With the fall of Rome and barbarian invasions, farming started to suffer. That may be an unexpected statement, but there were reasons. With the loss of the Pax Romana ("Roman Peace"; formally, it refers to a 200-year span that ended in 180CE, but its influence lasted longer), invasions led many rural communities to migrate to cities for safety. Farmers who remained outside cities were focused on safety and managing their land with perhaps fewer farmhands. Marching armies devastated the arable land.
Roman irrigation systems were not maintained, both those that brought water to where it was needed and those that drained water from lowlands. Italy became increasingly swampy and a breeding ground for malaria, driving farming into smaller hilly areas where fields were overworked and erosion was more likely.
Classical Rome understood about erosion and soil management—Cato and Vergil had written about farming, and there was an expert named Taurus Palladius who wrote definitive Roman works on agronomy in the 5th century—but as civilization faltered, so did education and the knowledge of efficient agricultural practices.
The Moorish lands maintained good practices, but Western Europe did not know about them, except in one area. Knowledge of the writings of Palladius and Mago the Carthaginian (whose 28 books written in Punic are lost, but we have Greek and Latin fragments) could be found in the enclaves that valued and collected and copied books: the monasteries. Monasteries in the Middle Ages maintained model farms, with the resources, knowledge, and manpower to get the most from the land without exploiting it.
In fact, it was the observation of farming techniques throughout Lombardy, and especially how monasteries managed their land differently, that got a jurist from Bologna thinking about agriculture. Although an expert in law with a reputation for fairness and legal knowledge, he started to take an interest in the differences he saw in farming techniques. When he retired to Bologna in his 70s, he decided to do something about what he had observed.
Tomorrow, we will see how this retired lawyer kick-started modern agronomy, the science of soil production and crop management.