Biochar is a traditional practice in Japan that goes back centuries. Today, Japanese scientists are at the forefront of research into understanding the physical, chemical and biological properties and effects of biochar in soil and compost. You can read about their work at the Japan Biochar Association.
The traditional farming practices of China, Japan and Korea recycled massive amounts of human waste, ash, crop residue and other biomass into agricultural fields. In 1909, the American agriculturalist F. H. King embarked on an eight-month tour of China, Japan and Korea in order to view and document agricultural practices. The resulting book, Farmers of Forty Centuries (King, 1911)has become an agricultural classic. Part of King's purpose in the book was to contrast the enduring agriculture of Asia with what he viewed as destructive and wasteful practices then advocated by the US Department of Agriculture (Paull, 2011). King declared: "One of the most remarkable agricultural practices adopted by any civilized people is the centuries-long and well nigh universal conservation and utilization of all human waste in China, Korea and Japan, turning it to marvelous account in the maintenance of soil fertility and in the production of food (King, 1911, p. 193).” As an indicator of the commercial value of this human waste he found that the city of Shanghai sold concessions to waste haulers, charging one contractor $31,000 in gold for the right to collect 78,000 tons of human waste for sale to farmers outside the city (p. 194).
King found compost making to be a high art in Japan where prizes were offered in each county for the best compost. Winners at the county level went on to compete for a prize for best compost in the prefecture (p. 397). Although he did not specifically describe the use of charcoal in these composts, he observed that ash materials were added in large amounts. Moved by the thrift and care for conservation of nutrients that he observed on his travels, King expressed his frustration with the wasteful practices of his own country, citing the "depleted fertility of our own older farm lands, comparatively few of which have seen a century's service," and the waste of the "enormous quantity of mineral fertilizers which are being applied annually to them in order to secure paying yields." Contrasting the Asian practices with those in America, he said: "The rivers of North America are estimated to carry to the sea more than 500 tons of phosphorus with each cubic mile of water. To such loss modern civilization is adding that of hydraulic sewage disposal.” (p. 197)
Some historical uses of charcoal in Japanese agriculture are documented in "Pioneering works in biochar research, Japan" (Ogawa & Okimori, 2010), which describes a Japanese agricultural encyclopedia published in 1697 that gives instructions for making biochar compost: "After charring all waste, concentrated excretions should be mixed with it and stocked for a while. When you apply this manure to the fields, it is efficient for yielding any crop." Ogawa & Okimori say that biochar has been in used in Asia since ancient times, and that rice husk charcoal has been used since the beginning of rice cultivation. Wood charcoal was not generally used in agriculture as it was too valuable as fuel. The article also reports: "The practice of using rice husk charcoal mixed with excreta had been very popular in wheat cultivation until about 100 years ago. There were double benefits, which are that the charcoal can absorb and retain chemical nutrients as well as deodorize excreta. However, this method was so commonplace for local people that scientists rarely paid enough attention to investigating it." Beginning in the 1980s, Ogawa and other scientists began to research these traditional uses of charcoal in agriculture in order to learn more about their effects. This revival of agricultural charcoal in Japan has been an important stimulus for the current attention to biochar.