Staff Publications

Staff Publications

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

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

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

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Logistical case study for the AragÓn region using the locagistics tool
Annevelink, Bert ; Galindo, Daniel García ; Espatolero, Sergio ; Staritsky, Igor ; Vanmeulebrouk, Bas - \ 2017
European Biomass Conference and Exhibition Proceedings 2017 (2017)25thEUBCE. - ISSN 2282-5819 - p. 41 - 47.
Decision making - Geographical information system (GIS) - Logistics - Supply chain
LocaGIStics is a support tool for the design of regional biomass delivery chains. It enables to further design and evaluate regional biomass delivery chains that are e.g. the result of initial planning by an energy company or a biobased producer. These general plans are translated in several biomass delivery designs using the variation in logistical concepts covering transport, pre-treatment and conversion options. The performance of every chain design can then be analyzed by comparing the different biomass delivery chains on the following environmental and economic indicators. A regional case study was performed in Aragón (Spain) using the LocaGIStics tool. In this case study maps were used where the biomass availability is specified for 2.5 x 2.5 grid cells. Data about the logistical components were supplied partly by the energy supplying company that was involved. This paper shows the main outcomes of this case study.
D3.4 + D3.6: Cover report Results logistical case studies : S2Biom Project Grant Agreement n°608622
Annevelink, E. ; Gabrielle, B. ; Carozzi, M. ; Garcia Galindo, D. ; Espatolero, S. ; Izquierdo, M. ; Väätäinen, K. ; Anttila, P. ; Staritsky, I.G. ; Vanmeulebrouk, B. ; Elbersen, B. ; Leduc, S. - \ 2016
S2Biom - 23 p.
biobased economy - europa - databanken - modellen - duurzaamheid (sustainability) - hulpbronnengebruik - biomassa - logistiek - europe - databases - models - sustainability - resource utilization - biomass - logistics
The S2Biom project - Delivery of sustainable supply of non-food biomass to support a “resource-efficient” Bioeconomy in Europe - supports the sustainable delivery of nonfood biomass feedstock at local, regional and pan European level through developing strategies, and roadmaps that will be informed by a “computerized and easy to use” toolset (and respective databases) with updated harmonized datasets at local, regional, national and pan European level for EU28, Western Balkans, Moldova, Turkey and Ukraine. A case based approach was followed, where optimal logistical concepts (conceptual designs) were matched with the specific regional situation. This was done in three logistical case studies that were performed: 1. Small-scale power production with straw and Miscanthus in the Burgundy region (France); 2. Large-scale power production with straw and with residual woody biomass in the Aragon region (Spain); 3. Advanced wood logistics in the Province of Central Finland.
Testing for functional convergence of temperate rainforest tree assemblages in Chile and New Zealand
Lusk, C.H. ; Jimenez-Castillo, M. ; Aragón, R. ; Easdale, T.A. ; Poorter, L. ; Hinojosa, L.F. ; Mason, N.W.H.W.H. - \ 2016
New Zealand Journal of Botany 54 (2016)2. - ISSN 0028-825X - p. 175 - 203.
Bioclimatic matching - environmental filtering - functional trait convergence - leaf dry matter content - leaf economics - leaf habit - leaf size - pollination syndrome - seed mass - wood density

An important tenet of biogeography and comparative ecology is that disjunct assemblages in similar physical environments are functionally more similar to each other than to assemblages from other environments. Temperate rainforests in South America, New Zealand and Australia share certain physiognomic similarities, but we are not aware of any statistical evidence that these disjunct plant assemblages share a distinctive suite of functional traits, or trait combinations. We compiled height, leaf, wood and reproductive traits from the 25 commonest arborescent species at Chilean and New Zealand sites matched for summer rainfall, summer maximum temperatures, and winter minimum temperatures. We then used multivariate tests of trait convergence. Tropical and subtropical assemblages served as out-groups. PERMANOVA showed convergence of trait centroids at the two temperate sites, where trees on average had denser wood and smaller leaves than trees at the (sub)tropical sites. Principal components analyses carried out separately on each assemblage showed that the Chilean and New Zealand assemblages were also the most similar pair in terms of trait relationships, although New Zealand also shared strong similarities with subtropical Argentina. The main axis of variation in both temperate assemblages ranged from small, short-lived understorey trees with soft leaves, to emergents with sclerophyllous leaves and fairly dense wood. However, the New Zealand assemblage was much richer in small trees with soft leaves than its Chilean counterpart; possible historical influences on this difference include conditions favouring radiation of small trees during the late Neogene in New Zealand, competition from Chusquea bamboos in Chile and the historical absence of browsing mammals from New Zealand. Environmental filtering has produced similar values of individual traits in Chile and New Zealand, but only partial convergence of functional trait combinations. As far as we know, this is the first study to statistically test whether disjunct tree assemblages on climatically matched sites are more functionally similar to each other than to assemblages from other environments.

Evaluation of three commercial enzyme-linked imuunosorbent assays for the detection of antibodies against Salmonella spp. in meat juice from finishing pigs in Spain
Vico, J.P. ; Engel, B. ; Buist, W.G. ; Mainar-Jaime, R.C. - \ 2010
Zoonoses and Public Health 57 (2010)Suppl. 1. - ISSN 1863-1959 - p. 107 - 114.
diagnostic-tests - enterica prevalence - control program - slaughter pigs - swine - elisa - surveillance - culture - herds - infection
The control of animal salmonellosis is considered as a major objective in Europe and indirect ELISAs will be important tools for the implementation of control programs for this infection in pigs. We analyse the results yielded by three commercial ELISAs (Herdcheck Swine Salmonella, SALMOTYPE Pig Screen, and PrioCHECK Salmonella) on meat juice samples from a population of slaughter pigs of Aragon, NW Spain, to assess their efficacy using traditional and latent-class approaches. Overall, the Herdcheck Swine Salmonella detected more Salmonella-infected pigs than the other two tests, but its relative sensitivity was low (65.9%). A similar result was observed when only serotypes detectable by this test were considered (69.1%). When a Bayesian approach was used the Herdcheck Swine Salmonella showed also the highest overall accuracy (sensitivity = 88% and specificity = 74%). Our results suggest that a relatively small proportion of the observed prevalence in herds would be explained by using these ELISAs. Also, this study points out that when different ELISA tests are used within the same herd, results may differ substantially. Thus, caution is advised if it is decided to use these assays for herd health classification in Spanish Salmonella control programs
Wind erosion in a semiarid agricultural area of Spain: the WELSONS project
Gomes, L. ; Arrue, J.L. ; Lopez, M.V. ; Sterk, G. ; Richard, D. ; Gracia, R. ; Sabre, M. ; Gaudichet, A. ; Frangi, J.P. - \ 2003
Catena 52 (2003). - ISSN 0341-8162 - p. 235 - 256.
atmospheric boundary-layer - size distribution - dust production - soil - transport - emission - sediment - tillage - aragon - niger
The co-ordinated European research project Wind Erosion and Loss of SOil Nutrients in semiarid Spain (WELSONS) was carried out from 1996 to 1999 to understand and predict the potential impacts of land-use change and management on soil degradation by wind erosion on agricultural land in Central Aragon, a semiarid desertification-threatened region in NE Spain. This paper gives a description of the project's experimental approach and an overview of the main results regarding the effects of agricultural practices (i.e. conventional, CT, versus reduced tillage, RT) on surface conditions affecting wind erosion, the mobilisation of soil particles in the saltation layer and the atmospheric emission of fine dust into the suspension layer. The characterisation of the soil surface showed that soil erodibility by wind under RT was lower than that under CT. Though strong Cierzo wind events occurred during the experimental period, only a limited amount of material was available for wind erosion mainly due to soil crusting, a common feature in the area. In spite of this, saltation transport flux was measured at CT plots for different erosion episodes. Also, significant vertical emission of dust was observed only in the CT plot. Finally, the sandblasting efficiency calculated in the present experiment could be interpreted as the result of a higher binding energy for the particles of the silt loam experimental soil compared to soils with a lighter texture.
Welfare inequality, regionalisation, and welfare policy : measurement and analysis for Spain
Quadrado, L. - \ 1999
Agricultural University. Promotor(en): H. Folmer; Wim Heijman. - S.l. : S.n. - ISBN 9789058081636 - 305
sociaal welzijn - gezondheid - onderwijs - armoede - inkomensverdeling - regio's - welvaartseconomie - overheidsbeleid - spanje - europese unie - welvaartsstaat - social welfare - health - education - poverty - income distribution - regions - welfare economics - government policy - spain - european union - welfare state
<p>This study is focused on the changes in regional inequality in Spain over the last four decades, with emphasis on regional welfare. The two most important items of welfare in Spain are, health and education, and so these are the main focus of this study. Attention is paid to the levels and trends in inter and intra-regional disparities in the welfare components of health, education and housing. The extent to which changes in inequality with respect to welfare relate to changes in regional welfare policy is evaluated. Various methodological issues are explored in the context of measuring welfare inequality between regions. A specific procedure to measure inequality in longitudinal analyses is developed. The study is organised in three parts. The first part includes Chapter 2 and 3, and deals with regional structure and policy to provide a foundation for the analysis. The second part focuses on the methodology developed in this study and the techniques used for that purpose (Chapter 4). The third part includes all the results of the analysis (Chapter 5, 6, and 7) and the conclusion chapter (Chapter 8).</p><p>Chapter 2 focuses on the development of the Spanish welfare state and its socio-economic context. A substantial part of the policy changes relating to the welfare system in Spain have resulted from the redefinition of the government's duties following the 1978 Constitution. Since the sixties the Spanish economy has been unstable and there have been important developments such as, the population explosion, and the ageing of the population. This situation has resulted in the need for significant changes in the welfare state as seen in a variety of policy changes.</p><p>The devolution of power to the regions and the <em>regionalisation process</em> of the welfare state in particular are of major interest in the present study. The regional state in Spain, known as Co <em>munidades Autónomas,</em> is a decentralised policy model composed of any of the nineteen Autonomies or admisnistrative regions consisting of one or several provinces (from a total of fifty two). The development of the welfare state in Spain has involved increased autonomy for the regions in welfare issues. The nineteen regions are responsible for welfare programs relating to basic infrastructure (ports, road networks, etc). But only seven out of the nineteen Spanish regions have gained full autonomy in education and health (the largest expenditure items of the welfare state). So the regionalisation process has not been symmetric among all regions. This situation may have some implications for the inequality between regions. The impact on inequality of the regionalisation of the welfare state is therefore one of the important issue investigated in the present study. In the coming years, regions with high levels of autonomy are likely to contribute greatly to policy making since they will be responsible for modelling the structure of the welfare state.</p><p>In Chapter 3, the regional policy of the European Union, and the Spanish regional policy is described in detail. Spain is today one of the leading beneficiaries of the EU's financial assistance for regional development known as the <em>Structural Funds</em> . The relevance of the European Union (EU) regional policy in mitigating existing disparities between regions is discussed. The rapid development of mechanisms for the regional support of (economically) weak regions has contributed to a reduction of inequality. The <em>Compensation Funds</em> which started in 1978 have played an important role in the regions although the Structural Funds remain more important.</p><p>In Part II we discuss the selection of a measure of inequality for our study. The <em>Theil's Second measure for multidimensional inequality</em> is selected (Chapter 4). A specific procedure is developed to estimate this measure for longitudinal analyses. We use several indicators to represent each of the welfare components under consideration. This involves defining a composite index of indicators. Inequality in regional welfare is investigated focusing on the following welfare components: health facilities and health status, education facilities and education enrollment and finally, household expenditures and housing conditions. The underlying multidimensionality of the welfare components is thus taken into account. In the present study, Maasoumi's (1986) aggregator function is used to aggregate the indicators. This function enables us to reproduce the maximum amount of information contained in the original indicators. The data used relates to the following years (or periods): 1964, 1974, 1981, and 1991. There are also no studies that have done a longitudinal analysis of welfare inequality. Regional disparities in Spain over time with respect to health and/or education facilities have not been analyzed using an inequality measure. Thus it is not possible to compare inequality results from other literature sources with our results.</p><p>For empirical purposes the use of Maasoumi's function requires weights associated with the indicators. Different weights are used for the different indicators. The estimation procedure for these weights developed in the present study is based on the <em>Partial Common Principal Component model</em> (PCPC) whenever appropriate or <em>Principal Component Analysis</em> (PCA) otherwise. The weights attached to the indicators are the component coefficients of the first component obtained using PCPC (or PCA). PCA has been applied for longitudinal analysis using Theil's second measure for multidimensional inequality (Maasoumi and Jeong, 1985;, Maasoumi and Nickelsburg, 1988; Zandvakili, 1992, 1999). When the periods under consideration share the same first component, the composite index is obtained on the basis of the component coefficients computed using a partial common principal component model. So the component coefficients are not sample-specific because they are the same in all the periods. In other words, the composite indexes for these periods depend on the values of the variables rather than the weights attached to variables. If the hypothesis of one partial common component is not rejected for a number of periods (for first three, and then two periods in this study), the composite index is then constructed on the basis of the maximum likelihood estimates for these periods together with the individual component coefficients for the remaining periods. When a partial principal component model does not fit the data, the composite index is based on individually computed component coefficients. Finally, the overall inequality of the Theil's second measure is computed.</p><p>The Theil's second measure is applied in the present study to achieve the following objectives. First, the magnitude and direction of <em>overall inequality</em> , <em>between-region</em><em>inequality</em> , and <em>within-region inequality</em> is computed with respect to each of the welfare components under study. The wide variations in the geographic and socio-economic structure of the Spanish regions require an in-depth analysis of inequality focusing on intra- and inter-region disparities. In addition, the estimates of the composite indexes for the geographical units (regions) have been used for a <em>statistical cluster analysis</em> which identifies the similarities between one group of regions in contrast with another group of (similar) regions. The cluster analysis identifies two groups of high similar values ( <em>most-favored regions</em> ) and low similar values ( <em>least-favored regions</em> ). A picture of the geographical distribution of welfare components is obtained, and changes over time are compared. The inequality results and the results from the cluster analysis form the main findings of our study.</p><p>The empirical results with respect to the welfare components are presented in Part III. <em>Health facilities</em> and <em>health status</em> are studied separately (Chapter 5). A substantial part of Chapter 5 is focused on health facilities. The inclusion of geographical effects ( <em>spatial</em><em>spillovers</em> ) resulting from the <em>contiguity</em> (or geographical proximity) between geographical units forms the major contribution of this study. Spatial spillovers across geographical areas are inevitable since individuals can commute from their own area to contiguous areas when health facilities are not available in the home area. A procedure is developed to incorporate contiguity into the analysis. The geographical units considered for contiguity are provinces which are the smaller territorial divisions of regions.</p><p>In the method developed for incorporating contiguity, the level of facilities available in a certain province is considered to consist of the facilities in the own province plus the facilities located in <em>contiguous provinces</em> weighted by <em>spatial weights</em> . <em>Spatial weights</em> used here correspond to the simple inverse distance (optimal distance by road) between the provincial capital of the Spanish provinces and the provincial capital in contiguous provinces. For health facilities and health status the notion of <em>contiguous provinces</em> refers to first-order contiguous provinces connected at <em>the first order of contiguity</em> . The first order of contiguity describes two provinces that have a common boundary, common vertex or both. The use of this order of contiguity is justified as patients seek a first contact with doctors or specialized treatment and diagnosis at the nearest place to their home province.</p><p>The results show improvements in inequality with respect to health facilities are between 1981 and 1991. The sharp drop in inequality coincides with the enactment of the <em>1986 Health act</em> (LGS). In addition there is also an important decline in the components of between-region inequality between 1981 and 1991. It is possible that regional policies and the devolution of power in health issues in the mid-eighties may have caused changes in the pattern of regional inequality.</p><p>The regionalisation process of the health system may also have had important implications for regions with transferred powers in health issues. In these regions the results reveal that within-region inequality decreases between 1981 and 1991. So it is possible that the regional policies have resulted in a more uniform distribution of health facilities within certain regions. The geographical distribution of facilities obtained using cluster analysis reveals a North-South pattern with facilities located mostly in the North of Spain. The group of most-favoured regions consists of regions with transferred powers, regions which are <em>central places</em> like Madrid, and regions with certain socio-economic characteristics. It is suggested, therefore, that the geographical distribution of facilities may be affected by the socio-economic conditions of regions.</p><p>The comparison of the contiguity and non-contiguity cases reveals that there are important spatial effects, especially among the regions situated in the North and the Centre of the Iberian Peninsula. Geographical proximity benefits only a few number of regions resulting in a dramatic increase in inequality in the contiguity case. When contiguity is not taken into account, the results for inequality show a very different impact for health policies. Inequality with respect to health status is investigated, but the results obtained are not very satisfactory possibly because of inaccuracies in the data used.</p><p><em>Education facilities</em> and <em>education enrollment</em> are studied in Chapter 6. With respect to education facilities, spatial spillovers are also incorporated since education is one of the most common causes of individuals commuting. But contiguity is not often taken into account in the literature on education. For computing available facilities in secondary education, the first order of contiguity is considered. The available facilities for university education consist of facilities located in contiguous provinces at the first order of contiguity plus the <em>second order of contiguity,</em> (plus the facilities in Madrid and Barcelona for 1964 and 1974). Here a second order of contiguity is defined as between two contiguous provinces, one of them being first-order contiguous (facilities in provinces adjacent to the neighbouring province).</p><p>The results for inequality with respect to education facilities show that inequality has declined between 1974 and 1991. This may be due to the promotion of non-compulsory education. Over the last few decades the Spanish government has pursued a policy intended to distribute university and vocational training facilities more evenly. The increase in the contribution to inequality of between-region inequality between 1981 and 1991 may be due to the impact of regional policies.</p><p>Intra-regional disparities are more important in Castilla León, Castilla la Mancha, and Andalucía. All these regions are bound by similar regional characteristics such as limited industry, abundant potential in natural resources, predominance of agriculture and their geographical situation in the Centre and South of the Iberian Peninsula. In addition, these three regions cover 53% of the Iberian Peninsula and 52% of the total land size. Regional authorities in Andalucía are responsible for education powers while there has been no devolution of power in Castilla León and Castilla la Mancha. The socio-economic characteristics of these regions appear to be more influential with respect to inequality than autonomy. The geographical distribution of facilities with respect to education has changed dramatically between the 60s and the 90s. This result from cluster analysis shows that changes in education policies have affected inequality.</p><p>Spillover effects have improved the education facilities in the Spanish regions resulting in smaller values of overall inequality in the contiguity case compared to the non-contiguity. Spatial spillovers are observed in the Centre of Spain in 1991 between the region of Aragón and its first or second order neighbours (Madrid, Cataluña and Navarra). Further, the trends in inequality in the contiguity case are more in line with the policy measures than results in the non-contiguity case. So the inclusion of spillovers in the contiguity case seems to be a good approach for the study of inequality.</p><p>Education enrollment in the non-compulsory education is also investigated in Chapter 6. The results for overall inequality and the inequality decomposition with respect to enrollment are very similar to those for education facilities. The results suggest that education facilities and education enrollment have been influenced by policy measures and the regionalisation process.</p><p>Trends in inequality with respect to household consumption and housing conditions are analysed in Chapter 7. The results suggest that the magnitudes, and the trends for inequality that might be expected with respect to household incomes are similar to those obtained with respect to household expenditures. Inequality in household consumption and housing conditions has narrowed significantly over the last four decades. This is consistent with the changes in the economic situation which occurred during this period.</p><p>Finally, Chapter 8 summarises and discusses the main conclusions based on the findings in this study. One of the main conclusions is that the procedure that we develop for the longitudinal analysis of multidimensional inequality in the welfare components is successful and performs satisfactory. In addition, spatial spillovers must be taken into account by using the procedure developed for incorporating contiguity. When contiguity is considered a more accurate picture of inequality is obtained. With respect to the empirical findings in this study, we conclude that firstly, the setting up of the welfare system and the social policies undertaken over the last few decades in education and health have had important consequences for inequality. Secondly, the impact of the regionalisation process on inequality with respect to education and health also appears to be important. New insights with respect to the relationship between welfare policies and the actual changes in welfare inequality may be provided by extending the present analysis.</p>
Drainage and reclamation of salt-affected soils in the Bardenas area, Spain
Martinez Beltran, J. - \ 1978
Landbouwhogeschool Wageningen. Promotor(en): W.H. van der Molen, co-promotor(en): P. Buringh. - Wageningen : ILRI - 322
alkaligronden - drainage - verbetering - irrigatie - land - polders - ontginning - zoute gronden - verzilting - natrium - bodem - bodemkunde - solonchaks - spanje - iberisch schiereiland - onvruchtbaar land - alkaline soils - improvement - irrigation - reclamation - saline soils - salinization - sodium - soil - soil science - spain - iberian peninsula - unproductive land
Chapter 1<p/>The 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.<p/>Chapter 2<p/>The 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.<p/>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.<p/>Within the Bardenas area ten major physiographic units were defined, each of them subdivided into minor components and indicated on the soil map.<p/>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.<p/>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.<p/>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.<p/>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.<p/>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.<p/>Chapter 3<p/>The 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.<p/>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.<p/>The irrigation water is of good quality as its EC is at the lower end of the C <sub><font size="-1">2</font></sub> -range. The SAR is also in the lowest range S <sub><font size="-1">1</font></sub> and the RSC is zero, so there is no danger of alkalinization.<p/>Chapter 4<p/>The 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.<p/>Five main soil associations were distinguished:<p/>a) The residual soils of the siltstone outcrops, which have only a thin surface horizon overlying the hard siltstone.<p/>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.<p/>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.<p/>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.<p/>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.<p/>Chapter 5<p/>The 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.<p/>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.<p/>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.<p/>The results of crop tolerance field tests correspond well with the generally accepted levels for salt tolerance.<p/>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.<p/>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.<p/>Chapter 6<p/>The 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.<p/>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.<p/>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.<p/>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.<p/>The reclamation process consisted of the following phases:<p/>a) Theoretical design of the drainage system based on hydrological soil properties measured by conventional field methods and on assumed drainage criteria.<p/>b) Implementation of the drainage system in the experimental fields.<p/>c) Collection of field data, followed by determination of the actual hydrological soil properties and of the drainage criteria.<p/>d) Design of the definitive drainage system which will form the basis of recommendations for the reclamation of saline soils with similar conditions.<p/>Chapter 7<p/>After 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.<p/>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.<p/>Chapter 8<p/>At 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 <em>merely by</em> the provision of a drainage system but also require deep subsoiling.<p/>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.<p/>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.<p/>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.<p/>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:<p/>- Hydraulic conductivity decreases with depth, becoming negligible below drain level.<p/>- 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.<br/>- For high water table conditions, the average hydraulic conductivity of the soil profile is 1 m/day.<p/>A comparison of hydraulic conductivity values obtained with field and laboratory methods and those obtained from the discharge/hydraulic head relation showed that:<p/>- The results obtained with the auger hole method (K = 0.2 m/day) were lower than those derived from the discharge/hydraulic head relation.<p/>- No satisfactory results were obtained from the inversed auger hole measurements above the water table.<p/>- The results obtained from laboratory measurements in undisturbed soil cores showed the anisotropy of the soil.<p/>The entrance resistance (W <sub><font size="-1">e</font></sub> ) 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 <sub><font size="-1">i</font></sub> ). 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:<p/>- The W <sub><font size="-1">e</font></sub> -values remained fairly constant with time, except for plastic pipes-with an envelope of esparto or coconut fibre for which an increase in W <sub><font size="-1">e</font></sub> was observed.<p/>- The best combination was clay pipes with a gravel cover (W <sub><font size="-1">e</font></sub> =2 day/m).<p/>- Corrugated PVC-pipes with gravel covering and clay pipes without gravel may be used also (W <sub><font size="-1">e</font></sub> = 5 day/m).<p/>- Corrugated plastic pipes without a filter gave less satisfactory results (W <sub><font size="-1">e</font></sub> = 13 day/m).<p/>- Plastic pipes with coconut fibre and esparto filters showed an even higher W <sub><font size="-1">e</font></sub> than plastic pipes without a filter.<p/>- Barley straw is an unsuitable cover material since it rots easily and clogs the pipe.<p/>Chapter 9<p/>The desalinization of the Alera field started with an initial leaching, followed by the irrigated cultivation of moderately salt- resistant crops.<p/>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.<p/>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.<p/>The following conclusions emerged from the study of the leaching process:<p/>- The leaching efficiency coefficient was not constant but increased with depth.<p/>- The leaching efficiency coefficient was higher at the beginning of the desalinization process and decreased gradually as the soil became less saline.<p/>- The calculated values reflected the differences in soil structure.<p/>- 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).<p/>- The initial salinity was related to soil physical properties (infiltration rate and permeability) which, in turn, were dependent on the compactness of the soil.<p/>- For an initial EC <sub><font size="-1">e</font></sub> 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.<p/>- Deep subsoiling and local gypsum applications improved the structure of the upper soil layer.<p/>- 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.<p/>- There was no risk of alkalinization during the leaching period.<p/>- To prevent secondary salinization after reclamation, good drainage conditions must be maintained and an irrigated crop rotation practised.<p/>Chapter 10<p/>From 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.<p/>The following conclusions could be drawn from the study:<p/>- 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.<p/>- 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.<p/>- 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.<p/>- A water table depth shallower than 65 cm prevents the movement of machinery and hampers seed-bed preparation in winter.<p/>The following drainage criteria were assessed:<p/>a) In winter, a water table drawdown from the soil surface to a depth of 0.65 m in 8 days.<p/>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.<p/>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.<p/>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.<p/>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:<p/>- 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.<p/>- Material with high entrance resistance involves much more risk of failure than a wider spacing with good material.
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