Ultimately, the future of food lies off-planet, because for long-term sustenance of humanity we need to eventually move into outer space.
NASA is already experimenting with growing produce in the International Space Station.
Not only will space travelers need to be able to grow food staples with the resources available in their isolated location, they will have to ensure regulated conditions to keep the process going indefinitely.
I thought this article gave a good overview of the challenges that space farmers and gardeners will face as they try to maintain plants in spaceships or on other worlds. It also gives some background on the development of plant life here on planet Earth.
Future farmers in space will have to deal with issues like atmospheric changes caused by the plants production of oxygen & humidity. The effects of any microorganisms present will also have to be understood. Recycling water supplies will also be very important for both plants & humans.
As the article states, it's possible that humans will not directly interact with the crops at all, and robots will actually do the growing & harvesting.
Here is a computer rendering of automated agriculture aboard a space craft, from one of the awesome projects at Spacehabs.com: