OXFORD, ENGLAND—The high levels of nitrogen-15 found in samples of wheat, barley, peas, and lentils from 13 early farming sites in suggest that European farmers were fertilizing their crops with manure as early as 8,000 years ago, or some 5,000 years earlier than previously thought. Archaeobotanist Amy Bogaard of the University of Oxford thinks that the farmers probably noticed that areas where their animals gathered became “patches of superfertile ground.” This evidence supports the idea that “cropping and herding developed in tandem,” and were “entangled from the start,” she added.