Europe's first farmers were far more sophisticated than previously thought, say researchers who found they manured and watered crops as early as 6,000 B.C.

While scientists had long assumed manure wasn't used as a fertilizer until Iron Age and Roman times, new research found enriched levels of nitrogen-15, a stable isotope abundant in manure, in the charred cereal grains and seeds taken from 13 Neolithic sites across Europe, researchers at Britain's Oxford University reported Tuesday.

The finding suggests Neolithic farmers used dung from their herds of cattle, sheep, goats and pigs as a slow release fertilizer for crops, indicating a long-term approach to farming and overturning the traditional view of scholars that Neolithic farmers were nomadic people who used slash-and-burn techniques to create temporary farmland for agricultural crops, the researchers said.

"The fact that farmers made long-term investments such as manuring in their land sheds new light on the nature of early farming landscapes in Neolithic times," Oxford archaeologist Amy Bogaard said.

"The idea that farmland could be cared for by the same family for generations seems quite an advanced notion, but rich fertile land would have been viewed as extremely valuable for the growing of crops," she said.