Plains in C-evo produce: 1 material, 2 food, 1 trade. You get an extra trade (but subject to Despotism's maximum of 2) in each of the following cases: there is a road and you have researched The Wheel there is a river and you have researched Map Making. Irrigation produces a third food, with an additional one for farmland if you have a supermarket and are not in Despotism. Plains are the equivalent of the Civ series "Grassland with resource". The C-evo "prairie" is the equivalent of Civ plains. For more food in C-evo, once you have emerged from Despotism, you need Grassland.