I want to know the answer to the following question:
What invention led to an increase in efficiency in the farming of heavy soils?
All the background I'm provided with is that "The development of a three-field rotation system for planting crops[AA] increased the usage of land from one half in use each year under the old two-field system to two-thirds under the new system, with a consequent increase in production.". Is that enough to answer the question?