Staff Publications

Staff Publications

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

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

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

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Do farmers internalise environmental spillovers of pesticides in production?
Skevas, T. ; Stefanou, S.E. ; Oude Lansink, A.G.J.M. - \ 2013
Journal of Agricultural Economics 64 (2013)3. - ISSN 0021-857X - p. 624 - 640.
damage control - alfalfa weevil - econometrics - economics - specification - inputs - costs
Pesticides are used in agriculture to protect crops from pests and diseases, with indiscriminate pesticide use having several adverse effects on the environment and human health. An important question is whether the environmental spillovers of pesticides also affect the farmers’ production environment. We use a model of optimal pesticide use that explicitly incorporates the symmetric and asymmetric effect of pesticides’ environmental spillovers on crop production. The application focuses on panel data from Dutch cash crop producers. We show that pesticides have a positive direct impact on output and a negative indirect impact through their effects on the production environment.
Designing the emerging EU pesticide policy: A literature review
Skevas, T. ; Oude Lansink, A.G.J.M. ; Stefanou, S.E. - \ 2013
NJAS Wageningen Journal of Life Sciences 64-65 (2013). - ISSN 1573-5214 - p. 95 - 103.
willingness-to-pay - damage control - economic incentives - moral hazard - chemical use - time-series - risk - econometrics - specification - agriculture
A European Union (EU) wide pesticide tax scheme is among the future plans of EUpolicy makers. This study examines the information needs for applying an optimal pesticidepolicy framework at the EU level. Damage control specification studies, empirical results from pesticide demand elasticity, issues on pesticide risk valuation and uncertainty, and knowledge on the indirect effects of pesticides in relation to current pesticidepolicies are analysed. Knowledge gaps based on reviewing this information are identified and an illustration is provided of the direction future pesticidepolicies should take.
Can economic incentives encourage actual reductions in pesticide use and enfironmental spillovers
Skevas, T. ; Spiro, A. ; Stefanou, S.E. ; Oude Lansink, A.G.J.M. - \ 2012
Agricultural Economics 43 (2012)3. - ISSN 0169-5150 - p. 267 - 276.
damage control - productivity - econometrics - specification - netherlands - pollution - taxation - systems - costs
Chemical pesticides constitute an important input in crop production. But their indiscriminate use can impact negatively agricultural productivity, human health, and the environment. Recently, attention is focused on the use of economic incentives to reduce pesticide use and its related indirect effects. The aim of this work is to assess the effectiveness of different economic instruments such as taxes and levies in encouraging farmers to decrease pesticide use and their environmental spillovers. A policy simulation model is employed using data from Dutch cash crop producers including two pesticide categories that differ in terms of toxicity and pesticides’ environmental spillovers. Four different instruments were selected for evaluation: pesticide taxes, price penalties on pesticides’ environmental spillovers, subsidies, and quotas. The results of the study indicate that even high taxes and penalties would result in a small decrease in pesticide use and environmental spillovers. Taxes that differentiate according to toxicity do not lead to substitution of high- with low-toxicity pesticides. Subsidies on low-toxicity products are not able to affect the use of high-toxicity products. Pesticide quotas are more effective in reducing pesticide use and environmental spillovers.
Economic analysis of water harvesting technologies in Ethiopia
Wakeyo, M.B. - \ 2012
Wageningen University. Promotor(en): Arie Oskam, co-promotor(en): Koos Gardebroek; Tassew Woldehanna. - S.l. : s.n. - ISBN 9789461738707 - 150
agrarische economie - ontwikkelingseconomie - ethiopië - regenwateropvang - econometrie - economische analyse - panelgegevens - bedrijfsgrootte in de landbouw - kunstmeststoffen - agricultural economics - development economics - ethiopia - water harvesting - econometrics - economic analysis - panel data - farm size - fertilizers

Rainfall shortage and variability constrain crop production of smallholder farmers in Ethiopia and climate change may even aggravate this problem. An attractive method to mitigate this is water harvesting. This thesis examines the economic aspects of water harvesting by exploring optimal water use and the impact of water harvesting using micro-econometric analyses of cross-section and panel data collected from Ethiopian farmers in 2005 and 2010.

In the first empirical chapter, the study estimates marginal values and elasticitiesof harvested water in the production of three vegetables to determine whether water allocation is economically optimal. The results are mixed, although the estimated marginal product values between onions and tomatoes show that farmers on average allocate water economically across these two crops.

The descriptive data show that the share of irrigated land is lower at larger farms. Because farm size may increase in the future, it is interesting to investigate what determines the share of irrigated land in relation to farm size. A random-effects tobit model is appropriate to estimate this relationship. The result shows that access to both credit and markets, farm-size, region, aridity, and plot distance to water source all affect the share. Encouraging water harvesting requires flexible and effective variables that will work also for larger farms.

Despite its weather-risk reducing advantage, the average disadoption rate of water harvesting technology between 2005 and 2010 was as high as 42%. To find out why farmers disadopt, binary choice models are estimated to investigate the factors that cause disadoption. Based on the estimation results, it is concluded that increasing availability of plastic sheets and labour-saving equipment (water pumps), easier market and credit access, and the cultivation of perennials can reduce disadoption.

The last empirical chapter focuses on the relation between water harvesting and fertilizer use. Due to weather risk, farmers may limit the use of purchased fertilizer, thereby continuing to grow a high share of low-risk and low-yield crops. To establish whether harvested water encourages fertilizer use, two variants of random-effect models are estimated. The results strongly support the idea that water harvesting technology induces fertilizer use, indicating that water harvesting can increase fertilizer use- and hence crop yields- in Ethiopia.

The concluding chapter discusses the results against the background of the research objective: what are the economics of water harvesting at micro level?

W-based versus latent variables spatial autoregressive models: evidence from Monte Carlo simulations
Liu, A. ; Folmer, H. ; Oud, J.H.L. - \ 2011
Annals of Regional Science 47 (2011)3. - ISSN 0570-1864 - p. 619 - 639.
regression-models - weights matrix - specification - econometrics
In this paper, we compare by means of Monte Carlo simulations two approaches to take spatial autocorrelation into account: the classical spatial autoregressive model and the structural equations model with latent variables. The former accounts for spatial dependence and spillover effects in georeferenced data by means of a spatial weights matrix W. The latter represents spatial dependence and spillover effects by means of a latent variable in the structural (regression) model while the observed spatially lagged variables are related to the latent spatial dependence variable in the measurement model. The simulation results based on Anselin's Columbus, Ohio, crime data set show that the misspecified latent variables approach slightly trails the correctly specified classical approach in terms of bias and root mean squared error of the coefficient estimators.
The agricultural world in equations: an overview of the main models at LEI
Woltjer, G.B. ; Bezlepkina, I. ; Leeuwen, M.G.A. van; Helming, J.F.M. ; Bunte, F.H.J. ; Buisman, F.C. ; Luesink, H.H. ; Kruseman, G. ; Polman, N.B.P. ; Veen, H.B. van der; Verwaart, T. - \ 2011
Den Haag : LEI, onderdeel van Wageningen UR (Memorandum / LEI Wageningen UR : Natural resources )
agrarische economie - modellen - economische modellen - gegevens verzamelen - bedrijfsgegevens - landbouwkundig onderzoek - econometrie - agricultural economics - models - economic models - data collection - farm accountancy data - agricultural research - econometrics
At LEI, several different quantitative models are being used. In many projects more than one model is used and in some cases information from one model is explicitly used in another model. This report attempts to sketch brief overviews of the main models used at LEI.
How do Agricultural Programmes Alter Crop Production? Evidence from Ecuador
Cavatassi, R. ; Salazar, L. ; Gonzalez-Flores, M. ; Winters, P.C. - \ 2011
Journal of Agricultural Economics 62 (2011)2. - ISSN 0021-857X - p. 403 - 428.
farmer field schools - pesticide productivity - bt cotton - econometrics
Evaluating agricultural programmes requires considering not only the programmes’ influence on input and output indicators, but also considering the relationship between these indicators as embodied in the production technology. This article examines the impact on production of an intervention in the Ecuadorian Sierra designed to improve returns to potato production through training and through linking smallholders to high-value markets. Critical to identifying the impact of the programme is the careful construction of a counterfactual and meticulous data collection. To assess the impact of the programme on production, a weighted estimation, where weights are constructed through propensity score matching, is employed to estimate a production function within a damage abatement framework. The function incorporates a series of interaction terms to assess the impact of the programme on the production technology. The findings provide evidence that the programme enhances yields both through a general shift in technology as well as increased input use. The results suggest that the use of effective farming techniques that are learned through the programme induce this technological shift
Econometric analysis of the performance of cooperatives and investor owned firms in the European dairy industry
Soboh, R.A.M.E. - \ 2009
Wageningen University. Promotor(en): Alfons Oude Lansink; Gert van Dijk. - [S.l. : S.n. - ISBN 9789085855538 - 133
zuivelcoöperaties - firma's - zuivelindustrie - efficiëntie - prestatieniveau - econometrische modellen - econometrie - analyse - economische analyse - internationale vergelijkingen - europa - dairy cooperatives - firms - dairy industry - efficiency - performance - econometric models - econometrics - analysis - economic analysis - international comparisons - europe
Keywords: Cooperatives, IOFs, European dairy industry, logistic regression, stochastic frontier analysis, inter- and intra-firm efficiency, catch-up component, data envelopment analysis, hyperbolic technical efficiency, overall efficiency, scale efficiency, bootstrapping.

In this study we measure the performance of cooperatives and investor-owned firms in the European dairy processing industry. Comparing the performance between cooperatives and investor-owned firms requires accounting for differences in their mission and objectives. Traditionally, cooperatives were established by farmers to gain access to markets, balance market powers and have a secured and sustainable income. Generally, there is a consensus in the economic literature that a cooperative can be defined as a (members)user-owned and (members)user-controlled organization that aims to benefit its (members)user. Cooperatives are transaction oriented, the members provide themselves with services they could not secure otherwise. In addition member are owners and determine the mission and strategy of cooperatives equally as the owners of the cooperative enterprise. Our study takes into account the consequences of members’ strategies for the cooperatives’ organizational structure and subsequently the significance of structure on (technical and economical) efficiencies. Although the theoretical literature emphasizes the difference in economic behavior between cooperatives and IOFs, the empirical studies have failed to follow up with theoretical approaches. The failure of the empirical studies to apply the models proposed by the theoretical literature seems to be due to either the inaccessibility of data, the inability to take into account the interests of all the various types of members and stakeholders of the cooperative, or the difficulty in testing the various hypotheses in practice. An empirical analysis of differences in financial indicators between IOFs and cooperatives in six European countries shows that cooperatives are less profitable but operationally more efficient, they have higher material costs and lower debts than IOFs. Furthermore, cooperatives display a substantially greater variation in financial indicators than IOFs. Stochastic Frontier Analysis is used to measure and compare the efficiency and production technology of cooperatives and IOFs. Cooperatives are found to have a more productive technology than IOFs, but they use their production potential less efficiently. A further empirical analysis of technical efficiency using Data Envelopment Analysis shows that explicit accounting for the objectives of cooperatives generates different outcomes compared with treating cooperatives as if they were IOFs. The results of the empirical analyses in this study promote the conclusion that measuring the performance of cooperatives as if they were IOFs produces misleading insights about the cooperatives’ performance suggesting performance suggesting that cooperatives’ performance is influenced by their organizational characteristics and members objectives.

Econometric analyses of microfinance credit group formation, contractual risks and welfare impacts in Northern Ethiopia
Berhane Tesfay, G. - \ 2009
Wageningen University. Promotor(en): Arie Oskam, co-promotor(en): Koos Gardebroek; Tassew Woldehanna. - [S.l. : S.n. - ISBN 9789085854258 - 146
krediet - landbouwhuishoudens - financiële instellingen - econometrie - risico - dynamische modellen - groepen - contracten - armoede - plattelandsbevolking - ethiopië - microfinanciering - panelgegevens - credit - agricultural households - financial institutions - econometrics - risk - dynamic models - groups - contracts - poverty - rural population - ethiopia - microfinance - panel data

Key words
Microfinance, joint liability, contractual risk, group formation, risk-matching, impact evaluation, Panel data econometrics, dynamic panel probit, trend models, fixed-effects, composite counterfactuals, propensity score matching, farm households, Ethiopia.

Lack of access to credit is a key obstacle for economic development in poor countries. The underlying problem is related to information asymmetry combined with the poor’s lack of collateral to pledge. New mechanisms in microfinance offer ways to deal with this problem without resorting to collateral requirements. The objective of this thesis is to examine the mechanisms of providing credit through microfinance and assess the long-run borrowing effects on household welfare in Ethiopia. The Ethiopian environment provides a suitable setting to examine these issues. To meet this objective, two unique data sets - a five-wave panel data on 400 and a cross-sectional data on 201 households - from northern Ethiopia are used.
Borrowing decision is first conceptualized using a dynamic stochastic theoretical framework. Two types of risks involved in joint liability lending are incorporated, i.e., risk of partner failure and risk of losing future access to credit. Empirical analysis using recent dynamic panel data probit techniques show that these contractual risks indeed impede participation in borrowing. The impediment is higher for the poorer, and for new than repeat participants. Second, group formation is analyzed within the framework of alternative microeconomic theories of joint liability where the commonly held hypothesis that groups formed are homogeneous in risk profiles is tested. Empirical results reject this hypothesis indicating that the formation of heterogeneous risk profiles is an inherent feature in group formation and repayment. In fact, there is evidence that borrowers take advantage of established informal credit and saving, and other social networks, which also suggests that group formation outcomes vary depending on underlying socioeconomic contexts.
Third, the impact of long-term borrowing on household welfare is assessed from the dimension of intensity and timing of participation in borrowing. Panel data covering relatively long period enabled to account for duration and timing concerns in program evaluation. Recent parametric and semi-parametric panel data techniques are innovatively employed to mitigate participation selection biases. Results from both approaches indicate that borrowing has increased household welfare significantly: the earlier and more frequent the participation the higher the impact partly due to lasting effects of credit. This also suggests that impact studies that are based on a single-shot observation of outcomes and that do not account for the timing and duration of participation may underestimate microfinance credit impacts.

Do Higher Financial Returns Lead to Better Environmental Performance in North America’s Forest Products Sector?
Yamaguchi, J. ; Kooten, G.C. van - \ 2008
Canadian Journal of Forest Research 38 (2008)9. - ISSN 0045-5067 - p. 2515 - 2525.
panel-data - specification - econometrics - tests
This study examines the relation between corporate environmental performance and corporate financial (economic) performance in North America’s forest products industry to determine whether there is a firm-level environmental Kuznets curve (EKC). An unbalanced panel of firm-level observations is constructed using data from PricewaterhouseCoopers, the US Environmental Protection Agency, and Environment Canada. The analysis focuses on methanol and formaldehyde emissions because these are the only pollutants for which consistent firm-level data are available in forestry. We find strong evidence of a firm-level EKC. The evidence is considerably weaker if endogeneity related to the effect of past pollution on current pollution or endogeneity resulting from a possible circular relationship between rate of return and pollution is taken into account, although the available time horizon is too short to conclude that endogeneity is a problem. Even so, there remains evidence of a negative relationship between financial performance and environmental performance for formaldehyde
How to get rid of W: a latent variables approach to modelling spatially lagged variables
Folmer, H. ; Oud, J. - \ 2008
Environment and Planning A 40 (2008)10. - ISSN 0308-518X - p. 2526 - 2538.
regression-analysis - weights matrix - econometrics
In this paper we propose a structural equation model (SEM) with latent variables to model spatial dependence. Rather than using the spatial weights matrix W, we propose to use latent variables to represent spatial dependence and spillover effects, of which the observed spatially lagged variables are indicators. This approach allows us to incorporate and test more information on spatial dependence and offers more flexibility than the representation in terms of Wy or Wx. Furthermore, we adapt the ML estimator included in the software package Mx to estimate SEMs with spatial dependence. We present illustrations based on Anselin¿s Columbus, Ohio, crime dataset.
Valuation of land use in the Netherlands and British Columbia: a spatial hedonic GIS-based approach
Cotteleer, G. - \ 2008
Wageningen University. Promotor(en): Arie Oskam; Kees van Kooten, co-promotor(en): Jack Peerlings. - [S.l.] : S.n. - ISBN 9789085049470 - 158
landgebruik - open ruimten - landgebruiksplanning - relaties tussen stad en platteland - landbouwgrond - geografische informatiesystemen - economische evaluatie - agrarische economie - econometrie - econometrische modellen - eigendomsoverdrachten - niet marktbare baten - bayesiaanse theorie - nederland - canada - parttime landbouwbedrijven - ruimtelijke analyse - regionale economie - ruimtelijke economie - ruimtelijke modellen - land use - open spaces - land use planning - rural urban relations - agricultural land - geographical information systems - economic evaluation - agricultural economics - econometrics - econometric models - property transfers - non-market benefits - bayesian theory - netherlands - part time farming - spatial analysis - regional economics - spatial economics - spatial models
The main reason for government intervention in land markets is market failure. Open space is a non-market output or externality of farmland and, although it might be important to people, there is no actual market for the good as such. The Netherlands and the Province of British Columbia in Canada both experience similar problems of expanding cities and pressure on open space, and they both use zoning to regulate land use and its externalities. The objective of this research is to evaluate the effect of zoning on the preservation of open space in the urban-rural fringe and to quantify the externalities that different types of land use impose on residential properties
Econometric specification of constrained optimization models
Jansson, T.G. - \ 2007
Rheinischen Friedrich-Wilhelms-Universität. Promotor(en): T. Heckelei; K. Frohberg. - Bonn : University of Bonn Library - 168
econometrie - optimalisatie - modellen - econometrics - optimization - models
The subject of this thesis is econometric specification of parameters of constrained optimization models, with special attention to issues that arise when (i) inequality constraints are involved and/or (ii) when the estimation problem is illposed (underdetermined) or data come from diverse sources. The general approach followed here is to estimate directly the optimality conditions of the optimization model, together with additional equations for including prior information.
Linking of repeated games: when does it lead to more cooperation and pareto improvements?
Folmer, H. ; Mouche, P.H.M. van - \ 2007
Milan - Italy : Fondazione Eni Enrico Mattei (Fondazione Eni Enrico Mattei Working Papers paper 19) - 15
speltheorie - milieubeleid - wiskundige modellen - economie - econometrie - milieueconomie - game theory - environmental policy - mathematical models - economics - econometrics - environmental economics
Specification and Estimation of Production Functions Involving Damage Control Inputs: A Two-Stage, Semiparametric Approach
Kuosmanen, T.K. ; Pemsl, D. ; Wesseler, J.H.H. - \ 2006
American Journal of Agricultural Economics 88 (2006)2. - ISSN 0002-9092 - p. 499 - 511.
bt cotton - pesticide productivity - increasing returns - econometrics - impact - efficiency - matters - choice - china
Productivity assessment of damage control inputs (such as pesticides) is complicated because their effect depends on the exposure to damage agents (such as pests). We discuss some open specification and estimation issues. The contribution is threefold. First, we elaborate the separability conditions for the damage control function and production function. Second, we employ a two-stage semiparametric technique to combine attractive features of both nonparametric and parametric approaches. Third, we model the interaction between pest exposure and damage control inputs by using slope dummies. An application to productivity analysis of small scale Bt cotton production in China illustrates the approach
Integrating agronomic principles into production function estimation: A dichotomy of growth inputs and facilitating inputs
Zhengfei, G. ; Oude Lansink, A.G.J.M. ; Ittersum, M.K. van; Wossink, G.A.A. - \ 2006
American Journal of Agricultural Economics 88 (2006)1. - ISSN 0002-9092 - p. 203 - 214.
damage control productivity - production ecology - production systems - crop response - econometrics - efficiency - model - hypothesis - matters - design
This article presents a general conceptual framework for integrating agronomic principles into economic production analysis. We categorize inputs in crop production into growth inputs and facilitating inputs. Based on this dichotomy we specify an asymmetric production function. The robustness of the asymmetric framework is tested using crop-level panel data on potato production in the Netherlands. The test results do not reject the proposed framework, and the asymmetric specification better represents the underlying production technology.
Damage control inputs: a comparison of conventional and organic farming systems
Zhengfei, G. ; Oude Lansink, A.G.J.M. ; Wossink, G.A.A. ; Huirne, R.B.M. - \ 2005
European Review of Agricultural Economics 32 (2005)2. - ISSN 0165-1587 - p. 167 - 189.
pesticide productivity - increasing returns - economic-analysis - econometrics - specification - heterogeneity - matters - output
The economic literature on pest control exclusively assumes a non-negative marginal product of pesticides based on a monotonic non-decreasing function of damage abatement, which may bias pesticide productivity estimates. This paper proposes a specification that allows for a negative marginal product of pesticides and a damage-abating role for labour and machinery. Pesticide productivity is found to be lower than previously reported. Conventional farms are found to rely substantially on pesticides and machinery for damage abatement, whereas organic farms mainly rely on machinery use and changes in cultural practices. Productivity analyses based on the asymmetric specification suggest that pesticides are used optimally in conventional farming, which contrasts with results in previous literature.
Dutch AG-MEMOD model; A tool to analyse the agri-food sector
Leeuwen, M.G.A. van; Tabeau, A.A. - \ 2005
Den Haag : LEI (Report / LEI : Domain 8, Models and data ) - ISBN 9086150284 - 128
landbouwbeleid - econometrie - econometrische modellen - landbouw - bosbouw - milieu - agro-industriële sector - europese unie - nederland - agricultural policy - econometrics - econometric models - agriculture - forestry - environment - agroindustrial sector - european union - netherlands
Agricultural policies in the European Union (EU) have a history of continuous reform. AG-MEMOD, acronym for Agricultural sector in the Member states and EU: econometric modelling for projections and analysis of EU policies on agriculture, forestry and the environment, provides a system for analysing the impact of policy changes across the EU. Teams from each EU member state have developed models for the specific agri-food sector in their own country, which were reviewed by experts. Country-specific differences with regard to the operation of the agri-food sector and how each responds to external influences such as EU policies and world market prices have been carefully modelled. Not only CAP policy variables, but also economic and biophysical variables have been inserted. As all country models were built on a common format, they could be combined and run as an overall system for the EU. Hence, AG-MEMOD is able to analyse the impact of policy changes on individual member states, in all their diversity, as well as on the EU as a whole. This report describes the construction of the Dutch agri-food sector within the AG-MEMOD framework and summarises the specification, estimation and testing procedures applied to build the Dutch model. An application of the model is provided for a sugar policy reform. Although there is scope for improvements, the current model version can already produce reasonable projections for agricultural commodities in the Netherlands.
Non-parametric production analysis of pesticides use in the Netherlands
Oude Lansink, A.G.J.M. ; Silva, E. - \ 2004
Journal of Productivity Analysis 21 (2004)1. - ISSN 0895-562X - p. 49 - 65.
damage control - econometrics - specification - matters - quality
Many previous empirical studies on the productivity of pesticides suggest that pesticides are under-utilized in agriculture despite the general held believe that these inputs are substantially over-utilized. This paper uses data envelopment analysis (DEA) to calculate non-parametric measures of the value of the marginal product of pesticides. Furthermore, the effect of pesticides on the value of the marginal product of productive inputs is investigated in order to analyze technical interdependence between pesticides and productive inputs. Results suggest, in general, substantial under-utilization of pesticides, which is consistent with earlier findings of parametric specifications.
Annual variation in weather: its implications for sustainability in the case of optimising nitrogen input in sugar beet
Koeijer, T.J. de; Buck, A.J. de; Wossink, G.A.A. ; Oenema, J. ; Renkema, J.A. ; Struik, P.C. - \ 2003
European Journal of Agronomy 19 (2003). - ISSN 1161-0301 - p. 251 - 264.
damage control - agricultural production - fertilizer application - netherlands 1948-1989 - vonliebig - model - crop - econometrics - efficiency - indexes
Efficient crop husbandry is crucial in order to prevent unnecessary emissions of environmentally damaging inputs and to maintain economic soundness, but it raises the question of which productivity and efficiency levels should be realised. Agronomists and economists are still debating this issue, as they base their insights on different production functions: economists assume decreasing returns of input use, whereas the response curve used by agronomists is often described as linear with a plateau (LRP). The first objective of this paper is to reconcile these points of view by showing that due to annual variation in weather individual LRP curves turn into a concave function with decreasing returns when aggregated. The second objective is to present empirical evidence on the impact of weather variation on optimal input levels for the case of nitrogen in sugar beet in The Netherlands. Two methods were used: bio-physical simulation and estimation with a regression model using panel data. Optimal crop growth and nitrogen input were simulated with the Water and Agro-chemicals in the soil and Vadose Environment (WAVE) model, using weather data for 43 years. Parameters were assessed with and without additional weather effects. An agronomic crop growth simulation model such as WAVE might underestimate the effect of variation in weather on the agronomic efficiency of nitrogen, because pests, weeds and diseases as well as the effectiveness of biocides, the sowing date and possible harvesting problems are strongly influenced by the weather. To test for this effect, weather indexes that include these indirect weather effects on the occurrence of pests and diseases were derived from panel data by means of a regression model. These weather indexes were used to re-assess the impact of weather variability on the agronomic efficiency of nitrogen in sugar beet cropping. The results of the bio-physical simulation showed that due to annual variation in weather the agronomic efficiency of nitrogen use was reduced by 10% at the current ratio of prices of nitrogen and sugar beet. The variation in weather, including indirect effects, caused the agronomic efficiency to decrease by 13%. This relatively small decrease suggests that at least some of the indirect weather effects might have an opposite effect on the agronomic efficiency of nitrogen use compared with the direct weather effects. This hypothesis seems to be supported by the absence of a significant correlation between the two weather indexes and by the lower estimated variance of the weather indexes based on panel data. (C) 2002 Elsevier Science B.V. All rights reserved.
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