This research was made possible with the encouragement,support and assistance of several people. Iam thankful to Art Stoecker, Hong Lee, Su j it Roy,Robert Rouse, and David Upton for their valuable commentsand suggestions, while I worked on my dissertationat Texas Tech University. I am grateful to JoseEmilio G. Araujo and Jose Alberto Torres for grantingme leave from the Interamerican Institute forCooperation on Agriculture (IICA), to complete mystudies at Texas Tech; to Mike Gudger for his encouragementthroughout my work; to Peter Hazell, GustavoArcia and Juan Antonio Aguirre for their...