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Land degradation is a large problem worldwide, especially in agricultural areas. Between 1-6 billion ha of land worldwide is affected by land degradation. With an increasing world population, more food production is needed and, therefore, more land is converted into agricultural areas. This conversion of land to agricultural areas, in turn, leads to more land degradation. Some common forms of land degradation are desertification, salinization and soil erosion by water. The negative effects of soil erosion have been recognized for a long time. Since the early 20th century, researchers have tried to quantify soil displaced due to water, and to measure and model the efficiency of management strategies. The implications of problems with upscaling, wrong process representation and equifinality include the difficulty to properly predict sediment sources, pathways and sinks within catchments. These problems then can translate into the implementation of sub-optimal management strategies. To deal with these non-linear processes and the lack of proper representation of water and sediment sources, pathways and sinks, the concept of connectivity was developed. Currently, many definitions of connectivity have been proposed, although the definition most used is that of hydrological connectivity by Pringle (2003): ‘Hydrologic connectivity is the water-mediated transport of matter, energy and organisms within or between elements of the hydrologic cycle’. A unified theory on what constitutes connectivity and how connectivity should be measured or inferred remains one of the biggest challenges within catchment science. In addition, it is unclear whether connectivity should be an output or an input of a model and if an input, whether this should be added explicitly or implicitly. The main objective of this thesis was, therefore, to assess and quantify hydrological and sediment connectivity in a meaningful way, which can further our understanding of hydrological and sediment transport processes and catchment system dynamics. The study was carried out in three catchments in Navarre, northern Spain. Two catchments, ‘Latxaga’ and ‘La Tejeria’, are agricultural catchments with sizes of 2.07 km2 and 1.69 km2, respectively. The ‘Oskotz Forestal’ catchment is a (semi-)natural catchment, with a size of 5.05 km2. Land cover in the agricultural catchments is mainly winter wheat and barley, while in the Oskotz catchment it is grassland and forest. Latxaga and La Tejeria are mainly underlain by marls and within La Tejeria some sandstone is also present. The geology in Oskotz is characterised by an alternation of marls and sandy limestone. In chapter 2, I used networks (graph theory) to characterise and quantify overland flow connectivity dynamics on hillslopes in a humid sub-Mediterranean environment by using a combination of high-resolution digital-terrain models, overland flow sensors and a network approach. Results showed that there are significant differences between overland flow connectivity on agricultural areas and semi-natural shrubs areas. Significant positive correlations between connectivity and precipitation characteristics were found. Significant negative correlations between connectivity and soil moisture were found, most likely due to soil water repellency and/or soil surface crusting. The combination of structural networks and dynamic networks for determining potential connectivity and actual connectivity proved a powerful tool for analysing overland flow connectivity. In chapter 3, I determined the functioning of hillslope-channel connectivity and the continuation of transport of these sediments in the channel. To determine this functioning, I obtained data on sediment transport from the hillslopes to the channels while simultaneously looking at factors that influence sediment export out of the catchment. For measuring hillslope-channel sediment connectivity, Rare-Earth Oxide (REO) tracers were applied to a hillslope in the Latxaga catchment preceding the winter of 2014-2015. The results showed that during the winter there have been no sediments transported from the hillslope into the channel. Analysis of precipitation data showed that although total precipitation quantities did not differ much from the mean, the precipitation intensities were low. Using a Random Forest (RF) machine learning method, I showed that hillslope-channel connectivity in Latxaga is dominated by sediment mobilisation during large (high intensity) precipitation events. Sediments are for a large part exported during those events. Large events also leave behind large amounts of sediments in and near the channel, which is gradually removed by small events. In chapter 4 I demonstrated that existing data can be used to assess governing factors of connectivity, and how these factors change over time. Data from three catchments in Navarre, Northern Spain, were used to assess factors that influence hydrologic and sediment connectivity. These factors were used as components in a spatially-lumped linear model for discharge and suspended-sediment yield. Three components of connectivity were distinguished: topographical, biological and soil. Changes in the topographical component for the studied periods were considered relatively small, and, therefore, kept constant. Changes in the biological component were determined using the Normalised Difference Vegetation Index. Changes in the soil component were assessed using an Antecedent Precipitation Index. Nash-Sutcliffe model efficiency coefficients were between 0.49 through 0.62 for the discharge models and between 0.23 through 0.3 for the sediment-yield models. I recommended applying the model at smaller spatial scales than catchment scale to minimize the lumping of spatial variability in the components. In chapter 5, the objective was to better understand the implications of model calibration at different spatial scales on the simulation of hydrology and sediment dynamics of an agricultural catchment. I applied the LAPSUS-D model to the Latxaga catchment. The model was calibrated and validated (4 years: 2011-2015) using three datasets at varying spatial scales: hillslope, catchment and the combined dataset (combined-calibrated model). The hillslope-calibrated model showed mainly infiltration-excess overland flow, the catchment-calibrated mainly saturation-excess overland flow at the footslopes and the combined-calibrated model showed saturation-excess overland flow from the midslopes to the footslopes. For hydrology, the combined-calibrated model simulated the large discharge peaks best, while at the hillslope scale, the hillslope-calibrated model performed best. The hillslope-calibrated model produced the highest model efficiencies for sediments, for calibration (0.618) and validation (0.269). The hillslope-calibrated model was the only model that showed observed gully erosion on a high-resolution DEM and displayed channel sediment dynamics. However, absolute quantities of erosion and deposition within the catchment were too high. The results show that modellers need to be aware of problems associated with automatic calibration, over-calibration and not incorporating measured data at multiple spatial scales. We advocate incorporating runoff and sediment tracing data at multiple scales whenever this is possible and to, furthermore, carry out specific measuring campaigns towards this end, ultimately to get a more comprehensive view on hydrological and sediment connectivity within a catchment. The combination of chapters in this thesis showed that the connectivity concept is useful for a wide range of studies, from hillslope scale to catchment scale. Using the concept, I was able to determine sediment dynamics for a humid-Mediterranean catchment and show that this behaviour is different than previously thought. Depending of the aim of the study, various concepts of connectivity are useful. Different geologic and climatic settings cause large differences in catchment (sediment) dynamics. It might, therefore, not be necessary, or even possible, to strive for a single, unifying conceptual framework for connectivity. Instead, a collection of frameworks for different settings should be developed. These frameworks should, however, always aim at helping to understand which measurements need to be taken and which type of models and indices should be used for that particular setting. It is my honest opinion that connectivity is definitely a useful concept to advance our knowledge on water and sediment transport processes further. However, careful consideration is also required as this particular concept will not necessary provide the ultimate explanation and insights in dynamic behaviour within watersheds around the world. The gap between the different spatial and temporal scales is too complex to be bridged with a single concept like connectivity. However, the many studies about connectivity that will be published in the near future will be able to advance knowledge on water and sediment transport processes.

Bodemkundig InformatieSysteem informeert over actuele toestand èn dynamiek. De bodem die we kennen vanaf het eerste moment dat we een bodemkaart zagen, lijkt onveranderlijk. Maar kijken we wat beter naar de bodem zelf, zoals bodemkundigen dat doen, dan zien we volop beweging

Eind 2010 hebben Alterra en HKVlijn in water in opdracht van Waterschap Zuiderzeeland een methode ontwikkeld om de berging in permanente kleischeuren te berekenen en ruimtelijk in kaart te brengen, om het vervolgens te implementeren in de SOBEK-modellen van het waterschap. In dit artikel zijn de belangrijkste resultaten van het bodemkundige deel van het onderzoek samengevat

Water retention and hydraulic conductivity properties from the Staring series have been attributed to the315 soil typological units of the Soil Map of the Netherlands, scale 1: 50,000, and functional characteristicsfor these units were calculated using a model. Based on commonalities between these functionalcharacteristics, the 315 soil typological units have been clustered to form 72 soil physics units, which makeup the new soil physics units map ‘BOdemFysische EenhedenKaart’ (BOFEK2012). To make these dataavailable for use in models to calculate water and nutrient transport in soils, a dataset has been compiledcontaining information on (i) the GIS database, with the geographical distribution of the BOFEK units in theNetherlands, and (ii) profile diagrams showing the soil layers to a depth of 1.2 metres below ground level,together with the relevant soil physical properties. For the award of A Status to the BOFEK database anumber of aspects of the mapping methodology were reviewed, including the clustering method used, thevalidation and verification of the calculations made, the verification of the conversion from the soil map tothe soil physics units map, and the addition of meta information. Aan de 315 bodemeenheden behorende bij de bodemkaart van Nederland, schaal 1 : 50.000, zijnwaterretentie- en doorlatendheidskarakteristieken uit de Staringreeks toegekend. Met een model zijn voordeze eenheden functionele kenmerken berekend. Op grond van verwantschap in functionele kenmerken zijnde 315 bodemeenheden geclusterd in 72 bodemfysische eenheden en afgebeeld in de nieuweBOdemFysische EenhedenKaart (BOFEK2012). Om bij modelberekeningen van water- en stoffentransport inde bodem deze gegevens te kunnen gebruiken, is een dataset samengesteld met informatie over (i) het GISbestand,met de geografische verbreiding van de BOFEK-eenheden in Nederland, en (ii) over profielschetsenmet de laagopbouw van het bodemprofiel tot 1,20 m-mv. en de daaraan gerelateerde bodemfysischekenmerken. Voor de toekenning van Status A aan het BOFEK-bestand zijn een aantal onderwerpen naderonderzocht zoals gebruikte clusteringmethode, validatie van en controle op uitgevoerde berekeningen,controle op de omzetting van de bodemkaart naar BOFEK-kaart en toevoeging van meta-informatie

Tijdens bodemkartering werkzaamheden in het veenweidegebied ten noordwesten van Purmerend, zijn op een perceel enkele koepelvormige bulten van zo'n 5 meter in doorsnee ontdekt. Karakteristiek daarin zijn verstoorde veenlagen. Bij de boeren ter plekke bekend onder de naam 'veenkringen'. In dit artikel wordt het verschijnsel (daliebulten genoemd) nader toegelicht. Een onderzoek in opdracht van DLG

Waterschap Vallei & Eem, Hoogheemraadschap De Stichtse Rijnlanden en Alterra Wageningen UR hebben samen een nieuwe bodemfysische schematisatie voor Nederland ontwikkeld. Deze schematisatie geeft een gedetailleerd beeld van de bodemfysische eigenschappen van de afzonderlijke horizonten waaruit de bodem is opgebouwd, en verschaft daarmee belangrijke invoergegevens in modelstudies naar het transport van water en opgeloste stoffen in de onverzadigde zone. Deze nieuwe schematisatie vervangt de veelgebruikte PAWN-schematisatie uit 1988.

Bodemkundig InformatieSysteem informeert over actuele toestand èn dynamiek. De bodem die we kennen vanaf het eerste moment dat we een bodemkaart zagen, lijkt onveranderlijk. Maar kijken we wat beter naar de bodem zelf, zoals bodemkundigen dat doen, dan zien we volop beweging

Bodemfysische gegevens, zoals de waterretentiekarakteristiek en doorlatendheidskarakteristiek, organisch stofgehalte, textuurgegevens, profielbeschrijving en andere metagegevens zijn belangrijke basisgegevens bij het modelleren van transport van water en opgeloste stoffen in de onverzadigde zone, maar vinden ook tal van andere toepassingen. Omdat er grote behoefte is aan actuele bodemfysische gegevens van hoge kwaliteit en omdat de huidige databases onvoldoende opschalingsmogelijkheden bieden, zijn in dit project 100 nieuwe bodemfysische gegevens van goede kwaliteit gegenereerd. De bodemfysische gegevens en de bijbehorende beschrijvende gegevens zijn ondergebracht in het BIS (Bodem Informatie Systeem). Aanvullend is van 91 bestaande bodemfysische gegevens van hoge kwaliteit in Priapus een koppeling gelegd met beschrijvende gegevens in BIS en de literatuur, zodat er in totaal 191 bodemfysische monsters beschikbaar zijn.

Bodemfysische gegevens, zoals de waterretentiekarakteristiek en doorlatendheidskarakteristiek, organisch stofgehalte, textuurgegevens, profielbeschrijving en andere metagegevens zijn belangrijke basisgegevens bij het modelleren van transport van water en opgeloste stoffen in de onverzadigde zone, maar vinden ook tal van andere toepassingen. Omdat er grote behoefte is aan actuele bodemfysische gegevens van hoge kwaliteit en omdat de huidige databases onvoldoende opschalingsmogelijkheden bieden, zijn in dit project 100 nieuwe bodemfysische gegevens van goede kwaliteit gegenereerd. De bodemfysische gegevens en de bijbehorende beschrijvende gegevens zijn ondergebracht in het BIS (Bodem Informatie Systeem). Aanvullend is van 91 bestaande bodemfysische gegevens van hoge kwaliteit in Priapus een koppeling gelegd met beschrijvende gegevens in BIS en de literatuur, zodat er in totaal 191 bodemfysische monsters beschikbaar zijn.

The effects of kaolinite additions and drying temperature on the persistence of soil water repellency, induced by humic acids from peat, were assessed in this study. It was found that additions of 5 and 10% kaolinite (referred to as the most effective material in combating the water repellency) did not result unambiguously in a decrease of the persistence of water repellency. In case of the higher humic acids contents, an increase of the persistence of water repellency was even noticed in comparison with the samples without kaolinite. Establishment (re-establishment) of water repellency was observed for the samples wetted to 30% after drying at temperatures of 30, 60°C (in both cases 36 of the 48 samples containing humic acids became water repellent) and after drying at 210°C (a few samples with the higher humic acids contents became slightly water repellent).

Viticulture and fruit culture in Mediterranean areas demand frequent tractor traffic in vineyards and orchards for tillage and for the application of herbicides and pesticides, resulting in soil compaction. The aim of this study was to investigate the extent of soil compaction and its effect on infiltration in vineyards and orchards in an area in southern France, known for its wine and fruit production (Vaucluse). Compaction of both the topsoil and the subsoil was demonstrated with measurements of bulk density, penetration resistance and water retention characteristics. Subsoil compaction was attributed to wheel load, not to tillage, and was alleviated within 5 years after termination of tillage operations in vineyards. No effects of topsoil compaction on infiltration were expected on account of the slight differences in the values of infiltration parameters between wheel tracks and inter-rill areas. Effects of subsoil compaction on infiltration were examined with rainfall simulation tests. Under wet initial conditions and high rain intensities, no effect of soil compaction on infiltration was observed. This implies that the frequent tractor traffic associated with viticulture and fruit culture does not enhance run-off on loamy soils in Mediterranean areas.

Adverse effects of soil water repellency (hydrophobicity) are of concern during or following rainfall or irrigation, and are often preceded by conditions of high atmospheric relative humidity (RH). Assessments of repellency are, however, commonly conducted on air-dried samples at ambient laboratory conditions. This study explores the effects of differing antecedent RHs (32-98%) on the water repellency of air-dried soils of wide ranging characteristics under laboratory conditions using water drop penetration time (WDPT) and ethanol-percentage tests. Most samples exhibited considerably higher water repellency after exposure (< 1 d) to 98% RH compared with lower RHs, typical of ambient laboratory conditions. This work suggests that previous studies mayhave incorrectly classified some soils, likely to exhibit water repellency in the field, as wettable, and that tests carried out following exposure of samples to high RH provide assessments that best reflect critical field conditions.

A Surface Energy Balance System (SEBS) is proposed for the estimation of atmospheric turbulent fluxes and evaporative fraction using satellite earth observation data, in combination with meteorological information at proper scales. SEBS consists of: a set of tools for the determination of the land surface physical parameters, such as albedo, emissivity, temperature, vegetation coverage etc., from spectral reflectance and radiance measurements; a model for the determination of the roughness length for heat transfer; and a new formulation for the determination of the evaporative fraction on the basis of energy balance at limiting cases. Four experimental data sets are used to assess the reliabilities of SEBS. Based on these case studies, SEBS has proven to be capable to estimate turbulent heat fluxes and evaporative fraction at various scales with acceptable accuracy. The uncertainties in the estimated heat fluxes are comparable to in-situ measurement uncertainties.

Assessments of water repellency of soils are commonly made on air-dried or oven-dried samples, without considering the soil water content. The objectives of this study were to examine the spatial and temporal variability of soil water content, actual water repellency over short distances, and the variations in critical soil water contents. Between 22 April and 23 November 1999, numerous samples were collected from a grass-covered dune sand (typic Psammaquent), at six depths, eight times in transects and two times in soil blocks. The water drop penetration time (WDPT) test was used to measure the actual water repellency of the field-moist samples and the potential water repellency after drying the samples at 25, 65, and 105 °C. Highly spatial and temporal variability in water content and persistence of actual water repellency was found between the samples from all soil depths. At each depth we established an upper water content, below which samples were water repellent and a lower water content, above which samples were wettable. This water content range, called the transition zone, was different for each depth, and, for example, assessed at 0 to 2.5 cm depth between soil water contents of 18 and 23% (vol./vol.), and at 16.5 to 19 cm depth between 2 and 5% (vol./vol.). The potential water repellency of samples dried at 25 and 65 °C was on some days less severe than the actual repellency of field-moist samples on other days, thus underestimating the maximal persistence of water repellency that can occur in the field. Drying of the samples at 105 °C significantly increased the potential water repellency.

The precision of design-based sampling strategies can be increased by using regression models at the estimation stage. A general regression estimator is given that can be used for a wide variety of models and any well-defined sampling design. It equals the estimator plus an adjustment term that accounts for the differences between the estimators for the spatial means of the auxiliary variables and the true spatial means of these variables. The regression estimator and ratio estimator follow from certain assumptions on the model and the sampling design. These are compared with the estimator in two case studies. In one study a bivariate field of linearly related variables was simulated and repeatedly sampled by Simple Random Sampling without replacement and sample sizes 10, 25, 50, 100 and 200. For all sample sizes the ratio of the standard error of the simple regression estimator to that of the estimator was approximately 55ÐThe bias of the simple regression estimator was negligibly small. The confidence interval estimators were valid for all sample sizes except for n = 10. Also the ratio estimator was approximately unbiased, and the confidence interval estimators were valid for all sample sizes, even for n = 10. This is remarkable because the ratio estimator assumes that the intercept of the regression line is 0 which was incorrect for the simulated field. On the other hand, only approximately 55␘f the potential gain was achieved because the model was inappropriate. In a second study the spatial means of the Mean Highest Watertable of map units were estimated by Stratified Simple Random Sampling and the combined (multiple) regression estimator. The NAP elevation, the local elevation, the Easting and the Northing were used as auxiliary variables. For all map units except one the combined (multiple) regression estimator was more precise than the estimator. The ratio of the standard errors varied from 0.36 to 1.04. The domain for which the regression estimator was less precise than the estimator showed strong variation between strata. For this domain it was more efficient to group the strata into two groups and to fit simple models for these groups separately.

Many environmental and agricultural problems are not restricted to national boundaries and therefore require international cooperation if solutions are to be found. Often, these solutions require the ability to use soil data as input in simulation models, however, despite a number of recognised international standards, soil data are rarely compatible across national frontiers. This problem was encountered when creating the HY draulic PR operties of E uropean S oils (HYPRES) database. The data, which includes particle-size distributions, were collected from 20 institutions in 12 countries. Only a few of these institutions adhered strictly to a recognised international system. Therefore, interpolation of the cumulative particle-size distribution was required to achieve compatibility of particle-size distributions within the HYPRES database. In this study, four different interpolation procedures were evaluated. The accuracy of the different procedures was found to vary with size intervals between measured points of the particle-size distribution. The loglinear interpolation of the cumulative particle-size distribution has previously been used in various studies but was found to give the least accurate estimation of the four procedures. Fitting the Gompertz curve, which is a special asymmetric type of curve described by a closed-form equation, showed less sensitivity to size intervals between measured points. However, interpolation within some of the particle-size distributions was not sufficiently accurate and this procedure could not be applied to particle-size distributions where the number of measured size fractions was less than the number of model parameters. Fitting a nonparametric spline function to the particle-size distributions showed a considerable increase in accuracy of the interpolation with decreasing size intervals between measured points. As a novel approach, the similarity procedure was introduced which does not use any mathematical interpolation functions. It uses an external source of soil information from which soils are selected with particle-size distributions that match the distribution of the soil under investigation. This similarity procedure was capable of giving the most accurate interpolations. Once an extensive external reference data set with well-quantified particle-size distributions is available, the similarity procedure becomes a very powerful tool for interpolations. Based on the number and distribution of measured points on the particle-size distributions, a general rule was formulated to decide whether to fit a spline function or use the novel similarity procedure to estimate missing values. Results of this study were used to classify all soils in the HYPRES database into the same soil texture classes used in the 1:1.000.000 scale Soil Geographical Database of Europe.

Inventarisatie van gebruikers, toepassingen en gewenste typen van bodeminformatie. Dit in het kader van Landsdekkend Beeld Bodemkwaliteit, sinds januari 2005 BIELLS genaamd: BodemInformatie Essentieel voor Locale en Landelijke Sturing. Het project valt onder het uitvoeringsprogramma van de Beleidsbrief Bodem. De partijen, die onderscheiden zijn (als belanghebbenden) zijn: VROM, LNV, V&W, provincies, gemeenten, natuurorganisaties, landbouworganisaties en waterwinners

Het beschreven onderzoek in dit rapport is onderdeel van het onderzoeksproject ‘gedrag van verdroogde kades’ van het Hoogheemraadschap Delfland. Het onderzoek van Alterra is een bureau- en modelonderzoek en is gericht op scheuren door krimp, die ontstaan in lange perioden met droogte. Onderzocht zijn veenkaden en kleikaden op veen, met een accent op kleikaden omdat deze in Delfland het meeste voorkomen. Bij kleikaden lijkt het grootste risico preferente stroming via de scheuren te zijn. Bomen kunnen door hun diepe beworteling en grote verdamping een extra risico vormen. Langsscheuren in de kruin kunnen met water gevuld worden en dit kan resulteren in een bezwijkmechanisme. Dit is door Deltares nader onderzocht in een parallel rapport.

Het beschreven onderzoek in dit rapport is onderdeel van het onderzoeksproject ‘gedrag van verdroogde kades’ van het Hoogheemraadschap Delfland. Het onderzoek van Alterra is een bureau- en modelonderzoek en is gericht op scheuren door krimp, die ontstaan in lange perioden met droogte. Onderzocht zijn veenkaden en kleikaden op veen, met een accent op kleikaden omdat deze in Delfland het meeste voorkomen. Bij kleikaden lijkt het grootste risico preferente stroming via de scheuren te zijn. Bomen kunnen door hun diepe beworteling en grote verdamping een extra risico vormen. Langsscheuren in de kruin kunnen met water gevuld worden en dit kan resulteren in een bezwijkmechanisme. Dit is door Deltares nader onderzocht in een parallel rapport.

Traditionally, soil science, atmospheric science, hydrology, plant science and agriculture have been studied largely as separate subjects. These systems are clearly interlinked, however, and in recent years a great deal of interdisciplinary research has been undertaken to better understand the interactions. This textbook was developed from a course that the authors have been teaching for many years on atmosphere-vegetation-soil interactions at one of the leading international research institutes in environmental science and agriculture. The book describes the atmosphere-vegetation-soil continuum from the perspective of several interrelated disciplines, integrated into one textbook.

Traditionally, soil science, atmospheric science, hydrology, plant science and agriculture have been studied largely as separate subjects. These systems are clearly interlinked, however, and in recent years a great deal of interdisciplinary research has been undertaken to better understand the interactions. This textbook was developed from a course that the authors have been teaching for many years on atmosphere-vegetation-soil interactions at one of the leading international research institutes in environmental science and agriculture. The book describes the atmosphere-vegetation-soil continuum from the perspective of several interrelated disciplines, integrated into one textbook.

This paper investigates methods to compare spatial patterns of pearl millet [Pennisetum glaucum (L.) R. Br.] yield with spatial patterns of soil variables in a farmer's 1-ha field on an undulating sand plain in Niger near ICRISAT-SC. Spatial pattern comparisons are important for precision farming applications. Methods included the correlation coefficient, linear regression, a distance measure to compare separate maps and the cross-correlation function. Millet grain yield varied from 0 to 2885 kg ha -1 on 5 by 5 m sub-plots. Pearl millet yield was correlated with measured soil variables at three different depths, elevation, and crust formation for two successive years. Only 30% of the total variation in millet dry yield was explained by regressing yield against soil variables. Detrended elevation showed a significant negative relation with yield (r = -0.421). The cation-exchange capacity (CEC) at all the depths showed a significant negative relation with yield (r of -0.238 to -0.290) because crusting and erosion increase with CEC extending to distances up to 30 to 40 m. Pattern comparison using the cross-correlogram related local hillocks in the area with high yields and local dips with low yields at a distance of 15 to 20 m. From this study, we concluded that the cross-correlogram was beneficial to compare data at various distances. Yield patterns are best explained by soil variables related to erosion as the major determining factor in the area.

Onlangs bundelden onderzoekers van LEI en Alterra hun ervaringen met het wesetelijk veenweidegebied. Het grootste probleem is het waterprobleem, waarbij ook aspecten van inklinking, recreatie, bewoning, waterberging, en daardoor ruimtelijke inrichting een rol spelen

Uncertainties in major input variables in water and solute models were quantified and their effects on simulated functional aspects of soil behaviour were studied using basic soil properties from an important soil map unit in the Netherlands. Two sources of uncertainty were studied: spatial variability of basic soil properties, and the use of pedotransfer functions to predict soil hydraulic functions. Depending on the type of process studied, variability of basic soil properties explained between 40 and 99.9% of the total variance. Uncertainty of pedotransfer functions is of importance mainly when physical soil behaviour (e.g. workable days and aeration status) is studied.

Snelle stijgingen in het verloop van het freatisch vlak onder relatief steile veenkades als gevolg van perioden met veel neerslag kunnen gevolgen hebben voor de mate van stabiliteit van dijklichamen. Door middel van irrigatieproeven zijn op een tweetal kades onderzocht hoe het freatisch vlak reageert op neerslaghoeveelheden die eens in de 100 jaar voorkomen, en die over een periode van 1 tot 9 dagen lengte vallen. Met behulp van het 2 dimensionale model HYDRUS-2D is geprobeerd deze situaties na te bootsen. Hiermee komt dan een instrumentarium beschikbaar waarmee alternatieve scenario’s kunnen worden doorgerekend. Tevens wordt inzichtelijk gemaakt hoe de waterstroming door het dijklichaam plaatsvindt.

Snelle stijgingen in het verloop van het freatisch vlak onder relatief steile veenkades als gevolg van perioden met veel neerslag kunnen gevolgen hebben voor de mate van stabiliteit van dijklichamen. Door middel van irrigatieproeven zijn op een tweetal kades onderzocht hoe het freatisch vlak reageert op neerslaghoeveelheden die eens in de 100 jaar voorkomen, en die over een periode van 1 tot 9 dagen lengte vallen. Met behulp van het 2 dimensionale model HYDRUS-2D is geprobeerd deze situaties na te bootsen. Hiermee komt dan een instrumentarium beschikbaar waarmee alternatieve scenario’s kunnen worden doorgerekend. Tevens wordt inzichtelijk gemaakt hoe de waterstroming door het dijklichaam plaatsvindt.

In large areas worldwide, both in semi-arid and humid climates, the availability of good quality water for primary production in agriculture or natural vegetations is limited. Whereas soil and groundwater pollution are nowadays general problems, much larger areas have to deal with the hazards of soil and groundwater salinity. For soil types that are susceptible to physical degradation in view of their swelling and shrinking behaviour, also the salinity associated hazard of soil sodicity needs to be anticipated. Sodicity related soil physical degradation may be quite irreversible and is a major candidate for preventive rather than curative measures. The process of salt displacement has received much attention, and spatial variability has been given explicit attention by Dagan and Bresler (1979). Temporal variability of the boundary conditions has been investigated only recently, when both primary and secondary salinity were studied with so-called minimalist ecohydrological modelling (Suweis et al., 2010, Shah et al., 2011, Vervoort and Van der Zee, 2012). This work emphasized the atmospheric forcing of erratic rainfall on water and salt dynamics in the rootzone layer, either envisioned as a Poisson process, or with seasonal periodicity. Taking such erratic rainfall as well as spatial variability of the depth of the groundwater level into account, an impression can be obtained of the importance of different sources of variability. For our parameterization, we find that both spatial and temporal variability were responsible for the variation in root zone salinity, C, but that root zone sodicity, expressed with the Exchangeable Sodium Percentage, ESP, depends predominantly on spatial variability. The difference is understandable from the buffering mechanisms involved with C and ESP.

De doelstelling van de hier gerapporteerde studie was om te onderzoeken of de bodembelasting door verschillende typen landbouwmachines in de afgelopen 30 jaar inderdaad toegenomen is, zoals wordt verondersteld. Het begrip bomdembelasting wordt gebruikt voor zowel het drukpatroon op de bodem onder de wielen van machines (bodemdruk) als voor de daardoor veroorzaakte drukken op verschillende dieptes in de grond (grondspanningen). In het rapport wordt eerst de ontwikkeling van de bodemdruk van verschillende machines geïnventariseerd. Het bodemdrukpatroon wordt hoofdzakelijk bepaald door de wiellast, het type band, de bandenmaat en de banddruk (luchtdruk in de band). Om de belasting van de ondergrond te karakteriseren werd met de uit de machinegegevens afgeleide drukpatronen onder de wielen berekend wat de piekspanningen op 25, 40 en 50 cm diepte in de ondergrond waren, in 1980 en 2010.

Aan de 315 bodemeenheden behorende bij de bodemkaart van Nederland, schaal 1 : 50.000, zijn waterretentie- en doorlatendheidskarakteristieken uit de Staringreeks toegekend. Met een model zijn voor deze eenheden functionele kenmerken berekend. Op grond van verwantschap in functionele kenmerken zijn de 315 bodemeenheden geclusterd in 72 bodemfysische eenheden en afgebeeld in de nieuwe BOdemFysische EenhedenKaart (BOFEK2012). Om bij modelberekeningen van bodemwatertransport en stoffentransport in de bodem deze gegevens te kunnen gebruiken is een dataset samengesteld met informatie over: - GIS-bestand, met de geografische verbreiding van de BOFEK-eenheden in Nederland. - Profielschetsen met de laagopbouw van het bodemprofiel tot 1.20 m-mv. en de daaraan gerelateerde bodemfysische kenmerken.

Recent trends and future projections suggest that the need to produce more food and fibre for the world’ s expanding population will lead to an increase in the use of marginal-quality water and land resources (Bouwer, 2000; Gupta and Abrol, 2000; Wild, 2003). This is particularly relevant to less-developed, arid and semi-arid countries, in which problems of soil and water quality degradation are common (Qadir and Oster, 2004). The aim, therefore, should be to increase yield per unit of land rather than the area cultivated. More efforts are needed to improve productivity as more lands are becoming degraded. It is estimated that about 15% of the total land area of the world has been degraded by soil erosion and physical and chemical degradation, including soil salinization (Wild, 2003). The main sources of soil salinity and sodicity development are groundwater and irrigation water. In discharge areas of the landscape, water exits from groundwater to the soil surface bringing the salts dissolved in it. The driving force for upward movement of water and salts is evaporation from the soil plus plant transpiration. Salt accumulation is high when the water table depth is less than a threshold. However, this threshold depth may vary depending on soil hydraulic properties and climatic conditions. Groundwater associated salinity and sodicity affects around 350 X 104km2in the world (Szabolcs, 1989). In this thesis, the focus is to quantify and understand the salinity and sodicity dynamics, and the feedback on dynamics in groundwater dependent agro-ecosystems. First we have considered the impact of salt coming from groundwater on capillary fluxes and on the root zone water and salt dynamics. Groundwater can be a source of both water and salts in semi-arid areas, and therefore capillary pressure induced upward water flow may cause root zone salinization. To identify which conditions result in hazardous salt concentrations in the root zone, we combined the mass balance equations for salt and water, further assuming a Poisson-distributed daily rainfall and brackish groundwater quality. For the water fluxes (leaching, capillary upflow, and evapotranspiration), we account for osmotic effects of the dissolved salt mass using Van‘t Hoff’s law. Root zone salinity depends on salt transport via capillary flux and on evapotranspiration, which concentrates salt in the root zone. Both a wet climate and shallow groundwater lead to wetter root zone conditions, which in combination with periodic rainfall enhances salt removal by leaching. For wet climates, root zone salinity (concentrations) increases as groundwater is more shallow (larger groundwater influence). For dry climates, salinity increases as groundwater is deeper due to a drier root zone and less leaching. For intermediate climates, opposing effects can push the salt balance in either way. Root zone salinity increases almost linearly with groundwater salinity. With a simple analytical approximation, maximum concentrations can be related with the mean capillary flow rate, leaching rate, water saturation and groundwater salinity, for different soils, climates and groundwater depths. A Soil sodicity (quantified by ESP) model based on the soil salinity model (as discussed above) has been developed. For sodicity calculations, we have used the Gapon equation favored in salinity research. The simulation results show that soil salinity and sodicity development in groundwater driven agro-ecosystems play a major role in soil structure degradation. To identify which conditions can make soil sodic, we have modeled the coupled water, salt, and cation balances. The root zone salinity Cand sodicity ESPgradually change to their long term average values. These long term average values are independent of the cation exchange capacity CEC. The rate of change depends inversely on the size of the root zone reservoir, i.e., on root zone thickness for C, and additionally on CEC, for ESP.Soil type can have a large effect on both the rate of approach of the long term steady state salinity and sodicity, and on the long term levels, as it affects the incoming and out-going water and chemical fluxes. Considering two possible sources of salts, i.e., groundwater and irrigation water (here represented by rainfall), the long term salt concentration Cof the root zone corresponds well with a flux weighted average of infiltrating and upflowing salt mass divided by the average water drainage. In full analogy, the long term ESPcan be approximated very well for different groundwater depths and climates. A more refined analytical approximation, based on the analytical solution of the water balance of Vervoort and Van der Zee(2008), leads to a quite good approximation of long term salinity and sodicity, for different soils, groundwater depths, and climates. Modeling is an efficient tool to investigate water and solute movement in groundwater driven agro-ecosystems. However, in most available models (SWAP,MODFLOW/MT3D) continuing degradation of soil hydraulic properties as a result of rising Na+concentrations is ignored. Disregarding the soil hydraulic degradation due to sodicity level in some cases makes modeling water and solute movement within the soil profile questionable. We have translated the effects of soil salinity and sodicity into reduction in saturated hydraulic conductivity to quantify the feedback effects of reduction in saturated hydraulic conductivity on root zone fluxes, salinity, and sodicity under different groundwater depths and climates of Oenpelli and Tennant Creek Airport located in the North Territory of Australia. The reduction in saturated hydraulic conductivity due to salinity and sodicity (Ks(C,ESP))has been calculated by using the procedure developed by McNeal(1968). The significant feedback effects of Ks(C,ESP) on salt concentration and soil ESPdepend on many important parameters like groundwater depth, leaf area index, weather seasonality and non-seasonality, and soil type. Out of these important parameters, weather seasonality is the main driver that can develop significant feedback effects of Ks(C,ESP) onsalt concentration and soil ESP. Furthermore, Ks(C,ESP) although decreasing the capillary flux, leaching flux, and evapotranspiration, it increases the magnitude of runoff. Also when Ks(C,ESP)affects both capillary and leaching flux under seasonal rainfall, the feedback effects are significant compared to the partial feedback (Ks(C,ESP)affects only leaching flux, but not capillary flux). In the second theme of this thesis, we have focused on optimizing irrigation water between two farms under water scarcity and salinity regimes. In arid and semi-arid regions, irrigation water is scarce and often saline. To reduce negative effects on crop yields, the irrigated amounts must include water for leaching and therefore exceed evapotranspiration. The leachate (drainage) water returns to water sources such as rivers or groundwater aquifers and increases their level of salinity and the leaching requirement for irrigation water of any sequential user. We develop a sequential (upstream-downstream) model of irrigation that predicts crop yields and water consumption and tracks the water flow and level of salinity along a river dependent on irrigation management decisions. The model incorporates an agro-physical model of plant response to environmental conditions including feedbacks. For a system with limited water resources, the model examines the impacts of water scarcity, salinity and inefficient application on yields for specific crop, soil, and climate conditions. As a general pattern we find that, as salinity level and technical inefficiency increase, the system benefits when upstream farms use less water than is available to them, to provide downstream farms with more and better quality water. We compute the marginal value of water, i.e. the price water that would command on a market, for different levels of water scarcity, salinity and levels of water loss. In summary this thesis aims to understand theoretically how soil salinity and sodicity develop under different climates, groundwater depths, soil types, root zone thicknesses, and different groundwater salinities. The developed salinity sodicity model can be applied in potential salt affected areas to predict the long term salinity, sodicity trends. Furthermore, quantification of feedback effects of reduction in saturated hydraulic conductivity (Ks(C,ESP)) on root zone fluxes, salinity, and sodicity guide us towards better management of soil, vegetation, and irrigation/groundwater.

Aan de 315 bodemeenheden behorende bij de bodemkaart van Nederland, schaal 1 : 50.000, zijn waterretentie- en doorlatendheidskarakteristieken uit de Staringreeks toegekend. Met een model zijn voor deze eenheden functionele kenmerken berekend. Op grond van verwantschap in functionele kenmerken zijn de 315 bodemeenheden geclusterd in 72 bodemfysische eenheden en afgebeeld in de nieuwe BOdemFysische EenhedenKaart (BOFEK2012). Om bij modelberekeningen van bodemwatertransport en stoffentransport in de bodem deze gegevens te kunnen gebruiken is een dataset samengesteld met informatie over: - GIS-bestand, met de geografische verbreiding van de BOFEK-eenheden in Nederland. - Profielschetsen met de laagopbouw van het bodemprofiel tot 1.20 m-mv. en de daaraan gerelateerde bodemfysische kenmerken.

Recent trends and future projections suggest that the need to produce more food and fibre for the world’ s expanding population will lead to an increase in the use of marginal-quality water and land resources (Bouwer, 2000; Gupta and Abrol, 2000; Wild, 2003). This is particularly relevant to less-developed, arid and semi-arid countries, in which problems of soil and water quality degradation are common (Qadir and Oster, 2004). The aim, therefore, should be to increase yield per unit of land rather than the area cultivated. More efforts are needed to improve productivity as more lands are becoming degraded. It is estimated that about 15% of the total land area of the world has been degraded by soil erosion and physical and chemical degradation, including soil salinization (Wild, 2003). The main sources of soil salinity and sodicity development are groundwater and irrigation water. In discharge areas of the landscape, water exits from groundwater to the soil surface bringing the salts dissolved in it. The driving force for upward movement of water and salts is evaporation from the soil plus plant transpiration. Salt accumulation is high when the water table depth is less than a threshold. However, this threshold depth may vary depending on soil hydraulic properties and climatic conditions. Groundwater associated salinity and sodicity affects around 350 X 104km2in the world (Szabolcs, 1989). In this thesis, the focus is to quantify and understand the salinity and sodicity dynamics, and the feedback on dynamics in groundwater dependent agro-ecosystems. First we have considered the impact of salt coming from groundwater on capillary fluxes and on the root zone water and salt dynamics. Groundwater can be a source of both water and salts in semi-arid areas, and therefore capillary pressure induced upward water flow may cause root zone salinization. To identify which conditions result in hazardous salt concentrations in the root zone, we combined the mass balance equations for salt and water, further assuming a Poisson-distributed daily rainfall and brackish groundwater quality. For the water fluxes (leaching, capillary upflow, and evapotranspiration), we account for osmotic effects of the dissolved salt mass using Van‘t Hoff’s law. Root zone salinity depends on salt transport via capillary flux and on evapotranspiration, which concentrates salt in the root zone. Both a wet climate and shallow groundwater lead to wetter root zone conditions, which in combination with periodic rainfall enhances salt removal by leaching. For wet climates, root zone salinity (concentrations) increases as groundwater is more shallow (larger groundwater influence). For dry climates, salinity increases as groundwater is deeper due to a drier root zone and less leaching. For intermediate climates, opposing effects can push the salt balance in either way. Root zone salinity increases almost linearly with groundwater salinity. With a simple analytical approximation, maximum concentrations can be related with the mean capillary flow rate, leaching rate, water saturation and groundwater salinity, for different soils, climates and groundwater depths. A Soil sodicity (quantified by ESP) model based on the soil salinity model (as discussed above) has been developed. For sodicity calculations, we have used the Gapon equation favored in salinity research. The simulation results show that soil salinity and sodicity development in groundwater driven agro-ecosystems play a major role in soil structure degradation. To identify which conditions can make soil sodic, we have modeled the coupled water, salt, and cation balances. The root zone salinity Cand sodicity ESPgradually change to their long term average values. These long term average values are independent of the cation exchange capacity CEC. The rate of change depends inversely on the size of the root zone reservoir, i.e., on root zone thickness for C, and additionally on CEC, for ESP.Soil type can have a large effect on both the rate of approach of the long term steady state salinity and sodicity, and on the long term levels, as it affects the incoming and out-going water and chemical fluxes. Considering two possible sources of salts, i.e., groundwater and irrigation water (here represented by rainfall), the long term salt concentration Cof the root zone corresponds well with a flux weighted average of infiltrating and upflowing salt mass divided by the average water drainage. In full analogy, the long term ESPcan be approximated very well for different groundwater depths and climates. A more refined analytical approximation, based on the analytical solution of the water balance of Vervoort and Van der Zee(2008), leads to a quite good approximation of long term salinity and sodicity, for different soils, groundwater depths, and climates. Modeling is an efficient tool to investigate water and solute movement in groundwater driven agro-ecosystems. However, in most available models (SWAP,MODFLOW/MT3D) continuing degradation of soil hydraulic properties as a result of rising Na+concentrations is ignored. Disregarding the soil hydraulic degradation due to sodicity level in some cases makes modeling water and solute movement within the soil profile questionable. We have translated the effects of soil salinity and sodicity into reduction in saturated hydraulic conductivity to quantify the feedback effects of reduction in saturated hydraulic conductivity on root zone fluxes, salinity, and sodicity under different groundwater depths and climates of Oenpelli and Tennant Creek Airport located in the North Territory of Australia. The reduction in saturated hydraulic conductivity due to salinity and sodicity (Ks(C,ESP))has been calculated by using the procedure developed by McNeal(1968). The significant feedback effects of Ks(C,ESP) on salt concentration and soil ESPdepend on many important parameters like groundwater depth, leaf area index, weather seasonality and non-seasonality, and soil type. Out of these important parameters, weather seasonality is the main driver that can develop significant feedback effects of Ks(C,ESP) onsalt concentration and soil ESP. Furthermore, Ks(C,ESP) although decreasing the capillary flux, leaching flux, and evapotranspiration, it increases the magnitude of runoff. Also when Ks(C,ESP)affects both capillary and leaching flux under seasonal rainfall, the feedback effects are significant compared to the partial feedback (Ks(C,ESP)affects only leaching flux, but not capillary flux). In the second theme of this thesis, we have focused on optimizing irrigation water between two farms under water scarcity and salinity regimes. In arid and semi-arid regions, irrigation water is scarce and often saline. To reduce negative effects on crop yields, the irrigated amounts must include water for leaching and therefore exceed evapotranspiration. The leachate (drainage) water returns to water sources such as rivers or groundwater aquifers and increases their level of salinity and the leaching requirement for irrigation water of any sequential user. We develop a sequential (upstream-downstream) model of irrigation that predicts crop yields and water consumption and tracks the water flow and level of salinity along a river dependent on irrigation management decisions. The model incorporates an agro-physical model of plant response to environmental conditions including feedbacks. For a system with limited water resources, the model examines the impacts of water scarcity, salinity and inefficient application on yields for specific crop, soil, and climate conditions. As a general pattern we find that, as salinity level and technical inefficiency increase, the system benefits when upstream farms use less water than is available to them, to provide downstream farms with more and better quality water. We compute the marginal value of water, i.e. the price water that would command on a market, for different levels of water scarcity, salinity and levels of water loss. In summary this thesis aims to understand theoretically how soil salinity and sodicity develop under different climates, groundwater depths, soil types, root zone thicknesses, and different groundwater salinities. The developed salinity sodicity model can be applied in potential salt affected areas to predict the long term salinity, sodicity trends. Furthermore, quantification of feedback effects of reduction in saturated hydraulic conductivity (Ks(C,ESP)) on root zone fluxes, salinity, and sodicity guide us towards better management of soil, vegetation, and irrigation/groundwater.

De doelstelling van de hier gerapporteerde studie was om te onderzoeken of de bodembelasting door verschillende typen landbouwmachines in de afgelopen 30 jaar inderdaad toegenomen is, zoals wordt verondersteld. Het begrip bomdembelasting wordt gebruikt voor zowel het drukpatroon op de bodem onder de wielen van machines (bodemdruk) als voor de daardoor veroorzaakte drukken op verschillende dieptes in de grond (grondspanningen). In het rapport wordt eerst de ontwikkeling van de bodemdruk van verschillende machines geïnventariseerd. Het bodemdrukpatroon wordt hoofdzakelijk bepaald door de wiellast, het type band, de bandenmaat en de banddruk (luchtdruk in de band). Om de belasting van de ondergrond te karakteriseren werd met de uit de machinegegevens afgeleide drukpatronen onder de wielen berekend wat de piekspanningen op 25, 40 en 50 cm diepte in de ondergrond waren, in 1980 en 2010.

In de landen van de Europese gemeenschap worden door de nationale overheden verscheidene experimenten voorgeschreven om de omzetting en het transport van pesticiden te karakteriseren. Een van deze experimenten, de kolomstudie verouderd residu (Aged Residue Leaching test), wordt uitgevoerd om het risico van uitspoeling van pesticiden en daaruit ontstane metabolieten te beoordelen. Dit rapport geeft een mathematische beschrijving van de dynamische processen die zich voordoen bij dit experiment. Er wordt een interpretatiemethode voorgesteld om de resultaten van de experimenten te vertalen naar stofeigenschappen zoals halfwaardetijd, vormingsfractie en sorptiecoefficient in grond. Deze stofeigenschappen kunnen gebruikt worden om met simulatiemodellen een risicoanalyse uit te voeren onder realistische milieuscenario's. De interpretatiemethode maakt gebruik van het PESTRAS-model, een simulatiemodel dat transport, transformatie, afbraak en sorptie van organische verontreinigingen in de bodem beschrijft. Het model wordt toegepast in de omgekeerde volgorde: de systeemparameters waarin men geinteresseerd is worden afgeleid uit de (gemeten) uitvoervariabelen. Er wordt geconcludeerd dat de nieuwe interpretatiemethode beter geschikt is om de resultaten van de ARL-test te verwerken dan de bestaande methoden. Vooral als aandacht wordt gegeven in het experiment aan documentatie van de experimentele condities en als voldoende metingen worden uitgevoerd kunnen relatief nauwkeurige schattingen worden gemaakt van de parameters.

Bodemhydraulische karakteristieken zijn relaties van vochtgehalte (θ) en doorlatendheid (K) met de capillaire drukhoogte (h) in de onverzadigde zone van de bodem. Deze karakteristieken worden gebruikt voor modelsimulaties van het transport van water en opgeloste stoffen in de onverzadigde zone van de bodem. Doel van deze studie is de bij Alterra beschikbare basisgegevens voor bodemhydraulische karakteristieken te controleren, aan te vullen en beschikbaar te stellen voor het Bodemkundig Informatie Systeem (BIS) van Alterra. Hiervoor werden meetgegevens, afgeleide gegevens en beschrijvende gegevens van grondmonsters in de bestaande database Priapus gecorrigeerd en aangevuld. De variatie door metingen, functiebeschrijvingen en ruimtelijke variatie werd inzichtelijk gemaakt. Voor een betere bepaling van afgeleide gegevens uit de meetgegevens werd een nieuwe functiebeschrijving voor bodemhydraulische karakteristieken ontwikkeld in de vorm van cubical splines. Om de selectie van bodemhydraulische karakteristieken meer flexibel te maken voor gebruikers werd een nieuwe indeling van Nederlandse gronden ontwikkeld met als criteria: afzettingsmilieu, textuur en organische stofgehalte.

Bodemhydraulische karakteristieken zijn relaties van vochtgehalte (θ) en doorlatendheid (K) met de capillaire drukhoogte (h) in de onverzadigde zone van de bodem. Deze karakteristieken worden gebruikt voor modelsimulaties van het transport van water en opgeloste stoffen in de onverzadigde zone van de bodem. Doel van deze studie is de bij Alterra beschikbare basisgegevens voor bodemhydraulische karakteristieken te controleren, aan te vullen en beschikbaar te stellen voor het Bodemkundig Informatie Systeem (BIS) van Alterra. Hiervoor werden meetgegevens, afgeleide gegevens en beschrijvende gegevens van grondmonsters in de bestaande database Priapus gecorrigeerd en aangevuld. De variatie door metingen, functiebeschrijvingen en ruimtelijke variatie werd inzichtelijk gemaakt. Voor een betere bepaling van afgeleide gegevens uit de meetgegevens werd een nieuwe functiebeschrijving voor bodemhydraulische karakteristieken ontwikkeld in de vorm van cubical splines. Om de selectie van bodemhydraulische karakteristieken meer flexibel te maken voor gebruikers werd een nieuwe indeling van Nederlandse gronden ontwikkeld met als criteria: afzettingsmilieu, textuur en organische stofgehalte.

The Ethiopian drylands occupy about 65% of the total land mass (close to 700,000km2) of the country. The predominantly rainfed agriculture in these drylands is highly constrained due to erratic rainfall, long dry-spells and excessive loss of rainwater through non-productive pathways (surface runoff, evaporation and deep drainage). Apart from this, deteriorated dryland soils have low infiltration and water holding capacity, shallow depths and are sensitive to crusting. Therefore, to keep in pace with the demand for food for the burgeoning population, the Ethiopian drylands should be made more productive through appropriate rainwater harvesting and management techniques. Therefore, the objective of this study was to develop appropriate rainwater harvesting and management techniques in the Central Rift Valley (CRV) drylands of Ethiopia through a participatory planning and development process. Primarily, an overview of the various rainwater harvesting and management techniques in sub-Saharan Africa was made. Moreover, the biophysical performances and socioeconomic implications of the most common practices were synthesized. The sub-Saharan Africa is actually the birthplace of a range of indigenous rainwater harvesting and management (RWHM) techniques. The micro-catchment and in situ RWHM techniques are more commonly applied than the macro-catchment techniques for supplemental irrigation on farm lands. Depending on rainfall patterns and local soil characteristics, appropriate application of in-situ and micro-catchment techniques could improve the soil water content of the rooting zone by up to 30%. Smart combinations of rainwater harvesting and soil improvements enable to increase crop yields by 200-600% as compared to the traditional farming without them. Following the implementation of rainwater harvesting techniques, the cereal-based smallholder farmers could shift to diversified crops, hence improving household food security, dietary status, and economic return. The interplay between drought vulnerability and the changing trends in land-use/cover and land management in the CRV drylands of Ethiopia was made using a combination of GIS/remote sensing, meteorological drought analyses and surveying techniques. Given late onset of rainfall seasons (for both livestock farming and crop cultivation) and long dry-spells (for crop cultivation only) as the perceived causes of drought, pastoral system was vulnerable to severe drought once in seven years while mixed crop-livestock farming was vulnerable to severe drought once in twenty eight years. Over the last 5 decades, cultivated lands increased to threefold while the dense acacia coverage declined from 42% in 1965 to 9% in 2010. Although conversion from pastoral life to mixed crop-livestock system was perceived important to cope with drought, long-term tillage using the traditional Maresha cultivation caused deteriorates of the soil water properties. Infiltration rate of the surface soil layer increases significantly immediately after conversion of acacia-based grasslands to cultivation. However, there is a weak decreasing trend in infiltration rate and a significant increase in soil evaporation with increases in cultivation durations. Thus, it was implied that improved soil management and appropriate tillage are needed to maximize rainwater use efficiency and achieve sustainable agricultural production in the CRV of Ethiopia. Two-year field experimentation was undertaken to calibrate and examine the role of the FAO’s AquaCrop model in simulating the effect of rainwater harvesting techniques in response to different rainfall patterns and soil fertility levels in the CRV of Ethiopia. After proper calibration of the FAO’s AquaCrop model, it was possible to simulate the effect of tied-ridges and soil fertility improvements on maize yield and water use efficiency in response to different rainfall patterns. The model simulation revealed that the effect of tied-ridges alone performed better than soil fertility improvements during below-average rainfall seasons. During above-average rainfall seasons, the combined use of tied-ridges and soil fertility improvement was found very effective to substantially improve maize yield. This is because the excess water held in the tied-ridges can be best utilized due to the enhanced water uptake capacity of maize growing in the fertilized soils. Depending on the seasonal rainfall patterns, the combined use of tied-ridges and optimum level of soil fertilizer doubles the rainwater use efficiency of maize. A field experiment during a normal rainfall in 2010 revealed that the combined use of farmyard manure (4.5 Mg ha-1) and tied-ridges increased maize yield by 47% while tied-ridges in isolation increased maize yield by 26%. Moreover, long-term simulation revealed that the effect of tied-ridges on yield improvements was higher for sowing in April than for sowing in May. Finally, this study enabled to develop a participatory planning approach for rainwater harvesting and management. The approach starts with investigation of the priority agro-meteorological determinants for crop production and identification of the existing knowledge and opportunities. The proposed approach also enables to plan an integrated rainwater harvesting and soil improvement techniques. The application of this new approach in the CRV implied that any effort on the introduction of new in situ rainwater harvesting techniques should assess existing tillage, hoeing and associated land management practices. The existing Dirdaro furrow system could be taken as a basis to introduce and develop tied-ridges using the Maresha-modified ridger. Overall, this approach may augment the recent efforts of dissemination of rainwater harvesting and management techniques for improved agricultural development in the vast drylands of Ethiopia.