In 1909, American agronomist F.H. King toured China, Korea and Japan, studying traditional fertilization, tillage and general farming practices. He wrote his observations and findings in Farmers of Forty Centuries, Or Permanent Agriculture in China, Korea, and Japan (1911, published shortly after his death by his wife, Carrie Baker King). King lived in an era preceding synthetic nitrogen fertilizer production and before the use of the internal combustion engine for farm machinery, yet he was profoundly interested in the challenge of farming the same soils in a 'permanent' manner, hence his interest in the agricultural practices of ancient cultures.