Measuring Technical Efficiency Under Factor Nonsubstitution: A Stochastic von Liebig Crop Response Model Margarita Genius (Department of Economics, University of Crete, Greece) Maria Mavraki (Department of Economics, University of Crete, Greece) Vangelis Tzouvelekas (Department of Economics, University of Crete, Greece) Address for Correspondence: Margarita Genius Dept. of Economics, Faculty of Social Sciences, University of Crete University Campus GR74100 Rethymno, Crete, Greece Tel.: +30-28310-77414; Fax: +30-28310-77406; e-mail: genius@econ.soc.uoc.gr The authors wish to thank Quirino Paris for kindly providing the data used in the present paper.