Nicolas Clootens Univ. Orléans, CNRS, LEO, UMR 7322, F45067, Orléans, France.   Rue de Blois B.P. 26739 Orléans, 45067 cedex 2 France   nicolas.clootens@centrale-marseille.fr   https://sites.google.com/site/clootensnicolas/           JEL Areas: Q : Agricultural and Natural Resource Economics O4 : Economic Growth and Aggregate Productivity: General