What was a system of farming that helped to grow more food?

There are many yield-improvement systems but a well known one is crop rotation, where fields would have different crops and be fallow (empty) for a time in between.

The reason for this is that different crops need different nutrients, so the soil would be used to maximum effect. The fallow year would allow the land to recover its minerals and nutrients, so that it would be fully ready to grow more crops.