From Smallholders to Shareholders: A Guide to Optimizing Partnerships with the Private Sector for Smallholder Impact
This is a good guide to approaches to partnerships in agriculture that strengthen the role of smallholder farmers. It offers a particularly useful discussion of different business models that can be used with concrete examples. In fact, it is probably the best summary of business models I've read so far. It was developed as part of USAID Bureau of Food Security's successful Partnering for Innovation activity (http://www.partneringforinnovation.org ).
Related Resources
Partnering for Innovation Guide to Partnerships, business models