Spencer Aitel grows corn, grains and alfalfa on his 275-acre organic farm in China. He stakes his reputation, and his family’s livelihood, on the fact that his crops are free of pesticides and added ingredients. Galen Larrabee also grows corn, about 400 acres worth, on his farm in Knox. He uses a genetically engineered variety of the grain that he says has increased yields. The two farmers soon may find themselves on opposite sides of a growing agricultural divide in the state over the use of genetically modified foods. It’s a debate that appears headed to the Legislature.