Mary McGucken, age 10, of South Charleston, West Virginia, for her question:

Who invented crop rotation?

Our remote ancestors learned farming very slowly by trial and error. They did not know that plants draw chemical nourishment from the soil and that when they are har¬vested these vital plant foods are taken away. But they did know that the same field would not yield a bumper wheat crop year after year. So after a good harvest, they left a wheat field idle, or fallow, for a year. In ancient times they did strip farming. They planted one or two strips while one stayed fallow. This method of farming was common in many parts of Europe 1,000 years ago and it continued through the Middle Ages.

These strip farmers, however, were way behind the times. When the Roman Empire was at its peak, the rich land owners of Italy practiced farming on a grand scale. They irrigated the soil to help their crops. Instead of leaving strips idle, they followed one crop with a different one. This is one of the earliest records of crop rotation. The Romans also learned by trial and error that crops of the pea family enrich the soil. Instead of leaving strips fallow, they planted them with peas and beans.