My background is in agricultural extension. Agricultural extensionists used the following text as the Bible for diffusion of innovations research. Late Everett M. Rogers ( professor and chair of the Department of Communication & Journalism at the University of New Mexico) wrote a few textbooks on the issue. Here is the last one, I suppose.
Everett M. Rogers, Diffusion of Innovations, fifth edition, Simon and Schuster, 2010.
Mehrdad Pouya (PhD candidate), Agricultural Extension Education Dept., Bu-Ali Sina University, Hamadan Hamadan Province, Iran