Farmer-buyer relationships and sustainable agricultural practices in the food supply chain : The case of vegetables in Chile - Benitez-Altuna, Francisco Javier (Wageningen University and Research. Department of Social Science) ; Materia, Valentina C. (Wageningen University and Research. Department of Social Science) ; Bijman, Jos (Wageningen University and Research. Department of Social Science) ; Gaitán-Cremaschi, Daniel (Universitat Autònoma de Barcelona. Institut de Ciència i Tecnologia Ambientals) ; Trienekens, Jacques (Wageningen University and Research. Department of Social Science)