I doubt you will find many firm positions on agriculture. Except that since Iowa has that early straw vote everyone is firmly in support of ethanol.
I can't remember a president who had strong ag positions. Ag is mostly the province of the Congress. Colin Peterson (D-MN) and Tom Harkin (D-IA) are the main players. Richard Lugar R-IN is a principled alternate voice.
If a candidate for president catches your eye, try to find out who he/she might appoint to be Sec of Ag. Then, investigate that person.
Ag policy is important, but not a driving issue. Ag policy is a long, dreary, process which takes in a thousand non-ag issues--i.e. food assistance and environmental issues.
I hope we find someone we can live with. The environmental groups are so flush with money and they aren't afraid of pushing moonbeam positions on ag issues. All they know is that the shelves were full the last time they went to Kroger. They don't realize how close this planet runs on food supply. The Bible speaks of the 7 fat years and the 7 lean years. If you don't store it up and work hard, the lean years are gonna get ya. Having experienced a drought this summer, I'm a believer.
The president is important, but your state and local officers are more important when it comes to ag. Can you pay your taxes? Treat your stock with your best judgement? Produce to the best of your ability?