Europe's first farmers helped spread a revolutionary way of living across the continent. They also spread something else. A new study reveals that these early agriculturalists were fertilizing their crops with manure 8000 years ago, thousands of years earlier than previously thought.

Fertilizer provides plants with all sorts of nutrients that they need to grow strong and healthy, including, most importantly, nitrogen, phosphorus, and potassium. That's why farmers all over the world, in countries rich and poor, put manure on their crops. Nevertheless, it may not be intuitively obvious that spreading animal dung around plants is good for them, and archaeologists had found no evidence for the practice earlier than about 3000 years ago. Farmers in the Near East—what is today Israel, Palestine, Syria, Jordan, and neighboring countries—began cultivating plants and herding animals about 8000 B.C.E., but there are no signs that they used animal dung for anything other than as fuel for fires.

So a team led by Amy Bogaard, an archaeobotanist at the University of Oxford in the United Kingdom, decided to look for evidence in Europe, where farming began to spread from the Near East about 8500 years ago. Manure has a higher than normal proportion of the rare isotope nitrogen-15, which is heavier than the more common N-14. The researchers took advantage of recent agricultural research showing that plants treated with manure also have more nitrogen-15. They measured the nitrogen-15 content of plant remains from cereals such as wheat and barley and pulses such as peas and lentils from 13 early farming sites. The sites dated to between 7900 and 4400 years ago and ranged from Greece and Bulgaria in the southeast to the United Kingdom and Denmark in the northwest. As the team reports online today in the Proceedings of the National Academy of Sciences, the nitrogen-15 levels in 124 crop samples, totaling more than 2500 individual cereal grains or pulse seeds, were high and consistent with the use of manure at most of the 13 sites.

Bogaard and her colleagues conclude that as agriculture spread to Europe, farmers began to invest more and more heavily in the long-term management of their fields. That meant spreading manure, which breaks down slowly and increases the fertility of farmland over many years. This long-term relationship with the land, the team suggests, fostered notions of land ownership and fueled the kind of stratified social hierarchies of wealthier and poorer peoples that other researchers have uncovered on the continent.

So how did early farmers figure out that spreading manure was a key to farming success? Bogaard says that there are several plausible scenarios. Areas of "natural dung accumulation," where animals hung out, would have provided "patches of superfertile ground that early crops would have colonized," she points out, adding that "subsistence farmers are extremely observant of small differences in growth and productivity among their plots." And new evidence from both the Near East and Europe, Bogaard says, suggests that "cropping and herding developed in tandem" and were "entangled from the start."

The team is on firm ground in claiming the earliest use of fertilizer, says Martin Jones, an archaeologist at the University of Cambridge in the United Kingdom. "We used to think that close integration of animal and crop husbandry" was a later development, he says, but the new research indicates "that it goes back to Europe's first farmers."