Abstracts Academic Publications



As far as possible, this page lists the abstracts or executive summaries of the academic publications by SOW-VU's staff since 2000.

Hard copies of these publications are available from the publishers.

Please click on a year for a shortcut to the corresponding list:

2005          2004          2003          2002          2001          2000




Keyzer, M.A. and C.F.A. van Wesenbeeck 'Equilibrium selection in games: the mollifier method'. Journal of Mathematical Economics, 41(3), 285-301.

This paper introduces an embedding of a Nash equilibrium into a sequence of perturbed games, which achieves continuous differentiability of best responses by mollifying them over a continuously differentiable density with compact support (window size). Along any sequence with shrinking window size, the equilibria are single-valued whenever the function has a regular Jacobian and the set of equilibria where it is singular has measure zero. We achieve a further reduction of the equilibrium set by inserting within the embedding a procedure that eliminates the strict interior of equilibrium sets. The mollifier can be approximated consistently using kernel density regression, and we sketch a non-stationary stochastic optimization algorithm that uses this approximation and converges with probability one to an equilibrium of the original game.


Keyzer, M.A., M.D. Merbis, I.F.P.W. Pavel and C.F.A. van Wesenbeeck 'Diet shifts towards meat and the effects on cereal use: can we feed the animals in 2030?'. Ecological Economics, 55(2), 187-202.

The paper argues that current international projections of meat and feed demand may underestimate future consumption patterns, for mainly two reasons: demand projections are based on income extrapolation with an assumed demand elasticity and feed requirements per unit of meat are taken to be fixed. Instead, we propose a structural specification that includes a dietary shift towards meat as per capita income increases, and we account for a shift from traditional to cereal intensive feeding technologies. Our finding is that under the commonly assumed growth rates of per capita income, world cereal feed demand will be significantly higher in the coming 30 years than is currently projected by international organizations, even if we allow for price effects. Compared to other factors that are generally expected to affect the future world food situation, the quantitative impact of the increased cereal feed demand greatly exceeds that of GMOs and climate change in the coming three decades.




Gerlagh, R. and M.A. Keyzer ‘Path-dependence in a Ramsey model with resource amenities and limited regeneration’. Journal of Economic Dynamics and Control, 28, 1159-1184.

This paper studies a Ramsey optimal control economy with one consumer good, extended to include several non-renewable resources with amenity value. The steady-state equilibria of this economy are shown to form a continuum. Selection of the steady state to which the economy converges depends on the initial resource stocks. Hence, unlike the usual Ramsey models, our model exhibits path-dependency, and postponement in the introduction of resource efficiency policies has long-term effects. If the resource is renewable, with a limited regeneration function, the continuum becomes a turnpike. That is, optimal paths move along it towards the unique steady state. The results also hold when there are several consumers.


Overbosch, G.B., N.N.N. Nsowah-Nuamah, G.J.M. van den Boom and L. Damnyag ‘Determinants of Antenatal Care Use in Ghana’. Journal of African Economies, 13(2), 277-301.

The paper investigates the determinants of antenatal care use in Ghana. In particular, we study how economic factors affect the demand for antenatal care and the probability that the number of visits falls below the recommended number of four. Estimation results from a nested three-level multinomial logit model (care or no care; doctor or nurse or midwife; sufficient or insufficient visits) show that indeed living standard, cost of consultation and in particular travel distance to the provider have a significant impact on the demand and sufficiency of antenatal care. In addition, pregnant women with more schooling have a higher propensity to seek sufficient antenatal care from all providers, while women of higher parity tend to use less antenatal care from less expensive providers. These results suggest that adequate antenatal care use in Ghana can be promoted effectively by extending the supply of antenatal care services in the rural area, by general education policies and by specific policies that increase reproductive health knowledge. Furthermore, contrary to findings elsewhere, our estimates provide little support for a special targeting of antenatal care according to religious background.


Voortman, R.L., J. Brouwer and P.J. Albersen ‘Characterization of spatial soil variability and its effect on Millet yield on Sudano-Sahelian coversands in SW Niger’. Geoderma, 121,  65-82.

Very local spatial soil variability on Sudano-Sahelian coversands hampers the interpretation of agronomic research and is an obstacle for the dissemination of research findings. In an earlier paper, we specifically accounted for this spatial soil variability: Using novel tools for data exploration, such as non-parametric kernel density regression and spatial econometrics, on spatially explicit data for topsoil N, P, K and millet yield, we could explain 81% of the yield variation. However, the macronutrients explained a modest portion of millet yield only, while the good explanatory power was largely derived from spatial dependence/autocorrelation. This implies that variables other than N, P and K determine spatial variability of soils and millet growth. In the present paper we identify these variables and show that the proportions of the cations (Ca, Mg, K and Na) at the exchange complex, in combination with the Al saturation profile are the main source of spatial variability at this scale. Equations including these soil properties explain 82% of the millet yield variation, without spatial autocorrelation being present in the residuals. High proportions of Mg and Na in the topsoil coincide with low Al saturation levels in the subsoil and under such conditions yields are low (and vice versa). The likely operating mechanism is the destabilizing effect that Mg and Na have on the clay fraction, which, in turn, causes surface sealing. The latter affects seedling emergence and water infiltration and, consequently, subsoil Al saturation levels. The evidence provided further suggests a parent material connection to local soil variability: coversands of different source materials and age occurring as shallow layers.


Voortman, R.L., J. Brouwer ‘Characterization of spatial soil variability on Sahelian coversands: implications for agro-pastoral research and extension’. In: Williams, T.O., Tarawali, S.A., Hiernaux, P., Fernandéz-Rivera (eds) Sustainable crop-livestock production for improved livelihoods and natural resource management in West Africa, pp. 199-219. Proceedings of an international conference held at the International Institute for Tropical Agriculture (IITA), 19-22 November 2001, Ibadan, Nigeria. CTA and ACP-EC, Wageningen, The Netherlands and ILRI, Nairobi, Kenya.

The spatial soil variability on Sahelian coversands hampers the interpretation of agro­pastoral research findings and is an obstacle to their dissemination. Site characterization and the establishment of site-specific plant performance and yield responses to external inputs are therefore of fundamental importance to achieving agricultural development. In this paper, we identified and characterized the sources of soil variability within a single farmer's field. Three soil types were identified and they were characterized by different proportions of calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na) cations in the exchange complex in combination with a different aluminum (Al)-saturation profile. The yield response to manure application varied between these soil types and the yield impact of cattle and small ruminant manure also appears to differ with soil type. Cattle manure was most effective on sites with low crusting levels and small ruminant manure was very effective in raising yields on sealed surfaces. At the same time evidence indicated that manure levels applied by farmers can be too high.

Substantial efficiency gains can be achieved by a more even spread of manure and by properly matching the manure type with site conditions. Evidence further suggests that external input applications of K and Ca may improve moisture availability and further enhance manure efficiencies. Such effects would be favorable for technology adoption since the risks associated with climate variability would then be reduced. Experiments are proposed to verify further what the empirical evidence suggests.





Albersen, P.J., H.E.D. Houba and M.A. Keyzer ‘Pricing a raindrop in a process-based model: general methodology and a case study of the Upper-Zambezi’. Physics and Chemistry of the Earth 28, 183-192.

A general approach is presented to value the stocks and flows of water as well as the physical structure of the basin on the basis of an arbitrary process-based hydrological model. This approach adapts concepts from the economic theory of capital accumulation, which are based on Lagrange multipliers that reflect market prices in the absence of markets. This permits to derive a financial account complementing the water balance in which the value of deliveries by the hydrological system fully balances with the value of resources, including physical characteristics reflected in the shape of the functions in the model. The approach naturally suggests the use of numerical optimization software to compute the multipliers, without the need to impose an immensely large number of small perturbations on the simulation model, or to calculate all derivatives analytically. A novel procedure is proposed to circumvent numerical problems in computation and it is implemented in a numerical application using AQUA, an existing model of the Upper-Zambezi River. It appears, not unexpectedly, that most end value accrues to agriculture. Irrigated agriculture receives a remarkably large share, and is by far the most rewarding activity. Furthermore, according to the model, the economic value would be higher if temperature was lower, pointing to the detrimental effect of climate change. We also find that a significant economic value is stored in the groundwater stock because of its critical role in the dry season. As groundwater comes out as the main capital of the basin, its mining could be harmful.


Gerlagh, R. and M.A. Keyzer ‘Efficiency of conservationist measures: an optimist viewpoint’. Journal of Environmental Economics and Management 46, 310-333.

We consider an economy with a consumer good, capital, a natural resource that provides amenity values, and heterogeneous overlapping generations. We compare a benchmark grandfathering policy that ensures efficiency through privatization with a policy of enforced resource conservation. It is shown that (i) conservationist measures do not cause any Pareto inefficiency, irrespective of whether they pass a cost–benefit test. Moreover, it is shown that (ii) there exist Pareto optimal allocations that can only be reached through resource conservation, and not through competitive markets, irrespective of compensating income transfers. Finally, (iii) equivalence is demonstrated between strict resource conservation and non-dictatorship of the present generations over future generations as formalized in Chichilnisky's ‘sustainable welfare function’. The results are shown to hold in both a first-best and a second-best setting.


Honfoga, B.G. and G.J.M. van den Boom ‘Food-consumption patterns in Central West Africa, 1961 to 2000, and challenges to combating malnutrition’. Food and Nutrition Bulletin, 24:2, 167-182, The United Nations University.

We discuss food-consumption patterns in Central West Africa from 1961 to 2000 and some implications for com­bating malnutrition. The availability of food in the region improved in the 1960s, declined sharply in the 1970s and the early 1980s, and has shown a modest positive trend since the mid-1980s. Notwithstanding obvious progress over the past decades and in the region as a whole, food availability today remains below the required levels for large parts of the population and appears unstable over time, particularly in the Sahelian zone. On average, diets in this zone contain fewer than 2,200 kcal, compared with almost 2,500 kcal in the coastal zone. Conversely, protein deficiency is more common in the coastal zone, where a typical diet contains only 45 g of protein, compared with 60 g in the Sahelian zone. Furthermore, consumption is showing a dietary shift toward cereals, while yield growth lags far behind population growth. The associ­ated import dependency and pressure on land seem to gain significance regardless of the region's agro-ecologi­cal capacity to increase and to substitute cereal imports for locally produced food. Moreover, food consumption appears responsive to income changes (calorie-income elasticity ranges from 0.25 to 0.62), while, in turn, it has a significant impact on nutritional outcomes (stunting-calorie elasticity of -1.42). We conclude that combating malnutrition requires first broad-spectrum income growth, and next specific policies that promote the yield and the contribution to diets of nutritious food produced within the region.


Nubé, M. and G.J.M. van den Boom 'Gender and adult undernutrition in developing countries’, Annals of Human Biology 30:5, 520-537.

Background: Information on the prevalence of undernutrition in adults in developing countries is mainly restricted to data on women. Literature reporting on the occurrence of female deprivation in developing countries, in particular in South Asia, suggests that differences between undernutrition prevalence in adult men and adult women might occur, but systematic information on the subject is lacking.

Aim: The study compares undernutrition prevalence rates, based on prevalence of low body mass index (BMI < 18.5), in adult men and adult women in developing countries. Regional comparison is made between the main developing regions: Sub-Saharan Africa, South/Southeast Asia and Latin America.

Subjects and methods: The study uses data as reported in 75 samples from 31 countries (divided over the three developing regions), in which anthropometric information has been collected in adult men and women within one and the same community.

Results: Results indicate that, in general, prevalence rates of undernutrition are rather similar in adult men and women. However, there are regional differences. In communities in Sub-Saharan Africa, prevalence of low BMI is, on average, a few percent higher in men than in women; in South/Southeast Asia the reverse is the case. In some communities differences in undernutrition prevalence between men and women are exceptionally large.

Conclusions: It can be concluded that, in general, information on undernutrition prevalence in women can be considered a proxy for undernutrition prevalence in all adults, men and women together. However, the finding that in South/Southeast Asia women's nutritional status relative to men's nutritional status compares unfavorably with results from other developing regions, in particular Sub-Saharan Africa, provides some support for the concept of female deprivation in South/Southeast Asia. Where large differences between prevalence of low BMI in men and women occur, gender-specific policies aimed at reducing undernutrition should be considered.


Sonneveld, B.G.J.S. Formalizing expert judgments in land degradation assessment: a case study for Ethiopia’. Land Degradation & Development 14, 347-361.

Expert judgments are potentially a valuable source of information in land degradation assessment, especially in areas where data paucity impedes the use of quantitative models. However, expert opinions are also much disputed because they are not tested for consistency, abstain from formal documentation, while their quantitative interpretation is inherently unidentifiable. This paper evaluates and formalizes the use of expert judgments to conduct a nationwide water erosion hazard assessment in Ethiopia. We, therefore, test the experts' judgment for consistency, its correlation with quantitative measurements on soil loss and its reproducibility. The study uses an Ethiopian and an international dataset for which experts gave qualitative judgments on water erosion hazard, for well-described sites under different types of land uses. Experts show a high consistency in their judgments on land degradation, but a comparison with quantitative soil losses from runoff plots reveals that boundaries of middle classes vary widely between experts, while they tend to overestimate soil loss. Reproducing expert opinions with an ordered logit model shows a reasonable accuracy in predicting presence or absence of erosion, yet the model is less precise in distinguishing between higher erosion classes. In 58 per cent of the cases, the model gives a similar classification as the experts, in 19 per cent the model estimates higher and, more seriously, in 23 per cent a lower erosion class. Mapping the model results for Ethiopia demonstrates a high erosion hazard for land under annual crop cultivation, while erosion under perennial crops, rangeland and forest is absent or moderate. The likelihood of the model to select the correct hazard class for rangeland is relatively high but medium to low probabilities prevail for erosion classes of other land uses. The model needs a further justification to give adequate results for arid areas.


Sonneveld, B.G.J.S. and M.A. Keyzer ‘Land under pressure: soil conservation concerns and opportunities for Ethiopia’. Land Degradation & Development 14, 5-23.

This paper evaluates the future impact of soil degradation on national food security and land occupation in Ethiopia. It applies a spatial optimization model that maximizes national agricultural revenues under alternative scenarios of soil conservation, land accessibility and technology. The constraints in the model determine whether people remain on their original site, migrate within their ethnically defined areas or are allowed a transregional migration. Key to this model is the combination of a water erosion model with a spatial yield function that gives an estimate of the agricultural yield in its geographical dependence of natural resources and population distribution. A comparison of simulated land productivity values with historical patterns shows that results are interpretable and yield more accurate outcomes than postulating straightforward reductions in yield or land area for each geographic entity. The results of the optimization model show that in absence of soil erosion control, the future agricultural production stagnates and results in distressing food shortages, while rural incomes drop dramatically below the poverty line. Soil conservation and migration support a slow growth, but do not suffice to meet the expected food demand. In a transregional migration scenario, the highly degraded areas are exchanged for less affected sites, whereas cultivation on already substantially degraded soils largely continues when resettlement is confined to the original ethnic-administrative entity. A shift to modern technology offers better prospects and moderates the migration, but soil conservation remains indispensable, especially in the long term. Finally, an accelerated growth of non-agricultural sectors further alleviates poverty in the countryside, contributing to higher income levels of the total population and, simultaneously, relieving the pressure on the land through rural-urban migration.


Sonneveld, B.G.J.S. and M.A. Keyzer ‘Development of decision support tools in LADA: a case study for Ethiopia’, in Jones, R.J.A. and Montanarella, L. (Eds.), Land degradation in Central and Eastern Europe (European Soil Bureau Report 10, pp. 89-129). Luxembourg: Office for Official Publications of the European Communities.

Land degradation in dryland areas affects the livelihood of millions of people, especially in development countries where reduced productivity jeopardizes food security while violent conflicts over scarce land become now a perilous possibility. Being a typical externality, land degradation justifies a public intervention and the ratification by national governments of the United Nations Convention to Combat Desertification in the early nineties gave land conservation a high political priority in dryland areas. This together with the implementation of Agenda 21 should have resulted in concerted National Action Plans (NAP), where strategies are developed to preserve the quality of natural resources. However, conservation policies formulated, so far, were mostly unsuccessful and the overall concern is that earlier enthusiasm on environmental issues has lost ground with historical goals agreed. Major reasons for this failure are a poor understanding of underlying mechanisms of the degradation processes and the absence of a quantified impact of degradation on land productivity. The objective of the Land Degradation Assessment in Dry Areas (LADA) project is, therefore, to support developing countries by monitoring and analyzing causes and consequences of degradation processes in relation to the land productivity. LADA focuses thereby on nation-wide assessments, the level where most policy decisions are taken and where the portfolio for environmental projects is coordinated. The implementation of new soil conservation strategies can be underpinned by the development of spatial decision support tools, which inform decision makers about environmental and economic impact of alternative land uses and management techniques while giving due consideration to the needs, aspirations and attitudes of different stakeholders. Key to these spatial decision support tools is a formalized relationship that quantifies the impact of the degradation processes on land productivity in its geographical dependence of biophysical variables and land use.

This paper presents a case study where such a decision support tool is used to analyze the future impact of soil degradation on national food security and land occupation in Ethiopia. The decision support tool uses a spatial optimization model to maximize national agricultural revenues under alternative scenarios of soil conservation, land accessibility and technology. The constraints in the model determine whether people remain on their original site, migrate within their ethnically defined areas or are allowed a trans-regional migration. Key to this model is the combination of a water erosion model with a yield function that relates natural resource characteristics and population distribution to spatially explicit estimates of agricultural yield. A comparison of the simulated land productivity values with historical patterns shows that results are interpretable and yield more accurate outcomes than postulating straightforward reductions in yield or land area for each geographic entity. The results of the optimization model show that in absence of soil erosion control, the future agricultural production stagnates and results in distressing food shortages, while rural incomes drop dramatically below the poverty line. Soil conservation and migration support a slow growth, but yet do not suffice to meet the expected food demand. In a trans-regional migration scenario, the highly degraded areas are exchanged for less affected sites, whereas cultivation on already substantially degraded soils largely continues when resettlement is confined to the original ethnic-administrative entity. A shift to modem technology offers better prospects and moderates the migration, but soil conservation remains indispensable, especially in the long term. Finally, an accelerated growth of non-agricultural sectors further alleviates poverty in the countryside, contributing to higher income levels of the total population and, simultaneously, relieving the pressure on the land through rural-urban migration.


Sonneveld, B.G.J.S. and M.A. Nearing ‘A non-parametric/parametric analysis of the universal soil loss equation’. Catena, 52, 9-21.

Due to its modest data demands and transparent model structure, the Universal Soil Loss Equation (USLE) remains the most popular tool for water erosion hazard assessment. However, the model has several shortcomings, two of which are likely to have prominent implications for the model results. First, the mathematical form of the USLE, the multiplication of six factors, easily leads to large errors whenever one of the input data is misspecified. Second, the USLE has a modest correlation between observed soil losses and model calculations, even with the same data that was used for its calibration. This raises questions about its mathematical model structure and the robustness of the assumed parameter values that are implicitly assigned to the model. This paper, therefore, analyzes if the USLE could benefit from mathematical model transformations that, on one hand, mitigate the impact of incorrect input factors and, on the other hand, result in a better fit between model results and observed soil losses. For the analysis, we revisit the original data set and consider the USLE factors as variables rather than their common interpretation as parameters. We first use both nonparametric and parametric techniques to test the robustness of the implicit parameter assignments in the USLE equation. Next, we postulate alternative mathematical forms and use parametric test statistics to evaluate parameter significance and model fit. A tenfold cross-validation of the model with the best fit tests the sensitivity of the parameters for inclusion or exclusion of the data. The results show that the USLE model is not very robust, however, only slight model improvements are obtained by drastic modifications of its functional form, thereby sacrificing the simple model structure that was intended by its designers.


Voortman, R.L and J. Brouwer ‘An empirical analysis of the simultaneous effects of nitrogen, phosphorus and potassium in Millet production on spatially variable fields in SW Niger’. Nutrient Cycling in Agroecosystems 66, 143-166, Kluwer Academic Publishers.

Low soil fertility is a major constraint for increasing millet production on the acid sandy soils of the West African Sahel. On these soils, all three macronutrients: nitrogen (N), phosphate (P) and potassium (K), may be expected to limit crop yields. The important question is therefore: which of them is the most critical and would, if applied in small amounts, increase yields significantly? This paper addresses this question with an empirical approach, thus avoiding the commonly observed difficulty in the interpretation of agronomic research, caused by the extreme local soil variability which characterizes Sahelian coversands. We actually exploit soil variability by using novel non-parametric techniques for data exploration in combination with spatial methods of parametric model estimation. Apart from N, P and K, the effects of surface crusting, local topography, manure levels, farmer behavior and spatial dependence are taken into account, since these may confound the true effects of N, P and K. A quadratic formulation conforms best to the data and explains 81 percent of the yield variation. The equation highlights the importance of interactions among variables and thus confirms the possible impact of native soil conditions on the outcome of fertilizer treatments in experimental research. The results of much earlier, multi-year, research are confirmed remarkably well by this single year study. In addition, a spatially explicit assessment on the crop response to increasing nutrient levels highlights that blanket fertilizer applications are inefficient, because yield increases in some places will be accompanied by yield decreases at other sites. Cash-constrained farmers therefore have to resort to precision farming techniques to maximize returns from minimal external input packages. However, a large part of the good explanation of millet yield variability over space derives from spatial autocorrelation, and not directly from topsoil N, P and K. This calls for further research on the factors that affect millet yield and on the characterization and classification of sites, followed by experimental work to design site-specific fertilizer technologies.


Voortman, R.L., B.G.J.S. Sonneveld and M.A. Keyzer ‘African land ecology: opportunities and constraints for agricultural development’. Ambio 32:5, 367-373.

Compared to other continents, the economic growth performance of Sub-Saharan Africa has been poor over the last four decades. Likewise, progress in agricultural development has been limited and the Green Revolution left Africa almost untouched. The question raised in the literature is whether the poor performance is a question of poor policies or of an unfavorable biophysical environment (policy versus destiny). This paper, with a broad perspective, analyzes adaptation of current land use to environmental conditions in Africa and compares the physical resource base of Africa with Asia. In doing so, we search for unifying principles that can have operational consequences for agricultural development. We argue that some specificities of the natural resource base, namely local homogeneity and spatial diversity of the predominant Basement Complex soils, imply that simple fertilizer strategies may not produce the yield increases obtained elsewhere.




Florax, R.J.G.M., R.L. Voortman, and J. Brouwer ‘Spatial dimensions of precision agriculture: a spatial econometric analysis of millet yield on Sahelian coversands’. Agricultural Economics, 27(3), 425-443.

The identification of local soil variability caused by within-field differences of macronutrients and ecological features is of paramount importance for the effectiveness of precision agriculture. We present several spatial statistical and econometric techniques to capture local differences in soil variation, ecological characteristics, and yield more effectively than the analytical techniques traditionally used in agronomy. The application of these techniques is illustrated in a case study dealing with precision agriculture in the West African Sahel. The production of millet on acid sandy soils constitutes a typical example of low soil fertility areas exhibiting small absolute but large relative differences in crop production conditions over short distances.


Keyzer, M.A. ‘Labeling and the realization of cultural values’. De Economist, 150(4), 487-511.

Labeling plays a role of increasing significance as a technique to reveal, with adequate certification, the content of a product in both a physical and a moral sense by reporting, say, on labor conditions, environmental sustainability or animal friendliness of the product chain. Whereas voluntary labeling leaves all initiative to the private sector, under mandatory labeling the state imposes an obligation to label, often in conjunction with the requirement to meet official standards. Besides aiming to ensure product safety, standards derive from paternalistic motives and seek to mitigate external effects of consumption, to manage catastrophic risks, to improve the representation of the poor, and to preserve the cultural heritage. Nowadays, they are also used in the fight against crime and terrorism and for the protection of intellectual property rights. Standard-based labeling is a source of recurrent conflict because it serves both to protect the own culture and to export it. Developed countries fear that dis­cretionary policies at a national level would harm their exports. They call for international harmoni­zation of the standards but developing countries are reluctant to participate, because their exports might suffer, while antiglobalists denounce it as an instrument of domination by the North. The paper reviews the arguments on both sides. It adopts a WTO perspective in proposing that for non-product standards, international harmonization, rather than being attached to products, should apply to terri­tories, be organized by subject and delegated to specialized international agencies that operate under the mandate of separate international treaties. But we differ from the WTO position when we argue first, that product as well as non-product standards should be modulated so as to reflect the cultural diversity across countries and their different stages of development, and second, that it should be permitted that countries refusing to sign a treaty should face import restrictions by signatories.


Keyzer, M.A., M.D. Merbis and B.G.J.S. Sonneveld ‘Economic models of land evaluation II: regional and global decision making’, in: Natural Resources Policy and Management, Encyclopedia of Life Support Systems (EOLSS). Oxford: Eolss Publishers.

This is the second of two chapters that review the use of economic models in land evaluation. While the first chapter introduced the subject and described the main steps in model construction and dealt with applications at farm and local level, the present chapter turns to models that deal with larger areas of study, at the watershed, regional and global level. It relates models' objectives, defined by the clients and the users, to model structure and data requirements. The chapter concludes with an overview of the pitfalls of this class of models and identifies challenges for future research.


Keyzer, M.A., B.G.J.S. Sonneveld and R.L. Voortman ‘Economic models of land evaluation I: local decision making’, in: Natural Resources Policy and Management, Encyclopedia of Life Support Systems (EOLSS). Oxford: Eolss Publishers.

Economic models of land evaluation inform potential users about unforeseen threats and opportunities of land use changes while giving due consideration to the needs, aspirations and attitudes of different stakeholders. The role of these models is to inform users about the effect of dynamic and spatial externalities that cannot efficiently be managed by private agents and markets, and about ways to cope with these. However, these external effects also cause special analytical difficulties that are accommodated in the economic models of land evaluation via simplifying assumptions that maintain a modular structure so as to keep the analysis tractable and amenable to empirical investigation. Four steps in model building can be distinguished: compilation of data, specification of equations, estimation of parameters, and scenario simulation. The implementation of these phases in model building varies widely and is generally tuned to client needs and priorities. The present paper ( focuses on applications at local level. An accompanying paper ( deals with higher administrative levels, discusses the pitfalls and identifies challenges for future research.





Gerlagh, R. and M.A. Keyzer ‘Sustainability and the intergenerational distribution of natural resources entitlements’. Journal of Public Economics 79: 315-341.

The paper describes an OLG economy with a single exhaustible resource that has amenity value. The steady states of this economy form a continuum, implying path-dependency. We compare three policy scenarios; first, a ‘zero extraction’ policy of enforced conservation that avoids environmental degradation, possibly at the expense of intertemporal efficiency. Second, a ‘grandfathering’ policy that endows the present generations with all resources, and that ensures efficiency but cannot prevent a persistent decline in lifetime utility from one generation to the next. Third, a ‘trust fund’ policy, where future generations receive claims for the natural resource. Of the three, only the trust fund ensures efficiency and protects welfare of all generations.


Gerlagh, R. and M.A. Keyzer ‘Limits-to-Growth theory’, in: Gerard H. Kuper, Elmer Sterken and Els Wester (eds.) Coordination and growth. Essays in honour of Simon Kuipers, pp. 219-231. Boston: Kluwer Academic Publishers.

The paper studies the implications for growth theory of the limit-to-growth debate, discussing three issues that have occupied a prominent place since the seventies. (1) maintaining growth: can growth be sustained in the rich and still growing countries despite the limited supply of production factors such as land and labor? (2) Initiating growth: will per capita growth also be possible for those who are currently poor? (3) Avoiding decline: how to manage the exhaustibility of natural resources and the possible irreversible degradation of the reproductive systems?


Keyzer, M.A. and B.G.J.S. Sonneveld ‘The effect of soil degradation on agricultural productivity in Ethiopia: a non-parametric regression analysis’. Chapter 16 in: N. Heerink, H. van Keulen and M. Kuiper (eds.), Economic Policy and Sustainable Land Use: Recent Advances in Quantitative Analysis for Developing Countries, pp. 269-292 Heidelberg: Physica-Verlag.

The paper estimates the effect of soil degradation on crop yields for dominant cereals in Ethiopia at a nation-wide level and analyses its relation with population density and fertilizer use. A soil degradation index is derived from an ordered qualitative classification on the degree of soil degradation and the area extension. Biophysical variability is incorporated by using, as dependent variable, the yield ratio (actual/potential yield) to correct for agro-climatic and crop genetic differences, and by including soil fertility as explanatory variable. The data set is cross sectional and obtained from gridded overlays on soil degradation, climate, soil, land form, population (and cattle) density. The relationships are estimated via non parametric (kernel density) regression and the estimation results are depicted in 3-D graphs. It appears that the relationship between yield ratio, land degradation and soil fertility is not very strong. Yet, three stylized facts can be identified. First, land degradation has its major impact on soils of lower fertility, where population levels are low. Secondly, on fertile soils, land degradation is largely compensated by fertilizer application. Finally, most people can be found on the slope facing a deep and dangerous precipice. A spatial representation of the elasticity of crop productivity with respect to soil degradation indicates that most vulnerable areas are located in the northern part of the county.


Nubé, M. ‘Confronting dietary energy supply with anthropometry in the assessment of undernutrition prevalence at the level of countries’. World Development 29:7, pp. 1275-1289.

Estimates on the prevalence of undernutrition at the level of regions in the world are widely divergent, whether assessed on the basis of food energy inadequacy or on the basis of anthropometry. In this study a comparison between the two approaches in the assessment of undernutrition has been made at the level of individual countries, utilizing until recently unavailable anthropometric data for adults. Results indicate that the two approaches yield strongly divergent and even contradictory results. In view of the complex methodology and tremendous data needs for estimating prevalence of food energy inadequacy and the relative straightforwardness of anthropometric assessment, it is concluded that anthropometric data are likely to be a more reliable source of information for estimating prevalence rates of undernutrition. Findings call for a re-assessment in current practices with respect to measuring and reporting undernutrition.


Sonneveld, B.G.J.S., M.A. Keyzer and P.J. Albersen ‘A non-parametric analysis of qualitative and quantitative data for erosion modeling: a case study for Ethiopia’. In: Sustaining the global farm. Selected papers of the ISCO 1999 conference, pp. 979-993. West Lafayette, Indiana: Purdue University.

The objectives of this paper are twofold. First, it compares the discriminatory power of qualitative expert judgments with actual soil losses to express class boundaries in physically measured, quantitative terms. Secondly, it investigates the properties of a postulated functional relationship between soil loss and readily available explanatory variables on both, their reliability of fit and behavior. The study uses quantitative soil erosion data of runoff plots of the Soil Conservation Research Project in Ethiopia. Qualitative expert judgments on the state of erosion for the same runoff plots were obtained through a questionnaire. The study applies a non-parametric technique that uses a flexible method of curve fitting. The first exercise applies this technique to determine the quantitative boundaries (soil losses) of qualitative classes. The results reveal a positive relationship between erosion hazard assessment by the expert and actual soil losses, however, experts tend to overestimate. In the second exercise, the mollifier program is used to visualize non-parametric estimates in 3-D graphs that show non-linear relationships and reliability of the estimates. The results indicate that soil loss should be modeled separately for annual crops and land use types with a permanent coverage. Further findings show that annual runoff has an almost linear relation with annual soil loss. An index derived from monthly rainfall data and the adjusted Cooks' method seems promising to represent the hydrological factor in the model. Most relations show a poor `goodness of fit', which anticipates low correlation coefficients in future parametric, models and indicates that additional variables should be included.





Ermoliev, Yu., M.A. Keyzer and V. Norkin ‘Global Convergence of the stochastic tatonnement process’, Journal of Mathematical Economics 34:173-190.

The paper introduces stochastic elements into the Walrasian tatonnement process, both to make it more realistic and to ensure its global convergence, with probability 1. It is assumed that the aggregate excess demand satisfies standard assumptions but is subject to measurement error. We distinguish two cases. First, the true aggregate excess demand is assumed to satisfy the Weak Axiom of Revealed Preference. This condition will be met if the underlying economy has a single consumer, several consumers with identical homothetic utility functions, or if it maximizes a social welfare function. We prove that after two minor modifications, under a fairly general specification of the measurement error and by imposing a certain consistency property on the estimator of excess demand, the tatonnement process converges with probability 1 to an equilibrium. Second, we consider the case that the Weak Axiom only holds around some of the equilibria. The procedure proposed imposes a random shock at time intervals of increasing duration. We also discuss how the procedure could be extended to determine all equilibria, to deal with jumps in excess demand including those that do not satisfy the Weak Axiom, and to represent agents who only gradually learn how to find an optimum.


Keyzer, M.A. and M.D. Merbis ‘WTO and the failure of Seattle’, De Economist 148: 259-271.

In Seattle, between 30th November and 3rd December 1999, the World Trade Organization (WTO) organized its Third Ministerial Conference that was supposed to establish the agenda for the multilateral negotiations under the Millennium Round but the meeting failed.

The Millennium Round is the successor of the Uruguay Round that after seven years of negotiations resulted in the GATT 1994 Agreement and the establishment of the WTO. It might seem that with the establishment of the WTO as a permanent institution the need for further multilateral rounds has diminished, as member countries can now meet regularly to discuss upcoming issues, to set up specialized committees on contentious subjects and to reach compromises. Moreover, as the 1994 agreement laid down the basic rules for trade liberalization, one could expect that all attention can be devoted to the effective implementation of the reduction of bound tariffs as pledged by the participants and the dispute settlement procedure of arbitrage by independent panels. Nonetheless, it became already clear during the 1996 ministerial conference in Singapore that a new multilateral round was required because the internal process would be incapable of generating sufficient momentum to resolve outstanding issues and to table new ones. Hence, it was decided to start a new round that should deal with trade in agricultural commodities and services, and possibly is broadened to cover other topics to be decided upon at the Seattle conference.

The conference was preceded by a symposium to encourage an informal dialogue with the NGOs. Over ten thousand representatives of NGOs, trade unions and action groups came to Seattle for the occasion, signaling that the WTO round has become a major international forum for economic consultations. Outside the conference building a mixed company of protesters expressed their feelings about international trade liberalization and the WTO culture. But after their initial blockade on the street they were kept at great distance from the conference venue and cannot be given the blame of the eventual failure of the meeting.

The failure was due to organizational difficulties and to the complexity of the subject matter under discussion. Some of the organizational problems were attributable to unfortunate timing and to specific incidents but others are of a more structural nature and suggest that the WTO may have to reassess its approach and mode of operation and possibly even to rethink its mission. This communication reviews the organizational difficulties (section 2), briefly discusses the subject matter itself (section 3) and mentions the possible implications of the problems encountered for the future role and mandate of the WTO (section 4).


Keyzer, M.A. and M.D. Merbis 'CAP-reform in Agenda 2000: logic and contradictions'. Chapter 7 in: P. van Dijck and G. Faber (eds.), The External Economic Dimension of the European Union, pp. 151-173. The Hague: Kluwer Law International.

The Common Agricultural Policy (CAP) underwent significant reform in 1992, as the European Commission moved its agricultural policy into a new direction. The thrust of the reform was a shift from price to direct income support, achieved by lowering the intervention prices, while compensating farmers via acreage and headage premiums. As a means to reduce the production of cereals and oilseeds, a set-aside scheme was introduced, and professional farmers were only eligible for compensation payments if they participated by keeping a specified fraction of their land fallow. With the benefit of hindsight, it can be concluded that the measures relieved international tensions on agricultural export markets, and virtually saved the Uruguay Round, resulting into a new GATT, see GATT (1994). Furthermore, the compensation payments turned out to be generous as market prices became higher than anticipated.

The CAP essentially remained unchanged since, though pressures for further reform have been building up. In its Agenda 2000, as part of a broad package to prepare the European Union for the next century (CEC, 1997a,b), the European Commission argues that a deepening and widening of the 1992 reform is called for, in view of the developments within the agricultural sector itself, the upcoming international trade negotiations under WTO and the planned accession of Central and Eastern European countries (CEECs). The agricultural chapter of Agenda 2000 contains a first version that was subsequently elaborated upon in the draft regulations published in March 1998 (CEC, 1998a).

In a nutshell, the 1992 reform is pursued with a further lowering of internal prices and increase of headage and acreage premiums as compensating payments. The proposals seek to improve market conformity by cutting the set-aside rate to zero, and by allowing for some expansion of milk quotas. In addition, food quality and safety concerns figure more prominently, in response to the recent spread of animal diseases, and rural policies are to be strengthened (see also CEC, 1997d).

Since the proposals basically amount to an extension of the 1992 reform, they are best characterized by the elements that are kept unchanged: compensation through premiums that are not fully decoupled, strong restrictions on the import side, and no reform for sugar. It is noteworthy that the Commission has opted for such an extrapolative approach, rather than presenting a clear vision of the future of European agriculture. This is presumably because the EU member states appear to have widely diverging views on the matter. Indeed, the Agenda 2000 proposals so far found little endorsement by the various member states and yet, as of February 1999, no alternatives have been formulated that can count on a majority of votes in the council of ministers, where the final decisions are to made in the early spring this year.

The aim of the present paper is to look over the edge of the Agenda 2000. While it seems that the current proposals will be adopted shortly, presumably after minor amendments, the measures they implement will soon need more substantial modification. For although all the steps follow logically from the earlier reform, they nonetheless strengthen the inherent contradictions of the CAP. Their contribution to trade liberalization is unlikely to appease the negotiating partners of the coming WTO round. Especially in countries such as Germany and The Netherlands that are net contributors to the EU budget, taxpayers and financial authorities find it hard to accept the proposed increase in compensation payments. The planned accession of countries from Central and Eastern Europe will only make it more difficult to finance the CAP. Agenda 2000 also fails to draw the policy consequences of recent shifts in consumer concerns and the ongoing concentration in agribusiness. More generally, by choosing an extrapolative approach the Commission cannot look ahead to policies for a rural sector that will increasingly receive income from non-agricultural activities and whose agricultural operations will be integrated more closely within the processing chain. We will discuss these developments and point to their effects on developing countries. Our position will be that the contradictions of a CAP that claims to become more liberal while keeping its internal prices isolated from the world market and asking for more budgetary support, create artificial tensions. We will argue that such tensions can be avoided if the policies become more market oriented combining openness in trade with a good financial reward for environmental and other services rendered by farmers.

The paper starts with a brief assessment of the current proposals (section 2). Next, it discusses a number of unresolved issues that need to be addressed (section 3), as well as recent developments which the CAP will eventually have to account for, in international trade policy (section 4), and in the agribusiness (section 5). In section 6 the policy implications are sketched.


Keyzer, M.A. and M.D. Merbis ‘An opening bid for the Millennium Round’ (CAPMAT simulations), in: Agenda 2000. CAP reform decisions. European Commission, Directorate-General Agriculture, pp. 61-82.

In its Agenda 2000, the European Commission decided on new reform measures for the Common Agricultural Policy. These measures imply a further shift from price to income support, by lowering intervention prices for cereals, beef and milk, and by increasing the level and scope of acreage and headage premiums so as to compensate for income losses. However, the impact on farm incomes is negative. Acreage and headage premiums increase and become the dominant item on the agricultural budget of the EU. The Agenda 2000 decision facilitates the accession of new members, and constitutes an opening bid for the WTO negotiations whose successful completion will require further adjustments.


Keyzer, M.A., M.D. Merbis and M. van ‘t Riet ‘Reforming sugar, stronghold of agricultural protection’ in: CPB Report 2000/1, pp 42-47, The Hague: SDU.

For decades the EU has faced demands by agricultural exporters to reform its Common Agricultural Policy (CAP), reduce its export subsidies and open up for imports. In 1992, during the Uruguay Round, and with Agenda 2000, the EU made concessions in this respect, albeit reluctantly. However, the sugar sector has thus far escaped any reform. This note explores the scope for reform in the future. It describes the strong verti­cally integrated nature of the sector, which, however, may yet bow to the pressure for reform. The sector could absorb reductions in domestic prices relatively easily, as long as import restrictions and quotas on sugar substitutes are preserved. The margin for price reduction would even be wider if the CAP replaced its hectare support on cereals and oilseeds by multi func­tionality payments as a reward for services provided. Finally, deeper vertical integration could generate a premium on specialized products, thus easing the adjustments.