CropScience.org has a great paper on the potential use of social media and Internet access for rural farmers. What sets it apart from most Social Media for Development writings is that is takes a serious look at what must be in place for a project of this scope to work.
It compares farmers in Uganda and Australia, which is less ridiculous than it sounds. The Australian farmers - with training and a significantly higher support network (from government regulations all the way to average numbers of computers/100 people;
There are many technical links in the chain needed to connect a rural person to the Internet, and no-one takes responsibility for all of them. A lack of access may be caused by problems with the national or local telecommunications infrastructure, the ISP, the computer or the software being used (Easdown 1999). In rural Australia this is enough to put farmers off using the Internet, but it can be a major headache for Internet project managers in Africa. […] A promising alternative for some rural communities in Africa is the use of mobile telephony to access the Internet (Gerster and Zimmerman 2003). In Uganda the mobile phone services of MTN are widespread even in remote rural areas, and in many African countries the number of mobile subscribers exceeds those linked to the fixed network. Innovative African projects such as Foodnet in Uganda have made use of this to develop an online system using mobile telephony for farmers to access price information via messages (SMS) and information on commodity prices can easily be sent via teletext.
The authors hit on key elements of ICT-for-ag (and, really, any ICT4D/Poverty alleviation project), suggesting the costs and complications of Internet access, the time and skills needed, gender roles, and the need for social support networks, and naturally the lower level infrastructural needs:
For the Internet to be an effective means for farmers to access useful information three complementary things need to be in place. Government policies are needed to support and develop physical Internet access in rural areas. Farmers need to be skilled and supported in learning how to use the Internet and contextualizing its information, and institutions need to produce information in forms that are compatible with the way that farmers learn.
With all this hassle - why even bother?
The nature of social media and online tools provide a great match with the context-specific, experiential learning needs of farmers in ways that traditional 1-way media and Training&Visits/T&V ag extension efforts fall short of. If created in a social space and as part of a larger ag info ecosystem, it can provide a great tool:
The Internet will be of most use to cropping farmers when providers of agricultural information use it less like a library and more like an interactive field day. It is not its scarcity but the local contextualization of information that makes it valuable for farmers. The huge volume of information available on the Internet is of less value to farmers than the opportunities for interactivity with others that it provides to help make local sense of that information.
...But it's not going to be as easy as setting up a ning or drupal site and calling it a day.