurs effets sur les cultures. L'étude présente trois axes de recherche: (1) Une analyse de la gestion du système d'irrigation par un modèle hydraulique en régime transitoire, basé sur les équations de St. Venant, lié à un module prenant en compte les décisions opérationnelles de l'agence d'irrigation. La distribution de l'eau actuelle peut être améliorée en adoptant des règles opérationnelles alternatives pour le canal principal et en changeant les dimensions des prises d'eau tertiaires. Ainsi, une distribution équitable de l'eau ou une redistribution de l'eau à des prises tertiaires spécifiques pour le contrôle de la salinité peut être atteint. (2) Une analyse de l'effet des pratiques d'irrigation sur la salinité, la sodicité et la transpiration par un modèle de transfert hydrique et de solutés, basé sur les équations de Richards et l'équation de convection-dispersion, et par une équation entre le risque de sodisation et la qualité de l'irrigation et la texture du sol. Il est montré que la quantité et la qualité de l'eau d'irrigation influencent considérablement la salinité et la sodicité. La gestion de l'irrigation est donc un instrument important dans la lutte contre ces phénomènes. (3) Dans une étude économique parallèle, les processus de prise de décision des paysans concernant les choix de cultures, et l'obtention et la distribution de l'eau ont été formalisés dans des modèles LP.

An integrated approach is developed to assess a priori the effects of irrigation management interventions on soil salinity, sodicity and transpiration. The approach is tested for a 75,000 ha irrigation system in Pakistan, where canal and groundwater are used conjunctively. The main hypothesis is that by reallocating good quality canal water, the use of poor quality groundwater can be restricted, thus combating salinity and sodicity and mitigating their effects on crops. The study has three components. Firstly, interventions in canal water deliveries to tertiary units are analyzed using an unsteady state hydraulic model, based on the St. Venant equations, and linked with a regulation module, which captures the operational decisions of the irrigation agency. By changing the operational rules at the main canal, and by redimensioning the outlets in secondary canals, the water can be distributed equitably to tertiary units or delivered to those units that require it for salinity control. Secondly, the impact of irrigation on salinity, sodicity and transpiration is assessed for farmers' fields, using a combined soil water flow and solute transport model, based on Richard's equation and the convection-dispersion equation, and a regression equation, based on the irrigation quality and soil texture. A curvilinear relationship with a decreasing tangent was found between the irrigation quantity and sod salinity. Increases in the EC of the irrigation water result in a parallel curve with higher salinity levels. Adapting the irrigation quantity and quality to the existing soil types and depth to groundwater table can, therefore, reduce salinity and sodicity, thus 'avoiding soil degradation, which already occurs at an ESP of 4%. Thirdly, both components are combined with a parallel, socio-economic study, where farmers' decisions related to the crop portfolio and acquisition/application of water, were captured in Linear Programming models. The individual models of both studies are interfaced to develop a tool, capable of quantifying the effect of irrigation management interventions. For a secondary canal serving 14,000 ha, it is shown that the area threatened by sodicity is reduced by 40% by reallocating canal water, without affecting the agricultural production. The results of the developed tool should not be taken as accurate predictions, as there are likely to be unforeseen events due to the complexity of irrigation systems. Instead, the approach should be evaluated for its effectiveness in supporting actors' decisions in irrigation system management, by enhancing their understanding of the effects of interventions on salinity, sodicity and agricultural production. The application of the approach, in two case studies, shows that it allows the investigation of a wide range of policy and management interventions, and captures adequately the complexity of an irrigation system, thus providing indications about its transferability. However, the tools should be applied as part of an integrated concept, which includes phases of diagnosis, identification of relevant processes and parameters, and discussions with actors.

Increasing competition for water of good quality and the expectation that at least half of the required increase in food production in the near-future decades must come from the world's irrigated land requires to produce more food by converting more of the diverted water into food. Reuse of the non-consumed fraction ('drainage water') of the irrigation water already diverted is a proven but risky option for better fresh water management. This paper presents an overview of different options for reuse of drainage water and guidelines for its safe use. Criteria for maximum irrigation water salinity to prevent soil deterioration and crop yield reduction, for the maximum concentration of toxic substances and limits for bacteriological water quality are given. Examples of sustainable reuse of drainage water in Egypt, India and the USA are presented. The usefullness of simulation models for the analysis of regional water and salt balances is demonstrated.

Over a period of 6 years, various crops were grown in tanks, filled with loam and clay, and were irrigated with water of three different levels of salinity. A combination of soil water sampling, salt balance and salt model was used to study the change in the composition of the soil water and the development of soil salinity. After 3 years an equilibrium was attained in the exchange between soil water and adsorption complex. Precipitation of a mixture of calcium and magnesium carbonate occurred during the whole experimental period. During the last two cropping periods the average chloride concentration of the soil profile obtained from soil water sampling was about twice as low as that obtained from the salt balance, due to preferential flow through macropores attaining the porous cups. Model calculation indicated a bypass fraction of a about 0.15. The steady-state leaching model of USSL could be used to estimate the long-term chloride concentration of the soil profile.

To assess the drainable surplus of an irrigated area, a methodology based on a groundwater-balance approach was developed and applied in Schedule I-B of the Fourth Drainage Project near Faisalabad in Pakistan. To determine the seasonal net recharge in this area, a numerical groundwater model was run in inverse mode. The data input for the model consisted of the geometry of the aquifer system, the aquifer parameters, and historical watertable elevations. The seasonal net recharge values, calculated from the individual recharge and discharge components, were "tuned" with the results of the inverse modelling. The advantage of such an integrated approach is that all these components are linked. The design net recharge was estimated from the historical net recharge of the wettest monsoon in the study period. Its rainfall recharge values were then substituted for those of a design monsoon. In this substitution procedure, the rainfall recharge methodology and parameters were adopted from the tuning procedure. From this design net recharge, estimates could be made of the required drainable surplus, with and without drainage simulation.

In Punjab, Pakistan, scarcity of canal water has lead to a rapid growth of the number of tube wells, pumping poor quality groundwater. In recent years, concerns have been expressed about the threat of salinization through the increasing use of tube well water for irrigation purposes. This paper reviews research results of a model study on the impact of irrigation practices, i.e., irrigation quantity, quality and frequency, on soil salinity and crop transpiration of cotton and wheat in a conjunctive use environment. Four fields with a different soil texture and irrigation water quality were selected and monitored during three cropping seasons. The agro-hydrological model SWAP93 was used to analyse the water flow and salt transport for the prevailing conditions. In the calibration process, the simulated water and salt balance appear to be sensitive to rooting depth, crop factors, actual soil evaporation and the soil retention function. Two concepts were used to account for field-scale heterogeneity of water infiltration and preferential flow. Taking into account this heterogeneity, the percolation losses increase, while the leaching of salts decreases. The calibrated model was used to evaluate the effects of various irrigation practices on salinization and crop transpiration. The irrigation water quantity, in terms of under-irrigation, has a greater impact than the quality of the irrigation water. Irrigation frequency may have a significant impact on the water and salt balance, especially on sandy soils. Finally, long term effects of current irrigation practices are discussed, in relation to the different soils in the study area. Soil texture appears to affect crop transpiration and salinization considerably.

Spatial variability of soil salinity in coastal low lands results from a complex interaction of climate, river hydrology, topography and tidal flooding. The aim of this study was to determine the significant effects of these causal factors at different scales in the West African mangrove environment. The driving forces are the penetration of tidal saline waters and subsequent water evaporation in the flood plain, of which the magnitude is controlled by the causal factors. A hierarchical framework of the different factors was designed. Four river basins were selected: the Gambia, the Casamance (Senegal), the Geba (Guinea Bissau) and the Great Scarcies (Sierra Leone). Within each river basin, three strips of land (80 m wide, 500 to 1800 m long), perpendicular to the river at different distances from the mouth, were selected. In the dry season of 1991, soil samples were taken from the strips using a 40 m × 20 m grid at five soil depths to be analyzed for salinity. The contribution of the different sources to salinity spatial variability was analyzed with a nested ANOVA. Geostatistics were used to model spatial variability at micro-scale. As a result, main environments at macro scale (between river basins), sub-environments at meso scale (within river basins) and salinity classes at micro scale (within catena) were defined. Nested regression and geostatistics were found complementary to disentangle the complexity of the factors influencing salinity spatial variability.

To study the effect of salinity on the emergence and early seedling growth of sunflower and maize, experiments were conducted in pots filled with sandy clay and sandy loam. The experiments consisted of a control and four saline water qualities with chloride concentrations of 15, 30, 45, and 60 meq/l. The emergence of sunflower and maize were affected by salinity. Soil texture did not affect the emergence. During early seedling growth, salinity and soil texture affected the development of the seedlings that showed symptoms of water stress in the form of lower leaf water potential, stomatal conductance, and evapotranspiration. The higher the salinity, the lower the leaf area and the dry matter production. Leaf, stem, and root showed an almost similar growth reduction due to salinity. Seedlings on sandy loam were more affected by water stress than those on sandy clay.

In the mangrove environment of West Africa, high spatial and temporal variability of soil constraints (salinity and acidity) to rice production is a problem for the transfer and adoption of new agronomic techniques, for land use planning, and for soil and water management. Recently, several National and International Agricultural Centers have initiated research programs to characterize environments where their newly developed technologies have to be applied. However, the mangrove agro- ecosystems in West Africa have not been characterized in a detailed way. Most of the soils in this environment are potential or actual saline acid sulfate soils. The spatial and temporal variability of soil salinity and acidity in these coastal lowlands results from complex interactions between climate, coastal morphology, river hydrology, vegetation, landform and tidal flooding. Diagnosing the occurrence of both potential and actual acid sulfate soils is the first step in land use planning for such areas. But to cope with the intricacies of these soils, understanding the processes of soil salinization and acidification at different scales should be formalized to properly characterize mangrove environments.The main objectives of this thesis were: 1) to give a comprehensive characterization framework for the West African mangrove environments with emphasis on the possibilities of and constraints for rice cultivation; 2) to determine the various causal factors for soil salinization and acidification; 3) to test whether temporal variability of soil chemistry is sufficient to provide a time window of minimum stress during the rice growing period; 4) to relate the response of rice to improved agronomic practices in specific environments and to provide a means to characterize specific rice growing locations, and 5) to test rice varietal responses to saline and acid sods under different agronomic practices and to relate yields and yield components to the nutrient contents in leaves, in order to diagnose physiological disorders.First, a multi-scale approach was developed involving a range from Macro to Micro level based on the pre-conditions of acid sulfate soil formation. The main factors for classification are climate and coastal morphology at Macro scale; hydrology, physiography and vegetation complexes at Meso level; and topography (catena), vegetation species, tidal flooding and sedimentation rate at Micro level. Information from previous process-based studies on acid sulfate soil formation and data from secondary sources were used. Different environments were then distinguished and their characteristics were summarized by ecological zone. Constraints to rice production and potentials for agricultural development were matched with environmental conservation issues.To determine the significance of the causal factors developed in the multiple scale approach, 12 sites were selected along 4 river basins in West Africa, vz. from north to south the Gambia, the Casamance (Senegal), the Geba (Guinea Bissau) and the Great Scarcies (Sierra Leone). Along each river basin 3 sites were selected based on distance from the river mouth. Within a site a strip of land perpendicular to the river was selected for intensive grid sampling (40 by 20 m). Soil samples were taken at each grid node during the dry season of 1991. The relation between causal factors and soil salinization and acidification was determined at Macro and Meso levels by nested ANOVA and yielded a classification of the study area in main ecoregions and sub-environments within watershed. At a detailed scale, geostatistics were applied and zones within catena were defined in terms of their main soil characteristics. A nested statistical approach and geostatistics were used complementarily to disentangle the complexity of the causes of soil salinization and acidification.Temporal variability was studied by monitoring soil solution chemistry at each main landscape unit within the catena. Since the production of rice critically depends on the lowering of salinity and acidity by natural flooding during rainy season, time windows during which soil limitations are minimal were defined and matched with rice varietal duration.The response of rice to different improvement techniques were tested by means of a network of trials in the 1991 and 1992 rainy seasons. The residual effects of lime and phosphate rock (applied in 1991) during 1992 was also evaluated. Lime dressing (2 t ha -1) was found effective whenever dissolved Ca and Mg in the soil were low, and had a clear residual effect in the year after application. Application of phosphate rock did not seem to be effective in general. For iron toxicity, the molar fraction of Fe and (Ca + Mg) in soil solution and in flag leaves were found to be more relevant for diagnosing physiological disorders than the absolute Fe content in the soil solution and in rice flag leaves at panicle initiation.In the 1993 rainy season, rice varietal behavior under different improvement techniques within the main soil limitations in the mangrove environment was tested. Differences in yield and yield components and element contents in flag leaves at panicle initiation were observed between varieties in saline and less saline acid soils. Multiple correlation between rice yields, yield components, element contents in flag leaves at panicle initiation was found to be an effective diagnostic tool for assessing physiological disorders.The approach used in this study provides a logical framework to describe mangrove environments. The multiple-scale can assist in identifying the information required to cater for the needs of various decision-makers and land use planners. It also provides a key to develop technology packages for intensified and sustainable use. It can be used for the extrapolation of site-specific information to geographically different areas, with similar characteristics.

In the mangrove environment of West Africa, high spatial and temporal variability of soil constraints (salinity and acidity) to rice production is a problem for the transfer and adoption of new agronomic techniques, for land use planning, and for soil and water management. Recently, several National and International Agricultural Centers have initiated research programs to characterize environments where their newly developed technologies have to be applied. However, the mangrove agro- ecosystems in West Africa have not been characterized in a detailed way. Most of the soils in this environment are potential or actual saline acid sulfate soils. The spatial and temporal variability of soil salinity and acidity in these coastal lowlands results from complex interactions between climate, coastal morphology, river hydrology, vegetation, landform and tidal flooding. Diagnosing the occurrence of both potential and actual acid sulfate soils is the first step in land use planning for such areas. But to cope with the intricacies of these soils, understanding the processes of soil salinization and acidification at different scales should be formalized to properly characterize mangrove environments.The main objectives of this thesis were: 1) to give a comprehensive characterization framework for the West African mangrove environments with emphasis on the possibilities of and constraints for rice cultivation; 2) to determine the various causal factors for soil salinization and acidification; 3) to test whether temporal variability of soil chemistry is sufficient to provide a time window of minimum stress during the rice growing period; 4) to relate the response of rice to improved agronomic practices in specific environments and to provide a means to characterize specific rice growing locations, and 5) to test rice varietal responses to saline and acid sods under different agronomic practices and to relate yields and yield components to the nutrient contents in leaves, in order to diagnose physiological disorders.First, a multi-scale approach was developed involving a range from Macro to Micro level based on the pre-conditions of acid sulfate soil formation. The main factors for classification are climate and coastal morphology at Macro scale; hydrology, physiography and vegetation complexes at Meso level; and topography (catena), vegetation species, tidal flooding and sedimentation rate at Micro level. Information from previous process-based studies on acid sulfate soil formation and data from secondary sources were used. Different environments were then distinguished and their characteristics were summarized by ecological zone. Constraints to rice production and potentials for agricultural development were matched with environmental conservation issues.To determine the significance of the causal factors developed in the multiple scale approach, 12 sites were selected along 4 river basins in West Africa, vz. from north to south the Gambia, the Casamance (Senegal), the Geba (Guinea Bissau) and the Great Scarcies (Sierra Leone). Along each river basin 3 sites were selected based on distance from the river mouth. Within a site a strip of land perpendicular to the river was selected for intensive grid sampling (40 by 20 m). Soil samples were taken at each grid node during the dry season of 1991. The relation between causal factors and soil salinization and acidification was determined at Macro and Meso levels by nested ANOVA and yielded a classification of the study area in main ecoregions and sub-environments within watershed. At a detailed scale, geostatistics were applied and zones within catena were defined in terms of their main soil characteristics. A nested statistical approach and geostatistics were used complementarily to disentangle the complexity of the causes of soil salinization and acidification.Temporal variability was studied by monitoring soil solution chemistry at each main landscape unit within the catena. Since the production of rice critically depends on the lowering of salinity and acidity by natural flooding during rainy season, time windows during which soil limitations are minimal were defined and matched with rice varietal duration.The response of rice to different improvement techniques were tested by means of a network of trials in the 1991 and 1992 rainy seasons. The residual effects of lime and phosphate rock (applied in 1991) during 1992 was also evaluated. Lime dressing (2 t ha -1) was found effective whenever dissolved Ca and Mg in the soil were low, and had a clear residual effect in the year after application. Application of phosphate rock did not seem to be effective in general. For iron toxicity, the molar fraction of Fe and (Ca + Mg) in soil solution and in flag leaves were found to be more relevant for diagnosing physiological disorders than the absolute Fe content in the soil solution and in rice flag leaves at panicle initiation.In the 1993 rainy season, rice varietal behavior under different improvement techniques within the main soil limitations in the mangrove environment was tested. Differences in yield and yield components and element contents in flag leaves at panicle initiation were observed between varieties in saline and less saline acid soils. Multiple correlation between rice yields, yield components, element contents in flag leaves at panicle initiation was found to be an effective diagnostic tool for assessing physiological disorders.The approach used in this study provides a logical framework to describe mangrove environments. The multiple-scale can assist in identifying the information required to cater for the needs of various decision-makers and land use planners. It also provides a key to develop technology packages for intensified and sustainable use. It can be used for the extrapolation of site-specific information to geographically different areas, with similar characteristics.

Wheat and potatoes were grown in tanks filled with loam and clay and irrigated with water of three different levels of salinity and, for the wheat, with two irrigation regimes. A combination of soil water sampling and salt balance was used to study the development of soil salinity and the composition of the soil water. This revealed an increase in adsorbed sodium, a decrease in adsorbed calcium and magnesium, and precipitation of a mixture of calcium and magnesium carbonate. Predawn leaf-water potential and stomatal conductance can be used as parameters for water stress, and show good coherence with growth and yield. That potatoes are more sensitive to water stress than wheat was reflected by greater differences in leaf-water potential and stomatal conductance, and a more severe yield decrease. Soil, salinity and water regime affect water stress, growth, and yield. The water efficiency of wheat and potatoes was not affected by soil and salinity.

The sources and origin of salts in the basin of the two salt- affected Shapur and Dalaki rivers (Southern Iran) and the processes involved in salinization have been studied. The extent of water deterioration have been identified by examining spatial changes in the rivers water quality. Among salinity management measures pertaining to water quality, the engineering measures are investigated. It appears that the construction and management of the planned Jarreh Reservoir on the Shapur River is the most feasible one.The dynamic reservoir simulation model, - DYRESM (Imberger, et al., 1978, Version 6.4) is adapted to simulate the salinity/temperature distribution, long-term behaviour and response to various management policies in this reservoir. A simplified method to account for the effect of sediment particles on density of inflows and the inflowing processes in mild bed slope reservoirs is introduced. The method applies only to the steady motion of a turbidity current that is neither depositing nor eroding sediments. The vertical propagation of sediment has not been modelled. This applies to those substances (like dissolved salt) that are not reacting physically or (bio)chemically with suspended particles.Various management options to minimize the salinity build-up in the reservoir are examined. Among these, the diversion of the most saline part of the summer flows to a point downstream of the last irrigation intakes will result in a significant water quality improvement. At the end of a 5-year simulation, only a weak salinity gradient remains in the reservoir. Based on simulations, using 15 years of data, and the salt balance calculation, the long-term behaviour of the Jarreh Reservoir is studied, It is shown that the salinity in the reservoir is largely determined by annual variabilty in the river discharge.

Soils of the "Tannes region" of the Sine Saloum bassin, Senegal, are characterized by great heterogenity in morphology and physical and chemical properties. Their caracteristics are linked to topographic position, material and hydrology.Their recent pedogenetical evolution is a consequence of the severe drought period which occurred all over Senegal since 1971. The drought has had dramatic social consequences but also consequences for the ecosystem.The rainfall deficit started and amplified supersalinization and acidification of the soils throughout the region.The surpersalinity, not widespread before 1971, has rapidly reached all soils, from the low terraces up to "glacis de raccordement".Three main processes enhanced the supersalinization:a. Vertical migration of salts by capillary rise from soil solution and shallow groundwaters, caused by intensive evaporation due to high tempratures (25 - 40°C), which leads to an upward salt flux from 8 to 9 months of the year.b. Inundations by supersaline water from the creeks and rivers, having salt concentration 2 to 3 times that of seawater (46mS/cm).C. Aeolian accumulations: Saline silt blown from bare areas is deposited in places covered with a vegetation.Because of these processes, soils remain supersaline throughout the year. Nevertheless one can observe a decreasing of the salinity during the rainy season in sandy soils of the "glacis de raccordement" and of sandy levees, and also in loam soils of the upper terrace with a smooth topography, because of saturation by rain water.Soil acidification, unknown before 1971, has rapidly spread throughout the entire Sine Saloum basin.It is due to oxidation of pyritic sediments, provoked by the long drought period, which resulted in drainage, lowering the groundwater tables and evaporation.Pyrite oxidation seems to be the most important pedogenetic process. Its importance depends on the pyrite content of the sediment, local chemical conditions (exchangeable cations, salts) and topographic position.The importance of the topographic position can be illustrated as follows. Acid sulfate soils of the low terraces, which are subject to inundation, have recently formed jarosite of a pale yellow (2.5Y 8/4) colour, while soils in the mid-terraces and in the "glacis de raccordement", which are better drained, show a complete oxidation of pyrite to jarosite, followed by hydrolysis of jarosite to goethite (yellowish colours) and subsequently to haematite (10R 5/8). This evolution, which can be regarded as "chemical ripening", seems to be an extremely rapid phenomenon.In soils having oyster shells in their sediments pyrite oxidation doesn't lead to acidification, because of neutralization of the acidity by carbonates.The chemical ripening processes occur simultaneously with physical ripening, the importance of which depends on the topographic position, decreasing progressively from soils of "glacis de raccordement" to soils of the low inundated terraces.Supersalinity and acidifications have caused severe chemical soil degradation and have annihilated all possibilities of land reclamation.Research pointed out, that in view of the actual arid conditions and lack of scientific knowledge on soil development, the only possible form of land use remaining, is forestry and pasture by introduction of salt and acid tolerant species.In the large area of the Sine Saloum basin, land reclamation for other types of land use is only possible on long term periods, after having taken the necessary land and water management measures, focussing on desalinization and de-acidification of the soils.

The sources and origin of salts in the basin of the two salt- affected Shapur and Dalaki rivers (Southern Iran) and the processes involved in salinization have been studied. The extent of water deterioration have been identified by examining spatial changes in the rivers water quality. Among salinity management measures pertaining to water quality, the engineering measures are investigated. It appears that the construction and management of the planned Jarreh Reservoir on the Shapur River is the most feasible one.The dynamic reservoir simulation model, - DYRESM (Imberger, et al., 1978, Version 6.4) is adapted to simulate the salinity/temperature distribution, long-term behaviour and response to various management policies in this reservoir. A simplified method to account for the effect of sediment particles on density of inflows and the inflowing processes in mild bed slope reservoirs is introduced. The method applies only to the steady motion of a turbidity current that is neither depositing nor eroding sediments. The vertical propagation of sediment has not been modelled. This applies to those substances (like dissolved salt) that are not reacting physically or (bio)chemically with suspended particles.Various management options to minimize the salinity build-up in the reservoir are examined. Among these, the diversion of the most saline part of the summer flows to a point downstream of the last irrigation intakes will result in a significant water quality improvement. At the end of a 5-year simulation, only a weak salinity gradient remains in the reservoir. Based on simulations, using 15 years of data, and the salt balance calculation, the long-term behaviour of the Jarreh Reservoir is studied, It is shown that the salinity in the reservoir is largely determined by annual variabilty in the river discharge.

To draw up fertilizer recommendations for conifers in pots, experiments were carried out during two years and at three locations with rooted cuttings of Chamaecyparis lawsoniana 'Alumii' on Finnish sphagnum peat. At one location also other Chamaecyparis cultivars were tested. The amount of N, the form in which the N was given, viz., Ca(NO3)2 or (NH4)2SO4, the pH of the substrate, and at one location the amount of a nitrification inhibitor, were varied. The effect of all factors mentioned on the growth of Chamaecyparis cultivars was small, both quantitatively and qualitatively. The amount of N had the greatest effect if the zero N-level was included in the trial. For optimum growth, rooted cuttings should be fertilized with about 0.25 g N. For Chamaecyparis cultivars, it is unfavourable to give the N as NH4-N alone. The currently recommended pH-H2O for the substrate, 4.8–5.2, needs no revision. Presented are the contents of mineral nutrients in soil and plant at optimum levels.

Based on the assumption that discharge from the aquifer in the central part of Haryana State does not significantly contribute to the State's water balance, in the long term a solution has to be provided to maintain the overall salt balance in Haryana State. Since on many locations in the State the groundwater table has risen close to the surface the subsoil leaves not sufficient space for disposal of leached salts. It is recommended that alternatives such as: disposal to the sea through a transport canal; disposal by evaporation lakes in lower lying parts of the State, are evaluated.

Chapter 1The Ebro basin is situated in north-eastern Spain and forms a geographic unit bounded by high mountains. The Bardenas area lies in the Ebro basin and forms part of the Bardenas Alto - Aragón irrigation scheme, which was designed to make use of the surface water resources from the Pyrenees.Chapter 2The Ebro basin is a tertiary sedimentation basin in which the Ebro river and its main tributaries have incised alluvial valleys. The tertiary sediments consist mainly of mudstone, locally with interbedded gypsum layers, and very fine siltstone. Both sedimentary rocks are fine textured and, because they were deposited in a brackish lacustrine environment, contain harmful soluble salts.The main landscape-forming processes were erosion, transport, and deposition under semi-arid climatic conditions. The highest parts of the landscape consist of old tertiary formations which form the uplands of a dissected plain. At a lower level mesas occur, which consist of coarse alluvium covering the underlying tertiary sediments. Most of the eroded sediments were removed from the area but local sedimentation also occurred. Owing to the semi-arid conditions, both sediments and salts were deposited. The highest salt concentrations are found in the lowest parts of the alluvial formations, especially where the alluvium was derived from the eroded mudstone and siltstone. Between the residual uplands and the low-lying alluvial formations, piedmont and colluvial slopes occur.Within the Bardenas area ten major physiographic units were defined, each of them subdivided into minor components and indicated on the soil map.The Ebro basin is the driest part of northern Spain. The climate is semi-arid and becomes drier from the borders to the centre of the depression.The seasonal variation in temperature is great. Potential evapotranspiration exceeds total precipitation, which is extremely variable and is not concentrated in distinct rainy seasons. Wind velocity is high and both cold and warm dry winds are common. Evaporation thus occurs even in winter when temperatures are low.A great part of the area is cultivated, so that natural vegetation is restricted to residual and eroded soils not used for agriculture and to salt-affected soils where halophytes grow.Irrigated farming is influenced by soil conditions. Salt-free soils are under full irrigation, the main crops being maize, lucerne, sugar beet, and some horticultural crops.The cropping pattern on the saline soils depends on the degree of salinity. Barley and sugar beet are grown on moderately saline soils and lucerne on succesfully leached soils. On the higher lands, not under the command of the irrigation scheme, barley is grown.Chapter 3The study area comprises two drainage basins. The northern part drains to the Aragón river, the southern part to the Riguel river, which is a tributary of the Arba river.Drainage and salinity of the groundwater depend on the situation of each geomorphological unit and its relation to adjacent units. The groundwater in the fluvio-colluvial formations of the northern basin is shallow and highly saline. An ephemeral perched water table is found in the mesas, where the groundwater is non-saline. No shallow water table was found in other physiographic units.The irrigation water is of good quality as its EC is at the lower end of the C 2 -range. The SAR is also in the lowest range S 1 and the RSC is zero, so there is no danger of alkalinization.Chapter 4The physiographic approach was used to prepare the soil map. Each mapping unit is a broad association of soils having similar salinity hazards and possibilities of reclamation.Five main soil associations were distinguished:a) The residual soils of the siltstone outcrops, which have only a thin surface horizon overlying the hard siltstone.b) The soils of the mesas, which consist of a reddish loamy surface horizon overlying semi-consolidated coarse alluvium rich in calcium- carbonate but free of other salts. This in turn overlies the impervious mudstone. Texture and depth of the soil profile vary. Where moderately deep soils occur. a prosperous irrigated agriculture flourishes.c) The soils of the piedmont and colluvial slopes were developed from a mixture of fine colluvium. and material from the underlying tertiary sediments. They are generally deep and fine textured and have an intrinsic, though variable, salinity, increasing with depth. Because of the low permeability and the salinity of the subsoil, the most suitable irrigation method is sprinkling.d) The non-saline soils of the alluvial valleys of the main rivers. Soil conditions vary greatly, but the older terrace soils are usually shallower and less suitable for irrigation than the youngest deeper (alluvial) soils. In general, prosperous irrigated agriculture exists on these soils.e) The saline alluvial and fluvio-colluvial soils of valleys and fans, whose parent material was derived from denudation of the tertiary sediments. Soil conditions and the degree of salinity vary in each mapping unit, and consequently the possibilities of reclamation vary as well.Chapter 5The source of the salts is the intrinsic salinity of the parent materials and the secondary salinization in water-receiving areas that lack natural drainage. Under irrigation the mobilization and redistribution of salts continues and salinity increases.The saline soils of the area are mainly affected by sodium chloride, a component dominant in all samples. In addition, calcium and magnesium sulphates are found in the northern basin, while in the southern part, calcium and magnesium chlorides predominate over the sulphates.The SAR increases with the rise of EC. Soil alkalinity can therefore be regarded as a reflection of soil salinity since highly saline soils are sodic as well. Non-saline alkali soils were not found and pH-values greater than 8.5 do not occur.The results of crop tolerance field tests correspond well with the generally accepted levels for salt tolerance.The continued use of the slightly saline soils can be ensured by maintaining the present drainage system of open ditches and interceptor drains, and by keeping the soils under full irrigation. The normal percolation losses associated with basin irrigation will be sufficient to leach the salts from the rootzone.Sprinkler irrigation is suitable for the soils of the slopes, since no levelling is needed and the small water applications reduce the seepage of saline water. The only drainage system required is an interceptor drain between the slope and the adjacent valley.Chapter 6The saline alluvial soils require reclamation. For this purpose, they must be provided with a drainage system, followed by initial leaching to reduce their salt content.Because there was no local experience with such drainage and desalinization processes, it was decided to conduct an experimental reclamation. Two experimental fields were subsequently selected.The Alera field represents the poorly drained soils of the fluvio-colluvial formations of the northern basin. These are silty-clay soils whose porosity and permeability decrease with depth. Below a depth of 1.5 m the soil becomes almost impermeable. Salinity increases with depth, reaching values of between 20 and 35 mmhos/cm in the almost impermeable layer. Soil salinity in the surface layer varies.The Valareña field represents the saline soils of alluvial valleys and fans in the southern drainage basin. These are silty clay loam soils showing a marked stratification. At a depth of 2.5 m, coarse alluvium saturated with very saline groundwater occurs overlying impervious mudstone. Because of stratification, the hydraulic conductivity is highly anisotropic. Soil salinity is more uniformly distributed than in the Alera soils.The reclamation process consisted of the following phases:a) Theoretical design of the drainage system based on hydrological soil properties measured by conventional field methods and on assumed drainage criteria.b) Implementation of the drainage system in the experimental fields.c) Collection of field data, followed by determination of the actual hydrological soil properties and of the drainage criteria.d) Design of the definitive drainage system which will form the basis of recommendations for the reclamation of saline soils with similar conditions.Chapter 7After a detailed hydropedological survey, a drain spacing of 20 m at a depth of 1.5 m was calculated for both the Alera and the Valareña drainage systems. Both fields were subsoiled to a depth of 50 cm to improve their low infiltration rates.Piezometers were installed to monitor the water table. Precipitation was measured, as were the amounts of irrigation and drainage water. Soil samples were taken at fixed sites to determine the salinity during the leaching process.Chapter 8At the Valareña field, water flowed directly into the drain trench through the upper layer of soil, in which the stratification had been disrupted by levelling and subsoiling. Below this layer, there was no percolation of water and therefore no desalinization. These soils cannot be leached merely by the provision of a drainage system but also require deep subsoiling.At the Alera field, unsteady groundwater flow prevailed. At the end of tail recession, flow conditions approached those of steady flow. The discharge/hydraulic head relation had a parabolic shape showing that flow was restricted to the soil above drain level because the drains had been placed just above the impervious layer.The Boussinesq theory was very suitable to study the drainage of the Alera field. At the end of tail recession, if the term for flow below drain level was disregarded, the Hooghoudt equation could be applied.Drainable pore space was determined from the fall of the water table and the amount of drainage water during periods of low evapotranspiration. An average value of 4 per cent was found.The hydraulic conductivity was calculated from the discharge/hydraulic head relation using the Boussinesq and Hooghoudt equations for periods of low evapotranspiration. In general good agreement was found among the values obtained. It could thus be concluded that:- Hydraulic conductivity decreases with depth, becoming negligible below drain level.- The hydraulic conductivity between a depth of 0.5 m and drain level equals about 0.6 m/day, and is about 1.5 m/day in the upper layer.- For high water table conditions, the average hydraulic conductivity of the soil profile is 1 m/day.A comparison of hydraulic conductivity values obtained with field and laboratory methods and those obtained from the discharge/hydraulic head relation showed that:- The results obtained with the auger hole method (K = 0.2 m/day) were lower than those derived from the discharge/hydraulic head relation.- No satisfactory results were obtained from the inversed auger hole measurements above the water table.- The results obtained from laboratory measurements in undisturbed soil cores showed the anisotropy of the soil.The entrance resistance (W e ) of different combinations of drainage and filter materials was calculated from the drain discharge and the head loss of the water table measured in the drain trench (h i ). Another method, by which the head loss in the trench was calculated from the shape of the water table was also applied. Both methods gave similar results, yielding the following conclusions:- The W e -values remained fairly constant with time, except for plastic pipes-with an envelope of esparto or coconut fibre for which an increase in W e was observed.- The best combination was clay pipes with a gravel cover (W e =2 day/m).- Corrugated PVC-pipes with gravel covering and clay pipes without gravel may be used also (W e = 5 day/m).- Corrugated plastic pipes without a filter gave less satisfactory results (W e = 13 day/m).- Plastic pipes with coconut fibre and esparto filters showed an even higher W e than plastic pipes without a filter.- Barley straw is an unsuitable cover material since it rots easily and clogs the pipe.Chapter 9The desalinization of the Alera field started with an initial leaching, followed by the irrigated cultivation of moderately salt- resistant crops.The leaching efficiency coefficient was determined by comparing the actual desalinization process with theoretical models. Thus the leaching requirement could be predicted for different initial salt contents.To exclude the influence of slightly soluble salts, the desalinization curves were drawn in terms of chloride content. The correlation between chloride percentage and electrical conductivity was high.The following conclusions emerged from the study of the leaching process:- The leaching efficiency coefficient was not constant but increased with depth.- The leaching efficiency coefficient was higher at the beginning of the desalinization process and decreased gradually as the soil became less saline.- The calculated values reflected the differences in soil structure.- An average value of 0.5 was determined for the upper layer (0-50 cm), and a value of 1.0 for the deeper layer (50-100 cm).- The initial salinity was related to soil physical properties (infiltration rate and permeability) which, in turn, were dependent on the compactness of the soil.- For an initial EC e of 15 mmhos/cm, approximately 1000 mm of percolation water are required, which meant 1100 to 1400 mm of irrigation water. The leaching period could last up to 8 months, from early autumn to late May.- Deep subsoiling and local gypsum applications improved the structure of the upper soil layer.- The leaching of saline soils could be split into two phases: an initial leaching of the upper layer, followed by the irrigated cultivation of a moderately salt-resistant crop (sugar beet), during which percolation losses leached the deeper layers.- There was no risk of alkalinization during the leaching period.- To prevent secondary salinization after reclamation, good drainage conditions must be maintained and an irrigated crop rotation practised.Chapter 10From the relation between the depth of the water table, crop growth, and the mobility of agricultural machinery on the soil, and from a study of the groundwater regime in winter and during the irrigation season drainage criteria for unsteady-state conditions were derived. These criteria were converted to steady-state criteria for easier use in drainage projects.The following conclusions could be drawn from the study:- Little harm is done to winter cereals if a water table remains within a depth of 50 cm, for no more than 3 consecutive days.- With a water table between 75 and 100 cm, sugar beet grows well and is not harmed if a water table is within the top 50 cm for 3 to 4 consecutive days.- Lucerne is more sensitive than sugar beet to high water tables. For good yields, a water table must not remain longer than 3 days within the top 25 cm of soil, 4 or 5 days within the top 50 cm, and 5 or 6 days within the top 75 cm.- A water table depth shallower than 65 cm prevents the movement of machinery and hampers seed-bed preparation in winter.The following drainage criteria were assessed:a) In winter, a water table drawdown from the soil surface to a depth of 0.65 m in 8 days.b) In the irrigation season, a water table rise of 0.7 m caused by irrigation losses must be lowered in the 12 days between two consecutive irrigations, and must be deeper than 0.7 m after 7 days.Applying these criteria in the Boussinesq equation for unsteady flow and using the values for hydraulic conductivity and drainable pore space determined at the experimental field, a spacing of 25 m for drains installed at a depth of 1.2 m was obtained.Equivalent drainage criteria for steady flow are a minimum depth of 0.5 m for the unsaturated zone, with a corresponding hydraulic head midway between drains of 0.7 m and a drain discharge of 3 mm/day.If the entrance resistance was taken into account, the Ernst equation for steady flow and the Hellinga/de Zeeuw equation for unsteady flow could be used in calculating the drain spacing. The results obtained by both approaches agree well and allowed the following conclusions:- For drainage and filter materials with a high entrance resistance, the drain density (m/ha) required becomes twice that needed for materials with low entrance resistance.- Material with high entrance resistance involves much more risk of failure than a wider spacing with good material.

Bij gebruik van steenwol als substraat voor de teelt van tuinbouwgewassen kunnen problemen ontstaan verband houdend met het verdelingspatroon van de voedingsoplossing. In dit rapport wordt het transportproces van de voedingsoplossing beschreven aan de hand van proefnemingen met een kleurstof. Vanuit theoretisch oogpunt wordt aangegeven in welke mate doorspoeling nodig kan zijn bij gebruik van slecht of matig gietwater. Tenslotte worden praktische adviezen gegeven over de plaatsing van druppelaars en afvoerspleten

A greenhouse experiment was conducted to examine the effects of salinity and flooding level on interstitial solute speciation and solute uptake byPanicum hemitomum grown on intact marsh substrates. The experimental set-up consisted of a factorial arrangement of treatments (5 salinity levels×3 flooding levels) with 4 replications.

Based on the assumption that discharge from the aquifer in the central part of Haryana State does not significantly contribute to the State's water balance, in the long term a solution has to be provided to maintain the overall salt balance in Haryana State. Since on many locations in the State the groundwater table has risen close to the surface the subsoil leaves not sufficient space for disposal of leached salts. It is recommended that alternatives such as: disposal to the sea through a transport canal; disposal by evaporation lakes in lower lying parts of the State, are evaluated.

The Leziria Grande area consists mainly of poorly drained, saline clay soils of marine origin. Three experimental fields were laid out to find whether subsurface drainage can be effective in lowering the groundwater table and improving desalinization. Subsurface drainage results in a lower groundwater table than does surface drainage. With increasing spacing, the groundwater remains at a higher level for longer periods, which is expressed here by the sum of exceedances of the groundwater table above 30 cm during winter. Soil salinity, expressed as EC 1:2 , and sodicity, expressed as E.S.P., decreased during the first 3 years, in which precipitation varied between 600 and 750 mm and the average drain outflow was about 250 mm. The leaching efficiency decreased with time, indicating that the removal of salt is a slow process in fine-textured soil. Application of gypsum lowered the E.S.P. The infiltration rate and the drain outflow increased. Although the total amount of salts in the drainwater was 40% higher than for the untreated plots, no lower EC 1:2 values were found. This is ascribed to spatial variability in soil salinity.

Investigations with respect to the transport of water and salt in the irrigated cracking clay soils of the Kachhi Plains in Pakistan are reported. The leaching of salts under intermittently irrigated crops on deep fine-textured soils is insufficient. Hence, such crops can be grown only if deeper leaching under a wet crop is provided from time to time. The results of field observations and infiltration experiments indicate that more water transport and salt leaching occurs if the fine-textured topsoils are underlain by more permeable medium-textured subsoils at depths between 50 and 150 cm. This suggests that it is not the cracked topsoils but the uncracked subsoils that limit the water transport in deep fine-textured soils. The infiltration experiments show that swelling and the closing of cracks under water ponding is a slow process, lasting more than 1 month.

Soils of the "Tannes region" of the Sine Saloum bassin, Senegal, are characterized by great heterogenity in morphology and physical and chemical properties. Their caracteristics are linked to topographic position, material and hydrology.Their recent pedogenetical evolution is a consequence of the severe drought period which occurred all over Senegal since 1971. The drought has had dramatic social consequences but also consequences for the ecosystem.The rainfall deficit started and amplified supersalinization and acidification of the soils throughout the region.The surpersalinity, not widespread before 1971, has rapidly reached all soils, from the low terraces up to "glacis de raccordement".Three main processes enhanced the supersalinization:a. Vertical migration of salts by capillary rise from soil solution and shallow groundwaters, caused by intensive evaporation due to high tempratures (25 - 40°C), which leads to an upward salt flux from 8 to 9 months of the year.b. Inundations by supersaline water from the creeks and rivers, having salt concentration 2 to 3 times that of seawater (46mS/cm).C. Aeolian accumulations: Saline silt blown from bare areas is deposited in places covered with a vegetation.Because of these processes, soils remain supersaline throughout the year. Nevertheless one can observe a decreasing of the salinity during the rainy season in sandy soils of the "glacis de raccordement" and of sandy levees, and also in loam soils of the upper terrace with a smooth topography, because of saturation by rain water.Soil acidification, unknown before 1971, has rapidly spread throughout the entire Sine Saloum basin.It is due to oxidation of pyritic sediments, provoked by the long drought period, which resulted in drainage, lowering the groundwater tables and evaporation.Pyrite oxidation seems to be the most important pedogenetic process. Its importance depends on the pyrite content of the sediment, local chemical conditions (exchangeable cations, salts) and topographic position.The importance of the topographic position can be illustrated as follows. Acid sulfate soils of the low terraces, which are subject to inundation, have recently formed jarosite of a pale yellow (2.5Y 8/4) colour, while soils in the mid-terraces and in the "glacis de raccordement", which are better drained, show a complete oxidation of pyrite to jarosite, followed by hydrolysis of jarosite to goethite (yellowish colours) and subsequently to haematite (10R 5/8). This evolution, which can be regarded as "chemical ripening", seems to be an extremely rapid phenomenon.In soils having oyster shells in their sediments pyrite oxidation doesn't lead to acidification, because of neutralization of the acidity by carbonates.The chemical ripening processes occur simultaneously with physical ripening, the importance of which depends on the topographic position, decreasing progressively from soils of "glacis de raccordement" to soils of the low inundated terraces.Supersalinity and acidifications have caused severe chemical soil degradation and have annihilated all possibilities of land reclamation.Research pointed out, that in view of the actual arid conditions and lack of scientific knowledge on soil development, the only possible form of land use remaining, is forestry and pasture by introduction of salt and acid tolerant species.In the large area of the Sine Saloum basin, land reclamation for other types of land use is only possible on long term periods, after having taken the necessary land and water management measures, focussing on desalinization and de-acidification of the soils.

Bij gebruik van steenwol als substraat voor de teelt van tuinbouwgewassen kunnen problemen ontstaan verband houdend met het verdelingspatroon van de voedingsoplossing. In dit rapport wordt het transportproces van de voedingsoplossing beschreven aan de hand van proefnemingen met een kleurstof. Vanuit theoretisch oogpunt wordt aangegeven in welke mate doorspoeling nodig kan zijn bij gebruik van slecht of matig gietwater. Tenslotte worden praktische adviezen gegeven over de plaatsing van druppelaars en afvoerspleten