Demeter is the Greek Goddess of Agriculture, Fertility and the Cycles of Life. The Roman equivalent is Ceres the Goddess of Grain, Motherhood and Nourishment.
For simple hints and tips on working with a God or Goddess I have written a short blog article linked in this post, or check out my "Guide to Working with Deities", a downloadable ebook containing practical ways to bring a God or Goddess into your spiritual work.